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August 19, 2020 – Prolonged heat wave continues today with a break in the extreme heat Thursday and Friday. Areas of smoke will allow for cooler temperatures across portions of the region.

Discussion

IR imagery continues to show the heat from many large wildfires currently burning across interior NorCal. Two fires in particular are showing extreme heat signatures early this morning, the Hennesssy/LNU Lightning Complex (along the border of Napa, Yolo and Solano Counties) and the Doe Fire burning over western Glenn County.

Downslope westerly winds with gusts of 15-30 mph, along with temperatures in the upper 80s and 90s with humidity values in the upper single digits to low teens, continue along the western edge of the Sacramento and northern San Joaquin Valleys. Winds may relax a bit in this area this morning, but will likely increase again this afternoon and persist into tonight. Humidity values will remain very low. Red flag warning will be posted for this area into Thursday morning.

Hot and dry weather will continue today, though significant amounts of smoke may keep temperatures well below the forecast in certain areas.

Slight cooling expected late this week as upper trough off the PacNW coast nudges the ridge back to the southeast for a couple of days. Ridge forecast to extend back into NorCal beginning Saturday bringing a return of triple digit heat to the Central Valley.

Deeper moisture/elevated instability expected to be mainly east of the region the next several days.

Extended Discussion (Sunday through Wednesday)

Upper ridging from the Desert SW high extends over interior NorCal this weekend. Heights then lower some early next week as short wave troughing enters the PacNW.

Above normal temperatures continue through the extended forecast period. Guidance suggests highs will be in the upper 90s to around 103 for the Central Valley with mainly 80s and 90s for the mountains and foothills. Progs indicate Tropical Storm Genevieve off the Baja coast over the weekend, lifting NW early next week.

Some of the associated moisture could be entrained in the upper level flow and drawn into NorCal leading to increased potential for convective storms. At this time some deep moist convection advertised over the higher elevations of the Sierra Nevada Sunday and Monday afternoon. Moisture could also impact temperature forecast early next week.