Widespread Major to Extreme HeatRisk into next week. Critical fire weather conditions in the Sacramento Valley and adjacent foothills through Wednesday.

Key Points

  • Long-duration, major heat event this week impacting holiday outdoor events.
  • Excessive Heat Warning remains in effect for the Valley, Delta and foothills through Saturday evening.
  • Red Flag Warning is in effect for much of the Sacramento Valley and adjacent elevations below 3000 feet through Wednesday evening.
Maximum temp loop

Discussion

North to east surface pressure gradient has tightened overnight behind the short-wave trough now well east of the region. The MFR-SAC gradient is nearly 12.5 mbs while the RNO-SAC gradient is about 6.5 mbs. The result has been an increase in north to northeast breezes with gusts of 15-25 mph in the Sacramento Valley and 20-30 mph over the northern Sierra.

Red Flag Warning

Combined with a very dry airmass moving overhead, elevated to critical fire weather conditions are expected the next couple of days and a Red Flag Warning remains in effect for much of the Sacramento Valley and surrounding foothills.

Extreme Heat Risk

The long duration heatwave is underway and will continue into next week. Widespread Major to Extreme HeatRisk will last at least into the weekend, and an Excessive Heat Warning remains in effect through Saturday evening. Highs of 105-115 are expected across the valley and foothills this week with locally hotter temperatures possible toward the end of the week.

Excessive Heat Warning

With little or no Delta Breeze influence, overnight lows will be very mild as well, mainly in the 70s though some foothill thermal belts will only see lows in the 80s.

Extended Discussion (Saturday through Tuesday)

598-600 DM upper high progged over interior NorCal Saturday will push the mercury up to at or above 110 Deg F throughout much of the Central Valley. This will likely break record high temperatures for many areas. Upper high gradually shifts into the Great Basin Sunday into Tuesday resulting in a slow downward trend in max temps, but remaining upwards of 10 to 20 degrees above normal.

Overnight low temperatures forecast from the upper 60s near the Delta to mid 80s in the thermal belts of the foothills.

Minimum humidities remain in the teens and single digits with widespread moderate to poor overnight recoveries in the foothills and mountains.

Hazard outlook for next week

STO WATCHES/WARNINGS/ADVISORIES

Red Flag Warning until 8 PM PDT Wednesday for Carquinez Strait and Delta-Central Sacramento Valley in Glenn, Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-Northern Sacramento Valley to Southern Tehama County Line Below 1000 Ft- Northern Sierra Foothills from 1000 to 3000 Ft. Includes portions of Shasta-Trinity and Butte Units-Southeast Edge Shasta- Trinity NF and Western Portions of Tehama-Glenn Unit-Southern Sacramento Valley in Yolo-Sacramento Far Western Placer, southern Sutter and Solano County Below 1000 Ft.

Excessive Heat Warning from 11 AM this morning to 8 PM PDT Sunday for Carquinez Strait and Delta-Central Sacramento Valley- Motherlode-Mountains Southwestern Shasta County to Western Colusa County-Northeast Foothills/Sacramento Valley-Northern Sacramento Valley-Northern San Joaquin Valley-Shasta Lake Area / Northern Shasta County-Southern Sacramento Valley.