textproduct: San Joaquin Valley

KEY MESSAGES

1. Lingering precipitation and thunderstorms remain possible for much of the Sierra Nevada and adjacent foothills tomorrow afternoon.

2. A drying and warming trend is expected for much of this week into the next weekend.

3. There is low confidence for another storm system to move through the region by next Monday.

DISCUSSION

As the trough aloft continues to spin over Northern California tomorrow, continued lingering precipitation and thunderstorms remain possible through tomorrow evening, mainly over the Sierra Nevada and the Foothills. Currently there is a 20 to 25% chance for thunderstorm to develop along the mountainous terrain, and a 10 to 20% chance for development in the Valley into the Foothills from the late morning into the afternoon due to daytime heating combined with leftover moisture and the dynamics of the trough centered to the north. Any thunderstorm that forms will have the risk of lightning, small hail and localized heavy rainfall that may cause flooding.

As the trough moves east into Tuesday, the risk of thunderstorms reduces significantly as the leeward side of the trough moves overhead. This will also result in a warming trend as a new ridge builds into its place, as well as a drying trend that will continue through the week. Another trough is expected to get close to our area as it moves along the California/Nevada border, leading to a small chance for precipitation for the top of Yosemite NP, but will most likely cause strong winds for the majority of the region, especially along the Mojave Desert Slopes.

Warming and drying is expected to continue into the next weekend as zonal flow takes over the pattern aloft. Looking into the long term, the ensemble models are indicating a possible trough swinging through the region by next Monday, with current chances for a tenth of a inch of rainfall at 10-30% for the Sierra Nevada and less than 15% for the Valley. It is also possible that this trough comes in at a different location or tilt, resulting in continued dry weather, as indicated by the current ensemble model runs.

AVIATION

VFR conditions across the area through the overnight hours, with local MVFR and IFR in and near thunderstorms, expected to begin forming by 18Z Monday.

AIR QUALITY ISSUES

None.

CERTAINTY

The level of certainty for days 1 and 2 is high. The level of certainty for days 3 through 7 is medium.

Certainty levels include low...medium...and high. Please visit www.weather.gov/hnx/certainty.html for additional information and/or to provide feedback.

HNX WATCHES/WARNINGS/ADVISORIES

None.