Mountain thunderstorms possible, warming trend back by mid-week

May 4, 2019 – Mountain t-storms are possible this weekend with the threat continuing into next week. High temperatures will be cool to near seasonal norms Sunday into early next week. Warming trend mid to late next week.

Discussion

The closed off upper level low continues to churn offshore this morning. High clouds will continue to streamline in ahead of this low with overall conditions remaining dry. The exception could be over the higher elevation terrain within our CWA, where instability could lead to cumulus development. Should there be enough moisture, model and ensemble guidance suggest an isolated thunderstorm or two could be possible over the Sierra crests and perhaps over the Yolla Bolly. Precip chances will become more widespread on Sunday mainly over the mountains as the upper level low makes landfall in SoCal. We will see plenty of instability over the mountains, thus there is increased confidence in seeing thunderstorms during the afternoon and evening. As some energy spins north later in the day on Sunday we could see a few showers pop up in the southern Sac Valley and northern San Joaquin Valley. Instability in the valley will remain elevated above 500 mb and that should keep the activity to just showers and on the isolated side but a rumble of thunder or two can`t be ruled out. Mountain t-storms will be possible once again Monday afternoon and evening as the upper level low slowly tracks east out of CA.

Highs are going to remain on the warm side of average tomorrow but will cool to near average for most locations Sunday through Tuesday as the upper level low moves over CA.

Extended Discussion (Wednesday through Saturday)

Ensembles continue to be in reasonable agreement with the overall pattern featuring an upper low/trough lingering over SoCal/ Southwest with a strong blocking high offshore the PacNW. Thus, showers are possible over higher terrain next week with the best chances over the northern Sierra. Temperatures will be near or slightly above average across the southern portions of the region, but less cooling is expected across the northern areas. Valley highs expected to be in the 80s to around 90.