Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 172113 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 213 PM MST THU APR 17 2014 .SYNOPSIS...
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A PACIFIC STORM WILL MOVE INTO THE AREA STARTING TONIGHT BRINGING INCREASING MOISTURE AND CLOUDS. BY FRIDAY AFTERNOON THIS SYSTEM WILL SUPPORT SLIGHT CHANCES FOR SHOWERS FROM THE COLORADO RIVER EAST ACROSS SOUTH CENTRAL ARIZONA AND INTO THE HIGHER TERRAIN. DAYTIME TEMPERATURES FOR FRIDAY AND SATURDAY WILL FALL TO MORE SEASONAL VALUES. AFTER THE STORM AND CLOUDS MOVE TO THE EAST ON SUNDAY...TEMPERATURES QUICKLY WARM BACK INTO THE 90S FOR EARLY NEXT WEEK WITH MOSTLY SUNNY SKIES.
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&& .DISCUSSION...
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HIGH THIN CLOUDS ARE STARTING TO OVERSPREAD SOUTHEAST CALIFORNIA INTO SOUTHWEST ARIZONA THIS AFTERNOON. CURRENT WATER VAPOR IMAGERY AND OBJECTIVE ANALYSIS SHOWS AN UPPER LEVEL LOW CIRCULATION NEAR 31N/124W WITH EXTENSIVE MOISTURE AHEAD OF THE LOW AND SOME SUB-TROPICAL MOISTURE WRAPPING INTO THE LOW FROM THE SOUTHWEST. AS THE LOW APPROACHES THE DESERT SOUTHWEST TONIGHT...EXPECT CLOUDS TO THICKEN FROM THE SOUTHWEST TO THE NORTHEAST LATE TONIGHT INTO FRIDAY MORNING. SKIES WILL LIKELY BECOME MOSTLY CLOUDY AND POSSIBLY CLOUDY AT TIMES DURING MUCH OF THE DAYTIME HOURS FRIDAY. MODELS SHOW WEAK TO MODERATE DIFLUENCE ALOFT AND SUFFICIENT OMEGA IN A NEAR SATURATED 600-400MB LAYER STARTING FRIDAY MORNING. AM EXPECTING SOME HIGH BASED...12-15K FEET...SHOWERS TO DEVELOP SOMETIME FRIDAY MORNING INTO EARLY FRIDAY AFTERNOON...ESPECIALLY ALONG AND JUST BEHIND THE LEADING EDGE OF THE MID LEVEL MOISTURE PLUME. SINCE THE SUB-CLOUD LAYER WILL BE DRY...NOT QUITE BONE DRY...NOT EXPECTING TOO MANY LOCATIONS TO SEE RAIN HITTING THE GROUND...MAINLY HIGHER TERRAIN LOCALES. CHANCES INCREASE FRIDAY AFTERNOON AND EARLY FRIDAY EVENING...BUT OVERALL COVERAGE WILL BE LIMITED AND POPS STILL ONLY IN THE SLIGHT CHANCE CATEGORY AND MAINLY COVERING THE HIGHER TERRAIN. THE WARM AND DRY SUB-CLOUD LAYERS MAY BRING THE POTENTIAL FOR GUSTY WINDS AND OUTFLOWS IF A STORM GETS ORGANIZED ENOUGH. THE MAIN UPPER LOW CIRCULATION WILL HANG BACK ACROSS SOUTHEAST CALIFORNIA FRIDAY AFTERNOON...THEN SLOWLY PROGRESSING INTO CENTRAL ARIZONA DURING THE DAY SATURDAY. SLIGHT CHANCE POPS WILL REMAIN THROUGH FRIDAY NIGHT INTO SATURDAY EVENING ACROSS SOUTH-CENTRAL ARIZONA WITH CHANCE POPS ACROSS THE HIGHER TERRAIN IN GILA COUNTY. QPF AMOUNTS FOR THE ENTIRE EVENT WILL BE NEAR ZERO ACROSS THE LOWER DESERTS TO AROUND A TENTH OF AN INCH ACROSS GILA COUNTY. DRY WESTERLY FLOW TRANSITIONS INTO THE AREA SUNDAY...QUICKLY WARMING TEMPERATURES BACK INTO THE 90S FOR EARLY NEXT WEEK. BROAD AREA OF PACIFIC TROUGHING STILL PROGGED TO SWEEP INTO THE WEST LATE MONDAY INTO TUESDAY...ALTHOUGH LATEST MODEL RUNS VARY IN THEIR DEPTH AND STRENGTH AS IT MOVES IN FROM THE NORTHEAST PACIFIC. THE SET-UP STILL LOOKS PROMISING FOR A RETURN TO COOLER (AND MORE SEASONAL) TEMPERATURES BY MIDDLE PART OF NEXT WEEK...BUT ANY CHANCES FOR RAIN LOOK PRETTY REMOTE. MAINTAINED SOME INFLUENCE OF CLIMATOLOGY IN THE POP GRIDS GIVEN THE PRESENCE OF TROUGHING...BUT UNLESS THE MODELS EXPAND THE SOUTHERN EXTENT OF THE SYSTEM...EVEN THOSE SINGLE DIGIT VALUES MAY BE OVERDONE.
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&& .AVIATION... SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... A GRADUAL INCREASE IN MID AND HIGH CLOUDS IS EXPECTED OVER THE NEXT 24 HOURS AHEAD OF A LOW PRESSURE SYSTEM. WITH THE LOW IN OUR VICINITY...WINDS WILL ALSO RETAIN MORE OF A SOUTHERLY COMPONENT THROUGH FRIDAY AFTERNOON. HOWEVER...THROUGH 18Z FRIDAY...WINDS WILL REMAIN DIURNAL AND GENERALLY LESS THAN 10 KT. GIVEN THE DRY CONDITIONS NEAR THE SURFACE...THERE ALSO IS THE POTENTIAL FOR VIRGA PRODUCING LOCALIZED DOWNBURST WINDS...PERHAPS AS EARLY AS FRIDAY MORNING BUT MORE LIKELY FRIDAY AFTERNOON. SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... SOUTHERLY WINDS WILL BE THE PRIMARY AVIATION WEATHER IMPACT...WITH OCCASIONAL GUSTS TO AROUND 20 KT THIS AFTERNOON. WINDS WILL ABATE OVERNIGHT BEFORE INCREASING AGAIN FRIDAY AFTERNOON AHEAD OF A LOW PRESSURE SYSTEM. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... SUNDAY THROUGH THURSDAY... WESTERLY FLOW WILL BRING A WARMING AND DRYING TREND TO THE REGION THROUGH TUESDAY. THEREAFTER...A COOLING TREND IS EXPECTED AS AN AREA OF LOW PRESSURE MOVES THROUGH THE WESTERN STATES. THE BIGGEST IMPACT WITH THIS SYSTEM WILL BE AN INCREASE IN WIND...PARTICULARLY ON WEDNESDAY. LOW RHS DURING THE MIDWEEK PERIOD WILL ALSO PRESENT AN INCREASED FIRE DANGER THREAT. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...KUHLMAN/NOLTE AVIATION...HIRSCH FIRE WEATHER...HIRSCH

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