Warmer temperatures and mountain showers and thunderstorms into the weekend

May 29, 2019 – Mainly late-day and evening mountain showers and thunderstorms continue through the week. Temperatures warming to above average by the weekend.

Discussion

The short-term forecast, mainly for the higher elevations, will sound like a “broken record,” with chances of showers/thunderstorms each day. After minimal activity on Tue with just a few strikes over the NE portion of our CWA, increasing areal coverage of convection is forecast today, and greater areal coverage Thu-Sat. The HREF prob of REFL >40 dBZ suggests there is a high probability of >40 dBZ echoes in the Nrn Lake Co area and the Sierra this afternoon and into early this evening over the Sierra.

Formation of weaker upper low over the Pac NW has retarded the Ewd progression of the Ern Pac ridge. A batch or two of high cloudiness has worked its way SEwd over Norcal in the NWly flow over CA. As a passing short wave paralleling the CA coast moves farther SEwd later this morning, most of this cloudiness will spread southward and clear our CWA.

The weaker upper low over the Pac NW is still forecast to drop southward into our CWA on Thu. Although not as deep/cold as the previous system, the mid level CAA will steepen lapse rates while the late May sun angle destabilizes the lower atmosphere resulting in even higher probabilities of convection, especially over the mtns as suggested by the convective precip forecasts. As the upper low drops into Norcal on Thu there is also the chance of convection in the Sac Vly. Similarly, as the upper low drops south of our CWA Fri and Sat, cyclonic flow/backwash cloudiness will continue the chance of showers/storms over our CWA.

The most noticeable difference will be the warming trend this week and into the weekend. 8H temps are forecast to warm into the teens deg C for the rest of the week and into the lower 20s deg C in the Nrn Sac Vly on Sat allowing temps to warm to near normal in the Valley and into the low 90s in the Nrn Sac Vly at the end of the week. Cloud cover from convective cloudiness over the higher terrain will limit some of warming there, so temps are likely to continue to run a few degrees below normal.

Extended Discussion (Sunday through Wednesday)

Large upper low centered near KSBA Sunday keeps a threat of showers and afternoon thunderstorms over the foothills, mountains, and Northern Sacramento Valley. Upper ridging then builds into NorCal early next week for drier and warmer weather. Above normal temperatures expected through midweek with high temperatures 10 to 15 degrees above normal.