October 23, 2019 – Strong northerly winds into Thursday with elevated fire weather concerns. Dry weather with above average temperatures forecast through the remainder of the week. Red Flag Warning from 8 AM this morning to 4 PM Thursday, Wind Advisory from 11 AM this morning to 8 PM this evening for Central Sacramento Valley-Northern Sacramento Valley.
Discussion
A few high clouds are brushing across interior NorCal early this morning associated with short-wave energy passing in northwest flow aloft. Otherwise, skies are clear. Northerly surface pressure gradients have increased (KMFR-KSAC now over 11 mbs) and gusts of 15-30 mph are occurring over the northern Sacramento Valley with a few gusts approaching 40 mph over the foothills.
Current temperatures are running 10-15 degrees milder compared to 24 hours ago across the breezy northern Sacramento Valley, while temperatures elsewhere are running pretty similar to early Tuesday. Readings range from the upper 20s in the mountain valleys to the mid 70s across milder portions of the Sacramento Valley.
Warm and dry conditions continue through the remainder of the week as an upper level ridge remains centered over the eastern Pacific and NorCal. Highs will be around 10 to 15 degrees above average for late-October. Overnight lows will be mild across windier portions of the valley and in the foothills thermal belts, but will be close to normal elsewhere.
The main concern this week is critical fire weather conditions today and Thursday as an upper level shortwave digs into the Great Basin and dry conditions persist. The KMFR-KSAC gradient is expected to remain around 10 mbs. Winds will increase and spread south today as mixing develops and upper level northerly flow becomes aligned with terrain of the Central Valley. Wind advisory is in effect from late-morning until this evening.
Winds will continue tonight along the western edge of the Sacramento Valley, but will increase across the west slopes of the northern Sierra Nevada as the easterly surface pressure gradient tightens (KRNO-KSAC forecast to rise to around 10 mbs).
Breezy northerly winds continue Thursday, but won’t be as strong as today, as upper ridging moves overhead and surface gradients begin to relax.
Extended Discussion (Sunday through Wednesday)
While some model differences continue, there is general agreement with them and ensembles that an upper level trough will drop southward through the Great Basin on Sunday. Moisture will be limited and expect weather at this point to be dry. Will have to watch this, though, as a few ensemble members try to bring light showers over the Sierra in Tuolumne County.
Temperatures trend down early next week, with near normal highs expected Sunday then dropping below normal by Monday and continuing cool into mid week. North to east winds are forecast to return, strongest Sunday afternoon and evening. This would bring enhanced fire weather concerns into early Monday. Humidity levels might be a little higher and winds a little less strong, though, than in the current event. Light north winds continue into Wednesday.