COLORADO WEATHER by Josh Larson

Incredible Snow Statistics!

noreply@blogger.com (Josh Larson) — Tue, 07 Feb 2012 21:25:00 +0000

To put last week's incredible snow storm, as well as this season's unusual snowfall, into perspective, I asked my meteorological cohort, Brendan Heberton (@BrendansWeather) to do some number crunching.

Here are the very cool statistics he came up with:

Denver has seen 142% of average snowfall so far this season. We've recorded 50.3" so far this season, and on average we receive 35.3" through the entire month of February.
We could receive no snow between now and April and still be above average for the season!
We are at 85% of the entire seasonal average for snowfall in Denver right now, with two of our snowiest months to go!

Incidentally, last night's over-performing snow, which brought up to 4 or 5" in some spots like downtown Denver, only managed to bring 1" officially at DIA.

Next chance for accumulating snow -- though at least at this point, it doesn't look like a big deal -- would be late Saturday into Sunday of this coming weekend.

AM Update: Widespread 10-20" SNOWFALL

noreply@blogger.com (Josh Larson) — Thu, 02 Feb 2012 15:13:00 +0000

8:15am Thursday 2/2/12

Model data that has come in overnight does nothing to lessen confidence that this will be an extremely high impact, if not record-breaking, February snowfall. Crunching the most recent model data and bifurcating into a 4" forecast spread produces the following results:

DENVER: 15-19"
BROOMFIELD: 13-17"
FORT COLLINS: 9-13"

Showers of rain or wet snow will develop by late afternoon across much of the Denver metro area, with a rapid transition to all snow as temperatures drop below freezing. Snow will then continue, moderate to heavy in nature, all night Thursday and much of the day Friday, perhaps even lingering into the early morning hours on Saturday.

The bulk of the snow will probably fall during an 18-hour window from midnight Thursday through 6pm on Friday. During this time snowfall rates of 1"+ per hour are likely.

Note: the largest February snow event on record for Denver was a 14.1" storm during February of 1912. I think we have a 50/50 shot of breaking this record...

BREAKING: Upping Snowfall Totals forEntire Denver Metro area to 10-15"+

noreply@blogger.com (Josh Larson) — Thu, 02 Feb 2012 04:28:00 +0000

Updated: 9:40pm 2/1/12

Newest guidance suggests that the track of this upcoming storm, which had been somewhat uncertain earlier today, is going to move on a path that is nearly perfect for a disruptive and dangerous snowfall to plaster the entire Denver metro area.

I am, therefore, upping forecast totals for the duration of the storm event (late Thursday into early Saturday) to

10-15" ACROSS THE ENTIRE DENVER METRO AREA, WITH ISOLATED SPOTS UP TO 2 FEET...

Heaviest snowfall totals will be from downtown Denver and points east and northeast. As you head northwest away from Denver, snowfall totals will decrease somewhat. Fort Collins looks to receive more like 8-12" from this storm.

More updates to follow...

Significant Snowfall Likely Across Denver MetroMost Places Can Expect to See a Healthy 6-12"

noreply@blogger.com (Josh Larson) — Wed, 01 Feb 2012 23:48:00 +0000

There's been a lot of consternation from other forecast outlets about computer modeling making it difficult to pin down a forecast for this storm. I beg to differ. If you follow the trends, weighting the models that have been most consistent as well as the ones that are the best "initialized" -- i.e., what the model forecasts at Hour ZERO is as close to reality as observations suggest -- then it's relatively easy to come up with a forecast of decent confidence:

THE STRONGEST EVIDENCE NOW POINTS TO WIDESPREAD 6-12" OF SNOW ACROSS THE ENTIRE DENVER METRO AREA...

...with the highest totals to the east and northeast of downtown Denver. As you head northwest from Denver, totals will drop off somewhat. (Places like Fort Collins are likely to pick up more like 4-8".)

I'll have detailed forecast information, time line, Q&A, etc. in upcoming posts.

Significant Snowfall Thursday into Friday?

noreply@blogger.com (Josh Larson) — Tue, 31 Jan 2012 18:24:00 +0000

Newest model guidance is lending confidence to the fact that we'll see at least some snow late Thursday into Friday of this week, and is suggesting the potential for significant accumulations, especially in Denver and points south and east.

I now believe at least a few inches of accumulation are probable, with the potential of 6" or more certainly not out of the question.

Updates to follow...

Late Week Snow?

noreply@blogger.com (Josh Larson) — Mon, 30 Jan 2012 22:40:00 +0000

An early heads-up that several computer models are hinting at the possibility of an accumulating snowfall for central Colorado during the late Thursday through early Saturday time period late this week.

It's far too early to know with any confidence if it snows, whether it might be heavy or not, where highest amounts will be, and even if it will be an entirely-snow event. Temperatures may be marginal at the outset.

However, I have reason to believe that at least a few inches of snow are possible by this time Friday.

Stay tuned...

>4" More Snow Will Fall from 2 Events: Friday night/Sat & Sunday night/Mon

noreply@blogger.com (Josh Larson) — Fri, 02 Dec 2011 18:55:00 +0000

With cold air firmly entrenched over the entire region, two separate disturbances will push through the area over the next 3-4 days, providing two chances for light accumulations of snowfall.

The first event will take place from late Friday night into mid-day Saturday, with the likelihood for 1-3" of snow.

The second disturbance will probably bring 2-4" of snow late Sunday into mid-day Monday. Because of the bitterly cold temperatures associated with, particularly this second event, the atmosphere will be efficient at wringing a decent amount of snow out of only a little moisture.

Between these two events, I think most places stand a good chance of seeing more than 4" combined...

How Much Snow Do You Think Will Fall Thursday?

noreply@blogger.com (Josh Larson) — Thu, 01 Dec 2011 02:27:00 +0000

Just for fun, let me know how much snow will fall on Thursday in Denver?

Click here to take this survey

3-7" of Wind Whipped Snow Thursday Bitter Cold to Accompany and Set up Shop

noreply@blogger.com (Josh Larson) — Wed, 30 Nov 2011 17:27:00 +0000

We're looking at our first significant snow storm in about 3 weeks late tonight into Thursday, as temperatures drop 40+ degrees in 24 hours and wind chills by late in the day Thursday drop to the low single digits. In addition, periodic near-blizzard conditions may develop Thursday morning into the afternoon.

In addition, I have every indication that the next 10-14 days will feature much below normal temperatures across Colorado, and the potential for at least several different snow events; more snow appears likely this weekend, for instance.

I'll publish a detailed forecast later today for tomorrow's snow storm.

In the mean time, follow my latest updates here.

Another Significant Front Range Storm6-10" of Wind-Whipped Snow Likely

noreply@blogger.com (Josh Larson) — Tue, 01 Nov 2011 03:46:00 +0000

If you follow me on Twitter (@coloradowx or @joshlarson), the snow storm I've been advertising for several days now is nearly upon us. In many ways it will be fairly similar to last week's storm, falling almost exactly a week later and with fairly similar snow totals.

A couple main differences from last week's storm: 1) We're likely to see little in the way of distructive tree damage as most all of the leaves have now fallen and this will be a drier, lighter snow; 2) due to colder ground temperatures I expect snow from this storm will accumulate more readily on roads -- which was largely not the case last week, and will therefore make Wednesday morning's commute a rough one. 3) This system will feature more in the way of wind than last week's storm -- this will lead to reduced visibilities and the possibility of brief blizzard-like conditions, with wind gusts to 45mph possible at times.

I believe that the NWS is being a bit conservative in their current forecast for 4-8" and would not be surprised if they bump up their totals tomorrow. I believe that most places will see 6" or more inches of snow. MY FORECAST IS FOR 6-10" OF SNOW TO FALL FROM TUESDAY EVENING THROUGH WEDNESDAY MORNING across the Denver metro area including Boulder and Fort Collins.

I'll provide an updated forecast, along with more details and a storm time line by early afternoon on Tuesday.

Until then, stay tuned...

Significant Snowfall Likely Wednesday

noreply@blogger.com (Josh Larson) — Sun, 23 Oct 2011 19:04:00 +0000

1pm Sunday: The details for next week's snow storm are coming into clearer focus as we get closer and model consensus improves. I can say with high confidence that >4" of snow appears probable for the entire Denver metro area (including Boulder and Fort Collins.) Some models are even suggesting totals closer to 8 or 10", but I'm going to remain conservative for the time being.

A rain/snow mix is likely to develop late in the day Tuesday changing to all snow sometime after midnight. Moderate to heavy snow is likely much of the day Wednesday with high temperatures only in the low-to-mid 30s (after Monday's record highs near 80).

I'll have a full forecast with more details as we get closer...

Next Week's Snow Coming into Better Focus

noreply@blogger.com (Josh Larson) — Sat, 22 Oct 2011 17:50:00 +0000

11:50am Saturday: A quick update to say that several computer models are suggesting a high probability for >6" of snow to fall during the period from late Tuesday into early Thursday. While it's still too far out to say with high confidence whether this, indeed, will come to fruition -- as the storm's exact track is still uncertain, it is certainly in the realm of possibility. In fact, a couple models suggest that double digit snowfall totals might be possible...

More to follow...

Accumulating Snow More Likely Next Week Several Inches Possible Late Tue-Wed

noreply@blogger.com (Josh Larson) — Sat, 22 Oct 2011 01:36:00 +0000

My confidence has increased over the past 48 hours in regards to the probability for accumulating snow to fall during the late Tuesday to early Thursday time period next week.

At the moment it looks like rain or a rain/snow mix Tuesday night is likely to change to all snow by the early morning hours Wednesday, continuing throughout the day, with high temperatures in the low-to-mid 30s -- as a strong cold front and upper-level low conspire with surface high pressure to provide plenty of moisture and a supply of enough cold air.

Several inches of accumulation appears possible at this time, with areas from Denver northward more likely to pick up several inches or more than areas further south. This may be an instance where Fort Collins does better than Boulder or downtown Denver, at the latter two locations due better than locations further south, primarily due to the fact that cold air will spill into the region several hours earlier towards the Wyoming border than points further south.

Stay tuned to Coloradowx.com as I update and fine-tune my forecast during the weekend.

Season's First Snowfall Next Week? Models Suggest There's a Decent Chance

noreply@blogger.com (Josh Larson) — Thu, 20 Oct 2011 00:10:00 +0000

I am beginning to see the signs that a strong cold front and associated area of low pressure digging to our south may conspire to bring snowfall to central Colorado by the middle of next week. While confidence for an event a week out is low, the fact that several different computer models seem to support the chance for snowfall over the area warrants mention.

My gut feeling, based on the data I've analyzed thus far, is that we have a slightly greater than 50/50 chance at seeing snowfall sometime in the late Tuesday to early Thursday time period, with accumulations not out of the question.

I'll update as we get closer to the possible event...

84 Degrees to Snow in Fewer than 36 Hours?

noreply@blogger.com (Josh Larson) — Sun, 03 Apr 2011 05:57:00 +0000

Denver's high of 84 on Saturday shattered the previous record of 76 by 8 degrees. (That might not sound like a lot, but most records are broken by only a few degrees; I'm sure this record will stand for quite some time.)

That said, this is spring in Colorado, and those of us who've been here even for just a few years, know how volatile spring weather is around these parts.

So, let me set the picture for you: today's record heat was caused by southerly winds streaming north ahead of a strong cold front, which will cause temperature to plummet by 60+ degrees within a 36 hour window. (For instance: at 4pm on Saturday, the temperature was 83 at DIA; at 4pm on Sunday the temperature is likely to be in the low 50s; at 11pm on Saturday the temperature was 64 at DIA, and at the same time on Sunday, we're likely to see sub-freezing temperatures.)

However, this is not an easy forecast. Spring storms in Colorado are notoriously hard to predict, and models (not just some -- but all), have shown significant flip-flops over the past several days. Case in point: the two major US forecast models have a nearly 20 degree temperature difference at 2pm Sunday; one has us in the low 60s, while the other has us in the low 40s. The truth is probably somewhere in between. The discrepancy is because the models disagree on the timing of the cold front's passage.

That's not the only issue though. In addition to disagreement in timing of the cold front (hence temperatures), there's also a large disagreement in how much moisture this system will bring. One model shows less than an inch of snow, the other suggests at least 3 inches.

However, since I've been advertising since at least 4 days the probability of accumulating snow, I'm going to stick to my guns and issue a first call forecast for:

TWO to FIVE inches of snow Sunday night, the vast majority of which will stick only to typically colder surfaces such as grassy areas and cartops, though I can't completely rule out the possiblity of some secondary roads in normally colder areas across Denver metro to become slushy.

I'll issue my final forecast by mid-day tomorrow.

Current confidence: 2/5

Snow Tonight/Monday Likely to Overperform ...Thinking 6-10" vs NWS' 4-8"

noreply@blogger.com (Josh Larson) — Tue, 08 Feb 2011 00:23:00 +0000

I'll issue a final call later tonight, but new evidence coming in throughout the day has led me to believe that our snowstorm tonight into Monday is likely to "over-perform" -- much like the one last week.

My gut feeling is that we'll see 6-1o" from this event against the National Weather Service's call for 4-8"; while that may not seem like a big difference, the impact of 8 or 9" versus 4" is certainly tangible.

I'll release my final forecast by 10pm tonight...

ALERT: Staggering, Life-Threatening Cold this Week

noreply@blogger.com (Josh Larson) — Sun, 30 Jan 2011 20:49:00 +0000

Central Colorado is likely to see its coldest temperatures of the entire year late Monday into early Thursday of this week. A severe Arctic cold front presses south by mid-day Monday brining temperatures to record or near-record lows.

Highs Tuesday are unlikely to rise above ZERO, with overnight lows dropping to as low as -20 with wind chills to -35. These bitterly cold temperatures will be accompanied by at least a few inches of snow -- I'm thinking 2-5" Monday into Tuesday -- but the big story will be the shocking cold.

Updates to follow...

Major Snowstorm to Dump 6-12" of Windblown Snow Across Region

noreply@blogger.com (Josh Larson) — Sun, 09 Jan 2011 01:51:00 +0000

If you follow me on Twitter -- either @boulderXweather or @joshlarson -- you know that I've been hinting at the potential for a significant weekend snowstorm since early in the day on Tuesday. Well that early prediction will certainly come to fruition as an Arctic cold front, combined with a developing area of low pressure, will combine to bring sharply colder temperatures, moderate to heavy snow, and windy conditions primarily from early in the day Sunday into the first half of Monday.

To give you an example of how cold the air is with this system: today's high was 51; tomorrow's high is likely to be in the mid-20s; Monday and Tuesday's high will struggle to rise above 10 degrees with overnight lows of -7 to -14 both nights. We are talking dangerous, punishing cold.

But how about the snow, you ask? I expect that light snow will break out sometime within a few hours of sunrise. The first few hours of the snow are likely to be pretty light in nature. However, by the time we reach mid-afternoon, I expect snow will increase in intensity and become more moderate. Early highs in the mid-20s will fall to the teens by sunset, as winds pick up to 15-20mph at times.

Expect moderate to heavy snow Sunday night, with some blowing and drifting, and temperatures continuing to plummet to near ZERO by Monday morning. I expect that by sunrise Monday, snow will have begun to taper off a bit in intensity, and will continue to do so as the day wears on. I would expect that the vast majority of the snow associated with this system will have fallen by noon on Monday. The rest of the day should feature only scattered snow showers, with highs near 10.

BY THE TIME ALL IS SAID AND DONE, I EXPECT 6-12" OF SNOW TO FALL ACROSS THE REGION.

As is typical with systems like this, locations closest to the Foothills will see stronger upslope and are more likely to pick up higher amounts. As with the last system, then Boulder may will pick up several more inches than Denver, for instance.

Please, if you don't have to drive -- don't. Too many people out, and not enough common sense can cause situations like this: http://bit.ly/eScfKv

First Call Forecast for First "Real" Snowstorm of the Winter

noreply@blogger.com (Josh Larson) — Wed, 15 Dec 2010 00:01:00 +0000

A storm system passing through the front range will finally bring snow to the area late Wednesday into Thursday. This is a much anticipated snow for many, as we've had the least snowy fall on record this year. A dip in the jet stream, a developing area of low pressure passing just south of the region, and plenty of cold air means that I expect 3-6" of snow to fall from late night Wednesday into Thursday -- and it will stick.

More details to follow..

Pattern Continues to Imperil Snowlovers' Sanity

noreply@blogger.com (Josh Larson) — Mon, 06 Dec 2010 02:44:00 +0000

We have had near record-low snowfall over the past 6 weeks, and it appears that the pattern of much below-normal precipitation coupled with near- to slightly above-normal temperatures will persist for at least the next 10 days. By that point, if we compare to previous year's October 15 through December 15 statistics, it is quite likely we'll qualify for one of the least snowy periods on record.

But snow is not only an aesthetic thrill for those who love it, it's also important for our water tables. As I said in my previous post, we're now officially experiencing "moderate drought conditions"; assuming this dryness lasts for another two weeks (which I think is quite probable), by the end of the month we may be bumped into the "severe drought conditions" category by NOAA/USDA.

What's the reason for this exceptional dryness? Well there are a number of contributing factors, but the most obvious one is a jet stream that has more-or-less, except for brief exceptions, stayed farther north than average over the western US (resulting in a ridge of high pressure), and farther south than normal across the eastern half of the country (resulting in a trough of low pressure.) This has our region (with the exception of high country, which has experienced upslope snow events) experiencing much drier than normal conditions, with most storms impacting locations north and east of central Colorado.

Though it would be unwise for me to postulate about conditions nearly 3 weeks from now, I'm beginning to think that the odds or a White Christmas this year across the metro area are less than 50/50, though this dry pattern can't hang on forever; perhaps we're in store for a big dumping during the last third of the month...

Flakes to Fall Tuesday; Accumulating Snow Thursday

noreply@blogger.com (Josh Larson) — Tue, 09 Nov 2010 17:16:00 +0000

As the first major cold front/storm system of the late-fall/early-winter period pushes through Colorado on Tuesday the Denver metro area can expect to see some flakes of snow during the second half of the day, as temperatures turn sharply colder.

I'm highly skeptical of any accumulation below 7,000ft, even on grassy areas, but stranger things have happened. I can't rule out a dusting to an inch on colder surfaces tonight into early Wednesday in some locations.

After a respite in precipitation on Wednesday -- though a cold day -- another system dives into the region late Wednesday into Thursday. Temperatures will be some 20 degrees below normal, with afternoon highs on Thursday unlikely to rise much (if at all) above freezing. Snow is likely to develop overnight Wednesday and continue into Thursday. This time I'm confident snow will stick, and 1-3" of snow seems possible...

As an aside, I am inclined to believe that the majority of the rest of the month will feature below-normal temperatures for our area, with a potentially stormy pattern setting up.

Note: Image below courtesy Accuweather.com

Snow Increasingly Likely on Thursday

noreply@blogger.com (Josh Larson) — Mon, 08 Nov 2010 17:08:00 +0000

It's becoming clear to me that we have a high potential to see our first snowfall across Denver metro on Thursday. In fact, newest data suggests we may not even make it above 32 the entire day.

In my mind the question now is one of accumulation. At this time I think we're looking at only a dusting to 2" -- i.e., a minor event. Still (at least for me), the first snowfall of the season is an exciting one.

Updates to follow in the next couple days...

ALERT: Turning Sharply Colder; Snow Possible Thursday

noreply@blogger.com (Josh Larson) — Sun, 07 Nov 2010 22:58:00 +0000

After our recent 'Indian Summer' weather (yesterday's high was 2 degrees shy of the record for the date), which will extend into Monday, our weather will turn sharply colder to below-normal levels by Tuesday, continuing through at least the rest of the work week.

There are some indications that some light snow is possible on Thursday across Denver metro, with highs only in the mid-30s. Accumulation potential is unclear at this point.

I'll keep you posted...

Early Sneak Preview: Upcoming Winter

noreply@blogger.com (Josh Larson) — Thu, 23 Sep 2010 17:36:00 +0000

I'll have a much more thorough outlook in the coming weeks, but I believe that early indications suggest the potential for a colder-than-normal winter with near- to perhaps above-normal snowfall for central Colorado due, in part, to a rapidly strengthening La Niña event.

I'm more confident on the temperature outlook (colder than normal) than the precipitation/snowfall outlook.

I also believe that the first half of the winter (December through early February) is more likely than not to feature near- to above-normal snowfall, while the second half (late February through April) is more likely than not to feature below normal snowfall. Seasonally, it may well end up being a 'wash' for overall snowfall compared to normal. [Note that during the December to February period, on average central Colorado experiences above normal precipitation compared to "Neutral" or El Nino episodes: http://bit.ly/dsEvZE -- image seen at right; click to enlarge]

Stay tuned...

Warmer than Normal for the Next Week When Will Our First Snowfall Occur?

noreply@blogger.com (Josh Larson) — Thu, 23 Sep 2010 05:07:00 +0000

For the next five (to possibly 7-10) days, central Colorado can expect somewhat above normal temperatures. This will continue the trend of August thus far, with temperatures averaging -- a significant -- nearly 5 degrees above average to date.

That said -- whether you know it or not -- we are rapidly progressing into fall and the nascent stages of our snow season. Case in point: the average first date of measurable snowfall for Boulder/Denver is October 16. (The earliest ever recorded is September 12; the latest ever recorded is November 15.) At this moment, my gut feeling is that the first snowfall of this upcoming fall/winter season may well be later than the average of October 16, though it's too early to say with much confidence.

Above is my temperature forecast for the next 5 days for Denver metro. Unlike Wednesday, most of the upcoming days should remain dry.

Sometime over the next week I'll update you on how I think our current La Nina episode, which has developed at record speed, might affect fall/early-winter weather across Colorado...