Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 051220 AAA AFDPSR AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE PHOENIX AZ 520 AM MST WED AUG 5 2015 .UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS. && .SYNOPSIS... MOSTLY CLEAR SKIES AND DRY WEATHER WILL PREVAIL ACROSS THE REGION TODAY...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 ALONG WITH COOLER AFTERNOON TEMPERATURES REGION-WIDE. A MORE STABLE AND DRIER PATTERN WILL SHIFT MOST OF THE MONSOON MOISTURE AND THREAT FOR SHOWERS INTO EASTERN ARIZONA THIS WEEKEND. && .DISCUSSION... SATELLITE IMAGERY SHOWS VERY LITTLE IN THE WAY OF CLOUD COVER OVER OUR FORECAST AREA THIS MORNING. THE UPPER LEVEL ANTICYCLONE WITH 594- 596DM 500MB HEIGHTS CONTINUES TO CENTER OVER OVER ARIZONA/NEW MEXICO...AND ALONG WITH THE DRIER SOUTHWESTERLY FLOW...THERE IS LITTLE IN THE WAY OF ANY STORM ACTIVITY THAT IS EXPECTED TODAY. AT THE SURFACE...WITH THE LACK OF CLOUDS...MANY SITES ACROSS OUR CWA HAVE DROPPED NICELY INTO THE UPPER 80S. HOWEVER...AT PHOENIX SKY HARBOR...TEMPS HAVE BEEN SLOW TO FALL OVERNIGHT...AND THE THERMOMETER APPEARS TO BE STUCK AT A VERY WARM 96 DEGREES...KIND OF A SLIM OPPORTUNITY TO REACH THE COOLER FORECAST TEMP OF 88 DEGREES. WITH THE WARM START TO THE MORNING...THE EXCESSIVE HEAT WARNING WILL CONTINUE FOR OUR LOWER DESERTS...WITH AFTERNOON TEMPS TOPPING OUT IN THE 109-114 DEGREE RANGE. HOWEVER...THE HOT DRY SUBSIDENT PATTERN CHANGES LATTER THIS EVENING AS THE MID AND UPPER LEVEL FLOW BECOMES MORE SOUTHERLY AND BEGINS TO IMPORT INCREASING CLOUDS INTO SOUTHERN ARIZONA. ANY INCREASE IN LOW LEVEL MOISTURE INTO THE SOUTHWEST DESERTS IS EXPECTED TO ARRIVE OVERNIGHT INTO THURSDAY MORNING. THURSDAY AND FRIDAY...SOUTHERLY LOW LEVEL WINDS WILL START TO ADVECT INCREASING AMOUNTS OF LOW LEVEL MONSOON MOISTURE INTO SOUTHERN ARIZONA...EVENTUALLY OVERSPREADING THE AREA FRIDAY. THERE IS A THREAT OF AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS THURSDAY AS THE LOWER LEVELS OF THE ATMOSPHERE QUICKLY DESTABILIZE ACROSS PORTIONS OF SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA...AT THE SAME THIS AREA IS UNDER FAVORABLE UPPER LEVEL DEFORMATION/DIFFLUENCE. THE THREAT OF AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS WILL SHIFT OVER PORTIONS OF THE SOUTH-CENTRAL ARIZONA FRIDAY. SATURDAY AND SUNDAY...A DRIER AND MORE STABLE AIRMASS WILL SPREAD INTO OUR FORECAST AREA FROM THE WEST THIS WEEKEND...KEEPING STORMS CONFINED TO EASTERN ARIZONA. 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 OUR FORECAST AREA WILL BE DRY. MONDAY AND TUESDAY...MODELS CONTINUE TO SUGGEST A SIGNIFICANT UPPER LEVEL INVERTED TROUGH TO MOVE INTO FAR SOUTHEAST ARIZONA MONDAY AFTERNOON AND CONTINUE NORTH TOWARD PHOENIX MONDAY NIGHT. THIS COULD BE A SIGNIFICANT SHOWER/THUNDERSTORM EVENT...HOWEVER SINCE THIS SYSTEM IS STILL TOO FAR AWAY...THE BEST APPROACH IS TO INTRODUCE A THREAT OF SHOWERS AND THUNDERSTORMS OVER SOUTH CENTRAL AZ MONDAY...MONDAY NIGHT AND TUESDAY. && .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... ONE MORE DAY OF STRONG HIGH PRESSURE ALOFT KEEPING SKIES GENLY SUNNY. WINDS WILL STAY RATHER LIGHT AND FOLLOW NORMAL DIURNAL TENDENCIES IN THE CENTRAL AZ DESERTS. WINDS TO FAVOR THE SOUTH AT KBLH NEXT 24 HOURS WITH SOME GUSTINESS IN THE AFTERNOON...PEAKING TO NEAR 20KT AT TIMES. OVERNIGHT TONIGHT FLOW BECOMES MORE SOUTHERLY AND WE SHOULD SEE AN INCREASE IN MID/HIGH CLOUDINESS WITH BKN CIGS AOA 15K FEET POSSIBLE BY THURSDAY MORNING. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... FRIDAY THROUGH TUESDAY... AN INCREASE IN MOISTURE WILL BRING CHANCES OF AFTERNOON AND EARLY EVENING SHOWERS AND THUNDERSTORMS TO SOUTH CENTRAL ARIZONA ON FRIDAY WHILE ACTIVITY WILL BE MOSTLY LIMITED TO HIGHER TERRAIN AREAS EAST OF PHOENIX FOR THE WEEKEND. AN ADDITIONAL MOISTURE SURGE WILL THEN INCREASE CHANCES OF SHOWERS AND THUNDERSTORMS ACROSS SOUTHERN ARIZONA FOR EARLY NEXT WEEK. MINIMUM RELATIVE HUMIDITIES OF 15 TO 20 PERCENT RANGE WILL BE COMMON FOR MUCH OF THE PERIOD ACROSS THE DESERTS ALTHOUGH A DRIER SOUTHWEST FLOW ALOFT OVER THE WESTERN ARIZONA AND SOUTHEAST CALIFORNIA DESERTS WILL LEAD TO HUMIDITIES FALLING INTO THE SINGLE DIGITS TO LOW TEENS OVER THE WEEKEND. HIGH TEMPERATURES WILL BE AROUND OR SLIGHTLY ABOVE NORMAL. 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 WEDNESDAY FOR AZZ020>023-025>028. CA...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...MEYERS/VASQUEZ AVIATION...CB FIRE WEATHER...KUHLMAN/CB

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