June 16, 2020 – Unseasonably cool weather will continue today as a weather system passes to the north of the region. Warmer temperatures, lower humidity and breezy north winds will bring elevated fire weather concerns beginning Tuesday. Hot weather settles in for the end of the week and weekend.
Discussion
Cold front has stalled out across NorCal early this morning with satellite imagery indicating partly cloudy skies across the northern half of the forecast area while skies are clear to the south. Northerly surface pressure gradients have tightened behind the front with the MFR-RDD gradient now above 5 mbs, and northwesterly wind gusts of 15-30 mph are occurring across the portions of the northern Sacramento Valley and surrounding terrain. Current temperatures are cooler across most of the region compared to 24 hours ago and range from the 40s and lower 50s in the mountains, to the upper 50s to mid 60s across the Central Valley.
As the trough pushes east across the PacNW today, gusty northwest winds will continue across the northern portion of the forecast area while breezy southwest winds will continue to the south. Temperatures will remain around 5-10 degrees below average for mid-June.
Gusty northerly winds will develop and spread south across the Central Valley late tonight as the trough shifts further east and northerly gradients tighten. Gusts of 30-35 mph will be possible across western portions of the Sacramento Valley by late tonight and Wednesday morning as the MFR-SAC gradient rises to around 10-11 mbs. Gradients are forecast to relax on Wednesday into Thursday, but enough gradient will remain for locally breezy conditions into Thursday. The combination of the breezy north winds and lowering humidity will result in elevated fire weather conditions, and a red flag warning has been posted for the valley where fine fuels (seasonal grasses) have mostly cured.
A quick warmup is forecast beginning Wednesday behind the departing trough as high pressure builds into NorCal from the eastern Pacific. High temperatures will be around 15-20 degrees warmer by Thursday and Friday compared to today.
Extended Discussion (Saturday through Tuesday)
Strong upper ridging persists over interior NorCal Saturday through Tuesday resulting in continued hot and dry weather. High temperatures in the Central Valley expected to be in the 90s with triple digit heat in the Northern Sacramento Valley. Mountains and foothills will see highs from the 70s to 90s.