2009

Well, it certainly is spring. Warm and dry conditions have prevailed across the state as of late, but do expect these to come to an end by the beginning of next week as a cold cutoff low pressure system arrives on the coast. Tomorrow will likely be a very windy day across parts of the state, with north winds in excess of 50 mph, along with much colder afternoon temperatures due to strong cold advection aloft. The main story: a rather potent cutoff will slowly approach the NorCal coast late Sunday night and linger about central or northern CA for up to 72 hours. This low will have cold air aloft–as low as 0 C at 850 mb–which is by no means spectacular, but it is certainly enough to cause steep lapse rates at this time of year. I fully expect that some thunderstorm activity will develop by Monday afternoon over at least coastal NorCal, and possibly further inland. Flow patterns such as this one–with moist up-valley southerly surface flow, divergence aloft, and steep vertical temperature gradients–are very conducive to significant convective outbreaks over the Central Valley and Sierra foothills. By Tuesday, nearly the entire state will stand at least the chance of showers and thunderstorms due to steep lapse rates.  The low may linger for a bit or it could be rather progressive as depicted by recent GFS runs, with most precip done by Wednesday morning.  There are indications that an unsettled and unstable pattern–characterized by below normal temeratures and occasional convective precipitation–may redevelop by day 7 and continue for some time. This may be related to a recent uptick in MJO activity in the Pacific; only time will tell if this continues to be the case…