Extreme heat possible late this week and weekend

Dry and warm conditions are forecast to prevail through the week ahead. Temperatures will begin to warm on Thursday with continued warming into the weekend with widespread triple digits in the Valley and foothills.

Discussion

Skies remain mostly clear across the region except for some mid and high clouds that have begun to develop the past couple of hours. These are likely developing in response to weak lift generated by the offshore low as it moves north. The heat signature from the Salt Fire burning in northwest Shasta County is very subtle early this morning.

Elsewhere, IR difference imagery shows extensive stratus along the coast extending well inland across the Bay Area with even a narrow batch moving into the Delta south of Travis AFB. Surface pressure gradients are a little more onshore and temp/dew point spreads a bit narrower compared to 24 hours ago, so despite profiler data indicating a slightly more shallow marine layer, it wouldn’t surprise me to see some stratus make it briefly into the Sacramento area around sunrise.

Little change expected through Wednesday as the offshore low moves up into the PacNW. Onshore flow will continue to moderate temps closer to the Delta. Highs inland will remain a little above average while areas influenced by the Delta Breeze will see highs close to normal.

After mid-week, ensembles continue to indicate high confidence in the Southwest high strengthening and building westward into NorCal bringing another heatwave. This will lead to a warming trend as subsidence increases and marine influence wanes. Triple digit heat will expand across the lower elevations with milder overnight low temperatures resulting in widespread high to very high heat risk by Friday. While it does appear that some elevated moisture/instability will work its way into NorCal later Thursday into Friday, deep convection will likely be capped by warmer mid- level temps associated with the building ridge.

Extended Discussion (Saturday through Tuesday)

Ensembles and cluster analysis continue to favor hot temperatures returning to interior NorCal during the extended period as ridging over the Desert Southwest strengths. Widespread triple digits in the 100-111 deg F range are possible in the Valley as 850 mb temperatures soar to 28+ C.

Little to no overnight relief is expected as lows may only cool into the upper 60s to low 80s; warmest readings expected across the northern Sacramento Valley and thermal belts.

Dangerous to extreme heat risk could increase the risk for heat-related illnesses. If you have outdoor plans, stay weather ready and learn the symptoms of excessive heat exposure.

Gradual cooling possible early next week with lowering heights as the ridge potentially flattens. However, temperatures will still remain above normal except for near normal temperatures in the areas influenced by the Delta Breeze by the end of the forecast period. No thunderstorm chances are expected for the extended period.