11:30 AM, Thursday, December 29, 2016
The holiday weekend will start with a mild Friday but with the return of some gusty chinook winds in and near the foothills. After a cold front Friday night, near average winter temperatures will return. Then on Monday or Monday night an arctic cold front may begin a multi-day stretch of very cold weather with a chance for light snow or freezing drizzle.
Windy and mild Friday
Temperatures on Friday are likely to be in the 50s throughout much of the Front Range urban corridor, maybe even 60 in a few spots. Above average temperatures are likely throughout Colorado and southern Wyoming. Chinook winds may develop with some localized gusts exceeding 50 mph in and close to the foothills.
Trend toward colder
By Saturday a colder air mass should be in place across the region, but temperatures should be near average over the weekend with intervals of sunshine. There may be some areas of light snow in the mountains, particularly in southern Colorado.
The trend toward colder will kick into high gear early next week. It’s too early to tell if the very cold weather will arrive Monday or Monday night, but when it gets here we are likely to be in for a stretch of very cold and generally cloudy days with some snow or freezing drizzle around.
11:00 AM, Tuesday, December 27, 2016
For those of us who live in and along the foothills we don’t want a repeat of the Christmas Day windstorm that scoured parts of Jefferson and Boulder counties with winds exceeding 90 mph. Although I don’t expect the winds to be that strong, we are likely to see some strong westerly wind gusts late Tuesday and early Wednesday in some locations in and along the foothills. I would not be surprised to see a reports of over 70 mph.
Temperatures should be near average most of this week, and likely a bit above average by Friday. A cold front should cool us back down for the weekend, but neither bitter cold nor significant snowfall is expected at this time.
12:20 PM, Friday, December 23, 2016
There is little change to my update from yesterday. A strong storm moving from Colorado to Nebraska on Christmas Eve night and Christmas Day is not likely to bring major snow to the immediate Front Range area.
Where travel will be tough
Winter travel conditions can be expected by Christmas Eve night in western Colorado and last into Christmas Day. Some of the higher elevations near and west of the continental divide may pick up 6-12 inches.
Blizzard conditions are likely to develop on the northern plains on Christmas Day and into Monday (northeastern Wyoming, eastern Montana and the Dakotas).
For the Front Range
Christmas Eve should be a mild winter day. On Christmas Day as the storm moves through Colorado and into Nebraska, there may be some snow showers or even a brief snow squall along the Front Range to whiten the ground, but most areas will probably see little or no accumulation. You may notice a tendency for cold northwest winds as the day goes on.
In the higher foothills of the Front Range, there should be some light snow blowing over from the other side of the continental divide on Christmas Day, and an increasing tendency for gusty winds.
Although only a small shift in the storm can bring more wintry weather into the Front Range urban corridor, that appears to be a very unlikely scenario at this time.
12:40 PM, Thursday, December 22, 2016
A powerful storm system is expected to move from the California coast Friday to northeastern Colorado on Christmas day where it will really strengthen. That track is likely to be too far north for much impact along the Front Range urban corridor. But be ready for winter travel Christmas Eve night and Christmas Day if you are heading west over the higher passes of Colorado and Wyoming, or north across the northern plains.
Friday to Monday
After a few snow showers around today (mainly to the west of the Front Range), Friday and Christmas Eve should be dry and relatively mild. The Pacific storm should start impacting western Colorado Saturday afternoon or evening. Travel may become difficult in western Colorado. As the storm strengthens and moves from Colorado to Nebraska on Sunday, blizzard conditions are likely across the northern high plains (northern Wyoming, northwestern Nebraska and the Dakotas). Here along the Front Range there may be an increase in wind and some snow showers, but little accumulation is expected at this time in the lower foothills and eastern plains of Colorado. Up near the Wyoming border and in Cheyenne there is a better chance for accumulating snow, but they too will likely be south of the most severe conditions.
I’ll be watching for any shift in the storm track, but almost all indications are that the worst will not impact Denver-Boulder-Fort Collins.
The biggest storm of the weekend won’t be directly over any major airport hubs, so that may help reduce the chance of delays. There may be some weather related delays Friday at airports in California; on Saturday at Salt Lake City (snow), New York and Washington DC (rain); and on Christmas Day there is a small chance for low clouds and rain (not snow) at Chicago while Dallas has a small chance for thunder.
11:55 AM, Monday, December 19, 2016
Across Colorado and Wyoming the week should be mainly dry, not as cold, but windy at times in and near the eastern foothills. The next chance for a storm will come on Christmas weekend, at least for the mountains and West Slope areas, with big uncertainty regarding impact along the Front Range.
Breezy, cool front Wednesday
Milder temperature may be accompanied by occasional strong gusty winds in and near the foothills Monday afternoon and Tuesday. A cold front on Wednesday will not bring cold arctic air like the last two. Its main impact should be to disrupt the warming trend with slightly colder temperatures and temporarily spread gusty winds out onto the plains.
Recap of snow
I did not anticipate the persistence of a west-east band of heavy snow Friday evening. Given that it occurred over the Denver area, its impacts were certainly well observed. 7-11 inches of snow fell mainly in 6 hours on parts of Jefferson, Denver, and western Adams counties. DIA also set a record low when the temperature bottomed out at -15 just before midnight Saturday. Boulder bottomed out at -10 about the same time but did not set a record.
As with any weather phrase, “chinook” is sometimes attached to any wind in the winter. Although the Front Range is the national hot spot for chinook winds, a chinook describes a certain pattern. Strong west-to-east wind into and above the high peaks can be deflected by the mountains. Under certain conditions the airflow can get deflected upward at the mountain barrier and then downward over the east slope (similar to the flow of water in a creek when it encounters a row of boulders). If the downward deflection is strong enough the strong upper level winds can reach down to the surface in and near the foothills. So chinook winds come from above. That’s why you don’t necessarily see them observed at nearby stations before they hit. They can be very sporadic and variable in both space and time.
6:00 AM, Friday, December 16, 2016
At 6 AM the cold front was through Casper, Wyoming, but not particularly fast moving. It should pass through Cheyenne around midday, the Boulder-Devner area during the afternoon, and Colorado Springs this evening. Temperatures by Saturday morning will likely be around 0 and only get to the single digits during the day. Saturday night will likely see temperatures in the range of -5 to -10 although a few cold spots (like DIA) might get a little colder than -10.
Nothing too amazing here as we expect a light snowfall Friday evening through Saturday morning. Accumulation will likely range from an inch or less over parts of the northeastern plains of Colorado to about 5 or 6 inches near the continental divide. There will probably be some higher amounts at the passes west of the continental divide and north of Cheyenne. For the Front Range these are the most likely amounts:
4-6″ Brainard Lake, Eldora, and Eisenhower Tunnel
2-4″ Cheyenne, Boulder, Nederland, western suburbs of Denver, Castle Rock
1-2″ Colorado Springs, Aurora, DIA, Longmont, Fort Collins
After a very cold morning the temperature will moderate a bit on Sunday but still stay below freezing. By Tuesday we are likely to experience warmer Chinook conditions ahead of the next cold front either Wednesday or Wednesday night. The midweek cold front should not be as cold as today’s.
10:30 AM, Wednesday, December 14, 2016
We are in for a roller coaster of temperature this week. Cold today, mild Thursday and early Friday, then what will likely be the coldest air mass since December 2014 from Friday evening through Sunday.
After a cold start on Thursday, temperatures in most locations along the Front Range urban corridor should top 50. But watch out for some sporadic Chinook winds gusting past 50 mph in and along the foothills (much less windy east of the foothills). The mild weather will probably continue until at least Friday morning.
The cold air mass may surge down the Front Range during the day Friday, or is may wait until early evening, it’s too early to tell yet. But once here it will get very cold. Temperatures in the low elevations may fall to between 0 and 10 Friday night and stay there all day Saturday (more than 30 degrees below average). Saturday night will likely see a range for -5 to -15. Although the cold may moderate a bit Sunday afternoon, it will likely remain very cold into Monday.
At this point only light snow amounts are expected late Friday into Saturday morning. Although this could change, it’s looking like mainly to 1-5 inch range. In the higher mountains where snow will start Friday before the cold front, heavier accumulations are expected.