596
FXUS65 KPSR 220515
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1015 PM MST SUN DEC 21 2025
UPDATE
UPDATED AVIATION
KEY MESSAGES
- DRY AND TRANQUIL WEATHER CONDITIONS WITH WELL ABOVE NORMAL
TEMPERATURES WILL CONTINUE 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 0515Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT; AND
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO WEATHER CONCERNS WILL EXIST THROUGH MONDAY NIGHT UNDER GRADUALLY
INCREASING THICKER HIGH CIRRUS DECKS. WIND SPEEDS AND DIRECTIONS
WILL BE NEARLY IDENTICAL TO THE PAST 24 HOURS WITH PROLONGED PERIODS
OF NEARLY 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...18
FIRE WEATHER...LOJERO/BENEDICT
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