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May 9, 2021 – Dry weather with gusty north winds and critical fire weather conditions through the early part of this week. Warming trend develops through mid-week.

Discussion

A few high clouds are sliding south early this morning as the region remains on the backside of the trough to our east, otherwise skies are clear. The surface pressure gradient remains tight over NorCal early this morning (MFR-SAC is around 11-12 mbs and RNO-SAC is between 4-5 mbs). KDAX VWP indicates north winds of 25-45 kts from 2-3k ft above the surface.

Current surface observations show northerly gusts of 15-30 mph persisting along the western edge of the Sacramento Valley with local gusts of 25-40 mph over the northern Sierra Nevada and foothills.

Amplified upper air pattern continues early this week with troughing to our east and high pressure building off the coast. Northwest flow aloft will continue to support the strong surface gradient resulting in breezy north to east winds across the area through Monday.

Combined with the low RH, red flag conditions will persist. Winds will decrease later Monday, but breeziness will linger into Tuesday before lighter winds finally return by mid- week.

Highs today will be similar to Saturday’s across most of the region, though a little more cyclonic flow and weak cold-advection may bring a little cooling to the mountains.

After today, high pressure gradually builds resulting in a slow warming trend into Wednesday. Valley highs will max out in the lower to mid 90s, especially Tuesday and Wednesday.

Extended discussion (Thursday through Sunday)

EPAC upper ridge remains dominant synoptic feature over interior NorCal Thursday into Friday continuing above normal temperatures. Highs expected to be 10 to 20 degrees above normal.

Short wave trough approaches over the weekend with forecast uncertainties due to varying model solutions on the depth and progression. Forecast currently looks dry, with increased onshore flow and minor cooling over the weekend.