textproduct: San Joaquin Valley

UPDATE

Updated Aviation Section.

KEY MESSAGES

1. Red Flag Warning issued for the Sierra Nevada above 4000 feet due to high winds and low relative humidity through Friday evening.

2. Wind Advisory has been issued for the Mojave Desert zones through Friday night with wind gusting up to 60 mph.

3. A warming trend continues through the weekend before a cooldown next week.

4. A pattern change may be upon us early next week as a disturbance crosses the West and introduces unsettled conditions.

DISCUSSION

We have a red flag warning out tonight into tomorrow. We have a retrograding cutoff low moving west over the next few hours, which slides under the ridge of high pressure which forms a rex block and causes a big relationship issue. And that issue is the winds will increase overnight from the East over the Sierra Crest and Mojave Desert along with lower minimum RH values coupled with the warming temperatures from the ridge. The result is a Red Flag Warning through Friday night due to the combination which already has started some fires in SoCal on Thursday. Minimum RH values are expected to be in the teens across the entire area tomorrow. There is a 10 percent chance of 25 mph gusts along the foothills but a 20 to 40 percent chance of 35 mph gusts along the crest of the Sierra Nevada.

Luckily, the rex block weakens significantly on Saturday, as the ridge slides out. Temperatures remain warm but the winds finally die down for the time being. Sunday brings a shortwave trough which will pick up the cutoff low and lift out on Monday.

However, things get even spicier as we have a stronger trough slide in late on Monday through Thursday. This trough brings cooler temperatures as we go from a 55 to 85 percent chance of 80s in the Valley south of Merced on Monday to a 35 to 50 percent chance of reaching 70 on Tuesday. The probabilities continue to lower on Wednesday with a 30 to 35 percent chance of hitting 70 before going back up to 45 to 60 percent on next Thursday and Friday. Winds also pick up Monday and Tuesday in the Mojave Slopes and Desert due to this bigger trough.

This big pattern change also brings rain to the area. Tuesday has a 5 to 15 percent chance of a tenth of an inch before increasing to 35 to 45 percent on Wednesday. Thursday also looks to have a 20 to 30 percent chance of a tenth of an inch of rain. The CPC has a 50 to 60 percent chance of above average precipitation in the 6-10 day outlook thanks to this trough along with a 33 to 50 percent chance of below average precipitation. However, the 8-14 day CPC outlook shows a change to near normal temperatures except a 33 to 40 percent chance of above average temperatures along the west side and a 33 to 40 percent chance of below average precipitation for most of the Valley transition to near normal along the Sierra Nevada and Kern County.

AVIATION

VFR conditions will prevail for the next 24 hours.

FIRE WEATHER

Red Flag Warning in effect until 10 PM Friday evening for the Sierra Nevada, Tehachapi, and San Emigdio mountains above 4,000 feet due to strong winds from the east and low humidity. Confidence for easterly gusts exceeding 40 MPH is highest (70-90 percent chance) tonight into Friday morning, though isolated areas will experience gusts this fast through the entire warned period. Minimum relative humidity Friday expected between 15-25 percent in the warned areas, with dryer areas as low as 10 percent.

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

Wind Advisory until 10 PM PDT this evening for CAZ337>339. Red Flag Warning until 10 PM PDT this evening for CAZ592>597.