textproduct: San Joaquin Valley

KEY MESSAGES

1. Moderate to Major Heat Risk on Tuesday and Wednesday.

2. 30% probability of thunderstorms along the high Sierra and eastern Kern deserts through the week.

3. Slow moving mountain thunderstorms can produce excessive rainfall.

4. Dry lightning strikes in the high Sierra this week, 10% probability of occurrence, away from the excessive rainfall.

DISCUSSION

Moisture continues to be pulled up from the south, as indicated by the cloud cover over much of the Valley along with the light rain and virga that is moving through the region at this time. By tomorrow, enough moisture will be in the area along with additional heating that thunderstorms may develop along the Sierra Nevada crest. The strongest chances will be tomorrow and Tuesday, with Monday's chances at 25-45% along the crest and 15-25% into the foothills, and Tuesday's chances at 25-35% along the crest. And while these thunderstorms may produce localized heavy rainfall, some stray lightning strikes may occur outside the rain column.

Along with this moisture, the ridge pulling it in will also cause temperatures to rise into the mid 100's during the day and keep temperatures from cooling down as much with lows in much of the Valley in the low 70's and the urban areas in the mid 70's. The warmest temperatures are expected to be on Tuesday and Wednesday where widespread Moderate Heat Risk is expected with some areas of Major Heat Risk. The latter type of heat risk effected the majority of the population, especially those without adequate cooling at night.

Looking to the long term, these above normal temperatures seem likely to continue into next week, as ridging remains prominent over the southwest and California. The Climate Prediction Center is highlighting the 20th through the 26th with a slight risk (20-40%) for hazardous temperatures, as well as both the 6 to 10 and 8 to 14 day outlooks seeing both leaning and likely above normal temperatures. The Center also notes the majority of the west may also see above normal precipitation during those time periods, with likely above normal in the former and leaning above normal in the latter, possibly indicating further monsoon moisture influxes during those time periods.

AVIATION

High Sierra thunderstorms could lead to mountain obscuration, although VFR is expected through 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

None.