Dry conditions except for a slight chance of showers and thunderstorms over the mountains early this week. Drier conditions and hot weather returns by the middle of the week, becoming increasingly hot for the 4th of July holiday weekend.
Discussion
Skies are mostly clear across the region early this morning except for a few clouds across Shasta County. The marine layer remains moderately deep with IR imagery showing extensive stratus covering the Bay Area. Onshore surface pressure gradient persists, though not quite as strong as early Sunday. Nevertheless, the Sacramento area will likely see some early morning low clouds again this morning. Current temperatures are very similar to those from 24 hours ago and generally range from the 40s and 50s in the mountains, to the mid 50s to around 70 in the Central Valley.
The weak upper trough will linger across the region into mid-week keeping temperatures below average early this week, though highs are expected to gradually warm.
Late-day thunderstorm chances will persist the next several days over the northern mountains and northern Sierra, though better chances are likely in the Sierra on Wednesday. Stronger storms will be accompanied by occasional lightning, small hail, brief heavy rain and gusty winds.
The trough is finally forecast to shift east on Thursday marking the end of mountain thunderstorm chances and bringing significant warming as onshore flow tapers off. Highs are forecast to approach the century mark through most of the valley (the northern Sacramento Valley will see highs around 105) resulting in widespread moderate heat risk for the first time in more than a week.
Extended Discussion (Friday through Monday)
The first major heatwave of the season is looking more likely later this week and over the weekend as ensembles and clusters favor ridging from the eastern Pacific building across NorCal and suppressing the marine layer and Delta Breeze. Given the unseasonably mild weather of the past few weeks, the switch to hot weather is going to be especially brutal as highs jump from 5-10 degrees below average early this week to 10-15 degrees above average over the weekend.
Hottest portions of the Central Valley will see highs around 110 over the weekend. Overnight lows will also be significantly warmer with the northern half of the Sacramento Valley and foothill thermal belts likely to see minimum temperatures only in the 70s.
Heat risk, which has been minor recently, is forecast to jump into the moderate to high category Friday and over the weekend. People should be aware of the upcoming change in the weather and plan accordingly.