April 24, 2020 – Dry weather with above normal temperatures continues through the middle of next week, with Valley highs in the mid to upper 80s through early next week. Near record highs are expected Tuesday, with many locations in the 90s.
Discussion
Warmer temperatures are expected today with eastern Pacific ridging building in. Northerly winds will continue but will be a little less than yesterday as the ridge axis shifts closer and the surface gradient weakens. Wind gusts up to 15-20 mph are possible in the Valley in the afternoon. High temperatures today in the Valley will climb into the mid to upper 80s, which is 10 to 15 degrees above normal.
Guidance continues to show some flattening of the ridge over the weekend, as weak disturbances track through the Pacific Northwest. This should result in some minor cooling. Highs Saturday will be a degree or so less than Friday, then drop a few more degrees on Sunday, in the low to mid 80s. About the same is expected Monday, maybe a degree or two higher as the ridge begins to rebuild.
Extended Discussion (Tuesday through Friday)
A prominent upper ridge will be a fixture in the forecast over the western U.S. While the positive height anomaly is centered across the Desert Southwest, a northward extension of this ridge promotes ample warmth over northern California for Tuesday and Wednesday. Climatologically speaking, the 582-dm mid-level heights sit around 2 to 2.5 standard deviations above average. Forecast 850-mb temperatures sit around 19-21C which a deep, well-mixed boundary layer would support widespread highs in the low 90s, locally into the mid 90s in some locations. Relative to historical records, some of these forecast highs will close in on a few of these numbers. Based on the latest guidance suite, the eastern extent of an upstream trough will slightly reduce heights on Wednesday which could shave a few degrees off highs relative to the day previous. Overall high temperatures will run around 10 to 20 degrees above climatology. Considering overnight impacts, the persistent of northerly winds could keep numbers on the mild side, perhaps mid/upper 60s in the more favorable thermal belts (i.e., Sierra foothills).
From Thursday onward, as the early week ridge exits toward the Rockies, a gradual cooling trend is likely. Although daily temperatures will remain above average, highs in the 90s will be replaced with widespread 80s. Moving into the following weekend, the approach of a shortwave trough will introduce additional cloud cover along with further cooling. 24-hour precipitation probabilities are low, but non-zero, which suggests some light showers may return to the region, mainly over the mountains.