Possible critical fire weather conditions Sunday night through Tuesday morning

Confidence continues to increase for a period of rain late Saturday night through Sunday. Temperatures will also cool down with coolest day Sunday then warning back up early next week. Breezy winds are also expected Monday and Tuesday which will bring some fire weather concerns.

Discussion

Clear skies cover the region. Profiler data indicate the marine layer is not quite as deep as early Thursday and onshore surface pressure gradients have weakened a bit, so we’re unlikely to see a repeat stratus intrusion into the Sacramento area this morning. Current temperatures are mostly a little cooler compared to 24 hours ago and generally range from mid 50s to mid 60s across the Central Valley.

Short-wave ridging moves over the area today ahead of the weekend trough. This will bring a little warming to areas that saw significant cooling due to the Delta Breeze yesterday. Elsewhere, temperatures will be similar to Thursday’s.

Cooler and unsettled weather is expected over the weekend as the trough moves through. Gusty southwest winds on Saturday (ahead of the onset of precipitation) may bring a brief period of elevated fire weather concerns over the northern Sierra/southern Cascades. However, models have sped up the timing of precipitation just a bit with some light QPF possible across the northern third of the forecast area on Saturday afternoon which would rapidly alleviate potential.

Most precipitation will occur Saturday night into Sunday morning. Local amounts up to an inch will be possible over the northern mountains with generally a third up to half an inch over the Sierra north of I-80. Most of the Central Valley will see light amounts (less than a tenth of an inch), but the Redding area may see around a third of an inch and possibly more if deeper convection develops Sunday morning with the trough passage.

The trough shifts east early next week putting NorCal in a favorable position for gusty north to northeast winds in its wake. Strongest winds are expected in the Sacramento Valley and over the west slopes of the Sierra/Cascades. Combined with warming and drying conditions, increasing fire weather potential will be possible.

Extended Discussion (Tuesday through Friday)

Upper level ridging will be building in from the west on Tuesday. This will bring a continued warming trend with Valley highs pushing back into the lower 90s. With the ridge building in on Tuesday we will see less wind. A trough will push into the PacNW and the far northern part of the state on Wednesday. Models are having a tough time with this trough and are struggling with the depth and speed of it. Either way the impacts with it look very minimal as there will be little to no moisture around.

The main impact would be increased onshore flow with maybe some breezy ridgetop winds in the Sierra but even those look rather weak at this point. Ridging rebuilds in behind the trough for the end of the week into next weekend.