April 23, 2020 – Dry weather with a gradual warming trend continues into early next week, with Valley highs in the mid to upper 80s through the weekend, 90s early next week.
Discussion
Eastern Pacific ridging builds eastward into region, bringing dry weather across the area. A northerly surface pressure gradient will tighten over the region as the ridge builds and a shortwave trough exits. This will bring gusty northerly winds to the Valley, with gusts to 20 to 30mph, strongest over the northern San Joaquin Valley. Afternoon highs will be similar to a few degrees warmer than yesterday.
On Friday northerly winds will continue but will weaken slightly as the ridge axis shifts closer. High temperatures are expected to increase further, 10-15 degrees above average for Friday, with upper 80s across the Delta and Valley. Saturday and Sunday will be slightly less warm, as a shortwave passes to the north and the ridge axis shifts eastward. Valley highs in the mid 80s are forecast.
Extended Discussion (Monday through Thursday)
Abundant warmth and dry conditions will be on repeat for next week in response to renewed ridging over the southwestern U.S. While the synoptic flow de-amplifies slightly to commence the week, heights build considerably for Tuesday/Wednesday which will mark the warmest period thus far. Forecast 850-mb temperatures run between 18-21C which is a smidge below the earlier guidance. However, the expected well mixed boundary layer supports high temperatures in the low 90s, locally approaching 95 degrees. Area-wide temperatures anomalies will run around 10 to 20 degrees above average for late April. Fairly notable diurnal changes in min/max temperatures are likely given the dry nature of the air mass, likely running around 30 degrees. The upper ridge responsible for the warm weather will slide eastward by late in the week while the upstream flow becomes quasi-zonal. This will gradually shave off a few degrees each day while temperatures still remain above climatology.