June 3, 2019 – Afternoon and evening mountain thunderstorms today then decreased showers over the northern Sierra Tuesday. High snow levels. No shower activity across interior NorCal Wednesday through next weekend. Warmer than normal temperatures through mid week then closer to normal end of the week.
Some remnant cloud cover this morning has moved into the southern Sacramento valley, otherwise skies have cleared again this morning. Main upper level low that has been the main influence on the weather for the past several days has moved slightly south and east but still remains over southern California. Plenty of moisture continues to linger over the region with PW values over most of the forecast area showing PW values at nearly 1 and a quarter inches. Upper low continues to influence the region as well with forecast cape values continuing to run very high in the afternoon and evening hours over the mountain regions. Therefore, still looking at one more day of afternoon/evening mountain thunderstorms. Upper steering flow should be more northerly today rather than northeast so any activity later today will be less likely to drift into the central valley.
Overall airmass will warm slightly today so should see a bump up in daytime highs most areas. Skies will clear again tonight then a little more warming on Tuesday as weak high pressure pushes in over the state. By Tuesday afternoon, the upper low center is forecast to be over Arizona but still enough instability and moisture to warrant a slight threat of afternoon/evening showers or thunderstorms over the northern Sierra. Airmass warms a bit so daytime highs push up to between 10 and 15 degrees above normal for this time of year.
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Wednesday begins an extended period of dry conditions as high pressure pushes in over the southwest U.S. Southwest flow aloft should keep any afternoon or evening shower/thunderstorm threat south and east of the forecast area. Daytime highs should level off before taking a drop by the end of the short term period. An upper trough is forecast to move into the Pacific Northwest out of the eastern Pacific on Thursday bringing a significant cool off going into the extended period. Daytime highs Thursday afternoon are currently forecast to drop back down to near normal. At this time, any precipitation associated with the trough is forecast to remain well north of the forecast area leaving the forecast dry going in to the end of the week.
Extended Discussion (Friday through Monday)
An upper low will be situated over the Pacific Northwest Friday morning, continuing eastward through the weekend. The outlying ECMWF brings some precipitation chances to the area Friday night into Saturday, while the GEFS ensemble mean keeps these chances north of the area. Have opted to go with the dry solution for the extended period. As the trough moves across NorCal, a tight pressure gradient Saturday and Saturday night may bring some gusty winds to the Sacramento Valley. Another warm up will be seen late next week through Monday with Valley highs Friday in the low 80s, heating up into the mid-90s by Monday. Upper ridging begins to build in by late weekend.