wxgeek's weather-Dry/warmer, then more snow this weekend-Update 2/19

Warm and breezy day with temps well above seasonal norms most areas today. Then the change begins. First, just when I thought things were going very well and consistent with the upcoming system, a large flock of seagulls must have flapped their wings violently in the Gulf of Alaska overnight, as models have changed significantly from yesterday. Thus, confidence in the forecast for this weekend is much lower. The incoming system is not a traditional upslope system from an upper low in the 4 corners region. The upper trough moving down from the Gulf of Alaska has some complexities, and as we all know well, small changes in the pattern over CO can make significant changes in snowfall amounts. Using latest model guidance, forecast now looks something like this:

Precip moves into northern CO Friday afternoon, mostly over the northern and central mountains with snow level 7000-8000 ft. The first upper level impulse is expected to bring precip into eastern CO by late Friday afternoon into Friday evening, with snow level lowering to around 6000 ft by 5 pm, then down to plains level by 7-8 pm. Models then diminish precip by midnight except over the northern mountains where some light snow is likely to persist. The lull in snow is expected to persist into late Saturday morning before heavier snow is expected to arrive around Noon on Saturday. Moderate to heavy snow is then expected across much of CO from Saturday afternoon into Sunday morning. The other big change in models is that heaviest snowfall is now centered over the eastern plains. This is primarily due to the lack of a deep northeasterly wind component over eastern CO. The winds aloft will be mostly westerly, and surface winds vary from northerly to southerly during the course of the weekend. So, snowfall amounts are now in considerable flux. The bottom line is that much of CO is going to get snow from Friday afternoon through Monday morning, it is just defining how much for various areas of the state that is the challenge. It is also likely the models will be changing over the next 24 hours as system is taking shape in the Gulf of Alaska and moving southeast. So best guess for snow amounts from Friday afternoon through Monday morning are as follows:

Northern and Central Mountains: 1-2 feet
Southwest Mountains: 8-16 inches
Foothills and Palmer Divide: 6-16 inches
Banana Belt: 3-10 inches
Urban Corridor: 6-14 inches
Eastern Plains: 8-16 inches

Heaviest snow begins in the mountains Friday afternoon and night, shifts to the foothills, Urban Corridor and plains Saturday into Sunday morning, then shifts back over the mountains Sunday into Monday, especially Southwest Mountains Sunday afternoon into Monday afternoon. Snow looks to end east of the Divide by Monday morning, but could persist into Tuesday evening west of the Divide, especially south of I-70. Travel across much of CO this weekend will be difficult to impossible, as delays and closures will be likely. If you don't have to venture out and drive, it will be much safer hunkering down close to home.

Next system is forecast to move into CO beginning late Wednesday with some moderate to heavy snow Wednesday night into Friday morning, so several more inches of snow will be possible for the mountains, foothills and plains next week.

Then by next weekend, models continue to develop long wave upper trough along the West Coast which will allow Pacific storms into the western U.S. For CO, snow is forecast for much of next weekend west of the Divide with snow level around 6000 ft Saturday, lowering to 4000 ft Sunday. Some snow may make it into the foothills and adjacent plains on Sunday, but mountains will receive the vast majority of precip from these Pacific systems. Models continue to bring regular systems from the west coast into CO the following week.

_________________
"Climatology is what you expect, Weather is what you get".

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

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Mostly sunny statewide today as temps warm back to near seasonal norms. Windy conditions across the High Country and higher foothills this morning will give way to decreasing winds this afternoon. Thursday should be very similar to today with temps even warmer, so a tad above seasonal norms.

By Friday, influence from our next weather system will begin to be felt. Friday should start out nice statewide, but clouds will increase over western and northern CO Friday afternoon leading to a chance for precip mostly north of I-70 and west of the Divide with snow level 7000-8000 ft. Models continue to refine the evolution of this system. Upper trough will move south from Western Canada into the Great Basin. The elongation of the trough extends all the way to a parent upper low in the Hudson Bay region. Models slowly move the upper trough south over the weekend, then pinch off a piece of energy over central CA. The impact to CO will be an associated cold front plunging south Friday night across CO which will usher in deep upslope flow and cold air along with moderate to heavy snow over much of CO. Current models bring snow south of I-70 by Friday evening then turn snow to moderate to heavy Friday night into Saturday morning. Snow level lowers to plains level by Friday evening. Heaviest snow looks to be from Friday evening through Saturday afternoon, but models suggest light to moderate snow will persist through Sunday night. Thus, this could be a long duration snow event for most of CO. For snow amounts, latest models are suggesting 1.0 to 1.5 inches of liquid equivalent over much of the mountains, foothills and Urban Corridor. This would equate to 6-18 inches for the mountains and foothills, 4-12 inches possible for the Urban Corridor, and 2-8 inches possible for the plains. Of course these are initial estimates, as models could change quite a bit between now and Saturday. For example, if majority of energy slips farther west, CO would see much less snow than is currently predicted, but on the positive side, models have been fairly consistent with the current pattern, so confidence in this event is pretty high at this point. For roads, warm temps this week will cause initial snow to melt on many roads, but because snow begins overnight, roads are likely to be snow and ice packed Friday night into Saturday morning. Temps will become very cold Saturday night through Monday morning with temps below zero possible in the foothills. Roads at lower elevations may become wet and slushy Saturday, but with continued snow will likely again become snow and ice packed Saturday night into Sunday morning. Crews will have a tough time keeping up due to the long duration of the event, so expect tough travel conditions statewide this weekend. Delays and some closures will be possible. Snow should end sometime Sunday evening to Monday morning.

Conditions improve to mostly sunny Monday through Wednesday with temps back at or above seasonal norms. Next system is forecast to move into CO Wednesday night into Friday morning, when several more inches of snow will be possible across much of CO with colder temps. Beyond that, models continue to suggest major pattern change will occur the following week, bringing heavy rain to the West Coast and as these systems move east, CO will see warmer temps but lots of snow along and west of the Divide with some snow east of the Divide.

_________________
"Climatology is what you expect, Weather is what you get".

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

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Cool and blustery day today as temps will remain well below seasonal norms, and strong jet stream winds aloft will bring strong northwest winds to higher elevations of the mountains and foothills this afternoon into tonight. Some blowing and drifting of snow likely to occur at higher elevations through Wednesday morning, which may impact travel along prone routes (e.g. 285 through South Park).

Temps will begin to warm back near seasonal norms Wednesday under mostly sunny skies, and winds will diminish through the day on Wednesday. Dry conditions and near normal temps will prevail Thursday and Friday as well.

Next system will begin to impact northern CO late Friday. Models have been consistent in moving an upper trough from western Canada southeast into the Great Basin over the weekend. Associated cold front is expected to move south over CO Friday night which will bring snow to most of northern CO north of I-70. By Saturday morning, snow will move over nearly all of CO with some moderate to heavy snow during the day on Saturday. Snow level will begin at 7000-8000 Friday afternoon, but lower to plains level overnight, so this will be an all snow event for most of CO. Some very cold air moves into CO by late Saturday, with snow becoming mostly light Saturday night. Light snow looks to persist much of the day Sunday under very cold temps. Snow looks to move out of the state by Monday morning. Models showing liquid equivalent precipitation close to 1 inch over the foothills and Urban Corridor, so amounts could be similar to storm totals from last Sunday/Monday. If models remain consistent, foothills could see another 6-14 inches of snow, with 4-9 inches for the Urban Corridor. Mountains could see 8-16 inches, so travel this weekend could be difficult across much of CO.

Most of Co will see a break Monday and Tuesday, but Southwest CO could see some continued light snow and flurries. Models suggest another strong system could impact most of CO next Wednesday and Thursday with up to another foot of snow for mountains and foothills. Still too early to count on this, but pattern looks to remain in place to allow for this.

Snow from Monday brought February snow total to 20.5 inches on Conifer Mountain, so close to our 22 year average for February. With the additional snow this weekend and next week, February looks to be our first above average snow month of the season, which will hopefully continue into March and April. Long range models continue to suggest an upper long wave trough will replace the upper ridge along the West Coast in early March. This will help bring needed rain to CA, and would bring moisture into CO, especially west of the Divide where snow amounts are all now below seasonal norms.

_________________
"Climatology is what you expect, Weather is what you get".

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

Bump for 2/18 Update

Bump for 2/19 update