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April 24, 2019 – Dry weather and above normal temperatures through the week. A few thunderstorms could be possible over the high mountains this afternoon and Thursday. A cooling trend is possible over the weekend.

Discussion

Upper level ridge remains over NorCal this week with dry weather and warm temperatures. Another day of 90 degree temperatures today with readings 10 to 20 degrees above normal. Many locations will again approach or exceed record temperatures, which are in the low 90’s.

A system passing north of the area this afternoon and Thursday may bring extremely isolated thunderstorms to the Southern Cascades and northern Sierra near the crest. Model agreement remains poor, but will maintain low-end precip chances in line with HREF and mesoscale WRF models.

Temperatures will cool into the 80’s Friday and through the weekend with lowering heights, as disturbances pass north of the area.

Extended Discussion (Sunday through Wednesday)

To conclude the weekend and entering next week, a split flow regime is evident in the guidance. A compact upper low within the southern stream will stay well to the south of the region as it moves through extreme northern Baja California early Monday. The northern extent of the precipitation shield could reach Tuolumne County which affords a risk for a few showers. Have kept the threat of showers in the forecast into Monday given models have trended slower with the passage of the trough.

The longwave pattern within the northern stream should remain amplified into next week. Operational and ensemble solutions favor further elongation of this flow down into the Central Great Basin next Tuesday and Wednesday (Apr 30-May 1). If the forcing from this trough moves far enough west, some showers will be possible across the Sierra. A tightening pressure gradient should afford an uptick in dry, northerly winds across the Valley. Given modest ensemble spread with the pattern, expect some of these details to change in the upcoming days.

Temperatures should move closer to climatology next week given the presence of lower heights over the region. Mid to upper 70s will likely be the norm for Valley highs while mountain and foothill locations stay in the 50s and 60s, respectively.