Warm snow starting late Thursday begins new storm cycle

Wednesday, February 26, 2014

Two storms undercutting the west coast ridge will influence our weather from Thursday through the beginning of next week. We received another big fat zero inches of snow last night, even as areas to our south received a couple of inches. I’m surprised we could not generate any lasting precipitation when the storm moved through just before sunset, but dry air quickly moved in and shut down the precipitation.

The first storm will bring clouds into our area by tomorrow, and precipitation may start as early as the afternoon. Though the winds are initially westerly, they veer to the northwest around midnight, and I expect our best snow will wait until then. I would expect 3-6” of heavy snow by Friday morning with an additional 3-6” during the morning hours and early afternoon, which will be reported Saturday morning. Precipitation will likely start as rain in the valleys before changing over to very wet snow later in the evening.

Snow will diminish or even end later Friday as a small ridge moves over our area between the two storms. Clouds will quickly increase again by midnight Friday as a far stronger storm situated around central California spreads warm temperatures and moisture over our area. I don’t believe we will get significant precipitation until we get a bit of cooling associated with some energy ejecting from the storm Saturday morning.

While these storm are progressing eastward, a very cold wave rotating around the persistent Hudson Bay vortex moves first over the Washington / Oregon region before it begins sliding east. As mentioned in the previous blog, the amount of cold air, if any, that interacts with the warm southern storm will greatly influence our weather. At this time, it appears most of the cold air will remain to our north and east and any interactions will be minimized, as forecast by the European model several days ago. Still plenty of time for that to change, though!

Current forecasts have this impressively wet storm staying to our south, likely bringing the heaviest precipitation to southern Colorado and New Mexico, though central Colorado will also receive significant accumulations. I expect less precipitation over our area, though these southwestern storm can sometimes surprise, especially if there is a convective component where cooler air aloft destabilizes the atmosphere and increases upward motion (similar to bubbles rising in a pot of heated water, though the rising motion in the pot is caused by heating the bottom of the pot as opposed to cooling the top of the pot).

The flow does turn to the northwest after the storm passes by Sunday afternoon, and showers from this storm are likely to continue through Tuesday. Any breaks in precipitation look to be short-lived as a wave traveling over a transient ridge building over our area brings upward motion, cooling and the chance for more showers on Wednesday.

Longer term, I see continued storminess at least through mid-March as the Hudson Bay vortex continues to torment the east and Midwest with cold and stormy weather while the west continues to experience relatively warm and wet storms from the Pacific.

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.

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6 November 2022

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