Heat streak continues, monsoon moisture adds chance of thunderstorms

July 13, 2018 – Hot temperatures the next several days with the hottest temperatures early next week. Monsoonal moisture will bring occasional chances for showers and thunderstorms to the higher elevations next week.

Heat Advisory from noon Sunday to 8 PM Monday.

Discussion

Upper ridge of high pressure over the southwest U.S and weak low over the Pacific producing light southeast flow over most of California. This southeast flow has brought Monsoon moisture over the region and this has translated into some mid and high cloudiness over the north state. So far no precipitation has been reported over the CWA but a few echos are showing up on Radar just south of the forecast area and off the Bay Area coast and lightning detection is indication very isolated thunderstorms with this offshore activity.

Models all showing a weak disturbance pivoting up the north coast this afternoon so a slight thunderstorm threat over the coast range seems reasonable. Stability progs showing another area of instability over the northern Sierra so keeping afternoon thunderstorm threat for there today as well.

Overall airmass does not change much today but cloud cover should bring a drop in daytime temperatures by a degree or two. Upper ridge pushes back to the northwest on Saturday bringing a bit of warming most areas. Much of the central valley will continue to top 100 degrees with the northern Sacramento valley pushing 108.

The exception will be the delta influenced areas where the highs will remain in the 90s thanks to a moderate delta breeze.

Another shortwave disturbance may bring isolated thunderstorms to the northern mountains while monsoon moisture continues to bring a threat of thunderstorms to the northern Sierra.

Offshore upper low pushes into the Pacific Northwest on Sunday. Model consistency on details have varied over the last couple of runs so will need to monitor future runs to analyze for possible northern mountain shower threat. Southwest flow aloft on Sunday should push Sierra thunderstorm threat southward a bit but could still see isolated Sierra storms south of Tahoe.

Have warmed temperatures up a bit on Sunday but model variance has made this less certain. Warming temperatures a better bet on Monday as high pressure amplifies over the west coast. High temperatures are forecast to hit 110 in Redding Monday. Have therefore issued a heat advisory for the northern Sacramento valley and surrounding foothills for Sunday, leading in to the warmest day, and Monday when temperatures are expected to be the hottest of the week. The ridge should also bring enough stability for a temporary end in the Sierra thunderstorm threat.

Extended discussion (Tuesday through Friday)

Strong high pressure will maintain hot weather across the region next week. The Sierra Nevada south of Lake Tahoe will see a slight chance for late-day showers and thunderstorms. Highs across warmest portions of the forecast area will be around 5-10 degrees above average.