328
FXUS65 KPSR 211728
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1028 AM MST SAT DEC 21 2024
UPDATE
UPDATED 18Z AVIATION DISCUSSION.
SYNOPSIS
WITH HIGH PRESSURE PARKED OVER THE REGION, UNUSUALLY WARM
TEMPERATURES WILL PERSIST THIS WEEKEND BEFORE A GRADUAL COOLING
TREND COMMENCES NEXT WEEK. A SERIES OF WEATHER DISTURBANCES WILL
PUSH THROUGH THE REGION NEXT WEEK ALLOWING READINGS TO RETREAT
CLOSER TO THE SEASONAL AVERAGE. HOWEVER, WITH VERY LITTLE MOISTURE
AVAILABLE FOR THESE WEATHER SYSTEMS, DRY WEATHER SHOULD CONTINUE FOR
THE FORESEEABLE FUTURE.
DISCUSSION
A SPRAWLING HIGH PRESSURE RIDGE REMAINS SITUATED OVER NORTHERN
MEXICO AND SW CONUS WITH MIDTROPOSPHERIC HEIGHTS AND THERMAL
PROFILES HOVERING ABOVE THE 90TH PERCENTILE OF CLIMATOLOGY. AS SUCH,
CONFIDENCE IS EXCELLENT THAT ANOTHER DAY OF NEAR RECORD TEMPERATURES
WILL BE COMMON ACROSS THE FORECAST AREA. HOWEVER, A SERIES OF
WEAKENING EAST PACIFIC SHORTWAVES WILL BE BREAKING INLAND OVER THE
RIDGE APEX THE NEXT 72 HOURS, STEADILY DAMPENING HEIGHTS ALOFT SUCH
THAT LOCAL H5 READINGS NEAR 582DM TODAY WILL EDGE CLOSER TO 579DM.
WHILE NOT A TREMENDOUS COOLING TREND, THIS EVOLUTION SHOULD HALT THE
CURRENT STRING OF RECORD BREAKING TEMPERATURES WITH DAILY ANOMALIES
RETREATING FROM NEAR 15F ABOVE NORMAL CLOSER TO 10F WARMER THAN
NORMAL.
A PROGRESSIVE CONUS FLOW REGIME WILL PERSIST THROUGHOUT NEXT WEEK,
ALBEIT WITH AN UNDERLYING REFLECTION OF LONGWAVE RIDGING REMAINING
STATIONED OVER THE WEST. A BETTER DEFINED SHORTWAVE PROPAGATING
THROUGH THE REGION DURING THE MIDDLE OF THE WEEK WILL INTERRUPT THIS
PREVAILING HIGH PRESSURE DOMINANCE. ENSEMBLE MEMBERSHIP REMAINS IN
GOOD AGREEMENT DEPICTING THIS FEATURE WITH A NEGATIVE TILT
ORIENTATION, HOWEVER WITH THE PRIMARY PV ANOMALY, COLD CORE, AND
STRONGER FORCED ASCENT TRACKING ALONG THE AZ/UT BORDER. WHILE LOWER
TROPOSPHERIC COOLING SHOULD BE MORE PRONOUNCED WITH THIS WAVE AND
ASSOCIATED DECAYING PACIFIC COLD FRONT, BRIEFLY PUSHING READINGS
MUCH CLOSER TO CLIMATOLOGY, LITTLE ATTENDANT OR ADVECTED MOISTURE
WILL BE COINCIDENT WITH THIS SHORTWAVE PASSAGE. FORECAST BUFR
SOUNDINGS ALSO SUGGEST A NOTABLE MIDLEVEL SUBSIDENCE INVERSION
DEVELOPING SOUTH OF THE JET CORE MAKING ANY DEEP SATURATION VERY
DIFFICULT TO ACHIEVE. HAVE SIGNIFICANTLY CUT MANDATED NBM POPS OVER
PARTS OF SE CALIFORNIA AS A TYPICAL BIAS OF BLEEDING PRECIPITATION
MUCH TOO FAR INTO LEEWARD AREAS OF THE SAN DIEGO MOUNTAINS IS
CLEARLY EVIDENT. IN THE END, IT'S DIFFICULT TO SEE MUCH MORE THAN
VIRGA AND SPRINKLES MATERIALIZING FROM THIS PATTERN (AND EVEN THAT
MIGHT BE A STRETCH).
THE ONGOING WINTER (AND VERY LA NINA-LIKE) PATTERN OF SHORTWAVES
DIGGING AND INTENSIFYING WELL EAST OF THE FORECAST AREA SHOULD
CONTINUE DURING THE LATTER HALF OF NEXT WEEK AS ANOTHER PACIFIC
SHORTWAVE PROGRESSES THROUGH THE FOUR CORNERS AREA. ENSEMBLE SPREAD
GROWS WITH RESPECT TO THE TRAJECTORY OF THIS WAVE WITH SOME OUTPUT
CLIPPING HIGHER TERRAIN OF EASTERN AZ WITH FORCED, MOIST ASCENT.
HOWEVER, THE PREPONDERANCE OF ENSEMBLE SOLUTIONS SUGGEST THIS WAVE
SHEARING EAST INTO A MIDLEVEL HEIGHT WEAKNESS OVER THE PLAINS WHILE
STRONG HEIGHT RISES AND RESUMPTION OF STRONG RIDGING BUILDS BACK
INTO THE SW CONUS. WHILE UNCERTAINTY IS NATURALLY HIGHER IN A DAY 6-
10 FORECAST LIKELY RESTRICTING THE HASTE AND MAGNITUDE OF WARMING
VIA NBM OUTPUT, CONFIDENCE IS GROWING THAT ANOMALOUS WARMTH AND NEAR
RECORD TEMPERATURES COULD RETURN TO THE REGION NEXT WEEKEND TO CLOSE
OUT 2024.
AVIATION
UPDATED AT 1725Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT; AND
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
WINDS WILL CONTINUE TO FOLLOW THEIR TYPICAL DIURNAL PATTERNS,
WITH SPEEDS REMAINING AOB 6 KT. EXTENDED PERIODS OF LIGHT AND
VARIABLE TO CALM WINDS IS ALSO EXPECTED, ESPECIALLY DURING DIURNAL
WIND SHIFTS. FEW TO SCT HIGH CIRRUS CLOUDS WILL MOVE OVER THE
REGION TODAY.
FIRE WEATHER
DRY WEATHER WITH ABOVE NORMAL TEMPERATURES WILL CONTINUE ACROSS THE
REGION THROUGH NEXT WEEK, THOUGH A COUPLE WEATHER SYSTEMS WILL
CREATE AN ENVIRONMENT OF MARGINALLY INCREASING HUMIDITIES. THROUGH
EARLY NEXT WEEK, MINIMUM AFTERNOON RH VALUES IN THE TEENS WILL BE
COMMON FOLLOWING POOR TO FAIR OVERNIGHT RECOVERY OF 20-50%. BY THE
MIDDLE OF NEXT WEEK, MINIMUM VALUES SHOULD INCREASE CLOSER TO 20-
30% WITH OVERNIGHT RECOVERY IN A 40-60% RANGE. WHILE SOME LOCALIZED
ENHANCED BREEZINESS WILL BE POSSIBLE NEXT WEEK ALONG A WEAK COLD
FRONTAL PASSAGE, VERY LIGHT WINDS WILL BE MORE TYPICAL ACROSS THE
DISTRICTS.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
DISCUSSION...18
AVIATION... BERISLAVICH
FIRE WEATHER...18
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