This week highlighted by the battle between air masses
Monday, February 24, 2014
After a pleasant day today, snow should begin again tomorrow by late morning or early afternoon as another wave rotates around the persistent Hudson Bay vortex and moves over our area. Snow should become heavier by late Tuesday afternoon or evening as cooling and upward motion is maximized. The bulk of the snow should be over by Wednesday morning after 4-8” of snow is reported, though showers will likely continue through Thursday morning, leaving an additional 1-4” by the Thursday morning report.
A complicated weather regime then ensues as a major northern hemispheric pattern change occurs. As happened in the warm storms of last week, the west coast ridge is forecast to be undercut by the polar jet stream, bringing relatively warm and wet weather into our area by Thursday night. Furthermore, the mostly north-northwest - south-southeast oriented boundary between the arctic air to our north and east and the incoming warm storm to our west may provide a significant lifting mechanism that may produce periods of heavy snow.
That being said, the lead undercutting wave crosses the northern California coast Wednesday afternoon and moves quickly across the Great Basin to start precipitation by late Thursday afternoon or evening. Though this is a warm storm, current forecasts have northwest flow over our area with some slight cooling, increasing the chances for significant snowfall during the overnight hours. There may be rain in the valleys if the cold arctic air to our east does not make it over the Continental Divide, but I’m going to have to wait for further model guidance before making a snowfall prediction for Friday.
This complicated pattern only grows more complicated heading into the weekend as yet another wave rotating around the Hudson Bay vortex travels into southwestern Canada Friday evening. There is lots of model uncertainty with regards to where this energy goes and how it interacts with the second stronger and more organized warm and wet undercutting storm that enters central or southern California around the same time.
It is likely that this warm and wet storm will be a very significant precipitation producer for not only us but the entire moisture-starved southwest. The storm will be significantly stronger if cold air from the Hudson Bay wave is entrained, though that is just one possibility the models forecast. This interaction, or lack thereof, will also also influence the track of the storm, so the areas receiving the heaviest precipitation are uncertain at this time.
Snow continues overnight, with more for Tuesday and Thursday’ish
Saturday, February 22, 2014
The Steamboat ski area reported 1.5” mid / 2” top on the 11:20am update, though no snow was reported at 5am. Again, I’ve generally over-predicted our snowfall in these westerly wind events, especially when the atmospheric stability above mountain top is neutral or stabilizing.
Light snow is currently falling on the upper mountain, and another wave rotating around the Hudson Bay vortex will increase light snowfall this afternoon and overnight into tomorrow. We do have some cool air moving in around midnight, but generally westerly mountain-top winds are again predicted. These might affect snow quality, though wind speeds should be less than the last 2 days. I might expect 3-7” by tomorrow morning with snow ending around noon.
Current forecast have Sunday afternoon through early Tuesday dry before the final grazing wave rotating around the Hudson Bay vortex produces light snow by late Tuesday morning. There is some cool air associated with this that will help support snowfall rates, especially Tuesday afternoon, and we may see 3-6” by Wednesday morning.
Snow is forecast to diminish Wednesday, and may even end for a short time before a major northern hemispheric pattern change occurs behind the late-Tuesday wave. As happened in the warm storms of last week, the west coast ridge is forecast to be undercut by the polar jet stream, bringing relatively warm and wet weather into our area by the end of the workweek.
The first of these waves is timed for Thursday with pieces of another stronger wave affecting our weather by the weekend. Pattern changes are notoriously difficult to predict, especially when a dominant pattern like the west coast ridge is forecast to weaken and break down, so I expect changes to this forecast as we get closer to the event. It does appear that this pattern may persist for a week or so, bringing significant precipitation to the moisture-starved California area, while first the Midwest and then the East Coast are tormented by more arctic outbreaks during the workweek.
Cold front blasts through around 3pm and snows to last through the weekend
Wednesday, February 19, 2014
Cold air is currently pouring into our region accompanied with a burst of heavy snowfall. I’ve received 2” of snow on my deck that fell in the hour and a half between 3:50pm and 5:20pm, and I still expect 6-12” in the Thursday morning report. Snowfall will moderate and become more showery in nature as the morning progresses as additional weaker pieces of energy pass over our area.
Snow may end or become very light in the afternoon and evening before another wave carrying moist air in northwest flow increases snowfall again by early Friday morning. I might expect 3-6” on the Friday morning report, and moderate to light snowfall will likely continue through Friday evening before another brief lull. However, the flow backs from the northwest to the west, and some models predict westerly winds Friday, especially in the afternoon and evening as the airmass stabilizes a bit behind the morning wave.
I’m always concerned when I see moderate to strong westerly winds as not only can they adversely affect lift operations, but they blow directly up the slopes of Steamboat’s mostly west facing terrain, creating drifting and compacting the snow.
I might expect another 4-8” on the hill by Saturday morning before yet another moist wave in northwest flow will graze the area starting Saturday evening, leaving another 2-4” for the morning report. This will keep snow going on the hill through the day Sunday and into the evening. Again, this wave may be accompanied by westerly flow, though wind speeds will be less than on Friday.
Currently forecasts have snow ending by Sunday night, but for likely less than 24 hours as another system is forecast to impact our weather on Tuesday. This one is the result of cross-polar flow bringing frigid air from Siberia across the North Pole and into western Canada where it is forecast to be pulled southward by the persistent Hudson Bay low. As in some of the previous arctic outbreaks this winter, the brunt of the cold air will slide to our west, tormenting the midwest and eventually east coast with possibly their coldest temperatures of this winter season.
Quick view of our soon-to-be stormy weather through the weekend
Monday, February 17, 2014
I’ve run out of time today for a detailed forecast, but wanted to mention that the return of winter still looks to be on track for Wednesday afternoon.
The American model solutions have trended stronger and colder with the lead wave ejecting from the Gulf of Alaska low, similar to the European model. After a nice Tuesday with some high clouds in the afternoon, snow showers will begin around midday Wednesday. Moderate to heavy snow will become likely by sunset, around when the surface cold front is expected to pass through the area. I expect 6-12” on the hill by Thursday morning, with snow showers tapering off toward noon.
There will be breaks, but a number of waves embedded in the cool northwest flow promise unsettled conditions through the weekend, especially during the day Friday and overnight Saturday. This storm cycle will be unlike the previous 2 warm events, and more similar to the cold storms previous to those.
Snow for Sunday night before Gulf of Alaska low impacts our weather beginning Wednesday
Saturday, February 15, 2014
Wow - I had another bad forecast for this morning, as even my reduced 3-6” was far too optimistic. We received no snow in 24 hours. Zero. Zip. Zilch. Nada. Abasin and Loveland both picked up 5”, with 4” at Copper, and most resorts received something. It did appear on satellite that the moisture plume was south of us, but the models insisted we would see at least light accumulations.
I’m having a tough time forecasting these warm events. Last week, the models over-forecasted for our area, though we still received over 2 feet of snow. With significant precipitation falling from the previous storm, I was ready to believe part of the model forecast, but this time was a bust. My inclination is to be heavily biased against these warm events in a stabilizing atmosphere because we generally don’t do well from them. Evidently, today and yesterday were more the rule, and last week was more the exception, with the cold air trapped in the valleys possibly being a key player in producing snow.
With that being said, the next compact storm will bring light snow into the area by Sunday afternoon. This wave moves quickly over our area Sunday evening, likely bringing a burst of snowfall with falling temperatures. I’d like to think we’ll receive 3-6” from this as we do get some cool air and upward motion with the wave as it passes through.
Dry air quickly invades the area Monday behind the departing storm for around 24 hours as temperatures quickly warm. The storm currently in the Gulf of Alaska is forecast to move over the area in at least two pieces, with the first bringing high clouds into the area later on Tuesday and Wednesday. There is a surface cold front associated with this lead wave which should pass through the area Wednesday evening bringing a period of moderate to heavy snowfall.
Snows should decrease Thursday morning before another 24 hour break before the main part of the very cold Gulf of Alaska storm brings another front into the area on Friday. Snowfall in seasonally cold weather will likely continue through part of the weekend.