June 17, 2020 – Gusty north to east wind and low humidity today into Thursday will create critical fire weather conditions. Otherwise dry with warming temperatures and decreasing wind. Widespread triple digit heat expected in the Central Valley over the weekend into early next week.
Discussion
Upper low moving through the Intermountain West attm as upstream riding begins to build inland along the West Coast. 1031 mb EPAC surface high extends through Oregon into the Great Basin. KMFR-KSAC pressure gradient trending up to near 10 mb attm. KDAX wind profiler showing 30 kt north wind at 2k ft. Wind continues to increase this morning as momentum aloft mixes down. Strongest wind expected late morning into the afternoon and along the west side of the Sacramento Valley. Downslope drying occurs today with lowering humidity leading to critical fire weather conditions across lower elevations. AMS warms today under increased subsidence resulting in afternoon highs about 6 to 12 degrees above Tuesday’s readings.
Surface wind decreases in the Central Valley this evening as boundary layer begins to decouple. Wind however remains locally gusty tonight in the northern and eastern foothills and mountains. Wind picks up again Thursday morning in the Central Valley but not as strong as today and looks to diminish tomorrow afternoon. Max temps on Thursday rise another 5 to 10 degrees.
Locally gusty wind continues Thursday night into Friday morning in the foothills and mountains. Lighter wind forecast into the weekend as heights/thicknesses continue to rise. As a result, triple digit heat expands over the Sacramento Valley, north of Sacramento on Friday. Warming continues over the weekend with highs at or above the century mark across most of the Central Valley and 70s to 90s for the foothills and mountains.
Extended Discussion (Sunday through Wednesday)
From Sunday into much of next week, the longstanding ridge will shift its position into the Desert Southwest and Four Corners region. Despite this migration east, the northern extension of the ridge axis is forecast to sit over northern California supporting an extended period of heat. Valley high temperatures should range from the mid 90s into the low 100s although there is some room for readings above 105 degrees as noted by the ensemble spread.
Based on the experimental probability page from the Climate Prediction Center, anomalous heat may continue into the June 24-26 timeframe. Given the position of the anticyclone, some monsoonal moisture could get steered northward along the California/Nevada border. Aside from a few additional high clouds, any impacts will likely stay east of the Sierra crest.