Showery and unstable weather for California next 72 hours; seasonable weather to return over the weekend

Today’s system in Northern California was nothing especially impressive…except that it occurred during the last week in May. Over an inch of rain fell in parts of the coastal mountains, and nearly all of NorCal received at least a tenth to quarter inch. Snow did fall in the Sierras today, as well, though freezing levels were not especially low (6000-7000 feet or so). The broad trough associated with today’s cold front will deepen somewhat over the next 24 hours over California, bringing an unstable airmass and rotating a few spokes of energy and vorticity across the northern half of the state through Friday. Wednesday will see relatively clear skies in the morning hours, but cumulus will build through the day (especially over the higher terrain). Showers will probably pop up over the Coastal Mountains and foothills, and if we get enough surface heating, possibly the Central Valley as well.  Tomorrow does not appear to have any discernible focusing mechanism for more organized convection or thunderstorms, but some isolated lightning/hail is certainly possible (mainly N. Sac Valley and foothills).

Cyclonic spin associated with surface low off of British Columbia (NRL)

Thursday actually appears to be a much more active day, with models depicting the arrival of a shortwave trough coinciding with the coldest air aloft over CA. Convective parameters appear rather favorable for widespread showers and at least scattered thunderstorms over interior CA in the afternoon. I don’t see much of a severe weather threat, except possibly if the shortwave and initial band of showers/thunderstorms move through early in the day and allow for some stronger surface heating in the afternoon. Regardless, hail is quite likely in any of the stronger cells on Thursday.

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Friday will be the final day of precipitation in California for quite some time. Lingering showers are possible across NorCal, mainly over the mountains and foothills but possibly still over the Central Valley. After the weather-making low this week departs to the east by Saturday, temperatures will rise 15-20 degree to near seasonal norms. The models are beginning to hint at some rather warm/hot weather in the long range (week 2), which would be expected this time of year. It does appear extremely likely, though, that Sacramento’s first 90-degree day will not occur until June…

© 2010 WEATHER WEST


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