textproduct: San Joaquin Valley

KEY MESSAGES

1. Another round of monsoonal moisture will bring chances for thunderstorms across the Sierra Nevada crest tomorrow afternoon.

2. Extreme Heat Watch issued for the Mojave Desert and Indian Wells Valley Thursday through Monday. Major HeatRisk expected with afternoon highs 108 to 112 each day.

3. High pressure over the region will maintain temperatures near season averages for the remainder of Central California for most of the week.

DISCUSSION

As the ridge of high pressure continues to sit in place and is not likely to move for the next week or so, temperatures will remain a few degrees above normal throughout that time and likely into the long term forecast. The southerly flow pattern we've been seeing for the past few days will begin to become more westerly by Thursday, but before then, thunderstorms remain possible along the Sierra Nevada crest tomorrow afternoon, though with smaller chances compared to this afternoon at 15-25%. These chances are also mainly around Mt. Whitney and to the leeward side of the range towards Nevada.

As the ridge slowly shifts back west, the Mojave Desert is expected to see hot temperatures in the afternoon and warm lows overnight. These combine to make widespread Moderate Heat Risk with areas of Major Risk that are mainly in the southeastern corner of Kern County. This type of heat is dangerous to much of the population, especially to those without adequate cooling overnight. Due to these possible conditions, an Extreme Heat Watch has been issued for the Mojave Desert from Thursday morning through Monday night. The current expected temperatures in that area is between 108 and 112 degrees. This Watch will also be likely upgraded to a Warning by tomorrow due to the certainty of these highs during that time period. At the same time, the San Joaquin Valley will likely see highs just a few degrees above normal as the ridge will be centered more over the desert and further east than the Valley.

Looking to the long term forecast, however, this could change as the ridge may begin to retrograde further west and 500mb heights may begin to rise over more of Central California, causing an uptick in Valley temperatures. The Climate Prediction Center is also picking up on this as the orientation of the likely above normal temperatures tilts towards California on the 8 to 14 day outlook when compared to the 6 to 10 day outlook, even as both indict a similar likelihood for those kinds of highs. The 8 to 14 day Hazards outlook also has the slight risk (20-40%) for hazardous temperatures take up more of the San Joaquin Valley as well as into the Sacramento Valley, whereas previous outlooks had the slight risk capped in the lower Valley.

AVIATION

VFR conditions will prevail in the San Joaquin Valley for the next 24 hours.

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

Extreme Heat Watch from Thursday morning through Monday evening for CAZ337-339.