textproduct: San Joaquin Valley

KEY MESSAGES

1. High confidence of flooding across the foothills with continued rainfall. Soils are saturated, resulting in excessive runoff.

2. High confidence of heavy snow above 7000 feet, with snow load impacts on roofs in the high Sierra continues. Travel will be hard with winds gusting up to around 25 mph.

3. Thunderstorms are expected tonight and Friday across the Joaquin Valley.

DISCUSSION

It has been a relatively quiet Christmas evening in the valley while orographically-driven precipitation continues in the Sierra. A band of showers and and thunderstorms stretches from the Chico and Sacramento areas to just south of the Bay Area. This will continue to advance southeast overnight, degrading into scattered activity across the Joaquin Valley, while enhancing the heavy precipitation across the Sierra. The mid level trough will continue to dig across central CA. This will steepen low level lapse rates, providing enough instability to maintain isolated thunder and heavier sub-hourly precip rates overnight through Friday afternoon. With snow levels higher than normal this evening/overnight and already saturated soils, the heavy precipitation will continue to lead to the potential for flooding in the foothills due to excessive runoff. A Flood Watch remains in effect. The colder air moving in will lower snow levels by about 1 kft by late Friday morning as the trough swings through. HREF probabilities of additional snowfall greater than 2 feet (and QPF greater than 2.5 inches) are about 60 percent in the High Sierra. This will continue to pose a risk for snow load on roofs into Friday. A Winter Storm Warning continues through Friday evening.

The occluded low off the coast of northern CA will weaken through Friday as it finally moves inland. The base of the trough will also swing through, allowing sustained orographic lift to weaken considerably as the flow collapses. A few rain/snow showers may continue in the higher terrain into Friday evening, but will be of little additional consequence.

Heading through the weekend into early next week, the trough over the Desert Southwest will kick east and broad ridging will build into the Pacific Northwest and CA. A much more tranquil pattern will unfold with near to just below normal temperatures, light and variable winds, and clearing skies returning. Later in the week, an upper low over the tropical Pacific may lift north toward southern CA as another trough approaches from the north. This may lead to another active pattern developing but forecast confidence in that portion of the forecast is low.

AVIATION

VFR conditions are in place area wide this evening. Showers are beginning to advance into the MER and MCE areas, with scattered intermittent light showers farther south. Showers will build in coverage overnight and some MVFR conditions can't be ruled out, particularly at VIS. A break is anticipated in the morning, with additional showers developing Friday afternoon as instability increases. Some TS are also possible, but confidence is too low to explicitly mention at any TAF at the moment. Showers and any TS will dissipate Friday evening. Occasional gusty southeast winds will ease tonight at MCE and MER, then may return in the afternoon.

AIR QUALITY ISSUES

On Friday December 26, 2025, Fireplace/Wood Stove Burning Status is: Burning Discouraged in Fresno, Kern, Kings, Madera, Merced, and Tulare Counties, and Kern (Greater Frazier Park Area) and Sequioa National Park and Forest.

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

Flood Watch through Friday afternoon for CAZ300>339. Wind Advisory until 10 PM PST this evening for CAZ300>303-317- 318-324. Winter Storm Warning until 10 PM PST Friday for CAZ323-326>331.