2009

Well, wet weather has certainly returned to NorCal once again after a few dry days towards the end of the last work week. Generally light to moderate rainfall occurred today, but much of this is already running off given the significant rains as of late. A very impressive-looking subtropical tap is currently streaming onto the northern half of the state. Rainfall under this plume is perhaps a bit underwhelming, and this is mostly because dynamics are severely lacking and the parent low is well off the WA coast. This is a scenario where the presence of better dynamics could easily have led to a damaging storm (with a precipitable water plume in excess of 1.75 inches), but in their absence we are just seing a steady but respectable rain event. This is not, I might add, a bad thing for the state’s water resources. SoCal will see rather little rainfall for the first part of the week, and may not see much towards the end of the week either unless the cold air aloft makes it down there soon enough.

There is presently a Flash Flood Watch in effect for the burn areas of interior NorCal. Steady moderate rainfall with periods of more intense precipitation will occur over the next few days, and this could lead to hydrological problems on already saturated soils. There is also the possibility of some smaller rivers in coastal NorCal just exceeding flood stage in the near future, but any river flooding should not be particularly catastrophic. Urban-type and maybe some small stream flooding is possible in the Bay Area and Sacramento Valley this week during periods of convective precipitation.

Speaking of convective precipitation, I do expect there to be a fairly extended period during which there will be waves of convective activity. Tomorrow: although convective parameters are not excellent, conditions are favorable for organization with any storms that do develop. With the rapidly veering and relatively strong low level jet, storms could easily be induced to rotate in the Sacramento Valley tomorrow PM. Isolated thunderstorms are certainly possible…and one or two could become quite strong, potentially even tornadic. The SPC has a 2% tornado risk area covering the Valley for tomorrow. Not a hugely likely scenario, but certainly worth monitoring. Tuesday will actually see more widespread convective activity as temperatures aloft plummet and surface clearing develops at times. There may be an additional severe weather potential on Tuesday and also on Wednesday, but I want to wait and see how tomorrow goes before discussing that possibility in too much detail.

Stay tuned…it does look like the state will eventually dry out by days 5-7