Heavy Sierra Snow, Tornadoes East

In my previous post, I talked about the dearth of snow in the Sierra.  In timely fashion, a strong storm system is bringing heavy snow to the Sierra, with several feet of accumulation expected.  This is a cold, moist storm that originated over the Gulf of Alaska.  While not a big rain producer at lower elevations (only a quarter to half inch in the Bay Area), the dynamics and moisture profile associated with this system favors heavy snow in the Sierra.  As the system moved in, strong, moist west-northwesterly mid- and upper-level winds impinged on the Sierra.  This is evident in the map on the right, which shows wind up around 30,000 feet.  As this flow hit the Sierra, it was forced to rise and inevitably cools.  As the air cools, it is unable to hold as much moisture, so that moisture condenses out in the form of clouds and snow.  This also favors the heaviest snow on the western slopes of the Sierra up to the crest, with less snow on the eastern side.  Snow levels will be as low as 2000-3000 feet, with snow accumulations up to 5 feet for locations above 7000 feet elevation.  The snow will continue on and off through Thursday before a warmer, drier air mass moves in this weekend.  The copious snow will improve the water outlook picture somewhat as we head into the spring.  And, I think there are still signs of a more active weather pattern for northern California around mid-March.

Meanwhile, on the same upper-level wind map above, there is a strong jet stream over the southern United States.  This is associated with another storm system that produced severe thunderstorms with tornadoes across parts of the Mississippi Valley.  Unfortunately, many of the tornadoes occurred overnight and early this morning.  This is extremely dangerous since most people are sleeping without any idea a tornado is approaching, and since it is dark, tornadoes are difficult to see and track.  One tornado that moved across southern Illinois, causing several fatalities, has already been rated EF-4 (on a scale of 0 to 5), with winds of 175 mph.  It is not unusual to have tornadoes in late February, but this time of year they are more common across the Deep South as opposed to Missouri and Illinois.