wxgeek's weather-Wednesday snow forecast-Update 12/18

Update Tue Dec 18

Snow in the mountains continues today, although a slight retreat to the west is suggested by latest models, probably back to the actual Divide this afternoon. Upper trough will approach CO tonight and bring an increase in snowfall to the mountains west of the Divide. Strong southwest winds will accompany the system over the high country, so more blowing and drifting snow today into Wednesday. Upper level trough will be near the CO/UT border Wednesday morning, then into western KS by Wednesday evening. Snow will become heavy overnight west of the Divide, and spread east by Wednesday morning. Currently expecting 1-2 feet of additional snow for the high country, so travel will be difficult to impossible from this evening into Wednesday morning.

Latest model runs slow the system down a bit, so onset of snow in the foothills and Plains may hold off until early Wednesday morning. Latest trend in models also suggest slightly lower snowfall totals, as snow will only persist about 8-12 hours for most areas of eastern CO. I suspect the current Winter Storm Watch will become a Winter Weather Advisory later today. Strong northerly winds will still accompany the snow, so areas of blowing and drifting snow as well as reduced visibility will be prevalent on Wednesday, especially east if I-25.

So forecast for the foothills and Plains now looking like this:

Snow to move into the foothills and northern CO Plains between midnight and 6 am. Snow to become moderate to heavy at times from 6 am to 2 pm on Wednesday, accompanied by northerly winds of 15-35 mph, so blowing and drifting of snow may cause travel problems, especially east of I-25. Snow will gradually diminish by late Wednesday afternoon, persistsing longer across the far eastern Plains.

Snow accumulations:

Foothills and Palmer Divide: 3-7 inches
Banana Belt: 2-4 inches
Urban Corridor and northeast Plains: 2-6 inches
Southeast Plains: 1-3 inches

This will be a good snow event, but not a major storm. Some road delays and closures possible, especially over the high country and the eastern Plains. Flight delays are possible, and some cancellations possible, although I spoke with a friend at Southwest that makes weather calls for airports, and they currently plan to operate a normal schedule on Wednesday, although that may of course change. I am hoping they operate normally as I am currently scheduled to depart Wednesday morning.

Models still indicate the potential for a High Wind event Wednesday night into Thursday morning, as strong northwest flow aloft and a very strong surface pressure gradient form. Northwest 'bora" winds could reach 36-65 mph Wednesday night east of the Divide to the foothills and adjacent Plains. This could cause significant blowing and drifting of fresh snow, especially across roads like CO-93, US 285 and C-470.

CO then gets a snow break from Thursday through Sunday, with temps near seasonal norms, and breezy westerly winds at times.

Next system has very different solutions from the GFS and the ECMWF. Euro model brings the next system across Monday and the track is much farther north. GFS tracks the system to the south of CO and keeps it around much longer. Euro track would bring snow to the mountains Monday and maybe some light snow to the foothills and Plains Monday night. GFS would bring snow into western CO Monday, and push east into eastern CO Monday night into Tuesday morning, with snow persisting into Wednesday morning. This system has the potential to be quite potent if the GFS solution verifies, but of course still a long ways out. People should monitor this system closely if you are planning any travel in CO next Monday and Tuesday as it has the potential for a big snow event across the state. Of course Tuesday is the day I am scheduled to arrive back in CO, we'll see how that goes.

As these systems move east of CO, they will become large winter storms across the midwest and eastern U.S., so anyone traveling should keep a watchful eye out on your route and destination. As our system from Wednesday exits, major snowstorm across the central Plains and midwest Wednesday afternoon into Thursday, then the Great lakes and eastern U.S. Thursday into Friday. Chicago could be a mess for travel on Thursday, with ripple effects throughout the air travel system. Same situation will develop after our Christmas day storm for areas east, with this system potentially even bigger for the central and eastern U.S.

---

For today, more mountain snow west of the Front Range Crest, with some blow off snow possible for western foothill areas, but no accumulation expected. Mountains continue to get slammed under moist northwest flow aloft. Heaviest snow today will be north of I-70, but snow extends south into the San Juans. Mountain areas picking up 6-12 inches each day under this flow, with heavier amounts possible over west facing slopes. Strong westerly winds will continue to create difficult travel conditions across the high country. Westerly winds of 25-50 mph, gusting to over 60 mph will continue today and persist into Tuesday. These winds will also affect our foothills with westerly winds of 20-45 mph, with some gusts to 55 mph today through Tuesday.

Finally a snowstorm for eastern CO looks imminent. Models in fabulous agreement on upcoming system. Vigorous upper level trough will move across CO Tuesday night into Wednesday. Cold front associated with the upper trough will push south across CO Tuesday night into Wednesday morning. Snow will increase in western CO Tuesday into Tuesday night, so even more mountain snow. Snow will push east to the foothills by Tuesday evening/night, so snow should begin between 9 pm and 3 am, earliest far northern areas and later towards the Palmer Divide. Snow will become moderate to heavy Wednesday morning into Wednesday afternoon for all of eastern CO, with heaviest snow for the foothills between 4 am and 2 pm Wednesday. Snow should end Wednesday evening as upper trough moves into KS.

Now for snow amounts, always the hardest part to forecast. Mountains get a bunch, so will focus on the foothills and plains. Currently looks like areas north of the Palmer Divide will get heaviest amounts, but we should see snow across all of eastern CO. This would be an even bigger snowstorm, except system is moving east pretty quickly, so we only have about a 12-18 hour snow window.

Foothills and Palmer Divide: 4-10 inches, with up to a foot in favored areas
Banana Belt: 2-5 inches
Urban Corridor and northeast Plains: 2-6 inches
southeast Plains: 1-4 inches

Wednesday commute could be pretty ugly, so a good day to work from home if possible. May be fewer commuters due to the holiday period, so that may help, but roads will definitely be snow and ice packed most of the day Wednesday.

The fun won't end Wednesday evening however, as very strong northwest flow develops behind this system, triggering a Bora high wind event Wednesday night. Northwest winds of 30-60 mph will be possible across the foothills and adjacent plains, so with lost of fresh snow, blowing and drifting will create travel problems, so expect drifting across roads Wednesday night into Thursday morning.

CO will finally see a break from snow Thursday through Sunday with mild temps and occasional breezy westerly winds. Some northern mountain snow may be possible on Sunday, but only light accumulations expected.

Now long range models are beginning to paint an interesting picture for Christmas. Models are suggesting an upper level trough will dig into the central Rockies next Monday and persist into Wednesday morning. This would bring snow to nearly all of CO next Monday, with snow persisting through Christmas day and into Wednesday morning. This forecast still a long ways off, but if models are painting the picture correctly, this could be the biggest Christmas day snowfall for the Metro area ever, and insure nearly everyone in CO of a white Christmas. Time will tell.

Just a heads up to everyone that I will be away from Dec 19 through Dec 25, so may have limited ability to post any updates during this time. Fairly typical for a meteorologist to be attempting to travel by air during forecasted snowstorms, the universe definitely has a sense of humor or irony.
_________________

Bump for Tues Dec 18 update