June 30, 2020 – Temperatures around seasonal averages this week, with dry weather continuing.
Discussion
Surface pressure gradient and northerly winds have decreased overnight as upper level trough shifts northward. Some northerly winds around 15 mph are possible through mid day today, though, then shifting to more onshore flow in the afternoon. Afternoon highs will be about 3 to 5 degrees warmer than yesterday, a little above normal levels. A Delta breeze with cooler temperatures returns this later today and tonight in influenced areas. Light north and east winds will develop elsewhere overnight, keeping temperatures warm in those areas, especially in the foothills and northern Sacramento Valley.
The departing upper trough will get replenished with a weaker system which sets up over Pacific Northwest and Upper Intermountain West by mid-week. This lowering of heights will keep general troughing over the region, which will allow near normal temperatures to prevail. Valley and Delta high temperatures will run in the low 90s, locally up to 95 degrees in some spots through Wednesday.
By Thursday, increasing onshore flow from the Delta is forecast to lower temperatures into the mid/upper 80s in Delta influenced locations. With general troughing over the northwestern U.S. throughout the period, expect occasionally gusty winds around the Delta, likely into the 20 to 30 mph range. Overnight humidity levels in that area will be good to moderate.
Extended Discussion (Saturday through Tuesday)
Long wave troughing remains off the West Coast through the extended forecast period with weak embedded waves moving through the CWA. Dry weather expected with main impact being increased onshore flow as they track through. Little change in high temperatures expected Saturday through Tuesday with 90s in the Central Valley and 70s to low 90s for the foothills and mountains.