Cool, unsettled weather continues today. Showers and isolated afternoon thunderstorm chances mainly over the mountains. Dry conditions expected the rest of this week with well above normal temperatures this weekend.
Discussion
Latest GOES-West infrared satellite imagery illustrates some mid to high level clouds passing over portions of interior northern California early this Tuesday morning. Cool and unsettled weather remains in the forecast today, before drier and warmer weather returns later this week. Light, isolated rain and snow showers will be possible up in the mountains today, however minimal impacts are expected with those showers. A dusting up to 3 inches will be possible at the higher mountain peaks south of Interstate 80 today, and snow levels will generally be above 7000 feet.
Temperatures will be trending a few degrees warmer than yesterday, with low to mid 70s forecast for the Valley, 60s to near 70 for the foothills and 40s to mid 60s for the mountains.
Locally heavier precipitation amounts may be observed with any thunderstorms that develop this afternoon and evening, as the National Blend of Models (NBM) advertises a 10 to 20 percent probability of thunderstorm development mainly up in the Sierra Nevada and Coastal Range. Both the HREF and model soundings indicate some elevated CAPE, however current model reflectivity does not look too excited for convection. Confidence is low, but brief downpours, gusty winds, small hail and dangerous lightning will be possible with any thunderstorms that develop.
After today, we shift our attention to dry and warming weather for the rest of the week, as upper level ridging builds back into the region. Wednesday will still be cool, but will trend a degree or two warmer than today with some onshore wind. Then, 80s are forecast for portions of the Valley on Thursday.
By Friday, those daytime high temperatures will rise to the upper 80s to low 90s. This will bring low to moderate heat risk to the Valley and foothills, impacting heat-sensitive individuals, especially those without effective cooling and/or adequate hydration. The warming trend is expected to continue into the weekend.
Extended Discussion (Saturday through Tuesday)
NorCal will be on the edge of the strong blocking high that sets up over the weekend across the northern PacNW/southern BC. Hot weather is expected Saturday and Sunday with 90+ readings nearly certain across the Central Valley, and even a chance (30 to 50 percent) for the first triple digit heat of the season on Saturday for portions of the Sacramento Valley (north of Sacramento up to about Chico). Overnight lows will also be mild, in the upper 50s to mid 60s across the Central Valley. The result will be widespread moderate heat risk for the Valley over the weekend with some local spots of high heat risk on Saturday for the foothill thermal belts.
Uncertainty on temperatures increases early next week depending on the evolution of the block and elevated moisture/instability moving in on east and southeast flow aloft.
Appears that thunderstorm chances will increase over the mountains beginning Sunday as a stronger impulse approaches from the east, and a majority of GFS ensemble members even show some light precipitation potential for the Central Valley early next week.