textproduct: San Joaquin Valley

KEY MESSAGES

1. A Flood Watch is in effect for the Sierra Nevada below 9,000 feet and foothills, mainly Yosemite, as well as Mariposa and Madera Counties until Monday.

2. A significant pattern change is expected to take place by this evening with precipitation likely for the Sierra Nevada and its foothills from Fresno County northwards. Moderate to briefly heavy precipitation is possible in these areas from this evening into Sunday.

3. A second, stronger system is expected to arrive Tuesday, with a moderate risk for heavy precipitation throughout Central California, and a moderate risk for heavy snow in the Sierra Nevada expected from Christmas Eve through Friday of next week.

DISCUSSION

Showers have mainly passed to the north of our forecast area so far this evening, although expect some southward movement later tonight into Sunday morning. Another band of precipitation will also arrive later on Sunday. The best chances for measureable precipitation remain near Yosemite NP, currently at 70-80 percent, with snow levels above 9,000 feet until Monday. Until Sunday, chances for precipitation lower in the San Joaquin Valley, including a 40-50 percent chance towards Merced County while probabilities remain below 15 percent mainly south of Fresno County through Monday. Precipitation chances retreat northward a bit on Monday afternoon into early Tuesday morning before the next system arrives.

The initial surge of moisture and southerly flow associated with the system on Tuesday arrives Tuesday morning and gradually progresses inland over our region by the afternoon. Along this front, a plume of moisture from the tropical Pacific Ocean will traverse into our area. Precipitation begins in earnest over our entire forecast area by later Tuesday afternoon. Chances continue through at least Friday. The bulk of the precipitation occurs Christmas Eve and Christmas Day and tapers off a bit Thursday night into Friday. Snow levels lower to 7,000-8,000 feet on Tuesday and gradually lower to 6,000 feet by the evening of Christmas Day. Probabilities for at least one inch of precipitation per 24 hours each day ending Wednesday afternoon and Thursday afternoon are currently at 50-60 percent in the San Joaquin Valley and Kern County desert, and 90 to near 100 percent over much of the higher terrain into the lower foothills. As for 2 inches per 24 hours on each day, the probabilities are much less for the valley and desert (10-20 percent), but remain at 80-90 percent for the Sierra Nevada and adjacent foothills. This is generally due to the orographic nature of precipitation that is typical with these atmospheric- river type of systems. In addition to the threat of heavy precipitation, we are monitoring for increased southerly winds that could produce strong enough gusts to knock over trees. The probability for a 40 mph gust in the Central Valley is as much as 30-40 percent towards Merced County with even greater chances in the coastal ranges (50-60 percent). The time frame is from Tuesday until Christmas Day for winds this strong.

By Friday, the cold front passes, although an upper-level trough remains into the following weekend that will produce lingering showers. Above average precipitation remains favored in our area beyond next weekend, although the chances have lowered compared to the last couple of days. The 6-10 day outlook shows about a 40-50 percent chance, while the 8-14 day outlook lowers to 33-40 percent. Above average temperatures are at around 40-50 percent for both periods.

AVIATION

MVFR conditions are expected for mainly northern portions of the San Joaquin Valley during the next 24 hours with a slight chance of showers around MCE and MER 16Z-20Z Sunday. IFR ceilings due to precipitation over the Sierra Nevada and adjacent foothills from Fresno County northward. Otherwise, VFR conditions will prevail over the next 24 hours.

AIR QUALITY ISSUES

On Sunday December 21 2025, Fireplace/Wood Stove Burning Status is: No Burning Unless Registered in Fresno, Kern, and Madera Counties. Burning Discouraged in Kings, Merced, and Tulare Counties, and Kern (Greater Frazier Park Area) and Sequoia National Park and Forest.

CERTAINTY

The level of certainty for days 1 and 2 is medium. 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

Flood Watch from Tuesday afternoon through Friday afternoon for CAZ300>317-319>322-327>339. Flood Watch through Friday afternoon for CAZ318-323>326. Winter Storm Warning until 4 PM PST Friday for CAZ323. Winter Storm Watch from Tuesday afternoon through Friday afternoon for CAZ326>331.