After a glorious July 4 weekend with typical temperatures and sunny skies, we are set to roll into our first full week of July with much of the same splendid outdoors weather. Enjoy it now — it won’t be here for much longer.
Later this week, the pattern that has been keeping our temperatures mostly at or below average the past few weeks will change. We covered this last week — lower pressure in the upper atmosphere is associated with cooler temperatures. Even the “heat dome” in the eastern U.S. – itself a buildup of higher pressure in the upper atmosphere – plays a part in keeping the upper air pressure low and our temps cool.
As the heat dome erodes over the course of this week, the upper atmosphere begins to level out. That means higher upper atmospheric pressure for the western U.S. You will feel it this week as temperatures slowly rise between Monday and the weekend.
High temperatures Monday for Sacramento will peak in the upper 80s with sunny skies. Traveling south, temperatures quickly climb thanks in part to both higher pressure and less of the Delta breeze to cool things down. Modesto reaches into the low 90s, and Fresno and the southern San Joaquin Valley reach all the way into the upper 90s.
It only takes a few days for the return of the heat to really settle in. By Thursday, high temperatures in Sacramento stretch into the mid- to upper 90s, with triple digits for Modesto, Merced, Fresno and the rest of the San Joaquin Valley. This heat will likely persist all the way through the weekend, although some welcome passing clouds could shave off a few degrees Saturday and Sunday.
Even more heat on the horizon
Early signs point to the potential for our own West Coast “heat dome” developing in mid-July. The extent of our exact temperatures, wind pattern, marine layer, and fire risk will all be downstream of where the highest pressure conditions of the heat dome set up. If it is directly to our east, we may be watching for an increase in wildfire risk. If it sets up directly overhead, then we could be dealing with temperatures well above 100 degrees…