2009

Well, this is certainly panning out to be an interesting weather week for the state. Numerous high temperature records were shattered–in some cases, truly obliterated by 15 degrees–all across the state today, especially in the north. San Francisco hit 92, which is rare at any time of year, let alone April. Parts of the Bay Area set all-time records for the earliest 90+ and 95+ degree readings ever recorded in 100 years or more of record-keeping. Much of the state inched towards the century mark today, and some parts of SoCal and the interior Bay Area did manage to surpass it already. Tomorrow will be similarly hot and probably record-breaking once again, though there is one caveat: a significant mid-level disturbance is making its way northward just off the CA coast and is forecast to move inland over central and northern California tomorrow. The low currently has some extensive mid and upper level cloudiness associated with it. Convective parameters are not overly impressive except over higher terrain, including the Coastal Range and Sierras, where some scattered afternoon thunderstorms are likely tomorrow. Although not immediately likely, some elevated convective activity could occur in unexpected locations tomorrow given the mid-level moisture, extremely warm surface temps, and some instability aloft. This will certainly be something to keep an eye on. Also, afternoon temps may be a little lower tomorrow with the clouds than they would have been otherwise, but they will still make it into the 90s in most places.

A moderate cooling trend begins late Tuesday at the coast and spreads inland on Wednesday. By Thursday, temperatures will cool even more-to around average for this time of year–as a complex series of Pacific systems approach CA. The models…particularly the GFS…has been struggling monumentally with the upcoming drastic pattern change, with progs indicating everything from a massive cold low with low snow levels and widespread thunderstorms to a heavy subtropical rain event. The GFS…for its part…is currently dry for the weekend. I think this is unlikely, and the ECMWF agrees. There will be a strong competition between cold and extremely unstable but also very dry continental air to the north and east of the state trying to push south and a plume of extremely moist and relatively warm and unstable air to the west of the state trying to push east. The degree of interaction..if any…between these two elements will determine what the weather will be like from days 4 and beyond. Uncertainty is enormous for a change only a few days out, but only time will tell which scenario will win out. More updates on this potentially very active pattern later in the week.