October 14, 2021 – Gradual warming trend is expected for the rest of the week with breezy north winds and low humidity today leading to critical fire weather concerns in the Sacramento Valley. Cooler with a chance of precipitation Sunday afternoon and night.
Discussion
Clear skies cover the region early this morning. Yesterday’s short-wave is progressing east out of the Great Basin and northwesterly flow aloft is increasing over NorCal in its wake. The northerly surface pressure gradient has increased since Wednesday afternoon, and the MFR-SAC gradient has been holding between 6-7 mbs overnight. Northerly wind gusts in the teens and 20s mph have spread into parts of the northern Sacramento Valley and surrounding terrain.
Breezy north winds will spread down the Sacramento Valley early this morning. The strongest wind gusts are expected generally west of Interstate 5 and will occur from mid morning into early afternoon as stronger winds above the surface mix down. Some weakening of the wind is forecast by mid to late afternoon as the surface pressure gradient slackens and overall wind fields decrease as upstream ridging moves in. Combined with low RH (upper single digits and low teens) and dry fuels, critical fire weather conditions are likely and a Red Flag Warning remains in effect. Locally gusty northeast winds are also likely over the northeast foothills of the Sacramento Valley this morning.
Otherwise, the dry weather with gradual warming continues into the weekend. The warmest days are expected Friday and Saturday as upper ridging from the eastern Pacific covers the region. High temperatures will be around 5-10 degrees above average with valley highs mainly in the lower to mid 80s.
A return to cooler and more unsettled weather begins Sunday as another trough approaches, and then moves through NorCal later Sunday and Sunday night. Highs Sunday will be down about 10-15 degrees compared to Saturday, and light precipitation chances will spread south during the afternoon and evening.
Extended Discussion (Monday through Thursday)
By Monday morning, ensemble guidance shows the upper low moving east of the forecast area with dry conditions returning. Temperatures Monday are forecast to cool to around 5 to 15 degrees below the daily normal after the frontal passage with Valley temperatures in the mid to upper 60s and 40s to low 60s for the mountains and foothills. Dry weather continues Tuesday with daytime temperatures warming a few degrees from Monday.
For Wednesday through the end of the week, cluster analysis of ensemble guidance indicates a stronger trough approaching the West Coast, bringing potentially wetter weather to Northern California. Early indications suggest a shortwave along the flow could bring a wave of weaker precipitation Wednesday with the main moisture moving onshore later in the week. Of course, uncertainties exist this far out, so keep an eye out for forecast updates.