Hot temperatures return this week with widespread triple digit high temperatures in the Valley. Smoke from area wildfires will continue to impact portions of interior Northern California. Monsoonal showers and isolated thunderstorms will be possible around mid-week with best chances over the Sierra south of I-80. Excessive Heat Watch in effect from Tuesday morning through Friday evening.

Discussion

Temperatures on Saturday reached 102 at Redding, 100 for Downtown Sacramento and Red Bluff. Similar temperatures are expected today, with triple digit heat the norm this week, trending up even hotter through mid-week as the 4-Corners high pressure ridge expands westward.

By Monday temperatures in the low to mid 100’s will be present across the Valley and Delta, with hot weather extending up through the foothills. An extended period of hot weather is expected. Downtown Sacramento is forecast to have triple digit highs through Friday, bringing 7 days in a row with temperatures 100 or more. In July there was a stretch of 6 days in a row with triple digit temperatures, 8 in June.

An Excessive Heat Watch continues for the entire Central Valley forecast office starting late morning on Tuesday. The Watch has been extended into Friday evening, as the Extreme Forecast Index (EFI) suggests the heat will be slow to exit.

This could be especially true for areas away from Delta flow influence. Moderate to high heat risk is forecast for much of the Valley, Delta and foothills with highs ranging from 95 to around 109 and lows in the mid 60s to 80.

The warmest overnight lows will be along the thermal belts in the foothills. The hottest high temperatures for interior Northern California are expected in the northern Sacramento Valley.

While the high pressure building to the west will bring some monsoonal moisture over the Sierra, the amount of moisture and the threat of showers and thunderstorms west of the Sierra Crest has continued to trend down.

The best potential for convection is over the higher Sierra south of I-80 for Tuesday afternoon and evening, with a few showers late Wednesday.

Extended Discussion (Thursday through Sunday)

EFI continues to highlight a strong signature for anomalously high daytime and overnight temperatures through late week. Ensembles indicate high pressure will linger over interior NorCal through late week contributing to widespread moderate, and locally high, heat risk mainly over the valley and foothills.

In addition to the hot temperatures, monsoonal moisture will move northward. Thunderstorm chances are trending lower later in the week.

Next weekend, some clusters are favoring an upper level trough off the PacNW coast that may help shift the ridge eastward leading to some relief in temperatures.