June 12, 2020 – Cooler temperatures, breezy winds, and shower/thunderstorm chances today and Saturday. Dry and warmer weather Sunday into next week.
Early this morning, the main upper trough was located just off the coast of Northern California, expected to pass over the interior this evening. Low temperatures this morning will be a few degrees cooler than yesterday as onshore flow begins to bring cooler weather to the area. Highs this afternoon will be anywhere from 10 to 20 degrees cooler than yesterday with Valley temperatures generally topping out in the upper 70s to low 80s.
Breezy winds remain primarily in the vicinity of the Delta this morning, but are expected to strengthen late morning through tonight especially over the western portion of the Central Valley. Gusts up to 30-35 mph can be expected which will exacerbate fire weather concerns as these winds would increase the spread of any grass or fine fuel fires. Winds decrease overnight into Saturday, although some local gusts around 20 mph may be seen in parts of the Valley.
Chances for showers and thunderstorms will also be seen today beginning over the Coastal Range early this afternoon, spreading north and east over the far northern Sacramento Valley and surrounding mountains and foothills by mid-afternoon. Hi-res models indicate some scattered showers and isolated storms may also form over the Sierra mountains and upper foothills by late afternoon or early evening. Coverage for precipitation looks rather sparse in these areas with only isolated showers/storms expected. The better chances remain over the northern third of the forecast area. The main hazards with any storms will be heavy downpours, small hail, and lightning.
Scattered precipitation decreases overnight into Saturday although a few lingering showers may be seen north of a line from Alder Springs to Oroville. Temperatures will be a few degrees cooler on Saturday than those seen this afternoon (about 10-15 degrees below average for mid-June). The upper trough pushes east of California by Sunday and dry and warmer weather will return. The warm up happens quickly with Valley highs back into the low 90s by Monday.
Extended Discussion (Tuesday through Friday)
Seasonably hot and dry weather continue through the work week with the area on the east side of Pacific ridging. High temperatures are expected to gradually trend upwards through the week with low 90s across the Valley and Delta Tuesday, Wednesday through Friday generally mid to upper 90s, potentially reaching around 100 for the northern Sacramento Valley on Friday. Expect lowering humidity levels and drying fuels for the extended period, with no precipitation in the forecast. Northerly winds at times are expected, though they don’t currently look strong. Dry weather is expected through the extended period. There are some hints of a fairly dry trough/low dropping down through the Pacific Northwest that could bring a little cooling by next weekend.