Showers and thunderstorms over interior NorCal through Wednesday. High temperatures well below normal through mid-week, returning to near normal by next weekend. Ash & debris flow concerns on recent burn areas and urban flooding concerns today due to heavy downpours.
Quasi-stationary mid/upper low continues to spin off the coast west of the Bay Area. Strong short-wave that set off the thunderstorms with heavy rain from the Sacramento area westward late Monday afternoon and evening has lifted north of the region.
Quite a few reports of flooding were received to the west and northwest of Sacramento in the Davis and Woodland areas where 1.25″ to 1.75″ of rain fell. Radar indicates numerous showers continuing over the northern Sierra early this morning with a few occurring elsewhere. These are moving off to the north at a fairly good clip, so despite some moderate to heavy rain, amounts likely won’t be excessive through the remainder of the night.
Cool and unsettled weather will continue across the region today and Wednesday before warmer and drier conditions return at the end of the week. Latest HREF indicates the best potential for exceedance of 0.50″/hr rainfall rates will be this afternoon and evening along the western edge of the forecast area to the west and northwest of Sacramento, and this seems reasonable given the ensembles forecast the closed low to drift closer to the coast near the Bay Area later today leading to increasing instability and lift out ahead of it.
We will continue to monitor for potential impacts near the burn scars along the western edge of the Sacramento Valley. Across the northern Sierra, including the Mosquito Fire burn scar, models are indicating more scattered precipitation today with less potential for heavy rain, though fast moving showers and thunderstorms may bring brief heavy rain later this afternoon.
The low is still forecast to lift out across NorCal and into the PacNW on Wednesday with shower and thunderstorm chances continuing, especially to the north and east of Sacramento. Dry and warmer weather is expected to return Thursday and Friday as ridging builds in the wake of the departing low.
Extended Discussion (Saturday through Tuesday)
Dry weather through the extended period as upper ridge builds over the area this weekend, shifting into the Intermountain West early next week. High temperatures expected to be near normal to slightly above normal.