12:15 PM, Friday, March 31, 2017

Changes from my forecast yesterday are that I’m a little more inclined to go with the lower end of the snowfall forecasts that I gave yesterday. The heaviest snow reports are likely to come in from the southern Front Range (west of Pueblo down through the east slopes of the Sangre de Cristos). But you should still be prepared for significant wet snow this evening and tonight along the mountains and foothills from Colorado Springs northward.

Synopsis

The storm system in the four corners region this morning was at peak intensity and will be weakening as it moves across northern New Mexico through Saturday. The current observations (satellite and radar) suggest that the most likely period for some heavy precipitation is between late afternoon and about midnight, with more intermittent precipitation and dry intervals late tonight and Saturday.

Changeover to snow in the lower foothills and plains

Some pockets of heavier convective precipitation may speed up the changeover to snow late this afternoon, but most areas probably won’t change over until after dark. The result will be highly variable accumulation potential. Snow may accumulate rapidly including some on the roads during brief periods of heavier snow this evening, while other nearby areas may stay wet with very little snow.

Most likely snowfall

Above 7000 feet: 7-15 inches

6000- 7000 feet: 5-10 inches

Below 6000 feet: 0-6 inches

• Cheyenne, Boulder, Broomfield, Castle Rock, Colorado Springs, and Denver’s west and south sides are a little more likely to be in the 3-6 inch range.
• DIA, Longmont, Fort Collins are a little more likely to be under 3 inches.

Update at 2:55PM Friday:

The heavy bands do not appear to be coming together as expected. Will probably see the lower end of the snowfall ranges listed above.

Again late Monday?

The next storm in the series is due to begin late Monday.  It’s looking snowy all the way down to the plains, but keep in mind that the last couple storms evolved a bit differently than the 3-4 day model guidance suggested.

12:15 PM, Thursday, March 30, 2017

A storm system will be near peak intensity in the four corners region Friday and then slowly weaken as it moves east across northern New Mexico on Saturday. Deep easterly flow into the mountains should help generate wet weather, especially late Friday, with snow levels falling low enough to impact the Front Range urban corridor.

The biggest uncertainties

• The changeover to snow in lower elevations is likely to occur around the time of the most steady and heavy precipitation late Friday afternoon and evening. A small shift by a few hours can have a big impact on snow amounts.
• Convection: there is likely to be some short-term bands of intense convective precipitation (maybe even some thunder), possibly after the changeover to snow. This can increase localized snowfall rates for a few hours late Friday.
• The longest period of steady rain and snow may shift to the south of Colorado Springs Friday night. Although all of eastern Colorado should get significant precipitation, the timing of the shift will determine if the northern Front Range or the southern Front Range get the biggest totals (more on that tomorrow).

Most likely amounts (with greater uncertainty than usual)

• above 7500 feet: 10-20 inches. There will probably be some portion of the Front Range that gets over two feet, but it’s too early to tell if it will be in the northern or southern Front Range.
• foothills and Palmer Divide: 7-15 inches, with the greatest uncertainty in the lower foothills.
• lower elevations along the foothills (Colorado Springs, west and south sides of metro Denver, Broomfield, Boulder): 4-8 inches
• high plains and to the north (DIA, Longmont, Fort Collins, Cheyenne): 1-5 inches

Updates

I plan to update tomorrow. However, if this afternoon’s data trends toward the snowier potential for the Denver-Boulder area, you may notice a winter storm watch issued by the NWS for lower elevations.

Could it be a snowless March?

Official records in both Denver and Boulder show only a trace of snow has occurred so far this month, a rather unusual occurrence for March. In Boulder there have been 4 Marches with no measurable snow (1910, 1911, 1918, and 2012). Denver (DIA) will likely have measurable snow before midnight on March 31st. But in Boulder the climate day ends at 6PM. So if there is measurable snow in March 2017 it will be in the final hours or minutes leading up to 6PM Friday. Anything after 6PM counts in April 1st totals.

12:15 PM, Tuesday, March 28, 2017

The storm currently moving through will continue to produce periods of mainly rain below 6000 feet, mainly snow above 7000 feet, and some slushy snow between 6000 and 7000 feet.

Denver-Boulder-Fort Collins-Colorado Springs: intermittent rain into tonight. The rain may mix or change to snow toward morning, but little or no accumulation is expected (0-2 inches). If there is accumulation the chances are a little better toward the south side of Denver and the north side of Colorado Springs.

Foothills and mountains: Rain should change to snow in the lower foothills tonight, with mainly snow continuing above 7000 feet. Accumulations are likely to range from a few inches in the lower foothills to between 6 and 12 inches higher up. There may be some localized areas greater than 12 inches, especially southwest of Denver and in the Pikes Peak region. Watch for accumulating snow in the Palmer Divide region as well.

Next storm Friday and Saturday

Another storm late Friday and Saturday is looking like it could be a slow moving 4-corners  type system that has the potential to be quite wet along the Front Range. Early indications are that is may also be a few degrees cooler which could bring significant wet snow into the lower elevations.

4:30 PM, Monday, March 27, 2016

Two storms with mainly rain in the lower elevations and wet snow above 7000 feet are likely tomorrow afternoon and early Wednesday and again Friday afternoon into Saturday.

I will need to update tomorrow but here are the highlights for the Tuesday-Wednesday morning storm:

Heavy wet snow in the foothills and Palmer Divide region. Probably 6-18″ (the higher amounts as you go up in elevation). This storm is likely to have heavier amounts than last Friday’s storm.

Rain (maybe some thunder late Tuesday) for the lower foothills and urban corridor. It is likely to be mainly rain, with a changeover to wet snow in some areas by Wednesday morning. This is the part that I will update tomorrow. With heavier precipitation expected this time around a changeover to wet snow could accumulate quickly.

6:20 AM, Friday, March 24, 2017

If you are just getting started this Friday morning, the worst of the storm for the Front Range is over. For many areas north of Denver the precipitation came to an end before the changeover to snow. There are some major impacts south and east of Denver. A stretch of I-25 is closed between Denver and Colorado Springs, and a portion of I-70 is closed well east of Denver, and wintry conditions will continue out east through the morning.

Active storm track

We are in a more active storm track for Colorado now. The next period with precipitation likely in Colorado/Wyoming is Sunday, but that will likely be very minor along the Front Range. Another chance comes in around Tuesday, and probably another storm toward the end of next week.

6:00 AM, Thursday, March 23, 2017

Over just short distances the strong storm system tonight and Friday morning is likely to produce minor impacts in some areas (most likely the northwest Denver suburbs, Broomfield, Boulder, and Fort Collins) and major effects in other nearby locations (best chances for heavy snow and blowing snow in the Palmer Divide region and maybe across the south and southeast suburbs of Denver).  Colorado Springs will probably be south of the major impacts.

The storm appears to be evolving in a way that will produce strong northerly wind along the foothills beginning tonight, but not much easterly or northeasterly wind needed to concentrate precipitation development along the foothills. As you go south of Denver the north winds support upslope toward the Palmer divide and may aid in generating locally heavy precipitation there. Just east of Denver northeasterly winds nearer to the storm center may support a period of heavy precipitation and that may impact the eastern suburbs.

Most likely outcome:

Mountains: 6-12 inches of snow likely near and continental divide

Plains and lower foothills of northern Jefferson, Broomfield, western Adams, Boulder, and Larimer counties: rain showers this evening then snow toward Friday morning with accumulations ranging from 0 to 3 inches. Gusty north winds may develop.

Denver and DIA: rain showers this evening then snow and blowing snow toward morning with 1-4 inches

Plains and lower foothills of southern Jefferson, Douglas, and western Arapahoe counties: rain showers this evening then possibly some locally heavy snow and blowing snow by Friday morning with accumulations varying from 3-10 inches. Road closures may occur.

If you are traveling east on I-70 or on I-25 from Denver to Colorado Springs tomorrow expect winter driving conditions from wind and snow and possible closure.

What is the chance that the more intense precipitation will shift west?

It cannot be ruled out that an unexpected shift in the storm can bring heavier snow to Denver and Boulder, but that appears unlikely at this point.

11:15 AM, Monday, March 20, 2017

The equinox ushered in Spring at 4:29 AM MDT today, but temperatures of the last two days are more consistent with the average for June 1st. On Saturday and Sunday Boulder set record highs of 80 and 78. Denver was even warmer with 81 and 80, but both fell 1 degree short of the record. Today the record in both locations is 80 which is within reach, but it is likely that we will fall just a little short of those records.

Cooler Tuesday

A cold front is slowly oozing down the northern plains today and should move through the Front Range early Tuesday. This is the type of front that will be felt more in eastern Colorado than in western Colorado. There is a small chance it will be strong enough to trigger some low stratus clouds and localized drizzle in eastern Colorado. But it is more likely that it will just cool us down a bit but remain dry across most of the area.

Storm late Thursday and early Friday?

There has been good consistency for days regarding a significant storm moving through Colorado Thursday and intensifying as it moves to the east of the Front Range by Friday. Most indications are that it may only have minor impacts along the immediate Front Range foothills and adjacent plains. But recent guidance suggests the chance that the storm may slow down and track a little farther south which would put the Front Range region in a more favorable location for significant rain and wet snow Thursday night and/or Friday morning. More updates will come in the next few days.

11:50 AM, Friday, March 17, 2017

Warmth

The unusually warm weather will continue into early next week, with Saturday and Sunday likely to be the warmest days. Boulder tied a record high of 78 this past Wednesday, but Denver didn’t quite reach theirs. For Saturday and Sunday the records in Denver are 82 and 81, both set in 1907. In Boulder the records for Saturday and Sunday are both 77 (set in 2004 on the 18th and 1907 on the 19th).

Denver should get close to the record each day with a small chance of setting a new record. If it reaches 82 that would be the earliest that temperature has been recorded. The earliest 80-degree in Denver was set this year on February 10th, a remarkably early occurrence.

Boulder has a better chance of setting a new record on at least one day this weekend. The earliest 80-degree day in Boulder is 80 on March 16, 2015.

March snowfall

March is on average the snowiest month in Boulder and Denver (and most locations along the Front Range urban corridor). So far there has been no measurable snow in either location this month. The unusual warmth of February and the first half of March have coaxed some trees and shrubs out of dormancy making them more prone to damage from freezes or wet snow that are likely yet to occur.

Medium and long range forecasts suggest a more active storm track across the Rockies may develop later next week. Although there is more uncertainty in longer-range prediction, there has been agreement between models on this potential change. So I wouldn’t bet on a snowless March yet.

11:55 AM, Sunday, March 5, 2017

A Pacific cold front will bring wind and snow to the mountains tonight and Monday, and mainly just wind and cooler temperatures to the eastern foothills and plains. Accumulating snow may extend east of the continental divide enough to impact Nederland. Some flurries or snow showers may even make it to the urban corridor.

But the main impact for the lower foothills and plains on Monday will be temperatures 15-20 degrees cooler with a strong wind possible. There may even be some gusts over 60 mph in some areas.

By Wednesday mild spring weather is likely to be back in force.