988
FXUS66 KHNX 121745
AFDHNX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HANFORD CA
1045 AM PDT TUE AUG 12 2025
KEY MESSAGES
1. THE EXTREME HEAT WARNING FOR THE MOJAVE DESERT HAS BEEN
EXTENDED AND WILL NOW RUN THROUGH 8 AM ON WEDNESDAY, DUE TO
CONTINUED MAJOR HEAT RISK IN THE REGION AND OVERNIGHT LOWS IN
THE 70'S AND 80'S TONIGHT.
2. WHILE THE HEAT ADVISORY OR THE VALLEY HAS EXPIRED, MODERATE
HEAT RISK IS ONGOING FOR THIS REGION HAS TRIPLE DIGITS ARE
EXPECTED TO CONTINUE THROUGH WEDNESDAY.
3. THERE IS A 10 TO 15% CHANCE FOR THUNDERSTORMS IN THE SIERRA
NEVADA THIS AFTERNOON, MAINLY TO THE NORTH OF TULARE COUNTY.
4. MINOR FIRE RISK WITH WIDESPREAD MINIMUM RELATIVE HUMIDITY
BETWEEN 15 AND 25 PERCENT FOR THE NON-DESERT AREAS. MINIMUM
RELATIVE HUMIDITY EXPECTED TO BE LESS THAN 10 PERCENT IN THE
MOJAVE DESERT WITH BREEZY WINDS IN THE AFTERNOON TO EVENING.
DISCUSSION
THE HIGH PRESSURE RIDGE THAT HAD SAT IN THE NORTHEAST PACIFIC
HAS NOW BEGUN TO SPLIT AS A LOW PRESSURE TROUGH SLOWLY DROPS
DOWN FROM NORTHERN CANADA. THIS WILL CAUSE THE FORMATION OF A
RIDGE OVER THE FOUR CORNERS REGION AND 500MB HEIGHTS OVER
CALIFORNIA TO GRADUALLY DECREASE. THIS WILL LEAD TO A DECREASE
IN TEMPERATURES FOR MUCH OF THE STATE AND THEREBY A COOLDOWN FOR
OUR CWA. HIGHS BY THIS WEEKEND ARE EXPECTED TO BE A FEW DEGREES
BELOW NORMAL FOR THIS TIME OF YEAR, THOUGH KIND IN MIND THAT
NORMAL IN THE VALLEY RIGHT NOW IS MID TO UPPER 90'S AND INTO THE
TRIPLE DIGITS FOR THE DESERTS. HOWEVER, MAJOR HEAT RISK REMAINS
A CONCERN FOR THE DESERT REGION, SO THE EXTREME HEAT WARNING
WAS EXTENDED THROUGH 8 AM TOMORROW MORNING.
A SLIGHT CHANCE FOR THUNDERSTORMS (10 TO 15%) EXISTS FOR THE
SIERRA NEVADA THIS AFTERNOON, DUE TO A SLIGHT AMOUNT OF
INSTABILITY BROUGHT IN FROM THE WEAKENING OF THE RIDGE AND
INTRUSION OF THE TROUGH TO THE NORTH. THESE THUNDERSTORMS ARE
MOST LIKELY TO FORM TO THE NORTH OF TULARE COUNTY AFTER 2PM
TODAY. SLIGHTLY LOWER CHANCES FOR STORM FORMATION EXIST
TOMORROW, HOWEVER THESE CHANCES ARE FURTHER TO THE EAST ON THE
LEE SIDE OF THE SIERRA RANGE.
MINOR FIRE RISK CONTINUES FOR MUCH OF THE REGION TODAY, WITH LOW
MINIMUM RH'S IN THE VALLEY OF 15 TO 25%, AND SINGLE DIGITS IN
THE DESERT REGION ALONG WITH THE ABOVE NORMAL TEMPERATURES.
THESE CONDITIONS ARE EXPECTED TO CONTINUE TOMORROW, THOUGH DUE
TO THE INCOMING TROUGH, MINIMUM RH'S ARE LIKELY TO SEE AN
IMPROVEMENT WITH VALUES OF 25 TO 40% BY THIS WEEKEND, THOUGH
THE DESERT REGION WILL LIKELY STILL SEE SINGLE DIGITS. THE
INCOMING TROUGH WILL LIKELY ALSO LEAD TO A SLIGHT INCREASE IN
WINDS THROUGHOUT THE REGION, WHICH ALONG WITH THE DRY FINE FUELS
WILL CONTINUE THAT MINOR FIRE RISK IN THE REGION.
AVIATION
18Z UPDATE:
VFR CONDITIONS ARE EXPECTED IN THE SAN JOAQUIN VALLEY FOR THE NEXT
24 HOURS. THERE IS A 10 TO 15 PERCENT CHANCE FOR MOUNTAIN
OBSCURING THUNDERSTORMS TO FORM THIS AFTERNOON ALONG THE SIERRA
NEVADA CREST FROM 21Z TUESDAY THROUGH 03Z WEDNESDAY.
AIR QUALITY ISSUES
NONE.
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
EXTREME HEAT WARNING UNTIL 8 AM PDT WEDNESDAY FOR CAZ337>339.
PUBLIC/AVIATION/FIRE WEATHER...EW
DSS/PIO........................JPK
WEATHER.GOV/HANFORD
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