343
FXUS65 KPSR 211128
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
428 AM MST SUN DEC 21 2025
UPDATE...UPDATED 12Z AVIATION DISCUSSION
KEY MESSAGES
- DRY AND TRANQUIL WEATHER CONDITIONS WITH WELL-ABOVE NORMAL
TEMPERATURES WILL CONTINUE TO PREVAIL ACROSS THE REGION THROUGH
TUESDAY.
- AN UNSETTLED WEATHER PATTERN IS EXPECTED MID AND LATE WEEK WITH
INCREASED RAIN CHANCES AND COOLER TEMPERATURES.
SHORT TERM /TODAY THROUGH TUESDAY/
UPPER-LEVEL RIDGING, CURRENTLY SITUATED NEAR THE BAJA PENINSULA,
WILL CONTINUE TO PROVIDE DRY AND TRANQUIL CONDITIONS THROUGH THE
START OF THE WEEK. TEMPERATURES WILL CONTINUE TO RUN 10-15
DEGREES ABOVE NORMAL WITH AFTERNOON HIGHS ACROSS MOST OF THE LOWER
DESERT COMMUNITIES TOPPING OUT IN THE UPPER 70S TO AROUND 80
DEGREES BOTH TODAY AND MONDAY. WITH TEMPERATURES OF THIS
MAGNITUDE, DAILY RECORD HIGHS WILL BE WITHIN REACH, WITH PHOENIX
HAVING THE HIGHEST PROBABILITIES OF GREATER THAN 80% OF
EXPERIENCING DAILY RECORD HIGHS.
HEADING INTO TUESDAY, THE OVERALL PATTERN WILL BE IN A TRANSITIONAL
STATE AS THE UPPER-LEVEL RIDGE MIGRATES INTO TEXAS, ALLOWING FOR
A DEEP TROUGH TO SETTLE JUST OFF THE WEST COAST AND MARKING THE
BEGINNING WHAT IS EXPECTED TO TURN INTO AN UNSETTLED WEATHER
PATTERN HEADING TOWARDS THE CHRISTMAS HOLIDAY PERIOD AND LIKELY
PERSISTING INTO NEXT WEEKEND. AFTERNOON HIGH TEMPERATURES WILL
ONCE AGAIN BE WELL-ABOVE NORMAL, IN THE MIDDLE TO UPPER 70S
ACROSS MOST OF THE LOWER DESERT COMMUNITIES. THERE IS EVEN A
POTENTIAL THAT PHOENIX MAY ACTUALLY SEE ANOTHER DAILY RECORD HIGH,
GIVEN THAT CURRENTLY THE FORECAST HIGH IS 79 DEGREES WITH THE
RECORD BEING 79. AS A SOUTHWESTERLY FLOW PATTERN DEVELOPS BETWEEN
THE HIGH TO THE EAST AND THE TROUGH TO THE WEST, A RAPID MOISTURE
INCREASE ORIGINATING FROM THE DEEP SUBTROPICS IS EXPECTED WITH
BOTH THE EPS AND GEFS SHOWING PWATS REACHING 200-300% OF NORMAL
BY LATE TUESDAY EVENING. IN ADDITION, MODELS ARE SHOWING A WEAK
SUBTROPICAL SHORTWAVE MOVING THROUGH ARIZONA TUESDAY EVENING INTO
EARLY WEDNESDAY AND WILL LIKELY SPARK SOME LIGHT SHOWERS.
LONG TERM /WEDNESDAY THROUGH NEXT WEEKEND/
ANY SHOWER ACTIVITY EARLY WEDNESDAY WILL QUICKLY END AS THE
SHORTWAVE LIFTS AWAY WITH SOME MID-LEVEL DRYING AND SUBSIDENCE
LIKELY IN THE WAKE. ATTENTION WILL THEN TURN TO A MUCH STRONGER
SHORTWAVE ROUNDING THE BASE OF THE TROUGH OFF THE WEST COAST AND
WILL GUIDE A MODERATE AR (IVT VALUES IN EXCESS OF 500 KG/MS) THAT
WILL AFFECT MUCH OF CENTRAL AND SOUTHERN CA WITH HEAVY PRECIPITATION
DURING THE DAY WEDNESDAY. MODELS CONTINUE TO SHOW THE PRIMARY
FORCING WITH THIS SHORTWAVE TO MIGRATE FROM SOUTHERN CA
NORTHEASTWARD INTO THE GREAT BASIN AREA. WITH THE PRIMARY FORCING
STAYING TO THE NORTHWEST OF THE REGION, CONDITIONS AT THIS TIME DO
NOT LOOK TO BE TOO OVERLY FAVORABLE FOR WIDESPREAD RAINFALL
ACROSS THE LOWER DESERTS, WITH SOUTHEAST CA LIKELY TO BE RAIN-
SHADOWED. WITH THE MAIN IVT PLUME EXPECTED TO MOVE THROUGH AZ LATE
WEDNESDAY INTO THURSDAY, IT WILL ALLOW FOR SCATTERED SHOWERS TO
DEVELOP, WITH THE BEST CHANCES FOR MORE WIDESPREAD ACTIVITY ACROSS
THE UPSLOPE AREAS OF CENTRAL AND WESTERN AZ AS WELL AS THROUGH
PORTIONS OF SOUTHEAST CA, WHICH INCLUDES JOSHUA TREE NATIONAL
PARK. HOWEVER, IF THE SHORTWAVE TRACKS A BIT CLOSER, THEN THE
CHANCES FOR MORE WIDESPREAD RAINFALL INCREASES ACROSS THE LOWER
DESERTS DUE TO BETTER FORCING FOR ASCENT. BASED ON THE LATEST QPF
FROM WPC, TOTAL RAINFALL AMOUNTS BETWEEN LATE TUESDAY THROUGH
SATURDAY RANGE BETWEEN 0.25-0.75" ACROSS THE LOWER DESERTS TO AN
EXCESS OF 1" ACROSS THE UPSLOPE AREAS OF CENTRAL AND WESTERN AZ AS
WELL AS JOSHUA TREE NATIONAL PARK.
A BREAK IN THE RAINFALL ACTIVITY IS LIKELY HEADING INTO FRIDAY AS
THE MOISTURE CONTENT DECREASES AND SUBSIDENCE INCREASES IN THE WAKE
OF THE SHORTWAVE. THERE ARE HINTS OF WEAK RIDGING BUILDING
DOWNSTREAM OF THE MAIN TROUGH, WHICH WILL STABILIZE THE ENVIRONMENT
EVEN MORE. THE FORECAST THEN BECOMES HIGHLY UNCERTAIN HEADING INTO
NEXT WEEKEND AS BOTH THE DETERMINISTIC AND ENSEMBLE MODEL SUITE
DIVERGE SIGNIFICANTLY ON THE OVERALL STRENGTH, TIMING, AND
TRAJECTORY OF THE TROUGH AS IT MIGRATES INLAND THROUGH THE DESERT
SOUTHWEST. DEPENDING ON THE OVERALL STRENGTH AND TRAJECTORY OF
THE TROUGH, ANOTHER ROUND OF PRECIPITATION WILL BE POSSIBLE.
AS THIS UNSETTLED WEATHER PATTERN EVOLVES DURING THE MIDDLE AND
LATTER PORTION OF THE WEEK AND INTO NEXT WEEKEND, TEMPERATURES ARE
EXPECTED TO GRADUALLY COOL BUT WILL LIKELY REMAIN ABOVE NORMAL IN
THE LOW TO MID 70S. WITH THE ABUNDANT CLOUD COVER AND MOISTURE
EXPECTED TO BE IN PLACE, ESPECIALLY WEDNESDAY THROUGH FRIDAY,
OVERNIGHT LOW TEMPERATURES ARE EXPECTED TO BE QUITE WARM FOR THIS
TIME OF THE YEAR, IN THE UPPER 50S TO NEAR 60 DEGREES. IN FACT,
THERE IS A POTENTIAL FOR ALL THREE CLIMATE SITES (PHOENIX, YUMA, EL
CENTRO) TO BREAK RECORD WARM LOWS. A MORE SIGNIFICANT COOLDOWN WILL
LIKELY OCCUR ONCE THE MAIN TROUGH FULLY MOVES THROUGH.
AVIATION
UPDATED AT 1125Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT; AND
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO AVIATION CONCERNS ARE EXPECTED FOR MOST OF THE SITES DURING
THE TAF PERIOD UNDER SCT-BKN HIGH CIRRUS DECKS. THE ONE EXCEPTION
TO THIS IS AT KIPL WHERE THERE IS POTENTIAL FOR FG/BR DEVELOPMENT
THROUGH EARLY THIS MORNING. HOWEVER, CONFIDENCE REGARDING THESE
CONDITIONS IS LOW AND THEREFORE DIRECT IMPACTS AT THE TAF SITE
HAVE BEEN LEFT OUT OF THE FORECAST FOR NOW WITH A VCFG GROUP ADDED
FOR NOW. WINDS WILL CONTINUE TO BE LIGHT WITH SUBTLE DIRECTIONAL
SHIFTS. VRB TO CALM CONDITIONS WILL BE COMMON THROUGHOUT THE
PERIOD.
FIRE WEATHER
HIGH PRESSURE ACROSS THE REGION WILL CONTINUE TO PROMOTE DRY AND
TRANQUIL WEATHER, AS WELL AS UNSEASONABLY WARM TEMPERATURES UP TO
10 TO 15 DEGREES ABOVE NORMAL THROUGH THE START OF THE WEEK.
WINDS WILL GENERALLY BE LIGHT UNDER 15 MPH AND TEND TO FOLLOW
TYPICAL DIURNAL TRENDS. AFTERNOON MINRHS WILL RANGE BETWEEN 20-35%
WITH GOOD OVERNIGHT RECOVERIES OF 50-75%. A WEATHER SYSTEM IS
EXPECTED TO AFFECT THE REGION MID AND LATE WEEK BRINGING HIGHER
MOISTURE, INCREASED RAIN CHANCES, AND COOLER TEMPERATURES
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...LOJERO
LONG TERM...LOJERO
AVIATION...RW/LOJERO
FIRE WEATHER...LOJERO/BENEDICT
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