Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 231533
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
830 AM MST WED JUL 23 2014

.SYNOPSIS...
VERY STRONG HIGH PRESSURE OVER THE REGION WILL CONTINUE TO PRODUCE
VERY HOT TEMPERATURES THROUGH FRIDAY...WITH SOME LOCATIONS
APPROACHING...OR EVEN REACHING DAILY RECORD HIGHS. AT THE SAME
TIME...MONSOON MOISTURE WILL SLOWLY INCREASE OVER THE AREA...WITH
OCCASIONAL CLOUDINESS AT TIMES. A FURTHER INCREASE IN THE MOISTURE
LEVELS...COMBINED WITH SEVERAL WEAK WEATHER DISTURBANCES FROM
MEXICO...ARE FORECAST TO INCREASE THE CHANCE OF AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS...MAINLY ACROSS ARIZONA...THIS
WEEKEND...WITH A REDUCTION IN THE THUNDERSTORM ACTIVITY FORECAST FOR
EARLY NEXT WEEK.

&&

.DISCUSSION...
MORNING WEATHER BALLOON SOUNDINGS SHOWED THE NORTHERN EDGE OF THE
MONSOON MOISTURE BOUNDARY (MMB) MOVED INTO SOUTHEAST ARIZONA LAST
NIGHT FROM ITS RECENT ABSENCE. THE MMB WAS LOCATED BETWEEN PHOENIX
AND TUCSON...AND VERTICALLY STEEP OR A TIGHT THETA-E GRADIENT. SINCE
THE MMB GRADIENT WAS STEEP...LOW LEVEL EAST AND SOUTHEASTERLY WINDS
GLEANED FROM BOTH TUS AND PHX RADAR VAD DATA SHOWED THE MMB COULD
EASILY BE PUSHED WEST AND NORTH TODAY...I.E PROVIDING A LITTLE MORE
HUMIDITY TODAY ACROSS SOUTH CENTRAL AZ INCLUDING PHOENIX. COULD
HIGHER HUMIDITY TEMPER THE STRONG AFTERNOON SFC HEATING CURVE AND
SHAVE A FEW DEGREES OFF THE PREDICTED RECORD HIGH TEMP OF 114 DEG
TODAY IN PHOENIX? MAYBE ONE DEGREE BUT 113 IS STILL THE THRESHOLD
FOR OUR EXCESSIVE HEAT WARNING FOR THE LOWER DESERTS.

AT THE SAME TIME...A WEAK INVERTED TROF SEEN IN OUR UPPER LEVEL
STREAMLINE ANALYSIS JUST SOUTHWEST OF EL PASO TEXAS...AND ALSO
FORECAST BUY THE MODELS...WILL MOVE INTO SOUTHEAST AZ THIS AFTERNOON
AND LIKELY SPARK LARGE TSTMS SINCE MONSOON HUMIDITY HAS RETURNED TO
THE AREA. WEAK SOUTHEASTERLY MID LEVEL STEERING CURRENTS SHOULD
MOVE MOUNTAIN CONVECTION TOWARD THE EDGE OF THE SOUTH CENTRAL AZ
DESERTS NEAR CASA GRANDE AND COOLIDGE...LATE IN THE DAY WITH PERHAPS
SOME CONVECTIVE OUTFLOWS RACING ACROSS THE DESERTS TOWARD PHOENIX.
BLOWING DUST INCLUDED. ITS A LITTLE UNCERTAIN IF MONSOON MOISTURE
WILL BE DEEP ENOUGH...DUE TO THE TYPICAL AFTERNOON EXPANSON OF THE
BOUNDARY LAYER...IF CONVECTIVE OUTFLOWS WILL TRIGGER ADDITIONAL
DESERT CONVECTION THIS EVENING. UPDATES WILL BE TO SPREAD A SLIGHT
CHANCE OF EVENING SHWRS/TSTMS A LITTLE FARTHER WEST INTO MARICOPA
COUNTY...OR THE DESERTS WEST AND SOUTHWEST OF PHOENIX.

ON THURSDAY...MODELS CONTINUE TO FORECAST A DRIER AND MORE STABLE
MID LEVEL AIRMASS SPREADING INTO THE AREA FROM THE EAST. HOWEVE
RELATIVELY HIGH SFC HUMIDITY WILL REMAIN AND BE PUSHED FARTHER WEST
TOWARD THE COLORADO RIVER VALLEY.

OTHER THAT A FEW PRECIP PROBABILITY UPDATES FOR THIS EVENING IN
SOUTH CENTRAL AZ...REMAINDER OF FORECASTS LOOK OK. PREVIOUS
DISCUSSION STILL APPLIES.


.PREVIOUS DISCUSSION...
TODAY THROUGH THURSDAY...
A VERY STRONG DOME OF HIGH PRESSURE ALOFT...WITH 500MB HEIGHTS
REACHING 600DM OVER SOUTHERN CO/NORTHERN NM...AND 500MB HEIGHTS IN
THE 596-598DM RANGE IS FORECAST TO REMAIN OVER THE REGION TODAY.
THIS IS THE SAME AIRMASS THAT BROUGHT A HIGH OF 113 TO PHOENIX SKY
HARBOR ON TUESDAY. GIVEN THE FACT WE WILL BE STARTING OUT WARMER
THIS MORNING THAN WHAT WE SAW ON WED MORNING...WITH LOWS REMAINING
IN THE 90S ACROSS THE PHX URBAN CORE...AT FIRST BLUSH IT WOULD
APPEAR THAT WE WILL SEE EVEN WARMER HIGHS TODAY. HOWEVER...BOTH THE
GFS AND EURO ARE SHOWING AN INVERTED TROF ATTEMPTING TO MOVE
NORTHWESTWARD INTO SOUTH-CENTRAL AZ LATER TODAY AND TONIGHT. THE
COMBINATION OF THIS INVERTED TROF ALONG WITH MID-LEVEL MOISTURE
MOVING INTO THE REGION AHEAD OF IT IT EXPECTED TO INCREASE
THUNDERSTORM ACTIVITY ACROSS SE AZ TODAY...AND LIKELY AT LEAST
INCREASE THE CLOUDINESS ACROSS SOUTH-CENTRAL AZ. ALTHOUGH...AT THIS
POINT...IT APPEARS THAT STRONG SUBSIDENCE ALOFT AND A LACK OF
AVAILABLE MOISTURE BELOW 500MB WILL LIKELY KEEP MOST TS ACTIVITY OUT
OF OUR CWA...THERE IS A DECENT CHANCE OF AT LEAST SOME OUTFLOWS FROM
THESE STORMS WILL MAKE THEIR WAY INTO THE PHX AREA...WHICH COULD
TEMPER THE HEATING A BIT THIS AFTERNOON. HOWEVER...THE CURRENT
THINKING...AND THE LATEST HIGH-RES MODELS INDICATE THAT THESE
OUTFLOWS WILL LIKELY ARRIVE TOO LATE TO IMPACT OUR HIGH
TEMPERATURES...WITH ONLY THE INCREASE IN CLOUDINESS HOLDING OUR
WARMING BACK. THUS...HAVE PRETTY MUCH GONE WITH THE PREVIOUS SHIFT
IN OUR HIGH TEMPERATURES FORECASTS TODAY...STILL EXPECTING A
RECORD-TYING HIGH OF 114F AT SKY HARBOR. DEBRIS CLOUDINESS FROM
TODAY/S STORMS IS EXPECTED...TO ONCE AGAIN KEEP TEMPERATURES
ELEVATED TOMORROW NIGHT ACROSS THE PHX AREA...WITH SOME MORE 90F+
LOWS LIKELY ACROSS THE REGION ON THURSDAY MORNING.

THE FORECAST FOR THURSDAY/S HIGH IS A BIT MORE UNCERTAIN. ALTHOUGH
IT APPEARS THAT THE PASSAGE OF TODAY/S INVERTED TROF WILL WEAKEN THE
UPPER-LEVEL HIGH CENTER A BIT...WITH 500MB HEIGHTS FALLING INTO THE
593-594DM RANGE ACROSS OUR CWA ON THURSDAY AFTERNOON...DRIER AIR
WORKING ITS WAY IN FROM THE EAST WILL LIKELY DECREASE THE CLOUDINESS
ACROSS SOUTH-CENTRAL AZ AS THE MAIN MOISTURE PLUME SHIFTS OFF TO THE
WEST...WHICH WILL ALLOW FOR MORE SOLAR ISOLATION. THUS...EXPECTING
THURSDAY/S HIGHS TO RISE TO WITHIN A DEGREE OR SO OF WEDNESDAY/S
HIGHS...WHICH STILL SATISFY EXCESSIVE HEAT CRITERIA. THIS DRIER AIR
WILL LIKELY REDUCE CONVECTIVE ACTIVITY ACROSS SE AND SOUTH-CENTRAL
ARIZONA...WITH THE MAIN MOISTURE PLUME PERHAPS TRIGGERING AN
ISOLATED STORM OR TWO ACROSS SOUTHWEST AZ AND SOUTHEAST CA. THE MAIN
IMPACTS FROM THE STORMS WILL ONCE AGAIN BE GUSTY WINDS AND BLOWING
DUST RATHER THEN ANY SIGNIFICANT RAINFALL.

FRIDAY THROUGH SUNDAY...
COOLER AFTERNOON TEMPERATURES ARE FORECAST THIS PERIOD AS THE
UPPER-LEVEL HIGH WEAKENS A BIT MORE AND A MORE SOUTHERLY FLOW ALOFT
BRINGS MORE MOISTURE INTO THE REGION. HIGHER HUMIDITIES ARE
EXPECTED...ALONG WITH A BETTER THREAT FOR AFTERNOON AND EVENING
CONVECTION. HOWEVER...WITH RATHER WARM AIR STILL REMAINING ALOFT
(500MB TEMPS IN THE -4C TO -6C RANGE) AND THE BEST MOISTURE
REMAINING TO OUR SOUTH...EXPECTING ONLY ISOLATED THUNDERSTORMS
ACROSS THE LOWER DESERTS...WITH WIND/DUST REMAINING THE MAIN ISSUE
RATHER THAN HEAVY RAINFALL.

MONDAY THROUGH WEDNESDAY...
BOTH THE GFS AND EURO ARE NOW SUGGESTING THAT THE MAIN 500MB RIDGE
AXIS WILL SHIFT SOUTHWARD OVER AZ AND SE AZ DURING THIS PERIOD AS A
VERY DEEP TROF (FOR MID-JULY) DIGS INTO THE GREAT LAKES
REGION...WHICH WOULD LIKELY SHIFT THE BEST MOISTURE WELL TO OUR
SOUTH INTO SONORA AND STABILIZE THE ATMOSPHERE...WHICH WOULD RESULT
IN ANOTHER BREAK IN THE MONSOON OVER OUR REGION.

&&

.CLIMATE...

RECORD HIGH TEMPERATURE FOR THE MIDDLE OF THE WEEK.

CITY        JULY 23       JULY 24      JULY 25
----        -------       -------      -------
PHOENIX   114 IN 2006   114 IN 2006  115 IN 1943
YUMA      115 IN 1959   117 IN 1943  120 IN 1943

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

PERIODS OF BROKEN MID AND HIGH CLOUDINESS CAN BE EXPECTED
TODAY...MAINLY SOUTH-CENTRAL ARIZONA...THE REMNANTS OF CONVECTION
THAT DEVELOPED LAST EVENING OVER SOUTHEAST ARIZONA AND SONORA. CLD
BASES WILL BE AOA 15 KFT. WINDS AT KPHX...KIWA...AND KBLH WILL
REMAIN OUT OF THE SOUTHEAST THROUGHOUT THE DAY. AT KIPL...WINDS WILL
REMAIN LIGHT OUT OF THE SOUTHWEST. THERE IS AN INCREASED CHANCE OF
THUNDERSTORMS IN SOUTH-CENTRAL ARIZONA TODAY. THE GREATEST
LIKELIHOOD FOR ACTIVITY IS OVER THE HIGHER TERRAIN...THOUGH ISOLATED
STORMS COULD DEVELOP IN THE LOWER DESERTS. CONFIDENCE IS TOO LOW AT
THIS POINT TO INSERT ANY MENTION OF THUNDERSTORMS IN THE TAF/S...BUT
ANTICIPATE OUTFLOWS FROM DISTANT STORMS TO BE MORE LIKELY. THESE
COULD CAUSE GUSTY WINDS TO NEAR 20 KTS...PRIMARILY AT KIWA.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
SLIGHTLY COOLER AFTERNOON HIGH TEMPERATURES ARE EXPECTED THROUGH THE
PERIOD...AS UPPER LEVEL HIGH PRESSURE WEAKENS AND SLIDES FURTHER TO
THE SOUTH. EVEN SO...READINGS WILL STILL BE SLIGHTLY WARMER THAN
NORMAL. AN INCREASE IN MOISTURE IS POSSIBLE AS THE HIGH SLIPS TO THE
SOUTH...THOUGH MINIMUM AFTERNOON DAILY HUMIDITY LEVELS WILL STILL
DIP BELOW 20 PERCENT. OVERNIGHT RECOVERY SHOULD HOWEVER BE MODERATE
TO GOOD. THERE WILL BE A DAILY THREAT OF THUNDERSTORMS...BUT THESE
WILL BE MAINLY CONCENTRATED IN THE HIGHER TERRAIN OF EASTERN AZ.
OUTFLOW BOUNDARIES MOVING INTO THE LOWER DESERTS WILL BE CAPABLE OF
PRODUCING STRONG WIND GUSTS. FURTHER WEST ACROSS SE CA...THE CHANCE
FOR RAIN AND THUNDERSTORM IMPACTS WILL BE EVEN LOWER. GUSTY WINDS...
PARTICULARLY ALONG THE COLORADO RIVER VALLEY...ARE EXPECTED ON
FRIDAY...AND ACROSS THE ENTIRE REGION ON SATURDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...EXCESSIVE HEAT WARNING FROM WEDNESDAY MORNING THROUGH THURSDAY
EVENING AZZ020>023-025>028.

CA...EXCESSIVE HEAT WARNING FROM WEDNESDAY MORNING THROUGH THURSDAY
EVENING CAZ031>033.

&&

$$

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

DISCUSSION...VASQUEZ/PERCHA
CLIMATE...PERCHA
AVIATION....MCLANE/AJ
FIRE WEATHER...MCLANE/HIRSCH












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