Monthly Archives: December 2017

Windy and mild, then colder over weekend

2:30 PM MST, Thursday, December 28, 2017

Possible windstorm

Tonight and Friday may see some strong winds in the east slope foothills and maybe in some areas along the foothills like Boulder and Lakewood. The Chinook wind came in yesterday morning with a dramatic warm-up, but this morning the colder polar air to the east oozed back in and shut off the wind. Tonight the Chinook may succeed at pushing the cold air to the east again. It’s not certain that the wind will reach the surface all along the Front Range foothills, but where it does the gusts might exceed 70 mph. Other nearby areas might only have light and variable wind.


Return of the cold weather

The cold arctic air is not that far away and is likely to slide back in from the north and east this weekend. Its impact will be mainly from the mountains eastward. The far eastern plains of Colorado are likely to be cold all weekend. I think the Front Range urban corridor will be cold all weekend too. But Saturday is more questionable and there is a small chance that the Chinook pattern will keep it mild into Saturday.

The air is pretty dry and snow is unlikely, but we can’t yet rule out some clouds and minor amounts of snow with the return of the cold weather.

Holiday weekend outlook

11:45 AM MST, Friday, December 22, 2017

Very cold air in the north-central United States and mild air in the Southwest will be vying for control of the Front Range region Saturday through Monday, with the colder scenario likely being more dominant (but probably not bitter cold). Snow will be mainly in the mountains, with some heavy amounts above treeline Saturday and Saturday night.

Saturday-Saturday night

The Front Range can expect a surge of colder air from the north and northeast Saturday afternoon or evening (it may be morning in Cheyenne). At mountaintop level Pacific moisture on west winds will bring snow mainly near and above treeline (mostly west of Peak to Peak Highway).

Mountains: widespread 6 inches near and above treeline and over a foot along and west of the divide (heaviest along and north of I-70).

Nederland, Estes Park, and Cheyenne: 1-4 inches

Fort Collins, Boulder, Denver: little or no accumulation most areas, but some narrow east-west bands in the evening may bring 1-2 inches in some spots.

Colorado Springs: little or no snow

Christmas Eve

Dry and cold day across Wyoming and Colorado. There is some chance for the milder air from the Southwest to work its way in during the day, but just a small chance. If the milder air does manage to come in, it might get a bit breezy in and near the foothills.


Christmas Day

It appears that the next surge of colder air from the north or northeast will push its way down the Front Range on Christmas. Timing is uncertain, but probably during the day. It should be mainly dry in the foothills and plains, but low clouds and flurries can’t be ruled out. There is a better chance for some snow in the mountains.

Colder with some snow Thursday; weekend outlook

Noon MST, Wednesday, December 20, 2017

First, the one important change from my weather update yesterday morning is that the cold snap for the weekend is looking less intense and less prolonged than what I was thinking yesterday. But you should still expect colder weather with a couple periods of snow Thursday and Saturday. Monday (Christmas) is rather uncertain at this point but the trend has been toward dry and not so cold.

Thursday cold front and snow

A weakening storm system moving through southern Colorado Thursday should still be strong enough for some snow accumulation, mainly in the morning and mainly in and near the foothills. Temperatures should be well below freezing all day and snow may be underway in and near the foothills from Denver north by daybreak. Snow will probably become intermittent and end along the northern Front Range by early afternoon; early evening south of Denver.

2-4 inches: in and near the foothills (Cheyenne, Boulder, western Denver suburbs, and Castle Rock).

trace-2 inches: Fort Collins Longmont, eastern metro Denver, Colorado Springs.

Friday: dry with temperatures rising to near or a little above freezing in the low elevations after a very cold morning.



The next cold front on Saturday will keep temperatures in the teens (or drop them into the teens if the front doesn’t arrive until late morning), and then into the single digits for many locations at night. Minor accumulation of snow appears probable along the Front Range.

Sunday will probably be dry and cold, but the cold air mass may be easing up during the day.

Christmas Day is an interesting forecast. A reinforcing cold air mass will likely move south into the north-central U.S. and could slip into eastern Colorado. But it may be fighting against a milder airmass pushing in from the west. Right now it appears the dry and somewhat milder weather might win out, maybe even with some Chinook wind. But that forecast could change dramatically, so I’ll update toward the end of the week.





Cold wave taking shape for holiday weekend

6:00 AM, Tuesday, December 19, 2017

Two cold fronts, one Wednesday night and a colder one Friday evening are on the way. We will likely have two snowy days, Thursday and Saturday, as we head into the holiday weekend. The change will seem especially abrupt given that Wednesday is likely to see high temperatures around 60 in many low elevation areas.


Cold & snow, round 1

A cold front Wednesday night and a storm system moving across southern Colorado Thursday will make it seem like winter, and Thursday is the winter solstice. High temperatures on Thursday will probably remain below freezing which will be the first below-freezing day this season for many low elevation areas. Snow is likely to be underway before sunrise from Denver north. Most snow accumulation is expected during the morning to midday hours, but some snow may linger into the evening, especially from Denver south.

3-6 inches: Mountains and foothills. north slope of the Palmer Divide, and places immediate along the foothills (including Castle Rock , western suburbs of Denver, Boulder, Cheyenne)

1-3 inches: Denver/DIA, Colorado Springs, Longmont, Fort Collins

I will update accumulation forecast Wednesday.


Arctic cold & snow, round 2

The next cold front Friday evening will bring an airmass from the Canadian arctic.  Temperatures on Saturday and Sunday will struggle to reach 20 even in low elevation areas, and locations along the urban corridor will probably get a night that slips below zero by Sunday and/or Monday morning.

Intervals of snow are likely Friday night and Saturday. Heavy accumulations are not likely, but given the cold, even light snow can have impacts on major highways.


If you are traveling by air this weekend, major airports on the West Coast are probably okay in terms of weather. East Coast airports will be ahead of the arctic air and may see intervals with rain, fog, and low clouds. Chicago should be mainly dry, but with arctic air sweeping in over the weekend, there will probably be delays due to slower ground operations in the cold.

Next round of cold and snow Thursday, maybe more by weekend

11:45 AM, Sunday, December 17, 2017

The first half of this coming week should be dry and milder than average. But it is looking more likely that the next cold front and chance for snow will arrive Thursday.  And then it is looking like it could be a cold and unsettled period for a while. There is uncertainty with a forecast beyond 5 days, but there is some consistency in projections for a wintry period starting Thursday and being reinforced over the weekend leading up to Christmas. At least the chances for snow on the ground are increasing!



Mild Saturday morning, then colder

Noon MT, Friday, December 15, 2017

After a mild start on Saturday the next cold front will probably start turning it colder Saturday afternoon. The storm associated with this cold front is weak and not very moist. Still, low level upslope flow Saturday night and Sunday morning may be enough to turn the small amounts of moisture into low clouds and light freezing drizzle or snow. At this point it appears that there will be little or no measurable precipitation, especially as you move away from the foothills. Where there is any accumulation it is likely to be minor.


After a mild start to next week the next cold front and chance for snow should come along Wednesday night or Thursday.  That will be in time for the winter solstice which is at 9:28 AM mountain time on Thursday, Dec 21st.



A little snow and more seasonable temperatures

Noon, Wednesday, December 13, 2017

A storm system with a slug of Pacific moisture is moving southeastward from the northern Great Basin toward Colorado. It is likely that areas in and near the mountains will get a light snowfall overnight, and everyone will have more seasonable temperatures Thursday. Low level dry air will keep the initial snow that falls out of the clouds from reaching the ground in the lower foothills and plains. Snow may begin in the higher mountains by early evening but hold off until after 10PM in the lower elevations.


Accumulations are likely to range from 3-5 inches in the mountains and 1-3 inches in and near the foothills. Across eastern Denver, Colorado Springs, and the northeast plains 0-1 inch is more likely.


After a return to above average temperatures on Friday afternoon, we are likely to return to colder with another chance for snow Saturday afternoon or night.

Could snow be on the way?

4:20 PM, MDT, December 12, 2017

A cold front and upper level disturbance on Wednesday evening will likely have a bigger impact along the Front Range than what we were thinking as recently as yesterday. Accumulating snow (probably minor) is appearing likely in and along the mountains with less chance farther east. The timing is Wednesday evening through early Thursday. So, nothing big appears on the way, but it may very well be something different than what we have had lately. I will update tomorrow.



Mild weekend, colder Monday

Friday, December 1, 2017, 11:15 AM

Expect a mild, dry weekend with above average temperatures and possibly a bit breezy at times. A cold front overnight Sunday into early Monday will make the early part of next week more like December. Over the last few days it was appearing that the cold front would bring a snowfall with it on Monday. Although that still looks like a possibility, the magnitude is looking rather minor. I will update Sunday if there are major changes.

La Nina this winter

The Pacific Ocean is in a La Nina pattern this winter, with below average sea surface temperatures in the eastern Tropical Pacific. Although there is always a lot of talk about what it means for our winter season, the truth is that the El Nino-La Nina phases are important influences but they don’t act alone. For that reason there can be a lot of variability from one season to the next.  The general expectation is for wetter/snowier in the Pacific Northwest and northern Rockies, and drier for the Southwest and southern Rockies. Colorado is often in between these two tendencies. But more often than not the Front Range east slope region and eastern Colorado run on the dry side during La Nina. The West Slope is more uncertain with the best chances for a snowy winter in the northwestern and north central part of Colorado.


Although the snow pattern is somewhat uncertain, there appears to be a much stronger correlation between La Nina and downslope windstorms. So be prepared for frequent visits from Chinook winds.