015
FXUS65 KPSR 062351
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
451 PM MST TUE JAN 6 2026
UPDATE
00Z AVIATION DISCUSSION.
KEY MESSAGES
- A PAIR OF WEATHER SYSTEMS WILL PRODUCE UNSETTLED CONDITIONS
DURING THE MIDDLE PORTION OF THE WEEK WITH INCREASING RAIN
CHANCES AND BREEZY TO LOCALLY WINDY CONDITIONS.
- TEMPERATURES WILL COOL THROUGH THE REST OF THE WEEK BEFORE
REBOUNDING BY THE WEEKEND AS HIGH PRESSURE MAKES A RETURN.
SHORT TERM /TODAY THROUGH WEDNESDAY/
CURRENT OBJECTIVE ANALYSIS REVEALS THE DESERT SOUTHWEST UNDERGOING A
TRANSITION AS A PACIFIC LOW SPINS OFF THE CALIFORNIA COAST AND ZONAL
FLOW STRETCHES OVER MUCH OF THE SOUTHERN TIER OF THE CONUS. EVEN
WITH THE AFOREMENTIONED LOW IN RELATIVELY CLOSE PROXIMITY, NO
SIGNIFICANT WEATHER CHANGES ARE EXPECTED FOR TODAY AS TEMPERATURES
CONTINUE TO HOVER AROUND NEAR TO SLIGHTLY ABOVE NORMAL LEVELS AND
HIGH CLOUDS CONTINUE TO STREAM OVER THE REGION. DAY-TO-DAY
TEMPERATURES OUT IN SE CALIFORNIA WILL DIP SLIGHTLY COMPARED TO
YESTERDAY THANKS TO THEIR CLOSER POSITION TO THE COLD CORE BUT THE
TREND OF MIDDLE 60S TO LOWER 70S WILL CONTINUE FOR DESERT LOCATIONS.
THE MORE NOTICEABLE WEATHER CHANGES WILL COMMENCE WEDNESDAY AS THE
PACIFIC LOW BEGINS ITS ONSHORE MIGRATION, DRAGGING MOISTURE ALONG
WITH IT AND INCREASING RAINFALL CHANCES. WITH FAVORABLE DYNAMIC
FORCING DUE TO AN ASSOCIATED VORTICITY CENTER AND POSITION OF THE
UPPER-LEVEL JET, ALONG WITH A PERIOD OF ISENTROPIC ASCENT, THE
OVERALL SETUP LOOKS FAVORABLE FOR THE DEVELOPMENT OF SHOWERS BY
THE MID TO LATE MORNING HOURS. THE CORE OF THE LOW WILL NOT EXIT
THE REGION UNTIL LATER WEDNESDAY NIGHT, SO WITH THE ASSISTANCE OF
CONTINUED DYNAMIC FORCING AND COOLING, WE COULD BE LOOKING AT
SEVERAL ROUNDS OF SHOWERS THROUGH MUCH OF THE DAY. DUE TO A LACK
OF INSTABILITY AND ONLY MODERATE MOISTURE PROFILES (PWATS NEAR
0.80-1.00"), PRECIPITATION RATES WILL NOT BE OVERLY IMPRESSIVE SO
EVEN THOUGH THIS EVENT WILL PROLONGED, QPF TOTALS SHOULD REMAIN
LIGHT FOR LOWER DESERT AREAS WITH A FEW HUNDREDTHS TO MAYBE A FEW
TENTHS OF AN INCH APPEARING TO BE THE MOST LIKELY OUTCOME. HIGHER
TOTALS WILL BE FAVORED WHERE SHOWERS BECOME FURTHER ENHANCED BY
OROGRAPHIC INFLUENCES. COVERAGE WILL BE GREATEST EAST OF THE
COLORADO RIVER, BUT SOME ISOLATED ACTIVITY CANNOT BE RULED OUT
FOR SE CALIFORNIA.
LONG TERM /THURSDAY THROUGH MONDAY/
AS THE AFOREMENTIONED WAVE EJECTS EAST INTO THE SOUTHERN PLAINS
THURSDAY, A CLASSIC WINTER PATTERN WILL EVOLVE WITH NEGATIVELY
TILTED PV DIGGING INTO DEEPENING INLAND CYCLOGENESIS FROM THE
SOUTHERN ROCKIES THROUGH MIDWEST. MODEL TRENDS CONTINUE TO PUSH FOR
A MORE INTENSE VORTICITY CENTER CARVING OUT THE WESTERN PERIPHERY OF
THE LONGWAVE TROUGH OVER ARIZONA THURSDAY AFTERNOON. TIMING OF THIS
FEATURE STILL APPEARS NEARLY OPTIMAL FOR VORTICITY FORCED ASCENT
ALONG THE LEADING EDGE OF THE COLD CORE AND STEEP FRONTAL BOUNDARY
TO INTERACT WITH RESIDUAL MOISTURE BEING PULLED UPSLOPE INTO HIGHER
TERRAIN. THIS SCENARIO TYPICALLY ALLOWS MAINTENANCE OF SHOWERS INTO
LOWER ELEVATIONS AROUND AND EAST OF THE PHOENIX METRO WHERE
MARGINALLY UNSTABLE CONDITIONS (MLCAPE AROUND 100 J/KG) MAY DEVELOP
AND EVEN SUPPORT SOME GRAUPEL WITH LOWERING FREEZING LEVELS AND
SHALLOW CONVECTION. GIVEN THE STRONG FORCING, STEEP COLD FRONT, AND
DEEPENING SYSTEM JUXTAPOSED WITH THIS SHALLOW CONVECTION, THESE
SHOWERS MAY ALSO TAP HIGHER MOMENTUM TOWARDS THE SURFACE IN THE FORM
OF GUSTS 30+ MPH.
ANOTHER CONSEQUENCE OF A STRONGER VORTICITY CENTER AND SHARPER
NEGATIVE TILT ORIENTATION IS MORE INTENSE UPSTREAM PRESSURE RISES
AND ABILITY TO VERTICALLY MIX STRONGER WINDS BEHIND THE FRONTAL
PASSAGE. THE TREND IN MODEL OUTPUT STRONGLY SUPPORTS A PATTERN OF
RAPIDLY INTENSIFYING (40-50KT) POST FRONTAL H9-H8 WINDS SURGING DOWN
THE LOWER COLORADO RIVER VALLEY LATE THURSDAY AFTERNOON, PEAKING
THURSDAY NIGHT WITH ADDED THERMAL INFLUENCES. HAVE STARTED TO
INCREASE WIND SPEEDS DURING THIS TIME FRAME OVER THE MANDATED NBM
WHICH SEEMS TO NOT BE CAPTURING THE IMPACTS OF SUCH A PATTERN COMMON
DURING THE WINTER. ENSEMBLE MEMBERS SHOW GOOD AGREEMENT THAT THE
ENTIRE WAVE STRUCTURE WILL EJECT INTO THE PLAINS FRIDAY WITH STRONG
SUBSIDENCE AND A MUCH DRIER AIRMASS FILTERING INTO THE FORECAST
AREA. DEPENDING ON THE MAGNITUDE OF THE COOLER, DRIER POST FRONTAL
AIRMASS, LOCALIZED FROST/FREEZE IMPACTS MAY BECOME AN ISSUE FOR
RURAL VALLEY LOCATIONS SATURDAY MORNING. OTHERWISE, A BLOCKING
PATTERN SHOULD BEGIN TO DEVELOP OVER THE WEEKEND INTO EARLY NEXT
WEEK ALLOWING TEMPERATURES TO MODERATE BACK INTO A SLIGHTLY ABOVE
NORMAL RANGE.
AVIATION
UPDATED AT 2350Z.
SOUTH CENTRAL ARIZONA INCLUDING KPHX, KIWA, KSDL, AND KDVT:
NO MAJOR AVIATION WEATHER CONCERNS WILL EXIST THROUGH AT LEAST EARLY
WEDNESDAY MORNING UNDER GRADUALLY THICKENING AND LOWERING MID TO
HIGH-LEVEL CLOUD DECKS. THE OVERALL WINDS WILL REMAIN VERY LIGHT
AND DIURNAL WITH SPEEDS AOB 5 KTS. EXTENDED PERIODS OF VARIABLE TO
CALM CONDITIONS WILL BE COMMON OVERNIGHT.
BY EARLY WEDNESDAY AFTERNOON, DETERIORATING WEATHER CONDITIONS IN
THE FORM OF WIDESPREAD -SHRA CAUSING REDUCTIONS IN VISIBILITIES
AND LOWER CIGS CAN BE EXPECTED. THERE IS HIGH CONFIDENCE THAT
CEILINGS WILL FALL TO AROUND 4-5 KFT AS RAIN SHOWERS OVERSPREAD
THE PHOENIX METRO, AND THERE IS AT LEAST A 60% CHANCE FOR MVFR
CIGS AS LOW AS 2-3 KFT DEVELOPING AT ALL TERMINALS, MAINLY
BETWEEN 21Z-01Z TOMORROW AFTERNOON. VISIBILITIES MAY ALSO FALL TO
AS LOW AS 2-3 SM IN ANY HEAVIER POCKETS OF RAIN. WINDS WILL BE
PREDOMINANTLY EASTERLY FOR MUCH OF THE PERIOD, HOWEVER CONFIDENCE
IN TIMING OF THE WESTERLY SHIFT TOMORROW REMAINS HIGHLY UNCERTAIN.
WINDS MAY NOT BECOME ESTABLISHED OUT OF THE W-NW UNTIL LATE IN
THE PERIOD (AROUND 01Z-03Z THURSDAY).
SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH:
NO MAJOR AVIATION WEATHER CONCERNS WILL EXIST THROUGH EARLY
WEDNESDAY MORNING UNDER GRADUALLY THICKENING AND LOWERING MID TO
HIGH-LEVEL CLOUD DECKS. WINDS WILL BE PREDOMINANTLY W-NW AT BOTH
TERMINALS WITH EXTENDED PERIODS OF CALM AND VRB. CIGS ARE EXPECTED
TO LOWER TO AROUND 5-6 KFT AT BOTH TERMINALS BY 15-16Z WEDNESDAY
MORNING AS VCSH/SHRA PROGRESSES THROUGH SE CALIFORNIA. RAIN
SHOWERS SHOULD CLEAR OUT OF THE REGION BY WEDNESDAY AFTERNOON.
FIRE WEATHER
MOISTURE LEVELS WILL REMAIN ELEVATED THROUGH THURSDAY WITH WETTING
RAINFALL CHANCES HEIGHTENED ACROSS EASTERN DISTRICTS AS A PAIR OF
WEATHER DISTURBANCES PASS THROUGH THE REGION. MUCH DRIER CONDITIONS
WILL RETURN BY THE WEEKEND. FOR THE NEXT FEW DAYS, MINIMUM AFTERNOON
HUMIDITY VALUES WILL ONLY FALL INTO A 40-60% RANGE, HOWEVER READINGS
IN A 15-30% RANGE WILL BECOME MORE COMMON BEGINNING FRIDAY.
CONCURRENTLY, EXCELLENT OVERNIGHT RECOVERY BETTER THAN 75% WILL
DETERIORATE INTO A 40-70% RANGE BY THE WEEKEND. STRONG NORTHERLY
WIND GUSTS IN EXCESS OF 30 MPH WILL LIKELY SURGE INTO THE LOWER
COLORADO RIVER VALLEY THURSDAY AFTERNOON THROUGH FRIDAY MORNING
YIELDING AN ELEVATED FIRE DANGER. ELSEWHERE, GUSTS SHOULD BE
SOMEWHAT WEAKER WITH LESSER IMPACTS BEFORE RETURNING TO MORE
SEASONAL LEVELS OVER THE WEEKEND.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
SHORT TERM...18
LONG TERM...18
AVIATION...SALERNO
FIRE WEATHER...18
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