726
FXUS65 KPSR 211707
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1007 AM MST SUN DEC 21 2025
UPDATE
UPDATED 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 1705Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT; AND
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO AVIATION WEATHER CONCERNS ARE ANTICIPATED THROUGH THE TAF
PERIOD UNDER FEW-SCT HIGH CIRRUS DECKS, BECOMING BKN MONDAY
AFTERNOON. WINDS WILL FOLLOW A NEARLY IDENTICAL PATTERN TO THE
LAST 24 HOURS AND REMAIN LIGHT (GENERALLY AOB 6 KTS), WITH
EXTENDED PERIODS OF VARIABILITY OR CALM CONDITIONS.
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...WHITTOCK
FIRE WEATHER...LOJERO/BENEDICT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page