12:00 noon, Wednesday, March 30, 2016

A winter storm is in progress for Cheyenne with heavy wet snow (another 5-10″) and wind through the day today, and even heavier amounts to the north of Cheyenne. This blog will focus on the more variable weather along the Colorado Front Range (Fort Collins, Longmont, Boulder, Metro Denver, Colorado Springs).

The first round of unsettled weather yesterday afternoon and evening brought light snow in some of the higher elevations, and rain in the lower elevations. Two more rounds of unsettled weather are expected.

Round 2 (Wed): This afternoon and early evening will see gusty north winds (especially just east of the foothills), more numerous showers,  and colder temperatures. Where the showers are heavier or more persistent, a changeover to snow is likely, with spotty accumulations.

Nederland, Estes: 1-4 inches

Fort Collins, Longmont, Boulder, metro Denver: mainly 0-1 inch, but some local areas may get a fast 1-3 inches.

Colorado Springs: little or nothing

Round 3 (Thu): After a lull tonight, a final disturbance should move north to south and affect the Front Range on Thursday from late morning to early evening. Snow, or rain changing to snow, will probably be mostly in and near the foothills and Palmer Divide.

Nederland, Estes, Palmer Divide: 3-6 inches

Boulder, south and west suburbs of Denver: 1-3 inches

Fort Collins, Longmont, DIA, Colorado Springs: trace-1 inch

The weekend is looking dry and springlike.

3:00 PM, Tuesday, March 29, 2015

Areas around and north of Cheyenne should be ready for significant snow and wind late tonight and Wednesday. Meanwhile, the Colorado Front Range urban corridor (and adjacent foothills) should get the wind but probably not the snow. The storm is likely to track across the Front Range near the CO/WY border late tonight bringing snow to the north and some showery precipitation and a blustery wind to the south.

The sequence for the Front Range urban corridor: 1) showers and maybe a thunderstorm this afternoon or evening (changing to snow in mountains). 2) Becoming cold enough for snow in the predawn hours of Wednesday, but probably very few showers and only spotty accumulation. 3) Possibly a period of more numerous snowshowers Wednesday afternoon or evening, but still only spotty minor accumulation.

Most likely accumulation through Wed evening:

Cheyenne area: 5-10 inches, more immediately to the north.

Fort Collins: probably 0-2″, but close enough to the storm that there is a small chance of 2-4″.

Longmont, Boulder, metro Denver, Colorado Springs: mainly 0-1″, a few localized heavier showers may produce 1-2″

Nederland, Estes: 3-6, a bit more in the higher mountains.

Thursday: a weak disturbance following the storm looks likely to bring some areas of light snow Thursday afternoon or evening.

6:00 AM, Tuesday, March 29, 2016

The small chance that and eastern Wyoming snowstorm may shift south got even smaller. Snow accumulation on Wednesday is likely to be little or nothing for the Fort Collins-Boulder-Denver-Colorado Springs corridor. Heavy snow and blowing snow is likely for Cheyenne and north. Some light amounts (with wind) are expected today and tonight in the Front Range mountains. I’ll do a more complete update later today.

4:30 PM, Monday, March 28, 2016

A major spring storm moving through the central Rockies and into Nebraska Tuesday afternoon and Wednesday should cause rain and then snow. The biggest impacts are likely to be blizzard conditions in parts of eastern Wyoming and maybe the northeastern plains of Colorado. The Denver-Boulder-Fort Collins corridor will likely be south of the high impact region, but this one will be watched for possible shifts in the development.

Potential for heavy snow (at least 10 inches) and high wind:

Very likely: east-central Wyoming (don’t plan on driving I-25 north from Cheyenne)

40-50% chance: Cheyenne, and the Colorado/Wyoming border areas

10-20% chance: Denver-Boulder-Fort Collins (most likely much less here)

less than 10% chance: Colorado Springs

Timing:

Precip should be showery rain (maybe thunder) through Tuesday evening, except in Cheyenne area where it could change sooner.

Blustery Wednesday even if it’s not snowing

Thursday: a secondary disturbance following the big storm may bring widespread light snow late Thursday.

1:15PM, Friday, March 25, 2016

Given the recent storm that greatly exceeded expectation, you might be suspicious to hear that a relatively minor storm is moving in late tonight and Saturday. But it really is a different kind of storm. Wednesday’s storm was expected to be high-impact, but it ended up being high-impact in a different area than expected. Tonight’s storm is weaker and more of an upslope style that will favor areas in and near the mountains, mainly south of I-70.

A little rain may kick things off late Friday. Snow that does occur is likely in the late night and into Saturday. Accumulations should range from little or nothing to the northeast, to over 6 inches in the mountains and foothills southwest of Denver and in the Pikes Peak region.

0-2 inches: Cheyenne, Fort Collins, Longmont, DIA

1-3 inches: Boulder, Broomfield, Denver, Nederland, Estes

2-6 inches: Castle Rock, Lakewood, Colorado Springs

5-10 inches: mountains and foothills mainly south of I-70

2:35 PM, Wednesday, March 23, 2016

There are a number of 20-inch reports as of 2PM not only in some foothills locations, but also in a corridor roughly along and a little west of I-25, including Wheat Ridge, Westminster, Broomfield, Louisville, and Lafayette Wouldn’t be surprised to see a few more. At 2PM the snow was decreasing from the north and west in Larimer, Boulder, and Jefferson counties. Heavy snow still persisted near and east of I-25. Parts of the Denver area (and DIA) may have to deal with significant snow and blowing snow into the early evening, and the storm is likely to rage into the night on the northeastern plains.

The intensity was amazing:

I got the storm position incorrect which made a big difference in shifting the action  west toward the foothills last night. But just as important for the accumulation was the historic intensity of the snowfall rates. There were multi-hour periods of 2 inches per hour, and peak rates of 4 inches per hour! Snow adds up fast at those rates! As of noon the Boulder climate station topped 15 inches in just 10 hours, and that wasn’t as intense as some locations immediately to the east. An analogous storm occurred in March of 1992 when the Boulder climate station received 13 inches of heavy wet snow in 6 hours (with thunder), and 16 inches in 12 hours. Some areas immediately east got 20″ in that one too.

March and El Nino:

March averages the most snow of any month along the Front Range urban corridor, and El Nino years typically increase the odds of a snowy, wet March. After a very dry first half of the month, many parts of the Front Range are now on the snowy side of average, and we may add at least a little more Friday night or Saturday.

4:45 AM, Wednesday, March 23, 2016

I was awakened by transformer flashes at 4:30 AM caused by the most intense snowfall rates I’ve seen this year (about 2 in/h). Fascinating! I wish I had forecasted in better. I decided to do a quick blog in case I lose electricity.

The shift westward in the location of the mid-level storm intensification (to just south of Denver rather than near Limon) made a big difference in the focus of the storm. Areas along the foothills are getting clobbered in the pre-dawn hours. As the intensity eases up later this morning or afternoon, the worst may still be in store for the east side of metro Denver. Although there is a lot of variability, many locations from the Palmer Divide northward seem on the way to a 6-10 inch range. Be careful, it’s heavy wet snow for shoveling, and there may be some power outages around the region.

And we may get to enjoy shoveling snow again Friday night or Saturday.

8:45PM, Tuesday, March 22, 2016

The winter storm late tonight and Wednesday is still poised to produce quite a gradient in snow across the Front Range urban corridor. One change from the midday update is that it appears the storm may begin to intensify rapidly late tonight before it moves into eastern Colorado. That would allow a period of northeasterly upslope flow in the early morning hours and the potential for a brief period of heavy snow (or rain changing to snow) along the foothills before the storm really organizes to the east. There may even be a rumble of thunder. Be prepared for wintry travel tomorrow morning. And if there is little or no snow where you are, check on the conditions where you are going. Accumulation may be highly variable due to localized convective snow.

Most likely accumulation range (and the %chance for at least 10 inches):

Denver, Lakewood, Littleton: 4-8 inches  (20% chance of at least 10)

Castle Rock, Aurora, DIA: 5-10 inches (30% chance of at least 10)

Westminster, Boulder, Longmont, Fort Collins: 1-5 inches (10% chance of at least 10)

Cheyenne: 4-7 inches  (30 % chance of at least 10)

Colorado Springs: 0-3 inches (almost 0% chance of 10)

Northeastern plains: 6-14 inches (with at least a 50% chance of more than 10)

12:50 PM, Tuesday, March 22, 2016

The first of three potential Front Range snowfalls between now and the end of March will occur tonight and Wednesday. This storm, although strong, will not be characterized by deep upslope flow, so areas near the foothills have the smallest potential for heavy snow, while the northeastern plains (and possibly the east side of Denver) are likely to see some heavy snow and blowing snow.

The storm will first impact the mountains tonight, mainly west of Peak-to-Peak highway. As the storm system intensifies Wednesday morning in east-central Colorado, the northeastern plains are likely to see some areas with heavy snow and blowing snow, perhaps after some rain initially. Along the Front Range, north winds will not favor sustained snowfall, except to the south of Denver as the north winds push up the Palmer Divide. In some areas of light precipitation it may stay warm enough so that rain occurs.

Mountain & Palmer Divide accumulation: 4-8 inches, less in the foothills (below 8000′) of Boulder and Larimer counties.

Lower elevations:

3-6 inches: along and south of a Lakewood-Denver-DIA line, but not Colorado Springs.

6-12 inches with high wind: parts of the northeastern plains (~25% chance this will be as far west as Aurora and DIA.

0-3 inches: northwest suburbs of Denver, Boulder, Longmont, Fort Collins; and to the south of the Palmer Divide in Colorado Springs (yes, there may be areas with no snow).

The next 7-10 days: another storm Friday night and Saturday looks like it will be more of the classic “upslope” type bringing widespread snow, but it’s too early to pin down amounts. Mid to late next week may bring another snowy period to close out the month.

11:55 AM, Thursday, March 17, 2017

The initial snow kicked in a bit earlier than expected (mainly in Larimer, Weld, and Boulder counties) and is melting on the warm road surfaces as of noon. Expect conditions to get more wintry by this evening and into Friday morning.

An area of mainly light snow is expected to become more organized from north to south this afternoon and evening and continue into Friday.  Within the area of light snow we will likely get narrow east-west bands of heavy snow. Most places from Denver to the Wyoming border will probably get at least a brief period of heavier snow sometime late today through early Friday, and a small subset of the area (10-20% of the area) may get a multi-hour period of heavy snow. The chance for the heavy snow is lower south of Denver and north of Cheyenne.

Timing:

This afternoon: Intermittent snow is likely from Denver northward. The chance for heavier bands of snow will slowly increase, especially north of I-70.

This evening through Friday morning: Light snow, with some localized heavy snow periods.

Friday afternoon: snow becoming more intermittent and dissipating.

Amounts:

Metro Denver, Boulder, Longmont, Fort Collins, Cheyenne: most likely 3-6 inches, but a subset of the area will probably see 6-10 inches.

Nederland, Brainard, Estes: 4-10 inches

Colorado Springs: 1-3 inches

Impacts:

Road conditions may change sharply over just a few miles due to the variable nature of snow intensity this afternoon through Friday morning.

Slushy and icy roads likely Friday morning, possibly in some areas by late this afternoon.

Weekend Outlook:

Dry and mainly sunny. After a cold start on Saturday, it should warm up. The next chance for cold, unsettled weather is Tuesday or Wednesday next week.