March 23, 2021 – Mostly dry weather this week with a few lingering mountain showers this morning and again Thursday. Warmer temperatures expected most of this week. Windy today into Wednesday morning.
Discussion
The strong, quick moving, vort is moving rapidly southeast of the area early this morning with satellite imagery indicating a trend toward clearing to the north of I-80 as subsidence takes hold in its wake. The system brought some showers to the eastern edge of the Central Valley and the northern Sierra Monday evening into early this morning. Precipitation amounts were mostly only a few hundredths of an inch with a few spots reporting about a tenth of an inch (Chico airport reported 0.05 inches, and areas around Foresthill had 0.12 inches). The remaining showers are mostly winding down as radar indicates most current activity is east of the Sierra crest.
The north-south surface pressure gradient has been steadily increasing since Monday evening (MFR-SAC is currently approaching 10 mbs). Northerly winds are beginning to pick up across the region with a few spots already reporting gusts of 20-30 mph across the northern Sacramento Valley, and local gusts of 30-45 mph are occurring across the foothills surrounding the North Valley. Winds will continue to ramp up across the region as the pressure gradient slides south and mixing increases with daytime surface heating.
The strongest winds are expected today across the Central Valley and foothills where gusts of 40-50 mph will be possible, then shifts into the Sierra tonight where gusts of 60 mph or higher will be possible. The east gradient really ramps up this evening with RNO-SAC forecast to increase to around 8-9 mbs. Upper support on the backside of the departing trough also comes in alignment with the surface gradient to bring strong winds to the higher elevations of the northern Sierra overnight tonight into Wednesday morning.
Winds will begin to diminish Wednesday morning and short-wave ridging will lead to a brief period of quieter conditions. Another short-wave trough will slide southeast into Nevada on Wednesday night into Thursday. This trough looks to remain a bit further to the east than the current one, but may still be strong enough to wring out a few showers along the crest of the northern Sierra. Strong ridging will begin to build in Thursday night setting the stage for warmer and more settled weather heading into the weekend.
Extended discussion (Saturday through Tuesday)
Little change to the extended forecast and ensemble and cluster analysis support the high pressure building over NorCal. With this pattern we can expect above average daytime high temperatures, near average nighttime temperatures, lighter winds, and mostly clear skies to the area. In terms of high temperatures, most areas will be around 10-15 degrees above average this weekend, with the first 80 degree readings of the season being possible. A bit of spread is seen in the ensemble guidance via the cluster 500mb heights with the possibility of a trough moving across the PacNW on Monday. This could flatten the ridge if it pans out and would moderate temperatures back towards normal for late March.