Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 041511
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
810 AM MST TUE AUG 4 2015

.SYNOPSIS... CLEAR SKIES WITH DRIER AND HOTTER WEATHER IS FORECAST
THROUGH WEDNESDAY...WITH HIGH TEMPERATURES ON THE LOWER DESERTS
RANGING FROM 112 TO 115 DEGREES. MONSOON HUMIDITY WILL RETURN TO THE
AREA THURSDAY AND FRIDAY...PROVIDING A THREAT OF AFTERNOON AND
EVENING SHOWERS AND THUNDERSTORMS...MAINLY OVER SOUTH-CENTRAL
ARIZONA ALONG WITH COOLER AFTERNOON TEMPERATURES REGION WIDE. A LOW
GRADE MONSOON PATTERN WILL CONTINUE THROUGH THE WEEKEND AND INTO
EARLY NEXT WEEK.

&&

.DISCUSSION...

REGIONAL WEATHER BALLOON SOUNDINGS SHOWED MOISTURE LEVELS IN ARIZONA
HAD DECREASED A LITTLE MORE FROM YESTERDAY. FOR EXAMPLE...THE
MONSOON MOISTURE BOUNDARY SUNDAY MORNING EXTENDED TO LAS VEGAS.
MONDAY MORNING IT HAD RETREATED TO...TUCSON SOUTHWARD. OVERNIGHT IT
HAD PUSHED SOUTH INTO MEXICO...OR JUST ACROSS THE BORDER EXCEPT FOR
THE FAR SOUTHEAST AZ TIP.   AND...WITH STRONG UPPER LEVEL ANTI-
CYCLONIC SHEAR AND WARMER 500 MB TEMPS THIS MORNING...THE ATMOSPHERE
IS TOO STABLE AND DRY FOR ANY STORM ACTIVITY IN OUR FORECAST
AREA...SOUTHEAST CA TO SOUTH CENTRAL AZ TODAY. DITTO ON WEDNESDAY.

ALSO...BASED ON THE PHOENIX WEATHER BALLOON SOUNDING...SURFACE
DEWPOINTS IN THE GREATER PHOENIX AREA SHOULD FALL INTO THE LOWER
30S. YESTERDAY AFTERNOON SURFACE DEWPOINTS DROPPED INTO THE LOWER
40S. THEREFORE...A DRIER AND WARMER AIRMASS WILL LEAD TO WARMER
SURFACE TEMPS TODAY AND WED...PEAKING AT VALUES THAT MINIMALLY
QUALIFY FOR AN EXCESSIVE HEAT WARNING ON THE LOWER DESERTS...MEANING
112 DEG F FOR PHOENIX AND 114 DEG F FOR YUM...IPL...AND BLH. NOTE...
EXCESSIVE HEAT WARNING CRITERIA IS LOWER FOR THE MONTH OF AUG VS
JUNE AND JULY. EVEN LOWER FOR THE MONTH OF SEPT.

ON WEDNESDAY...CONSIDERABLE AFTERNOON CONVECTION OVER NORTHWEST
MEXICO...ALONG WITH INCREASING MID/UPPER LEVEL SOUTHERLY WINDS...
WILL ADVECT CONSIDERABLE MID AND HIGH LEVEL CLOUDS INTO AZ WEDNESDAY
EVENING. THEREFORE IT SHOULD BE A VERY WARM WED NIGHT/THU MORNING ON
THE DESERTS. MID/HIGH LEVEL CLOUDS WILL BE FOLLOWED BY INCREASING
LOW LEVEL MOISTURE INTO SOUTHERN AZ THURSDAY...AND A SLIGHT CHANCE
OF AFTN/EVE SHOWERS AND THUNDERSTORMS ON THE SOUTH CENTRAL AZ
DESERTS AND MTNS.

CURRENT FORECASTS SHOWING THE ABOVE MENTION TREND LOOKS GOOD. NO
UPDATES NECESSARY. PREVIOUS DISCUSSION BELOW STILL APPLIES.


.PREVIOUS DISCUSSION...535 AM MST...

TODAY AND WEDNESDAY...WATER VAPOR/IR SATELLITE IMAGERY SHOW AN
UNUSUALLY DEEP TROUGH APPROACHING THE WEST COAST IS KEEPING THE
DESERT SOUTHWEST UNDER A DRY SOUTHWESTERLY FLOW. CURRENT MODELS
SUGGEST THAT THE UPPER LEVEL RIDGE CURRENTLY FLATTENED AND STRETCHED
ACROSS NORTHERN MEXICO/TEXAS WILL CONTINUE TO AMPLIFY/STRENGTHEN...
AND POSITION A 594-596DM 500MB CENTER OVER ARIZONA/NEW MEXICO. THIS
PATTERN WILL INTRODUCE TEMPS THAT ARE -- PRETTY HOT -- IN THE 110 TO
115 RANGE ACROSS OUR LOWER DESERTS TODAY AND WEDNESDAY. WITH
FORECAST AFTERNOON TEMPERATURES APPROACHING AND MEETING EXCESSIVE
HEAT WARNING CRITERIA FOR MOST DESERT SITES ACROSS SOUTHEAST
CALIFORNIA AND THE SOUTHWEST ARIZONA DESERTS...AN EXCESSIVE HEAT
WARNING WILL REMAIN IN EFFECT TODAY AND WEDNESDAY. AS THE HIGH
REPOSITIONS...THERE WILL BE WINDOWS OF OPPORTUNITY FOR LOW-MID LEVEL
MOISTURE TO BEGIN SNEAKING BACK INTO THE REGION. A GOOD INTRUSION OF
MOISTURE MIGHT BE JUST ENOUGH TO KNOCK A DEGREE OR TWO OFF DAYTIME
HIGHS...BUT ANY HUMIDITY INCREASE WILL ALSO KEEP THOSE OVERNIGHT
LOWS QUITE WARM.

THURSDAY AND FRIDAY...LOW LEVEL WIND FLOW BECOMES MORE SOUTHERLY...
AND MONSOON MOISTURE SPREADS INTO SOUTHERN ARIZONA THURSDAY. BOTH
THE GFS AND EUROPEAN MODELS DIRECT A LOW LEVEL MOISTURE SURGE INTO
SOUTHWEST ARIZONA...WHICH OVERSPREADS THE REGION LATE THURSDAY AND
FRIDAY. AN UPPER LEVEL DISTURBANCE ALSO MOVES NORTH INTO CENTRAL
ARIZONA THURSDAY RENEWING THE THREAT FOR AFTERNOON/EVENING SHOWERS
AND THUNDERSTORMS OVER PORTIONS OF SOUTHWEST AND SOUTH-CENTRAL
ARIZONA...INCLUDING PHOENIX.

SATURDAY AND SUNDAY...DRIER AND MORE STABLE AIRMASS WILL SPREAD INTO
OUR FORECAST AREA FROM THE WEST THIS WEEKEND...AND EXCEPT FOR A
SLIGHT CHANCE OF AFTERNOON SHOWERS AND THUNDERSTORMS OVER THE HIGHER
TERRAIN AND MOUNTAINS OF SOUTHERN GILA COUNTY/ZONE 24...THE
REMAINDER OF THE FORECAST AREA WILL BE DRY.

MONDAY...MODELS FORECAST A SIGNIFICANT UPPER LEVEL INVERTED TROUGH
TO MOVE INTO THE SOUTHEAST QUARTER OF ARIZONA FROM MEXICO MONDAY
AFTERNOON...WHICH IS STRONG ENOUGH FOR A THREAT OF WIDESPREAD SHOWER
AND THUNDERSTORM ACTIVITY. HOWEVER...MODELS HISTORICALLY HAVE
FORECAST THESE INVERTED TROUGHS TO MOVE INTO THE REGION A LITTLE TOO
FAST. PERHAPS TUESDAY MAY BE THE BIG DAY INSTEAD.

&&

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

NO AVIATION CONCERNS AT ANY TERMINAL FOR AT LEAST THE NEXT 24 HOURS.
DRY WESTERLY FLOW ALOFT WILL CONTINUE ACROSS THE AREA AND KEEP SKIES
GENLY CLEAR AT THE TERMINALS. WINDS TO BE LIGHT AND FAVOR NORMAL
DIURNAL TENDENCIES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY... STARTING THURSDAY MOISTURE FLOW FROM
MEXICO WILL RETURN MAINLY TO AREAS EAST OF THE LOWER COLORADO RIVER
VALLEY. A SLIGHT CHANCE OF AFTERNOON AND EARLY EVENING SHOWERS AND
THUNDERSTORMS WILL RETURN TO SOUTH CENTRAL ARIZONA THURSDAY AND
FRIDAY WHILE ACTIVITY WILL BE MOSTLY LIMITED TO HIGHER TERRAIN AREAS
EAST OF PHOENIX FOR THE WEEKEND. MINIMUM RELATIVE HUMIDITIES OF 15
TO 20 PERCENT RANGE WILL BE COMMON FOR THE DESERTS DURING THE
PERIOD...EXCEPT FOR THE WEEKEND WHEN MUCH DRIER AIR SPREADS INTO
SOUTHEAST CALIFORNIA AND THE WESTERN ARIZONA DESERTS WITH HUMIDITIES
FALLING WELL BELOW 15 PERCENT. HIGH TEMPERATURES WILL BE WELL ABOVE
NORMAL THURSDAY... ESPECIALLY OVER THE WESTERN DESERTS INTO
SOUTHEAST CALIFORNIA...THEN WILL COOL DOWN TO AROUND OR SLIGHTLY
ABOVE NORMAL VALUES FRIDAY THROUGH THE WEEKEND. WINDS WILL BE LIGHT
THROUGH MUCH OF THE PERIOD FOLLOWING TYPICAL DIURNAL DIRECTIONS
EXCEPT FOR AFTERNOON UPSLOPE BREEZES GUSTING AT TIMES UP TO 20 MPH.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...EXCESSIVE HEAT WARNING FROM 11 AM TO 8 PM MST TODAY FOR
     AZZ020>023-025>028.

     EXCESSIVE HEAT WARNING FROM 11 AM TO 8 PM MST WEDNESDAY FOR
     AZZ020>023-025>028.

CA...EXCESSIVE HEAT WARNING FROM 11 AM TO 8 PM PDT TODAY FOR
     CAZ031>033.

     EXCESSIVE HEAT WARNING FROM 11 AM TO 8 PM PDT WEDNESDAY FOR
     CAZ031>033.

&&

$$

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

DISCUSSION...VASQUEZ/MEYERS
VASQUEZ AVIATION...CB FIRE
WEATHER...KUHLMAN/CB


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