DCweather

Risk of Snow Showers tomorrow, cold for Friday

2008-01-23T17:19:00.000-05:00

Current Weather:
Temperatures currently in the lower 40s should drop into the mid 20s overnight under mainly clear skies and light winds in and around the Beltway. Farther to the north and west, temperatures are presently in the mid to upper 30s, and should fall into the upper teens overnight.

Forecasts For the Next Few Days:
Thursday:
By 8 or 9 AM tomorrow, clouds should begin streaming in from the west, as energy associated with a tiny pocket of mid and upper level energy slides east from the Midwest. High temperatures tomorrow will hover in the lower to mid 30s in and around DC, which will support a few snow showers, which may develop during the late morning and into the late afternoon hours. Some minor snow accumulation is possible on grassy and elevated surfaces, but most roadways should remain snow-free due to above-freezing road temperatures.

Probability of Snow: 40%

Image at right: NAM forecast precipitation for Thursday afternoon showing the possibility of some light snow showers around the metro region. Image courtesy of the Penn State E-Wall

Friday:
Cold, Canadian air is expected to pour into the region overnight Thursday as a cold front sweeps through the Mid Atlantic. Temperatures early Friday morning will range from 15 around Hagerstown and surrounding areas, to near 20 near Washington, D.C.

Clouds should scour out by mid morning, leaving us with mainly sunny to skies. High temperatures will be in the upper 20s and lower 30s.

Saturday:
Clouds will increase late Friday night and into Saturday morning as a very weak upper level disturbance rotates through the region. At this point, there does not appear to be enough lift to get any precipitation over the mountains. Temperatures will hover around 40.

Paying Attention to What the Forecaster Actually Says:
With the recent forecasts of snow in the metro region, it has gotten to me when people ask me, "hey, the weather channel said there was supposed to be snow last night. How come there was none/How come it didn't stick?"

It seems incredible to me that, with all the precision and time forecasters put into their work, the vast majority of the public really doesn't pay attention to some of the crucial details. Here's a portion of the text forecast for Montgomery county for Thursday from the National Weather Service:

.THURSDAY...MOSTLY CLOUDY WITH SCATTERED SNOW SHOWERS. HIGHS IN THE UPPER 30S. NORTHWEST WINDS 10 TO 15 MPH. GUSTS TO 30 MPH IN THE AFTERNOON. CHANCE OF SNOW 40 PERCENT.

Seems simple enough, right? Now, take a quick look at the image to the right. It's The Weather Channel's forecast for Thursday. If it DIDN'T snow at all tomorrow, I would bet that most people would say, "the meteorologists got it wrong again. Where was the snow??"

Very few public viewers actually take the time to read the forecast text. Notice that little percentage at the bottom? In the NWS text forecast, this percentage is 40%, and in The Weather Channel's it's 30%. These are known as Probabilities of Precipitation.

Most people think of POP as the percentage of getting precipitation on that day. That, unfortunately, is only one part of the formula. POP is based on two things:

1) The probability that any precipitation will fall in the time period and
2) The predicted areal coverage if precipitation actually develops

So take this hypothetical situation (it would more than likely never happen, but what the heck):
Washington, D.C. records a POP of 20% for 100 consecutive days. If this POP were accurate over the long term, then Washington should have experienced some type of precipitation for 20 of those 100 days (not a great number, right?) The likelihood of precipitation being recorded when the POP is 20% is extremely low.

So, the next time you read or hear a forecast, it would be wise to also look or listen for the Probability of Precipitation. Weather isn't exactly and exact science.

Nuisance Snow storm tomorrow

2008-01-16T17:34:00.000-05:00

Current Conditions:
Temperatures are currently hovering in the mid to upper 30s across most of the region, with Reagan National as the warm spot at 41 degrees last hour. Temperatures are expected to fall into the low to mid 20s overnight as clouds thicken from the south and west, as a large developing surface low moves northeastward.

The snowfall forecast for tomorrow is a tricky one, since surface temperatures, once again, will be very marginal for accumulations.

Winter Storm Breakdown:
Snow should begin to fall by 12PM or so in the District, earlier to the southwest, and later to the north and east. The surface temperature profile will be critical to this forecast. At this point, our best estimate is that the snow will change to sleet and then rain by 4-6PM as warm air filters in from the east.

By the time the precipitation change-over occurs, however, there is the potential for a Trace to 2 inches of snow in and around the District, and 1-3 inches out to the north and west of town, where temperatures will likely remain colder.

If temperatures fall just a few degrees below forecast levels, a significant change to snowfall totals would be needed. At this point, however, I am not convinced areas in and around the District stay below 32 for very long after 4 or 5PM.

Snowfall Forecast:
I think most locations, even out towards Martinsburg, WV and Harisonburg, VA will change over to rain, it will just take longer, thus the higher snowfall totals out that way. There will likely also be a period of freezing rain in the lower portions of the Shenandoah and out towards Garret County, MD. I anticipate a light glaze of ice around the aforementioned areas.

Colder weather in the future

2008-01-14T14:55:00.000-05:00

Current Conditions:
Temperatures around the region are currently hovering near 40 degrees, but a weak surface trough has just cleared the area, which should usher in slightly colder temperatures for tonight.

Washington, D.C. reported 0.03" of rain with the storm system last night, and BWI only picked up about 0.07" from a thin line of showers.

Many areas to the north, were anticipating snowfall totals at or above 12", but most locations only received (generally) between 3 and 6 inches. Numerical computer models failed to accurately predict the dynamics of this coastal low, which lead to significant forecast busts across the Northeast.

Tonight and Tomorrow:
The sun is breaking out in many locations as a large winter storm, currently hammering upstate Maine with heavy snow, slowly pulls away to the northeast (see image above).

Skies will continue to clear, gradually overnight. Temperatures will fall into the mid to upper 20s around town, and near 20 farther to the north and west.

Expect partly cloudy conditions tomorrow, with temperatures rising in the lower 40s by mid afternoon. Breezy northwest winds will make it feel like it's in the upper 30s, however.

Entering a Cold and Stormy Pattern--Snow is again a Possibility:
STORM 1:
A few models have been hinting at the possibility of yet another coastal storm developing Thursday night and Friday morning. While precipitation may start off as either a mix of rain and snow, or pure snow Thursday night, thermal profiles would seem to favor everything changing over to rain by Friday morning.

(Image at right: Surface precipitation and temperatures about 10,000 feet up. Notice how DC is above freezing at this level (+2C or so) which, with surface temperatures above freezing, would translate into rain for the Mid Atlantic).

So at this point, here's the forecast: Brief period of rain/snow Thursday night, quickly changing to rain by midnight. Things could change, but significant changes look unlikely at this point.

STORM 2:
On the heels of the aforementioned storm is yet another disturbance which has the potential to drop snow on the region. While not a classic set-up, current forecasts offer us a slightly higher probability of snowfall Saturday through Sunday evening.

After these storms move by, a massive outbreak of Canadian Cold air is forecast to overrun much of the United States in below-average temperatures from around Sunday, January 20th, through the end of the month.

Coastal Storm Possible on Monday?

2008-01-10T16:06:00.000-05:00

Where's the Storm Now?
The feature we expect to develop into a coastal storm is currently a highly disorganized area of cloudiness associated with impulses of upper air energy over the northeastern Atlantic Ocean (see image at right). These little "packets" of energy are expected to slide southeastward, following the jet stream, and then combine--or phase--to produce a surface low pressure system in the Northwestern Gulf of Mexico sometime Saturday night.

This much of the forecast is pretty much a 100% certainty at this point.

What happens next, however, is difficult to assess with great confidence right now, as there are too many different things that have to click just right to produce a significant winter storm for our region.

What the models are saying:
Global Forecast System (GFS): We use this model the most to diagnose weather patterns over the United States. It has a decent track record (over the past several years), but has not been performing too well this winter. The past two runs of this model reveal a pretty much ideal situation for a significant snowstorm in the major I-95 Cities, from Washington, D.C. to Boston, MA.

North American Mesoscale (NAM): One of the worst performing numerical weather models beyond 48 hours this year. Nevertheless, it has begun to move towards a solutions that mirrors that of the aforementioned GFS. Surface temperatures will likely be an issue (mid to upper 30s).

Canadian Model: I feel this model has performed very well so far this winter. While it develops a significant surface low, it's roughly 200-300 miles off the coast--too far away to dump any appreciable precipitation on the region. (See image at right: bottom right panel is surface precipitation valid late Sunday night).

The European Model: By far, one of the best out there for medium-range forecasting, but is rather poor inside of 84 hours. Previous runs have developed a very nice storm for us, but this morning's run develops the low even farther east than the Canadian.

Current Thinking:
We are confident there will be a storm of some kind Sunday night into Monday. Whether it remains cold enough for snow, however, is still up in the air. Our airmass is not particularly cold, and any coastal low that develops will have to move within a swath 100 to 150 miles offshore to give us any hope of receiving snowfall.

At this point, temperatures look to remain in the upper 30s to near 40 for most of us, which would lead me towards a rain, or rain/snow mix solution for Sunday night/Monday. If the GFS does verify, however, much of the precip would be snow. Stay tuned.

Funky DC weather

2007-12-12T17:09:00.001-05:00

Most of the precipitation with this winter storm (at least before Sunday morning) will fall in the form of sleet or freezing rain. Areas in extreme Northwestern Maryland have the best chances of seeing accumulating snow, but even there, warm surface temperatures may turn things over to rain briefly during the afternoon.

As for the District and Baltimore, this now looks like a primarily rain event. We may see a few flakes or sleet pellets before the storm ends tomorrow afternoon as cold air filters down from the northwest.

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A Winter Weather Advisory is in effect from 3AM to Noon for areas north and west of the District including Montgomery, Loudon and Howard Counties. The National Weather Service anticipates icy conditions tomorrow morning.

Icy situation tomorrow morning:
Models over the past few days have trended cooler with a developing low pressure system in the southern United States. Temperatures are expected to cool into the low to mid 30s north and west of the District. As the upper levels warm above freezing, sleet and freezing rain are slated to develop around the aforementioned areas sometime tomorrow morning.

I don't really see this storm being much of a wintry event for the immediate metro regions, but northern sections of Montgomery and Loudon counties and points north and west could be in for a slippery ride tomorrow. Anywhere from a trace to one tenth of an inch of ice accumulation is expected before everything turns over the rain by midday.

After this storm exits the region tomorrow evening, our full attention turns to a potential large coastal storm.

To Snow or not to Snow:
Numerical model runs on Tuesday afternoon turned most Washington snow-lovers euphoric. The normally trustworthy GFS pumped out an eye-popping 18-24"+ of snow for most I-95 cities on Saturday through Sunday. Recent runs, however, have brought the storm farther inland, and instead of a monster pure snow event, forecasts snow changing over to plain rain.

But, there are some very promising signs that things are about to change. The newest computer model runs hint at the possibility that the low scoots a bit farther east, bringing a prolonged period of snow back into the equation. It's still too early, and I'm too uncertain, to make any calls at this point, but the potential for a large winter storm is still a very real possibility.

Soggy, wet pattern setting up this week

2007-12-09T18:41:00.000-05:00

Current Weather:
Presently, a developing area of low pressure around the Ohio River valley is pushing rain showers into northern Maryland from west to east.

The current thinking is that rain showers will stay generally north of Washington until tomorrow around noon as bands of light precipitation move southward as a small cell of high pressure pushes in from the northwest. Even with the high pressure in place for Tuesday, skies are expected to remain generally cloudy with high temperatures climbing into the upper 50s to near 60.

While our temperatures remain warm enough for a pure rain event, folks up in New York and northern Pennsylvania are in for a significant icing event. Freezing rain is expected to coat the region in over a quarter inch of ice.

Forecast through the rest of the week:
Another developing low during the middle of the week is expected to bring the area yet another shot at some light rainfall. Our chances for rain will slowly increase through the day on Wednesday as a warm front lifts north of the region before the low moves east by Thursday evening.

Even with all this rain in the forecast (looking at the National Weather Service forecasts, you'll see rain symbols every single period up until Thursday), just know it will not be raining every single minute for the next 4 days. We will have sporadic, elevated chances of rainfall through the week, with the best chances coming during the day tomorrow and Wednesday night into Thursday.

Rainfall accumulations are quite high through the week given all of these stubborn low pressure systems. The graphic to the right show total precipitation accumulations through Friday night as forecast by the GFS (Global Forecast System) model. Granted, I think the totals are too high for most locations, but it just gives you an idea of how much moisture there is in the atmosphere this week.

Image above: GFS Total precipitation accumulations through 00Z Saturday. Courtesy of Accuweather.

I thought Hurricane Season was over?
Hurricane season officially ended on November 30, but the National Hurricane Center is monitoring a disturbance in the Caribbean that may develop into yet another tropical system:

WATER TEMPERATURES ARE STILL WARM ENOUGH IN THIS AREA TO
SUPPORT TROPICAL CYCLONE FORMATION...AND UPPER-LEVEL WINDS ARE NOT ESPECIALLY PROHIBITIVE FOR DEVELOPMENT. THIS SYSTEM HAS THE POTENTIAL TO BECOME A TROPICAL OR SUBTROPICAL STORM DURING THE NEXT 24 HOURS

Hurricane Season hasn't given up yet.

Midweek Clipper and DC area's first snowfall

2007-12-03T16:52:00.000-05:00

Snowfall Update:
This clipper has turned out to be a fairly significant snow producer. Most locations north and west of the District will end up receiving 2-5 inches with locally higher amounts west of the Blue Ridge.

It appears as if at least light snow will continue around the metro region for another hour or two before everything shuts off from northwest to southeast.

--Previous Post--

The low that passed a strong cold front through the area yesterday is currently deepening off the coast of Maine, where up to two feet of snow is expected by tomorrow morning. The tight pressure gradient behind this storm is driving cold northwesterly winds down from Canada. Cold air continues to filter into the region, and temperatures tomorrow will struggle to get into the low 40s. Winds will also turn gusty in the afternoon with 30-40 mph gusts likely in most locations.

This new pool of cold air will set the stage for the Washington metro areas first snowfall of the winter season:

By late tomorrow night, a piece of energy from a strong Pacific Northwest storm system will have been ejected southeastward into the Midwest (image at right). Clear, to partly cloudy skies Tuesday night will allow much of the daytime heating to radiate out, allowing temperatures to drop into the mid to upper 20s.

At this point, timing the onset of precipitation is very difficult due to a dry surface (or boundary layer) that will be in place early Wednesday morning. Any precipitation that develops over the area will evaporate before reaching the ground. The current thinking is light snow will start falling between 5 and 7AM on Wednesday.

As the snow falls into the dry boundary layer, surface temperatures will likely fall a few more degrees towards the wet bulb, which is simply the temperature to which the atmosphere will cool at 100% saturation (i.e. when the snow falls).

Snow should become a little heavier during the early afternoon hours as the clipper begins to slide south of us. In the image above, snow growth levels have fallen to near 12,000 feet and have begun to intersect areas of moderate to high omega (lifting) values. This often indicates a period of heavier snowfall, depending on the magnitude of the forcing. In this case, forcing is decent, but not great, which would support a period of moderate snowfall rates around 12 to 5 or 6PM.

Afternoon temperatures on Wednesday may pose a problem for snowfall accumulations, as they may rise slightly above freezing. My best guess on snowfall totals at this point is between 1-3 inches on elevated or grassy surfaces, and a Trace-2 inches on untreated roadways and sidewalks.

This will only be a "nuisance" snow event, but since it's the first of the season, and snow will likely begin before rush hour, it may cause some problems for Wednesday morning commuters.

DCweather's Winter Outlook

2007-11-28T18:23:00.000-05:00

Precipitation Forecast:
Over the years, the ENSO (El Niño-Southern Oscillation) Index has been used, to great effect, to predict long term inter-seasonal variability in temperature anomalies across the United States. Generally, La Niña occurs when Sea Surface Temperature Anomalies from an area bounded from 5°N-5°S 120°W-170°W (also known as Niño 3.4) drop to less than 0.5 degrees Celsius.

Boxed areas represent the so-called Niño regions. Niño 3.4 is generally used in most long-term forecasts. Image courtesy of the Climate Prediction Center

At the end of the August-September-October time period, Niño 3.4 was at -0.8 and falling, meaning average SST anomalies for that region were 0.8 degrees Celsius below normal. Model forecast for the ENSO index indicate that SSTs should continue to fall through the remainder of the year and into next January. The NCEP CFS model, in particular, drops the ENSO index down below -2, which would approach some of the lowest monthly values every recorded.

More likely, however, is the threat of a moderate to strong La Niña through next January which would indicate drier than normal conditions across the Southeast and Mid Atlantic States, and generally warmer than average temperatures.

La Niña generally predicts precipitation anomalies a little better than temperature anomalies, at least in this part of the United States, so I am using the ENSO index more for this aspect of the winter forecast.

In short, I anticipate a drier-than-normal period from December through next January for the entire Southeast and Mid Atlantic. (This could be a bad thing for you snow-lovers, but keep reading).

Temperature Forecast:
Temperatures are normally a little harder to predict this far in advance. Unlike the teleconnections for precipitation, the comparisons aren't as black and white. Temperatures can be affected by the position of the jet stream, North Atlantic Oscillation, Pacific/North American Pattern, the Arctic Oscillation, Southern Oscillation Index, and a list that goes on too long to complete.

As a rule, though, the North Atlantic Oscillation (NAO) and Pacific/North American Pattern (PNA) are the most reliable predictors of temperature anomalies.

The NAO index, which measures pressure differentials between areas around Greenland, is currently at 0.45 and falling slowly. Likewise the PNA was 0.55 and falling rapidly. The years that best represented our current set-up are: 1963, 1969, 1995, and 2005. These years produced below-normal temperature anomalies across the Eastern third of the country, as seen at right.

Based on this information, and combining it with the fact that the ENSO should be negative for much of the winter, I think temperatures will be average to slightly below average through January.

Snowfall:
With La Niña in place, we will likely not be seeing an above average year for snowfall. However, I think we may be able to squeeze out a slightly below average year for most of the area (that works out to be around 10-14 inches at Reagan National, and 13-16 inches up north towards Baltimore. There will likely be more storms that drop a mixture of snow, rain, and freezing rain over the Mid Atlantic due to the milder air.

Running Clipper Happy

2007-11-08T16:48:00.000-05:00

If there is one thing I have learned over the years, it is that computer models do not ever do a good job with clipper systems. In fact, you'll see in my previous entry which came last weekend I talked about how a clipper could give us some snowflakes Friday night- Saturday if everything went as the GFS was showing on that day. But between Sunday and Wednesday, the clipper all but disappeared from the computer models.... until today.

It now looks likely that a clipper will pass through the area just to our south and west. As it does so, it will spread precip into the entire area. The question is, what form will it come in? Unfortunatly, I don't really have an answer. Looking at the conditional probabilities on the NAM and GFS, it could go either way. If I were to had to put something on it, I don't think anyone south and east of DC will see anything in the way of snow, and snow in the district may be a stretch. I do think it is fairly possible that the immediate suburbs of Montgomery, Fairfax, Frederick (etc) could see snow.

It will all come down to a couple of degrees Friday night, so if you are rooting for the first flakes of the year, stay close to a thermometer!

(I'd show you a picture here but there have been some technical difficulties...)

Welcome to winter next week!

2007-11-03T12:40:00.000-05:00

A strong cold front will cross the area Monday night and send us into a very winter-like pattern for the remainder of next week. Temps will fall during the day Tuesday, with highs in the low 50s and gusty winds. On Wednesday and Thursday, highs will struggle to get out of the 40s, with nighttime lows in the 20s to around 30 in the city. Things will get interesting on Friday:

The GFS and EURO models have been hinting that two clippers, particularly the latter, may give us our first snow of the year. The first clipper is the weaker of the two, and and would perhaps give us a few flurries/drizzle on Wednesday night-Thursday. The bigger storm would be Friday night-Saturday.

If this were January, I would say that this storm would have the potential for several inches of snow.... but its November. As such, it is possible that if everything were to go right that we get some snowflakes or a very chilly rain during the period in question. Lots can change between now and then, but the underlying theme here is that a winter-like pattern will take shape next week.

12z GFS showing moderate snow over the area on Friday.

Severe Storms Friday...An end to the drought pattern?

2007-10-17T16:50:00.000-05:00

Hello Everyone... just an update on the status of the blog first off. We haven't really done any updates in a week or so because, well, there hasn't really been much to talk about. This is a blog where we take a look into upcoming weather events in the area that might actually change your day-to-day activities...

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Friday's severe threat:

A very rigorous storm system has developed over the plains today spawning multiple tornadoes and a number of severe thunderstorms across the area ahead of the dry line in Oklahoma. This storm system will deepen as it moves east over the next couple of days, and does pose the risk for a severe thunderstorm outbreak on Friday.

NWS has gone with a 30% chance for Day 3, which is pretty high for storm outlooks beyond 48 hours.

Computer models are suggesting that EHI values (a measure that can indicate how probable a thunderstorm is of dropping a tornado) will be on the high side (2-3 across the area). The bigger risk, however, will be straight line winds; the cold front will be cruising across the area, and models are indicating that a number of long bow echos may evolve on Friday afternoon as the storm crosses the Apalachians. The one thing I see as a potential inhibbiting factor is the left-over cloud cover from tomorrows storms. We will talk about this more tomorrow.

Sheer is when wind directions at different levels of the atmosphere are moving in different directions. On Friday, winds will be coming out of the southeast at the surface, but out of the northwest aloft--- this will create spin in the atmosphere for supercells and long-lived bow echos

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A break from the Dry Pattern?

Yes we are a significant drought- "extreme" in some southwestern suburbs according to the NWS. The question is, are we going to break the dry pattern?

While I do see two good chances of significant rain over the week or so, I do not see a pattern change in near future. Hopefully, we will be able to get 1-3 inches of rain like the GFS indicates over the next week, because I still see strong Bermuda Highs sitting to our east 10+ days from now.

Storms lining up for Evening...

2007-09-27T15:56:00.000-05:00

A SEVERE THUNDERSTORM WATCH IS IN EFFECT UNTIL 10:00 PM EST FOR THE 1-81 CORRIDOR WESTWARD.

Discussion: A slow moving front will put an end to our unseasonable heat tonight, and as it does so, severe thunderstorms will be possible across the northern and western suburbs. The biggest risk for these storms is the heavy rainfall, which could exceed 1-3 inches/hour in heavier cells.

We need all the rain we can get, and its quite possible that the immediate metro area sees a solid half inch of rainfall tonight as the storms move weaken as they push into the area. I am confident that most locales will see some rain with this system, although the true soaking rain will stay north and west of the immediate DC area.

Projected times of the first drops:
Winchester: 5:30
Hagerstown: 6:00
Frederick: 6:30 (although a pop-up storm did drop some rain earlier today...)
Werenton: 7:30
Fairfax: 9:00
Rockville: 9:30
Washington D.C.: 10:00
Baltimore: 10:30
Anapolis: 11:00
Fredericksburg south: rain not likely.

A line of strong storms has the potential of dropping some significant rain over the area tonight.

Nice weather for Weekend...Watching Gulf of Mexico closely

2007-09-20T20:11:00.000-05:00

Nice weather is on tap for the weekend as a weak cold front approaches the area from the northwest. Winds wil shift to the southwest on Friday bringing in almost August-type heat and humidity. While we can't rule out a shower or thunderstorm on Saturday, skies will remain more or less clear for the weekend.

A weak cold front will fizzle out on Saturday as it approaches the area. Expect a Summer-like weekend with temps in the mid 80s both days.

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Watching Invest 93L:

The National Hurricane Center investigated invest 93L in the Gulf of Mexico near Florida and found a well-defined low-level center and a pressure of 1006mb (what you would expect in a tropical depression). The only issue is that the system doesn't have very many tropical features at the moment, with little convection near the low-level center. None the less, conditions are becoming favorable for 93L to become a sub-tropical or tropical storm in the next day or two as it drifts westward. People in the southern Gulf should pay attention to this system--- computer models seem to agree that the most likely place for the system to make landfall would be western Louisiana. From there, it is possible that we get some rain just as we did when Gabby came ashore in Texas last week.

Storms lining up for this evening....

2007-09-10T14:58:00.000-05:00

Heavy rainfall associated with slow moving thunderstorms will be possible over the next several hours as a wave of low pressure moves up a nearly stationary front and spreads moisture over the extremely humid air mass in place (Gabriel left behind very high dew points when it departed).

Although a widespread severe weather event is not anticipated, a couple of damaging wind reports are possible. The heavy rainfall, in some of the heavier cells though will be the main threat. Hopefully we can get some rain from this system...

Radar does not look too impressive right now, but by this evening, heavy thunderstorms will blanket the area...

Gabriel a close call...

2007-09-08T22:30:00.000-05:00

It took a little longer than expected, but the area of disturbed weather off the North Carolina Coast finally became tropical in nature this afternoon (at first, the NHS listed it as a subtropical storm....don't ask me what made it "tropical" by 5pm but "sub-tropical" at 2pm).

At this point, Gabriel is a weak tropical storm with winds sustained at 40mph (although I do think that may be underdone a bit). While the track of Gabby (below) indicates that nobody west of the Eastern Shore will be impacted by the storm, in recent hours, the tropical storm has wobbled a bit west which may in turn take the track a bit further west.

This westward trend must be monitored, and I do still think that there is an outside chance that Gabby reached hurricane status before making landfall in Eastern Carolina. Unless something drastic happens however, it doesn't look like Gabby will be one for the memories.

Gabriel looking better tonight...

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In other weather news, a slowly dropping front (the same front that is going to keep Gabriel away) will give us a chance for some storms Monday. Some of these storms on Monday may reach severe limits. After there, it looks like a clear and calm weather pattern will settle in, giving us seasonable weather for the remainder of the workweek.

Soon-to-be Gabriel is something to watch...

2007-09-05T16:36:00.000-05:00

At 3:30pm Wednesday, new recon reports showed that the area of circulation southwest of Bermuda is very close to tropical depression status. Chances are high that by Thursday we will have tropical storm Gabriel, and computer models are indicating that there is a chance that Gabriel will strenghten and move west towards the North Carolina Coast, potentially impacting the DC area by the end of this weekend with heavy rain and strong winds.

Stay tuned...

Perfect stretch of weather to continue... Felix, 98L developing...

2007-09-01T14:41:00.000-05:00

Sunday Night Update: Hurricane Felix strengthened rapidly today, reaching category 5 status this evening. Just to get a sense of the strength of this storm, when NOAA recon planes flew into the storm earlier today, they found lightning in all quadrents (usually something we only see in hurricanes that are truly exploding in intensity) and graupel (small frozen water droplets/hail that can were obviously large enough to damage the plane), and ultimately had to abort the mission. The plane also recorded a 1mb drop in pressure per mile when flying into the storm. That will make your ears pop like CRAZY!!! Felix should level out in terms of winds Monday, and continue fluxuating in intensity between strong CAT 4 or CAT 5 until its landfall.

There is little change in the forcasted path--- Felix should continue west-northwestward towards Northern Honduras and Belize. There is still a slight chance that Felix will move far enough north to make a US landfall in Texas after its initial landfall somewhere in Belize or the Yucatan.

CAT 5 Felix Sunday night

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On the home front, a strong ridge of high pressure has moved into the area, and there is no indication that anything other than sunny skies and warm temperatures will persist well into the future. Temperatures will start to get up there to around 90 by Labor Day, and stay in the upper 80s through the week with no rain in the forecast.

A perfect weekend followed by a perfect week of weather

On to the tropics, where things are starting to heat up again:

Felix: Hurricane Felix (winds sustained at 70mph on Saturday) will continue to move west-northwestward towards the southern Carribean. Most of the models keep the storm well south of the Gulf Coast and take the storm into the Yucatan Penninsula, however some models have begun to shift northward. Trends will need to monitored.

98L: This system has strengthened significantly today, and should reach tropical depression status by tonight or tomorrow. It is far to early to tell, but 98L has a chance to be threat to the east coast by next week.

Rain on the Way for DC, Dean to ravage Jamaica

2007-08-18T14:54:00.000-05:00

Weather over the next several days:
Clear skies dominate over the Mid Atlantic as a ridge of high pressure builds into the region from the northwest. Clouds will, however, begin to increase out of the southwest shortly as a developing storm system slides eastward from the Central Midwest.

Temperatures: The increased cloud cover on Sunday should hold high temperatures in the low to mid 80s, which is at or slightly below average for this time of year.

Precipitation: The chance for a few showers/thundershowers will slowly increase after 7 or 8 PM Sunday evening. It appears, however, that the majority of the rainfall from this system will stay north of the Mason-Dixon line until Monday night. A few numerical weather models depict the possibility of severe thunderstorms moving into the region Tuesday morning and early afternoon. Needless to say, from Monday through Wednesday, scattered to numerous showers and thunderstorms will plague the region, but should significantly cut into the areas rainfall deficit.

Gulf Coast be Warned! Catastrophic hurricane is on the way:
Scalding hot sea surface temperatures, low wind shear, and slow steering currents are all coming together, (or rather, have come together) to form the most intense tropical cyclone this year. Hurricane Dean is currently an upper Category 4 Hurricane with maximum sustained winds of 150 mph near his eye.

This tropical monster has already ravaged portions of the Lesser Antilles, and is headed towards the island of Jamaica as a potential Category 5, which would completely devastate the mountainous region. According to Associated Press, NASA has shortened its spacewalk by one day, and will bring the astronauts back on Tuesday to avoid any potentially dangerous ramifications.

Folks anywhere from New Orleans to Tampico in east central Mexico need to prepare for this dangerous storm. While computer models seem to have converged on a general solution for landfall (around Brownsville, Texas plus or minus 150 miles) climatology points towards Dean turning northeast once he enters the Gulf of Mexico--towards Louisiana and New Orleans (CLP-5 model is the National Hurricane Center's climatology model).

This is an extremely powerful and dangerous tropical system. Jamaica will likely suffer from a direct hit from Hurricane Dean's extreme winds, surge, and rainfall. I expect catastrophic damage on the island in 36 to 48 hours.

Time to focus on Dean

2007-08-16T21:59:00.000-05:00

Hurricane Dean continued to strengthen Thursday and it appears now that the computer models are beginning to hone in on the future track of the powerful storm.

Dean should cross the Windward Islands and Lesser Antilles Friday as a stong Category 2 storm, with winds between 100-110 mph. Some of the resort islands like Martinique may suffer substantial damage as the hurricane whips across the island chain.

After the islands, Dean should continue on a west-west/northwest track to just south of Jamaica Sunday with sustained winds of 120 mph or more. Next in line will be the Yucatan peninsula on Tuesday, with the storm possibly making landfall as a category 4 storm near Cozumel, Mexico.

After a short ride over the Yucatan, Dean should re-emerge in the Gulf of Mexico and continue re-organize itself before making a final landfall somewhere in the Gulf Coast, most likely Southern Texas.

Personally, I am not convinced that the computer models are doing to well dealing with Dean's rapid speed (on Thursday night it was traveling west at 25 mph), and the progression of the upper-level ridge in the northern Atlantic. As such, I think that Dean may head a little further north than indicated, and anyone west of the Alabama coast are game. None the less, it appears likely that a strong hurricane will potentially impact the Gulf Coast next Thursday or so.

Model spread for Dean

Severe weather outbreak Thursday... still watching tropics

2007-08-15T22:49:00.000-05:00

Severe Storms

A strong front will pass through the area late tonight and spark off some major thunderstorms. EHI values (a measure of the tornadic potential across the area) are expected to be tremendous this afternoon. I would expect a number of lines of thunderstorms with damaging winds, and a couple of isolated tornados this afternoon/evening. The deciding factor in whether or not we will see a major outbreak depends on how much sunlight we see during the day. Sunshine, of course leads to destabilization and enables thunderstorms to reach severe limits. Make sure to check watches/warnings as the day progresses.

Notice the very high EHI values on the top-right map. Isolated tornados are possible this afternoon/evening.

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Tropics:

Erin: Tropical storm Erin will make landfall in southern Texas today with winds of 40-50 mph. The major damage out of Texas will be flooding however.

Dean: Tropical Storm Dean is very close to reaching hurricane status. I would expect the storm to reach hurricane status later today. Recent computer guidence suggests that the storm will travel into the Gulf of Mexico. More to come...

Dean, Flossie, TD 5; Its going to be a long week....

2007-08-14T21:11:00.001-05:00

As announced several days ago here on DCweather, all of the computer models were indicating that the tropics were going to explode this week. They did not lie. We currently have 3 tropical systems, 2 in the atlantic, and one in particular to watch.

Flossie: Hurricane Flossie weakened Sunday as it moved over much cooler waters near Hawaii. None the less, Flossie is still a strong category 2 hurricane, and will give Hawaii a glancing blow of tropical storm force winds and several inches of rain Wednesday. I do think that the islands should get by without too much in the way of damage.Surfs up: Flossie will cause minimal damage as it travels just south of the Hawaiian Islands Wednesday. Meanwhile, surfers across the state are getting ready for some of the best waves of the year!

TD 5: At 11:00pm Tuesday night, the NHC announced that the tropical wave in the Gulf of Mexico had gotten itself together well enough to be considered a tropical depression. While this is not good news for southern Texas, if I could be selfish for a minute, it is great news for us. Recent computer runs are indicating that most of the moisture from TD 5 will get absorbed into a front that will give us a chance for substantial rain next week! Unfortunatly, TD 5 may drop 10+ inches of rain on southern Texas; an area that does not need another drop. Additionally, I believe that TD 5 will become Tropical Storm Erica before it makes landfall, and may cause some wind damage on the south Texas coast. Anybody from Galvalston to Corpus Christy should be on alert for updates.

TD 5 visible at the bottom of the image. Soon-to-be Erin will make a Texas landfall Thursday

Dean: Tropical Storm Dean had a rough Tuesday. Stronger than expected sheer infultrated the storm on the northeast end and made it dificult for development. None the less, the system is heading into a more favorable environment for development, and should reach hurricane status by Friday. Computer models shifted a bit further south today with regard to the track of Dean, but a NC landfall is not out of the question. If I were forced to make a bet, I would say that Florida would be the target of this storm, but again, the only thing we do know is that the storm will not be a 'fish-spinner' (a storm that hooks out to sea before reaching land) due to a ridge in the northern Atlantic.

Despite looking ragged on satellite, the center of Dean remained defined Tuesday, and further development is expected.

Invest 90 L strengthening in Atlantic...

2007-08-13T00:50:00.000-05:00

The tropical wave, Invest 90 L is likely going to upgraded to tropical depression status Monday. The system has strengthened significantly late Sunday, and now has an easily identified center of circulation. This system is still more than a week away from being something to seriously worry about, but none the less, still certainly worth watching.

Computer models suggest that Invest 90 L will strengthen as it heads due west over the next several days. After that--- who knows? The GFS has trended furthur south; to a landfall in southern Texas, but these models are wildly inaccurate for storms 10+ days away.

Rain anybody?

Some badly needed rain is in the forecast for later this week. Meanwhile, a couple of isolated storms are possible Monday, as a weak cold front approaches the area. Nothing severe is anticipated nor is any significant rainfall expected.

Later this week, a more vigorous cold front will give us our first taste of the fall. More importantly however, it will enable a number of systems to ride up along the boundary left by the front during the Friday-Sunday time frame and potentially give us some much needed rain.

Cooler temperatures and yes, maybe some rain (!), are in store for late this week.

(also note invest 90 L in the Carribean)

A few storms for Friday, tropics to explode next week...

2007-08-10T12:06:00.000-05:00

Friday will feature a couple of storms across the area. It does not look like any of these storms will reach severe limits because of a left-over storm complex from last night that is currently just off the Mid-atlantic coast. This storm complex will rob the area of the energy necessary for thunderstorm development.

Additionally, clouds have moved into the area in the last hour or so, and the spotty cloudcover will make it dificult for enough heating to go on for thunderstorms. That said, a couple of storms may reach severe limits this afternoon, so stay tuned.

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Now, to move important things--- the computer models (particularly the GFS) have been consistantly showing a tremendous CAT 4-5 Hurricane moving up the East Coast late next week. Now, an important question must be asked: hype, or time to worry?

Well obviously there is no definate answer, but at least last year, the GFS frequesntly showed hurricanes beyond 10 days into the future only to take them off in subsequent runs. What worries me is that this hurricane has been on the maps for all of the last 11 runs, spanning 3 days. Additionally, the UKMET and Euro both now show this 'super hurricane'.

We will need to watch computer model trends closely in the next several days, but the most important thing to note here is that multiple sources seem to be indicating that the tropics are finally going to get going next week. Remember, the NWS still thinks we will be well above average in hurricane #s this year despite the slowish start.

A scary sight: many computer models are indicating that a large hurricane will impact the United States around the 20th of the month.

Major severe weather outbreak this afternoon/evening...

2007-08-09T08:49:00.000-05:00

4:00 UPDATE: One down, one to go. The first line of storms weakened as they moved into the immediate metro area, however significant damage was felt in northern Maryland. Although the watch box expired recently, another one will be issued shortly. This next batch of storms is heading out of SW PA at the current time and should be in the immediate metro area by 7pm or so. Stay tuned.

11:30 UPDATE: SEVERE THUNDERSTORM WARNINGS ARE IN EFFECT FOR FREDERICK, WASHINGTON, AND CARROL COUNTIES IN MARYLAND. There will be significant wind damage associated with this line of storms as they move across Northern Maryland in the next hour.

10:20 UPDATE: As soon as I finished writing the entry, a watch WAS issued for the area until 4pm. I will be doing updates as this dangerous line of storms moves into the area.

These are the projected times of arrival:

Hagerstown: 11:30am
Frederick: 12:00
Leesburg: 12:15pm
Rockville: 12:30pm
Silver Spring: 1:00pm
Bethesda: 1:00pm
Washington DC: 1:15pm

The NWS has extended the slight risk area for severe storms today to completely encompass the entire DC metro area. A moderate risk has also been discussed for parts of the area. Dangerous winds appear to be the biggest threat, however a tornado is not impossible.

Discussion: A dangerous line of severe storms is progressing through southwestern PA this morning. As this line continues to move east and southeast, it will head into increasingly unstable air (dewpoints are well into the 70s (!) and MLCAPE values on the order of 2500-3000 J/KG), this line will likely strengthen on its southern end as it moves into the region.

I am surprised a watch has not been issued with this line, as there have already been a number of damaging wind reports from interior PA this morning.

After this line goes through, there may be additional storms through the 10pm hour (the line should be out of the area by 5pm or so). Make sure to check radar befor heading out this afternoon... this line is cruising at a clip of 40-50 mph!

A dangerous line of storms will move into the area by the noon-2pm hour.

Additionally, the NWS issued a slight risk for severe storms tomorrow.... this will be a busy couple of days.

Storms stay west tonight... Major storms on tap for tomorrow, Friday

2007-08-08T14:27:00.000-05:00

SEVERE THUNDERSTORM WATCH IS IN EFFECT NORTH AND WEST OF DC FROM WASHINGTON COUNTY, MARYLAND TO HARDY COUNTY, WV WESTWARD UNTIL 10:00PM EST

Discussion: A line of storms that dropped golf-ball size hail in extreme southwestern PA is decending southeasterly at the current time. Unfortunatly, it does not look like the immediate metro area will see anything in the form of rain; the atmosphere is surprising stable this afternoon in spite of the relentless heat/humidity).

The best bet for rain tonight, as mentioned earlier is west towards I-81.

Chances for a shower/storm tonight:

Baltimore: 0%
Frederick: 10%
Washington DC: 20%
Winchester: 50%
Fairfax: 30%
Fredericksburg: 20%

Radar at 3:40 showing the line of storms in the panhandle of Maryland

After reaching 100 degrees in many areas today, relief is finally on the way in the form of severe thunderstorms associated with a boundary that will slip south of the area Friday. More on the severe storms for Thursday tomorrow...