363
FXUS66 KHNX 250621
AFDHNX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE HANFORD CA
1121 PM PDT MON AUG 24 2026
KEY MESSAGES
1. TRIPLE DIGIT HEAT CONTINUES FOR THE SAN JOAQUIN VALLEY THIS
WEEK. MODERATE TO MAJOR HEAT RISK EXPECTED WITH A HEAT ADVISORY
IN EFFECT THROUGH WEDNESDAY EVENING, MAINLY FRESNO COUNTY
SOUTHWARD.
2. EXTREME HEAT WARNING IN EFFECT FOR THE MOJAVE DESERT THROUGH
WEDNESDAY EVENING WITH MAJOR HEAT RISK EXPECTED. AN 70 TO 80
PERCENT PROBABILITY OF TEMPERATURES OF 105 DEGREES OR HOTTER
WITH LITTLE OVERNIGHT RELIEF.
3. MOISTURE TRACKING OVER THE REGION IN THE LATE WEEK PERIOD
WILL BRING A 10 TO 15 PERCENT CHANCE FOR THUNDERSTORMS TO THE
SIERRA NEVADA CREST.
4. MOISTURE WILL ALSO BRING A 20 TO 30 PERCENT PROBABILITY FOR A
HUNDREDTH OF AN INCH OF RAINFALL TO THE NORTHERN SAN JOAQUIN
VALLEY ON FRIDAY.
DISCUSSION
HIGH PRESSURE REMAINS FIRMLY IN PLACE OVER THE FOUR CORNERS
REGION OF THE DESERT SOUTHWEST THIS EVENING AND WILL PERSIST
THROUGH MUCH OF THE UPCOMING WORK WEEK. MEANWHILE, A LOW
PRESSURE TROUGH IS LOCATED OFF THE COAST OF THE PACIFIC
NORTHWEST WHICH WILL GRADUALLY MOVE ONSHORE THROUGH THE LATTER
PORTIONS OF THE WEEK. WITH THE LOCAL AREA CAUGHT BETWEEN THESE
TWO AIR MASS SYSTEMS, PREVAILING FLOW IS FROM THE SOUTHWEST,
SIMILAR TO THIS PAST WEEKEND. THE RESULT IS WARMER TEMPERATURES
WITH SPORADIC HIGH- LEVEL CLOUD COVER TRACKING OVER THE REGION.
FOR TUESDAY AND WEDNESDAY, THERE IS AN 80 TO 90 PERCENT
PROBABILITY FOR MAXIMUM TEMPERATURES TO EXCEED 100 DEGREES IN
THE SAN JOAQUIN VALLEY SOUTH OF FRESNO AND, SIMILARLY, THERE IS
A 70 TO 80 PERCENT PROBABILITY FOR HIGHS TO EXCEED 105 DEGREES
IN THE MOJAVE DESERT.
IN THE MID-TO-LATE WEEK PERIOD, THERE WILL BE A SLIGHT PATTERN
CHANGE AS THE AFOREMENTIONED TROUGH TRACKS INTO WASHINGTON AND
BRITISH COLUMBIA. THE INFLUENCE WILL REACH SOUTHWARDS ALONG THE
PACIFIC COAST, HELPING TO SHEAR PORTIONS OF MOISTURE FROM
CURRENT TROPICAL STORM ISELLE AND PUSH IT OVER THE NORTH AND
CENTRAL SIERRA NEVADA. THROUGH 5 AM SATURDAY, THERE IS A 60 TO
70 PERCENT PROBABILITY FOR AT LEAST A HUNDREDTH OF AN INCH OVER
24 HOURS IN THE CENTRAL SIERRA, INCLUDING YOSEMITE NATIONAL
PARK. SOME PROBABILITIES ALSO EXTEND INTO THE NORTHERN SAN
JOAQUIN VALLEY, WHICH HAVE A 20 TO 30 PERCENT PROBABILITY FOR
THE SAME AMOUNTS OVER THE SAME TIME FRAME. THE WARMER VALLEY
TEMPERATURES INTERACTING WITH THE FLOW OF MOISTURE ALOFT WILL
ALSO RESULT IN A 10 TO 15 PERCENT CHANCE FOR THUNDERSTORMS
ACROSS THE SIERRA CREST FRIDAY AFTERNOON.
AS THE WEEKEND APPROACHES, A SECOND WAVE OF INFLUENCE FROM THE
AFOREMENTIONED TROUGH WILL PASS THROUGH CALIFORNIA, ERODING THE
HIGH PRESSURE RIDGE AND STARTING A COOLING TREND THAT WILL
CONTINUE INTO NEXT WEEK. TEMPERATURES WILL HAVE LESS THAN A 20
PERCENT PROBABILITY TO EXCEED 100 DEGREES ON SUNDAY.
HOWEVER, BEFORE REACHING THE WEEKEND, WARM AND DRY CONDITIONS
WILL PERSIST. MINIMUM RELATIVE HUMIDITIES ACROSS THE VALLEY
AREAS ARE EXPECTED BETWEEN 15 AND 25 PERCENT THROUGH MOST OF THE
WEEK, WITH DESERT RHS FLIRTING WITH SINGLE DIGITS ONCE AGAIN.
RHS IN THE SIERRA NEVADA WILL BE SLIGHTLY BETTER THAN IN
PREVIOUS HEAT EVENTS DUE TO THE FLOW OF MOISTURE BEING SHALLOW
ENOUGH TO REACH THE PEAKS OF THE RANGE. MINRH VALUES ARE
EXPECTED BETWEEN 25 AND 35 PERCENT IN THE HIGHER ELEVATIONS AND
WILL IMPROVE IN THE LATTER PORTIONS OF THE WEEK NEAR 40 PERCENT.
AVIATION
VFR CONDITIONS PREVAILING FOR THE NEXT 24 HOURS.
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
EXTREME HEAT WARNING UNTIL 11 PM PDT WEDNESDAY FOR CAZ337>339.
HEAT ADVISORY UNTIL 11 PM PDT WEDNESDAY FOR CAZ304>316.
PUBLIC/AVIATION...MCCOY
WEATHER.GOV/HANFORD
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