textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

1. Warming trend continues into Sunday.

2. The risk for fire starts remains elevated into the weekend due to lowering humidity and warmer temperatures.

3. Another chance for unsettled weather as precipitation, winds, and periodic thunderstorms return by the middle of next week.

DISCUSSION

A high pressure ridge that was previously over central California is now pushing into the Great Basin region, leaving behind southwesterly flow in its wake. Warm air from the southwest will continue a warming trend into Sunday and Monday, with expected temperatures up to 15 degrees above season averages. For Sunday, ensemble guidance expresses a 70 to 80 percent probability to exceed 85 degrees in the San Joaquin Valley, falling slightly to 60 to 70 percent on Monday. A cooling trend will start on Tuesday as winds track out of the northwest, however expected temperatures remain above normal for Tuesday and Wednesday.

A developing low pressure system over the eastern Pacific will gradually push eastward into California in the mid- to late-week period, bringing chances for rainfall for much of the region Thursday through Saturday. Between Friday and Saturday, there is a 25 to 35 percent probability for more than one-tenth of an inch across the San Joaquin Valley, with increasing probabilities moving up in elevation. Little snowfall is anticipated with this system as winds track out of the south to southwest, resulting in snow levels largely between 8,000 to 8,500 feet. During the same time frame as above, there is only a 30 o 40 percent probability for snowfall greater than one inch above these snow levels. The incoming moisture-rich air interacting with the warmer temperatures in the valley and foothill areas brings a threat for thunderstorms to develop each afternoon starting Wednesday, with about a 10 to 15 percent chance each day.

AVIATION

VFR conditions will prevail across central California for the next 24 hours.

FIRE WEATHER

Fuel moisture continues on the downtrend into the weekend and early next week due to warming temperatures resulting in lower relative humidities. This especially rings true for the Mojave Desert where minRH values are expected below 10 percent through Sunday. The low RH values will extend further into the San Joaquin Valley and Sierra Nevada, being between 20 and 25 percent for Sunday afternoon. Moisture pushing into the region next week will help raise RH values, but also brings the risk for lightning-induced fires from potential thunderstorm development; current chances for storms is at 10 to 15 percent each afternoon from Wednesday through Saturday.

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.