wxgeek's weather-Cooler Temps and Snow coming-Update Dec 6

Update Thu Dec 6

A few flurries and sprinkles today, but nothing significant expected. Maybe 1-2 inches of snow over the mountains above 8000 ft.

Friday will be mostly dry with temps near seasonal norms. A few flurries possible across the central and northern mountains.

Saturday will begin our change to a more winter like pattern for a while. Upper trough approaching from western Canada will dig into CO Saturday night into Sunday. Models today are a little more agressive with the trough. Cold front will move into northern CO Saturday morning and move south through the state during the day, moving into southern CO by Saturday evening. Snow will move south across the northern and central mountains during the day on Saturday, and snow and upslope flow will develop behind front along the foothills and Plains by late Saturday afternoon and evening. Moderate snow is possible Saturday night into Sunday morning, with snow hanging on now until Sunday afternoon. The GFS is pretty heavy for snowfall, while the NAM is still pretty light, so confidence in snowfall amounts still marginal, although beginning to trend towards the GFS which is also supported by the Euro model. Hence, here is my latest snowfall estimates from Saturday through Sunday evening:

Northern and Central Mountains: 5-10 inches
Foothills and Palmer Divide: 3-7 icnhes
Banana Belt: 2-5 inches
Urban Corridor and Plains: 2-4 inches

Temps will also drop dramatically behind cold front on Saturday, so temps in the single digits and teens Saturday night and Sunday. Temps close to zero possible on Sunday night.

For next week, chance for snow, mostly west of the Divide Monday/Tuesday, then again late next week into next weekend. Temps to remain at or below seasonal norms next week.
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"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Update Wed Dec 5

One last day of warm temps before winter actually makes it's arrival in Colorado. System currently moving through UT and CA will progress eastward and bring snow to the mountains west of the Divide tonight. Latest models now indicate we may see some precip from this system in the foothills and Plains Thursday as well. Majority or precip will be north of I-70, but areas farther south may see precip as well. Mountains look to get 1-4 inches of snow above 7000-8000 ft, with the foothills seeing anywhere from a dusting to an inch or two during the day on Thursday. Precip could begin by 6 am along the foothills, including some fog and low clouds to reduce visibility. Precip could persist into Thursday afternoon and evening in some areas. With warm temps today, the commute should not be too bad with the snow level at 7000-8000 ft, as most snow likely to melt on asphalt below 8000-9000 ft. Some roads above 8500 ft could have slick spots Thursday morning.

Friday should be cool with temps near seasonal norms, and dry except for some lingering flurries across the northern and central mountains. No additional accumulation expected Friday.

Next system, which will be much stronger, is on track to arrive Saturday afternoon in Colorado. Models in better agreement today that the system will be strong, but move through CO relatively quick, so limiting snowfall amounts. Still, system will have strong enough dynamics to produce decent snow amounts from Saturday afternoon into Sunday afternoon. Heaviest amounts will be in the northern and central mountains where 5-10 inches will be possible. For the foothills and Plains, we will see a decent period of upslope from Saturday afternoon into Sunday morning, so currently expect 3-6 inches for the foothills, with 1-4 inches for the Urban Corridor and Plains. That could still change if the track and speed of the system change, but currently fairly confident in track and speed.

The good news is that CO will remain under a moist northwesterly flow with systems moving from the Gulf of Alaska into the Rockies every few days. Next chance for snow next week would be Mon/Tue and again Wed/Thu and again next weekend. Timing will likely change, but you get the idea of systems moving through regularly over the next 7-10 days. Hard to tell if one of these will dig and cut off to produce a big upslope event, as models currently suggest they will be fast moving systems, so limiting snow amounts for the foothills and Plains, but at least providing regular chances. The central and northern mountains will greatly benefit from the northwest flow, as this is the favored direction for orographic snow in these ranges. Southwest mountains will not benefit nearly as well. I would expect 1-2 feet of snow for the mountains over the next week, so great news for skiers and winter outdoor enthusiasts, as well as for our water supply. Fire danger should become very low after Thursday and remain low for a while. A white xmas for many in CO looking much better now.
_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

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Well, not right away, but later this week. Wednesday will be yet another warm and breezy day across most of the state. The good news is that all models are indicating that the forecasted change in the global upper air pattern will begin to take place this week. The stubborn upper level ridge will migrate into the eastern Pacific centered in the Gulf of Alaska. This will begin to allow storms to track from the Gulf of Alaska southeast into the Inter-Mountain region, with a long wave upper trough centered in the Rocky Mountain region to the Great Plains.

The first of these systems will move into northwest CO Wednesday night into Thursday. Snow will move into northwest CO after midnight Wednesday with snow level 7000-8000 ft. Snow to persist mostly west of the Divide and north of I-70 Thursday into the evening, with some flurries persistsing into Friday morning. Light accumulations expected, generally in the 1-4 inch range. Then things get more interesting across CO. Models still providing a variety of solutions, so the confidence in the weekend forecast is fairly low, but overall we are in for much colder temps and the possibility for accumulating snow. Cold front associated with a digging upper level trough will bring colder temps beginning Friday, with snow moving into northwest CO during the day on Friday. The forecast then becomes much more uncertain for the weekend. Depending on the track of the upper level trough, we could see anything from a pretty good snow Saturday and Sunday, to a brush with some light snow Saturday. Will need to wait and see subsequent model runs to see how they will eventually handle this system. If the system digs and slows down, we have the potential for a good dump, say up to a foot or more in the foothills. If the system moves through fast and north, maybe a few inches. I'm certainly rooting for the snowier solution to verify.

The better news is that models are now consistent in keeping the upper level pattern with the ridge in the Pacific through the end of December, so we will continue to see chances for snow every 2-4 days from next week through the end of December it appears. How much snow will depend on the track each system takes, and if any single system will develop into a big upslope event. For sure the mountains will see much more frequent snow under the northwesterly flow aloft, so good news for ski resorts and skiers. Colder temps and more moisture also spells reduced fire danger. Whoever made the request to fat red man for snow, thanks for your efforts as they have appeared to work. It will take some effort to get back to normal snowfall, but this is a start.
_________________
"Climatology is what you expect, Weather is what you get".

"It is better to be roughly right than precisely wrong".

I'm liking this forecast! SNOW!

Bump for Dec 5 Update

Bump for Dec 6 update