April 12, 2021 – Dry, warm, and breezy conditions through Wednesday with strongest winds expected Tuesday. Chances for mountain showers over the Sierra on Tuesday and Wednesday.
Satellite imagery early this morning shows a few upper level clouds streaming across interior Northern California as a weak shortwave over the area is bringing in some Pacific moisture. This wave is tightening surface gradients over the north state today, bringing locally gusty winds to the mountains and northwestern Sacramento Valley. Gusts up to 15 to 25 mph, up to 35 mph in the mountains, are expected to continue through the morning hours, decreasing through the afternoon.
High pressure remains over the eastern Pacific today which combined with the north winds will keep daytime temperatures around 10 to 15 degrees above normal. Highs are expected to peak once again in the low to mid 80s across the Valley and 50s to 70s for the mountains and foothills.
Ensembles continue to show an upper level closed low dropping south from the Pacific NW into the California/Nevada border tonight into tomorrow and stalling over Nevada Wednesday. This will drop temperatures around 5 to 10 degrees through midweek. Surface pressure gradients expected to tighten again tomorrow with the initial approach of the upper low.
Breezy winds will increase again tomorrow with gusts up to 25 to 40 mph in the mountains and northern Sacramento Valley. Strongest winds are expected late morning through the early evening hours again for the mountains and northern Sacramento Valley. Winds could increase slightly again on Wednesday, though they are trending weaker with current model runs.
Current model runs continue to bring a little instability (CAPE of 100-300 J/kg) along with some moisture over the mountains with this upper low. A slight chance of scattered showers and potential afternoon thunderstorms is possible Tuesday through Wednesday evening.
Precipitation amounts look fairly light with anywhere from a few hundredths of an inch up to 0.25 inch in the highest elevations possible over the timeframe, though higher amounts are always possible in stronger cells. Light snow amounts are possible for elevations above 5000-6000 feet.
By Thursday, ensembles show the upper low moving east into the Great Basin. A calm weather day is expected for interior NorCal with sunny skies, dry weather, and calmer winds.
Extended discussion (Friday through Monday)
Large blocking ridge along the West Coast forecast to be the dominant feature affecting our weather late this week and next weekend. Ensemble clusters differ a bit in the position of the ridge axis and the amount of lingering trough over the Southwest that hangs back into NorCal.
Nevertheless, expect to see the warmest temperatures so far this season by late in the weekend and early next week as the overall airmass continues to warm.
Highs in the Central Valley may reach the upper 80s to lower 90s by Sunday and Monday, around 15-20 degrees above average.