Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 311106 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
405 AM MST MON AUG 31 2015

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.SYNOPSIS...
SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE AGAIN TODAY ACROSS THE
PHOENIX AREA AND POINTS EAST...ALTHOUGH A SLIGHT DRYING TREND IS
EXPECTED BY THE MIDDLE OF THE WEEK. MOISTURE IS EXPECTED TO RETURN TO
THE AREA BEFORE THIS WEEKEND WITH ADDITIONAL SHOWERS/STORMS POSSIBLE
FRIDAY THROUGH THE WEEKEND. TEMPERATURES WILL GRADUALLY RETREAT THIS
WEEK...EVENTUALLY RESIDING WITHIN A DEGREE OR TWO OF NORMAL FROM
WEDNESDAY ONWARD.

&&

.DISCUSSION...
EARLY MORNING WATER VAPOR IMAGERY REVEALS SOUTHWESTERLY FLOW ALOFT
OVER SOUTHERN CALIFORNIA AND PORTIONS OF THE ARIZONA
DESERTS...MEANWHILE A SERIES OF CONVECTIVE COMPLEXES CONTINUE TO
DECAY OVER SOUTHERN SONORA. A FEW GRAVITY WAVES ARE EVIDENT ACROSS
THE REGION...ONE OF WHICH APPEARED TO MOVE THROUGH THE PHOENIX METRO
AROUND 06Z. HOWEVER CONDITIONS REMAIN RELATIVELY QUIET AS OF 0930Z
WITH ONLY SOME DEBRIS MID CLOUDS ACROSS THE AREA. NATURALLY THE CLOUD
COVER HAS ALLOWED TEMPERATURES TO REMAIN ON THE MILD SIDE WITH MOST
DESERT LOCALES ONLY IN THE MID/UPPER 80S.

SOUTHWESTERLY FLOW ALOFT WILL PREVAIL AGAIN TODAY COURTESY OF
LONGWAVE TROUGHING OFF THE WEST COAST BUT AS HAS BEEN THE CASE THE
PAST SEVERAL DAYS...THIS WON`T NECESSARILY RESULT IN QUIET WEATHER.
MID/UPPER LEVEL FLOW ISN`T PARTICULARLY STRONG TO BEGIN WITH BUT
MOST IMPORTANTLY...WINDS IN THE 925-700MB LAYER REMAIN OUT OF THE
SOUTH/SOUTHEAST. HARD TO EFFECTIVELY SCOUR OUT LOW LEVEL MOISTURE
WHEN IT SIMPLY ADVECTS BACK INTO THE AREA EACH EVENING/OVERNIGHT.
00Z SOUNDINGS AND BLENDED TPW IMAGERY SUGGEST THAT DESPITE
SOUTHWESTERLY FLOW ALOFT...PWATS REMAIN AT OR SLIGHTLY ABOVE NORMAL
ACROSS THE REGION THIS MORNING. HI-RES MODELS AND THEIR RESPECTIVE
ENSEMBLES SUGGEST A SIMILAR CONVECTIVE REGIME THIS AFTERNOON COMPARED
TO SATURDAY AND SUNDAY. STORMS WILL BE MOST LIKELY TO THE
NORTH/SOUTH/EAST OF PHOENIX...WITH OUTFLOWS LIKELY TO DROP INTO THE
DESERTS FROM ALL DIRECTIONS AND SPAWN ISOLATED STORMS OVER THE PHX
METRO AREA. UNTIL THE BOUNDARY LAYER HAS SUFFICIENTLY DRIED OUT OR
HAS BEEN SUFFICIENTLY OVERTURNED...I DON`T SEE ANY REASON WHY IT
WON`T BE ACTIVE. MADE SOME UPWARD ADJUSTMENTS TO POPS THIS
AFTERNOON/EVENING. ACROSS THE WESTERN HALF OF THE FORECAST AREA WHERE
THE BOUNDARY LAYER HAS ACTUALLY DRIED OUT /AND HAS BEEN DRY THE PAST
FEW DAYS/...STORM CHANCES REMAIN SLIM TO NIL.

FORECAST CONFIDENCE TUESDAY THROUGH THURSDAY IS LOW. DETERMINISTIC
GUIDANCE TAKEN AT FACE VALUE WOULD SUGGEST A DOWNWARD TREND IN STORMS
THROUGH MID WEEK...HOWEVER PROBABILISTIC TOOLS SUGGEST THE BL WILL
REMAIN MOIST WITH MODEST INSTABILITY ACROSS THE REGION. OF COURSE THE
MISSING INGREDIENT IS A TRIGGER TO KICK OFF STORMS IN THE FIRST PLACE
AND NONE OF THE DETERMINISTIC GUIDANCE INDICATE MUCH IN THE WAY OF
INVERTED TROUGHS OR LARGER SCALE FEATURES. WILL HANG ONTO SOMEWHAT
ELEVATED POPS /HIGHER THAN CLIMO/ THROUGH MID WEEK ON THE PREMISE
THAT STORMS WILL BE TRIGGERED BY COLLIDING OUTFLOWS.

FORECAST CONFIDENCE ISN`T MUCH HIGHER LATER IN THE FORECAST PERIOD.
IT WOULD APPEAR THAT MOISTURE WILL BE DRAWN INTO THE REGION FROM THE
TROPICS LATE IN THE WEEK /FRIDAY-SATURDAY/ ALTHOUGH EXACTLY WHERE
THIS AXIS OF DEEPEST MOISTURE RESIDES IS STILL UP FOR DEBATE.
00Z DETERMINISTIC GFS AND ECMWF SUGGEST ANOMALOUSLY HIGH PWATS AND
MIXING RATIOS WILL OVERSPREAD MUCH OF THE DESERT SOUTHWEST WHEREAS
GEFS AND NAEFS KEEP THIS MOISTURE SOUTH OF THE INTERNATIONAL BORDER
AND SHIFT IT TOWARD THE AZ/NM BORDER. GIVEN THE MAGNITUDE OF THE
700-300MB FLOW DURING THIS TIME PERIOD /AROUND 30-40KTS/...I`M
SKEPTICAL THE MOISTURE WILL REMAIN CONFINED TO THE BORDER AND POINTS
SOUTH. DEWPOINTS HAVE BEEN BUMPED UP LATE IN THE WEEK AND POPS HAVE
ALSO BEEN ELEVATED A BIT OVER INHERITED VALUES /MORE IN LINE WITH
CLIMO/. COULD END UP SEEING ELEVATED RAIN CHANCES LATE IN THE WEEK
INTO THE WEEKEND...BUT COULD JUST AS EASILY SEE INCREASE CLOUD COVER
AND DRY CONDITIONS DEPENDING ON WHERE THE MOISTURE AXIS POSITIONS
ITSELF. THUS CONFIDENCE IN PRECIP CHANCES IS LOW. FAIRLY HIGH
CONFIDENCE IN LOWER TEMPERATURES LATE IN THE WEEK WITH SOME OF THE
RAW UN-CORRECTED GUIDANCE POINTING TO HIGHS IN THE UPPER 90S. LOWERED
TEMPERATURES A FEW DEGREES FROM FRIDAY ONWARD ACCORDINGLY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...

DESPITE FLOW ALOFT BECOMING MORE SOUTHWESTERLY...LOWER LEVEL FLOW
REMAINS MORE SOUTHERLY AND THE BOUNDARY LAYER MOISTURE WILL REMAIN
IN PLACE FOR AT LEAST THE NEXT 24 HOURS. THUS ANOTHER ROUND OF
CONVECTION IS LIKELY ACROSS THE GREATER PHOENIX AREA LATER THIS
AFTERNOON AND THIS EVENING. CONDITIONS ARE SIMILAR TO YESTERDAY AND
TIMING OF STORMS MAY BE SIMILAR. WE WILL CONTINUE THE PREVIOUS TAF
THINKING AND INCLUDE VCTS IN THE AREA TAFS AFTER ABOUT 02Z...ALSO
MENTIONING A WIND SHIFT AS STORMS INITIALLY FIRE OVER HIGHER TERRAIN
TO THE SOUTHEAST OF CENTRAL PHOENIX. HIGH BASED CUMULUS TO FORM
LATER THIS AFTERNOON AND SHOULD STORMS MOVE THROUGH CIGS WILL LIKELY
STAY ELEVATED...MAINLY AOA 8K FEET.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

NO SIGNIFICANT AVIATION IMPACTS EXPECTED NEXT 24 HOURS AS FLOW ALOFT
REMAINS DRY SOUTHWESTERLY. MAY SEE SOME SCT-BKN CIRRUS AT TIMES WITH
LITTLE OR NO LOWER CLOUD DECKS EXPECTED. WINDS TO FAVOR THE WEST AT
KIPL NEXT 24 HOURS...AND THE SOUTH AT KBLH. A FEW AFTERNOON GUSTS TO
20KT POSSIBLE ALSO AT KBLH.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
A LOW PRESSURE SYSTEM ACROSS THE PACIFIC NORTHWEST WILL DISPLACE THE
MONSOON HIGH SLIGHTLY TO THE SOUTH AND EAST THROUGH THE WEEK. THE
TREND WILL BE TOWARDS COOLER CONDITIONS ACROSS THE DESERT SOUTHWEST
WITH HIGH TEMPERATURES NEAR OR SLIGHTLY BELOW SEASONAL NORMALS EACH
DAY. HOWEVER SUFFICIENT MOISTURE WILL LINGER ACROSS EASTERN ARIZONA
TO KEEP AT LEAST A SLIGHT CHANCE FOR THUNDERSTORMS FROM PHOENIX EAST
WEDNESDAY INTO THURSDAY. MINIMUM RH VALUES WILL FALL BELOW 15
PERCENT WEDNESDAY AND THURSDAY ACROSS SOUTHEAST CALIFORNIA WITH
VALUES ABOVE 15 PERCENT EXPECTED EAST OF THE LOWER COLORADO RIVER.
FOR FRIDAY INTO THE WEEKEND...LATEST GUIDANCE MORE INSISTENT UPON A
RETURN TO DEEPER MOISTURE...HIGHER HUMIDITY AND BETTER RAIN
CHANCES...PARTICULARLY ACROSS SOUTH CENTRAL ARIZONA.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT CONDITIONS ACCORDING TO STANDARD
OPERATING PROCEDURES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&

$$

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

DISCUSSION...LEINS
AVIATION...CB
FIRE WEATHER...CB/HIRSCH



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