Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 160927
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
227 AM MST TUE SEP 16 2014

.SYNOPSIS...
MOISTURE WILL CONTINUE TO INCREASE ACROSS THE AREA TODAY AS TROPICAL
STORM ODILE APPROACHES THE REGION. THERE WILL BE AN ELEVATED RISK OF
HEAVY RAIN AND FLOODING ACROSS THE AREA THROUGH LATE WEEK BEFORE
DRIER AIR RETURNS BY THE WEEKEND.

&&

.DISCUSSION...
SHOWERS CONTINUE TO DEVELOP AND DISSIPATE ACROSS SOUTHERN ARIZONA
THIS MORNING ALONG A STRONG MID LEVEL THETA-E GRADIENT. A STRONG
SURGE OF MOISTURE PRECEDED THESE STORMS LATE MONDAY NIGHT AS
DEWPOINTS JUMPED INTO THE MID 60S AND LOWER 70S AND PWATS CLIMBED TO
AROUND 1.6-1.7 INCHES. ALONG WITH THE SHOWERS...CLOUDS HAVE
INCREASED QUITE A BIT THIS MORNING WHICH HAS KEPT TEMPERATURES WELL
INTO THE MID 80S AS OF 09Z.

IN THE SHORT TERM...THE MID LEVEL INSTABILITY GRADIENT AND
ASSOCIATED SHORTWAVE TROUGH WILL SLOWLY MOVE NORTHWARD TODAY AND
COUPLED WITH THE RECENT INCREASE IN AVAILABLE MOISTURE...SCATTERED
SHOWERS AND THUNDERSTORMS ARE EXPECTED ACROSS NEARLY THE ENTIRE AREA
LATER TODAY. WINDS IN THE 700-300MB LAYER SHOULD BE STRONG ENOUGH TO
KEEP STORMS MOVING AND MITIGATE A WIDESPREAD FLASH FLOOD THREAT
TODAY...BUT LOCALLY HEAVY RAIN IS POSSIBLE ALONG WITH THE USUAL
HAZARDS /LOCALIZED BLDU AND GUSTY WINDS/. SINCE IT DOESNT APPEAR
THAT THERE WILL BE A COMPLEX OF STORMS OVER THE NORMALLY FAVORABLE
DUST-PRONE AREAS TO OUR SOUTHEAST...I WILL LEAVE BLOWING DUST OUT OF
THE FORECAST TODAY AS IT SHOULD BE VERY ISOLATED IN NATURE.
SHOWERS/STORMS COULD PERSIST INTO THE EVENING AND OVERNIGHT HOURS AS
THE SHORTWAVE TROUGH WILL BE SLOW TO EXIT THE AREA AND MOVE INTO
NORTH/EAST ARIZONA.

WEDNESDAYS FORECAST IS TRICKY AS THE BEST FORCING ASSOCIATED WITH
T.S. ODILE WILL STILL BE WELL TO THE SOUTH AND SUBSIDENCE BEHIND THE
DEPARTING SHORTWAVE COULD ALSO MITIGATE WIDESPREAD STORM COVERAGE.
THE GFS AND EUROPEAN REMAIN IN GOOD AGREEMENT THIS MORNING WITH BOTH
00Z RUNS INDICATING THE REMNANT LOW FROM T.S. ODILE WILL MOVE INTO
ARIZONA WEDNESDAY NIGHT. THE MODELS ARE CONTINUING THEIR SLIGHT
EASTWARD TREND WITH THE TRACK WHICH IS CAUSE FOR CONCERN. AS THE
CIRCULATION MOVES INTO SOUTHEAST ARIZONA ON WEDNESDAY...SLIGHTLY
DRIER AIR FROM THE NORTH WILL BE ADVECTED INTO THE
AREA...DOWNSLOPE...AND DRY OUT EVEN FURTHER. THIS WILL LIKELY RESULT
IN A VERY PRONOUNCED BACK EDGE TO ANY PRECIP THAT DEVELOPS. THE
TRICKY PART IS TRYING TO ASCERTAIN EXACTLY WHERE THIS BACK EDGE WILL
RESIDE. SOME OF THE EARLIER HI-RES WRF MODELS /ADMITTEDLY THEY HAVE
A BIT OF A DRY BIAS/ SUGGESTED THE BACK EDGE WOULD BE IN THE WEST
VALLEY OF THE METRO AREA. THIS MORNINGS 00Z RUNS OF THE SAME MODELS
/AND THE NAM FOR THAT MATTER/ ARE ALSO FARTHER EAST AND SUGGEST THE
BACK EDGE WILL RESIDE SOMEWHERE ACROSS THE EAST VALLEY WITH THE
GREATEST IMPACTS IN THE MOUNTAINS EAST OF PHOENIX. NEVER A GOOD IDEA
TO BUY INTO ONE RUN OF ONE MODEL 100 PERCENT...BUT THIS TREND WILL
CERTAINLY NEED TO BE MONITORED. FOR NOW I MADE SLIGHT REDUCTIONS TO
THE POPS ACROSS SOUTHEAST CALIFORNIA ON THURSDAY WITH MORE FOCUS
PLACED ON SOUTHERN GILA COUNTY. THE FLASH FLOOD WATCH WILL REMAIN IN
PLACE UNCHANGED.

BOTH ECMWF/GFS SEEM TO BE ON THE SAME PAGE EJECTING THE REMNANT LOW
LATE THURSDAY/EARLY FRIDAY WITH MODEST DRY ADVECTION FRIDAY THROUGH
SUNDAY. BL MOISTURE WON`T BE SCOURED OUT ENTIRELY AND THERE SHOULD
STILL BE A CHANCE OF AFTERNOON SHOWERS/STORMS EAST OF PHOENIX
FRIDAY/SATURDAY. DECENT FLOW /AROUND 20-25KTS/ IN THE 700MB-300MB
LAYER AND A FEW PV PERTURBATIONS COULD BE ENOUGH TO SERVE AS THE
TRIGGER FRIDAY/SATURDAY AND I WILL KEEP POPS AS-IS. FROM THAT POINT
INTO EARLY NEXT WEEK I WILL HANG ONTO CLIMO POPS AS MIXING RATIOS
WILL REMAIN ABOVE 6-7 G/KG EAST OF PHOENIX.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
MOISTURE SPREADING NORTHWARD FROM REMAINS OF HURRICANE ODILE IS
EXPECTED TO KEEP BKN-OVC CIGS OVER THE PHOENIX AREA TERMINALS
THROUGH THE FORECAST PERIOD. CIGS...THAT COULD FALL AS LOW AS 7K FT
AGL THIS MORNING...COULD FALL AS LOW AS 5K FT AGL LATE TONIGHT AND
EARLY WEDNESDAY AS SHOWER ACTIVITY BEGINS TO DEVELOP OVER THE
REGION. WINDS ARE EXPECTED TO REMAIN MAINLY EASTERLY THROUGH THE TAF
PERIOD...OUTSIDE OF ANY CONVECTIVE ACTIVITY...WHICH COULD BRING A
BRIEF PERIOD OF GUSTY WINDS TO THE AFFECTED TERMINAL(S).

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
A VERY MOIST AIRMASS MOVING INTO THE REGION IS EXPECTED TO KEEP
BKN-OVC CIGS OVER THE TERMINALS THROUGH THE TAF PERIOD...WITH CIGS
AS LOW AS 3K FT AGL AT KBLH THIS MORNING AS A VERY MOIST AIRMASS
SURGES NORTHWARD FROM THE GULF OF CALIFORNIA. ADDITIONAL MOISTURE
ASSOCIATED WITH THE REMAINS OF HURRICANE ODILE THAT WILL BE MOVING
NORTHWARD INTO THE REGION LATE THIS AFTERNOON/EVENING WILL LIKELY
PRODUCE SCATTERED SHOWERS/THUNDERSTORMS OVER THE REGION...THUS WILL
INTRODUCE VCSH INTO THE TAFS DURING THIS PERIOD.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
LINGERING MOISTURE FROM THE REMAINS OF HURRICANE ODILE WILL KEEP THE
CHANGES FOR SHOWERS/THUNDERSTORMS GOING OVER THE REGION ON THURSDAY
AND FRIDAY...WITH HEAVY RAINFALL AND LOCALIZED FLOODING POSSIBLE
OVER SOUTH-CENTRAL AZ. INCREASING WESTERLY FLOW ALOFT WILL THEN
GRADUALLY PUSH DRIER AIR INTO THE REGION FROM THE WEST FROM THIS
WEEKEND INTO EARLY NEXT WEEK...REDUCING THE CHANCES OF
SHOWERS/THUNDERSTORMS OVER THE REGION...WITH CONVECTIVE ACTIVITY
LIKELY TO BE CONFINED TO THE HIGHER TERRAIN NORTH AND EAST OF
PHOENIX BY MONDAY. AFTERNOON HUMIDITY VALUES...WHICH WILL REMAIN IN
THE 35-50 PERCENT RANGE WITH EXCELLENT OVERNIGHT RECOVERIES ON
THURSDAY AND FRIDAY...ARE EXPECTED TO FALL INTO THE 20-35 PERCENT
RANGE BY MONDAY. WINDS TO REMAIN MAINLY ON THE LIGHT SIDE...EXCEPT
AROUND THUNDERSTORMS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FLASH FLOOD WATCH FROM WEDNESDAY MORNING THROUGH THURSDAY
     AFTERNOON AZZ021>024-027-028.

CA...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...LEINS
AVIATION...PERCHA
FIRE WEATHER...PERCHA





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