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.