112
FXUS65 KPSR 212122
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
222 PM MST SUN DEC 21 2025
KEY MESSAGES
- DRY AND TRANQUIL WEATHER CONDITIONS WITH WELL-ABOVE NORMAL
TEMPERATURES WILL CONTINUE TO PREVAIL ACROSS THE REGION THROUGH
MONDAY.
- AN UNSETTLED WEATHER PATTERN IS EXPECTED MID AND LATE WEEK,
DURING THE CHRISTMAS HOLIDAY TIME PERIOD, WITH INCREASED RAIN
CHANCES AND SLIGHTLY COOLER TEMPERATURES.
SHORT TERM /TODAY THROUGH TUESDAY/
STRONG HIGH PRESSURE (589-590DAM) REMAINS IN PLACE JUST SOUTHEAST OF
AZ THIS AFTERNOON. THIS HIGH CONTINUES TO DRIVE WELL ABOVE NORMAL
TEMPERATURES FOR THE DESERT SOUTHWEST. LOWER DESERT HIGHS WILL
REACH THE UPPER 70S TO AROUND 80 DEGREES TODAY. HIGHS WILL BE
WITHIN A COUPLE DEGREES OF DAILY RECORDS TODAY, AS WELL AS
TOMORROW, WITH HIGHEST ODDS (~80%) IN PHOENIX. INCREASING HIGH
CLOUDS MAY BE AN INHIBITING FACTOR IN RECORD CHANCES MONDAY.
HEADING INTO TUESDAY, THE OVERALL PATTERN WILL BE IN A
TRANSITIONAL STATE AS THE UPPER-LEVEL RIDGE MIGRATES FURTHER EAST
TO THE GULF STATES, ALLOWING FOR A DEEP TROUGH TO SETTLE JUST OFF
THE WEST COAST WHICH WILL KICK-OFF A SIGNIFICANT MOISTURE FLUX
INTO THE SOUTHWEST U.S. HEADING INTO THE CHRISTMAS HOLIDAY PERIOD
AND LIKELY PERSISTING INTO NEXT WEEKEND. A STRONG AND RAPID PUSH
OF SUBTROPICAL MOISTURE IS EXPECTED THROUGHOUT THE DAY TUESDAY,
COMING UP FROM THE SOUTHWEST, WITH MODELS SHOWING PWATS GOING FROM
0.3-0.4" EARLY TUESDAY MORNING TO 1.0-1.1" (250-300% OF NORMAL)BY
LATE IN THE EVENING. A SHORTWAVE TROUGH MOVING UP WITH THIS PUSH
OF MOISTURE IS LIKELY TO HELP DRIVE A BAND OF VIRGA AND LIGHT
SHOWERS THROUGH THE REGION, MOVING FROM WEST TO EAST, FROM LATE
MORNING OUT WEST TO SOUTH-CENTRAL AZ TUESDAY EVENING/NIGHT. VERY
LITTLE, IF ANY, RAINFALL ACCUMULATION IS EXPECTED WITH THIS
INITIAL WAVE.
AFTERNOON HIGH TEMPERATURES TUESDAY WILL ONCE AGAIN BE WELL-ABOVE
NORMAL, BUT COOLED SLIGHTLY, ESPECIALLY OUT WEST, DUE TO THE
PATTERN CHANGE. LOWER DESERT HIGHS WILL REACH THE LOW TO MID 70S
IN SOUTHEAST CA AND SOUTHWEST AZ AND MID TO UPPER 70S IN SOUTH-
CENTRAL AZ. THERE IS EVEN A POTENTIAL THAT PHOENIX WILL SEE
ANOTHER DAILY RECORD HIGH, GIVEN THAT CURRENTLY THE FORECAST HIGH
IS 79 DEGREES WITH THE RECORD BEING 79.
LONG TERM /WEDNESDAY THROUGH NEXT WEEKEND/
FOLLOWING THE SHORTWAVE TROUGH, WITH THE INITIAL SURGE OF
MOISTURE TUESDAY, THERE MAY BE A BRIEF BREAK IN SHOWER ACTIVITY
WEDNESDAY MORNING DUE TO SUBSIDENCE AND DRIER MID-LEVEL AIR IN
THE TROUGH'S WAKE. HOWEVER, ONCE THE HIGH-END MOISTURE LEVELS
ARRIVE THERE WILL BE SHOWER CHANCES AT NEARLY ALL TIMES THROUGH AT
LEAST THURSDAY (CHRISTMAS DAY). PWATS ARE FORECAST TO REMAIN AT OR
ABOVE 1" (ABOVE THE 90TH PERCENTILE) THROUGH THURSDAY, BASED ON
THE GLOBAL GRAND ENSEMBLE. A MODERATE-STRONG AR, WITH IVT VALUES
OVER 500 KG/MS, WILL SHIFT FURTHER EAST INTO THE INTERIOR DESERT
SOUTHWEST WEDNESDAY AFTERNOON THROUGH THURSDAY MORNING. GLOBAL
ENSEMBLES CONSISTENTLY SHOW THIS TO BE THE TIME PERIOD WHEN MOST
RAIN WILL FALL ACROSS THE REGION AND LATEST NBM POPS HAVE
INCREASED AND ARE HIGHEST (70-90%) DURING THIS TIMEFRAME ACROSS
SOUTHEAST CA THROUGH SOUTH-CENTRAL AZ. HEADING INTO THURSDAY
AFTERNOON AND FRIDAY, A GRADUAL DECLINE IN MOISTURE IS EXPECTED,
WITH MODEL SOUNDINGS SHOWING NOTABLE DRYING AND SUBSIDENCE ABOVE
700MB. THIS WILL SUBSEQUENTLY RESULT IN A DECLINE IN RAIN CHANCES.
HOWEVER, WITH THE LINGERING MOISTURE IN THE BOUNDARY LAYER, BELOW
700MB, ISOLATED SURFACE-BASED LIGHT SHOWERS MAY CONTINUE TO
DEVELOP, FAVORING THE AZ HIGH TERRAIN, THURSDAY AFTERNOON THROUGH
FRIDAY.
OVERALL, DYNAMIC FORCING WILL BE A BIT LIMITED TUESDAY-FRIDAY,
WITH THE PRIMARY TROUGH AND BEST FORCING STAYING TO THE WEST AND
NORTHWEST. A LOT OF THE FORCING IN THE INTERIOR DESERTS WILL COME
FROM ISENTROPIC ASCENT AND UPSLOPE WARM-AIR ADVECTION. THE RICHEST
LOW-LEVEL MOISTURE WITH THE AR WILL RAIN OUT MOSTLY ON THE
WINDWARD SIDE OF THE MOUNTAINS IN SOCAL, WITH A LOT OF SHADOWING
INTO SOUTHEAST CA AND PARTS OF FAR SOUTHWEST AZ. FOR THESE REASONS
THE HIGHEST ACCUMULATING RAINFALL AMOUNTS WILL FAVOR SOUTHWEST-
FACING SLOPES AND MOUNTAINS WHERE OROGRAPHIC LIFT IS MAXIMIZED.
LATEST QPF FROM WPC HAS STORM TOTAL RAINFALL AMOUNTS RANGING FROM
A FEW HUNDREDTHS OF AN INCH IN THE SOUTHERN-MOST DESERTS TO AROUND
0.50-0.75" IN PHOENIX AND ALONG PHOENIX'S LATITUDE TO OVER 1" IN
THE FOOTHILLS NORTH OF PHOENIX AND IN WESTERN JOSHUA TREE NP.
LATEST 12Z RUNS OF THE GEFS AND ENS MAINTAIN THE HIGHEST
PROBABILITIES (70-90%) FOR STORM TOTAL PRECIP >1" ACROSS YAVAPAI,
MOHAVE, AND WESTERN COCONINO COUNTIES. THIS IS WHERE MOST OF THE
RAIN IS EXPECTED TO FALL WITH THIS EVENING. THERE IS ALSO
POTENTIAL FOR HIGH RAINFALL AMOUNTS IN WESTERN JOSHUA TREE NP,
WHICH IS BEING MONITORED FOR A POTENTIAL FLOOD WATCH IN THE NEXT
COUPLE DAYS.
THE FORECAST BECOMES HIGHLY UNCERTAIN HEADING INTO NEXT WEEKEND
AS BOTH THE DETERMINISTIC AND ENSEMBLE MODEL SUITE CONTINUE TO
DIVERGE SIGNIFICANTLY ON THE OVERALL STRENGTH, TIMING, AND
TRAJECTORY OF THE TROUGH AS IT EVENTUALLY 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. EVEN MORE OF
A COOLDOWN IS NOT EXPECTED UNTIL THE MAIN TROUGH FULLY MOVES
THROUGH, LIKELY TOWARD THE END OF NEXT WEEKEND/EARLY THE FOLLOWING
WEEK, AND EVEN STILL TEMPERATURES MAY ONLY DROP TO SEASONAL
LEVELS.
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 AT LEAST MONDAY. 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. THE INITIAL
STRONG PUSH OF MOISTURE WILL COME DURING THE DAY TUESDAY, WITH
MAXRH VALUES TUESDAY NIGHT JUMPING TO 75-100%. IN THE FOLLOWING
DAYS, MINRHS WILL BE IN THE 45-70% RANGE.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...BENEDICT
LONG TERM...BENEDICT
AVIATION...WHITTOCK
FIRE WEATHER...LOJERO/BENEDICT
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