Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000 FXUS65 KPSR 282153 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 250 PM MST THU APR 28 2016 .SYNOPSIS...
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ANOTHER AREA OF LOW PRESSURE WILL CONTINUE TO MOVE ACROSS THE AREA THIS EVENING WITH BREEZY CONDITIONS AND A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS...MOST SIGNIFICANT OVER THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX. MORE SEASONABLY WARM WEATHER WILL RETURN FOR SATURDAY BEFORE YET ANOTHER WEATHER DISTURBANCE IMPACTS THE REGION SATURDAY NIGHT INTO SUNDAY. HIGH PRESSURE WILL RETURN BY THE MIDDLE OF NEXT WEEK...SUPPORTING WARMING TEMPERATURES AND CLEARING SKIES.
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&& .DISCUSSION...
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UNSETTLED WEATHER PATTERN CHARACTERIZED BY A LONG SERIES OF TRANSITORY UPPER LEVEL LOW PRESSURE SYSTEMS CONTINUES...AS YET ANOTHER UPPER LOW IS IN THE PROCESS OF SHIFTING EAST ACROSS THE DESERT SOUTHWEST THIS AFTERNOON...BRINGING BREEZY AND COOLER CONDITIONS ALONG WITH ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS. EARLY THIS AFTERNOON THE MAIN LOW CENTER WAS MOVING ACROSS NORTH CENTRAL ARIZONA...WHILE A VORT SPOKE ROTATING AROUND THE LOW WAS WORKING ACROSS THE LOWER DESERTS. AS ADVERTISED PREVIOUSLY MOISTURE HAS BEEN LIMITED WITH THIS SYSTEM...AND SINCE THE UPPER JET HAS MOVED SOUTH TO NEAR THE MEXICAN BORDER...THE DYNAMICS HAVE WEAKENED AND THERMODYNAMICS ARE PLAYING A BIGGER ROLE IN HELPING GENERATE INSTABILITY SHOWERS. RADAR AT 2 PM SHOWED MOST OF THE CONVECTION ACROSS THE NORTHERN HALF OF THE STATE WITH MAINLY ISOLATED SHOWERS OVER THE LOWER DESERTS...MOST NUMEROUS OVER HIGHER ELEVATIONS NORTH AND EAST OF PHOENIX. BREEZY TO WINDY CONDITIONS WERE ALSO PRESENT OVER THE LOWER DESERTS...WITH THE STRONGEST WINDS PERSISTING OVER IMPERIAL COUNTY. EARLIER IN THE MORNING THE WINDS IN THE IMPERIAL VALLEY EXCEEDED ADVISORY CRITERIA AND A WIND ADVISORY WAS ISSUED. SINCE NOON THE WINDS GRADUALLY TAPERED OFF AND WERE BELOW CRITERIA BUT THEY WERE STILL OCCASIONALLY GUSTING OVER 30 MPH AT EL CENTRO AND IMPERIAL. OTHERWISE...AFTERNOON TEMPS WERE RUNNING 5-10 DEGREES COOLER THAN 24 HOURS AGO AND MOST READINGS WERE IN THE LOW TO MID 70S. WE WILL CERTAINLY TOP OUT 10 DEGREES OR MORE BELOW SEASONAL NORMALS OVER MUCH OF THE LOWER DESERT TODAY. FOR THE REST OF THE AFTERNOON AND THROUGH THE EVENING...AS THE LOW AND ASSOCIATED VORT LOBE PUSH EAST...AND AS THE MAIN LOW CENTER MOVES INTO THE FOUR CORNERS AREA...A CLEARING AND DRYING TREND FROM THE WEST WILL DEVELOP AS MORE SUBSIDENT AIR WORKS IN FROM THE WEST. THERE WILL BE A LINGERING SLIGHT CHANCE OF SHOWERS THROUGH THE EVENING FROM PHOENIX NORTH AND EAST WITH THE BEST CHANCES ACROSS HIGHER TERRAIN OF SOUTHERN GILA COUNTY. AFTER MIDNIGHT TONIGHT POPS SHOULD BE JUST SINGLE DIGITS FROM THE GREATER PHOENIX AREA WESTWARD UNDER PARTLY CLOUDY SKIES. THE DRY SUBSIDENT NORTHWEST FLOW BEHIND THE EXITING LOW WILL CONTINUE FRIDAY...GIVING CLEARING SKIES FROM THE WEST ALONG WITH WARMING TEMPERATURES. HIGHS IN THE CENTRAL DESERTS WILL RISE INTO THE LOWER 80S...BUT REMAIN BELOW NORMAL WHILE THE WESTERN DESERTS CLIMB CLOSER TO NORMAL AND INTO THE MID TO UPPER 80S. THERE WILL BE A LINGERING SLIGHT CHANCE OF SHOWERS AND MAYBE AN AFTERNOON THUNDERSTORM ACROSS SOUTHERN GILA COUNTY HOWEVER AS A BIT OF WRAP AROUND MOISTURE WORKS THROUGH THE AREA AND COOLER AIR ALOFT PERSISTS CREATING SLIGHT INSTABILITY. AND YET ANOTHER PACIFIC LOW WILL FOLLOW HOT ON THE HEELS OF TODAYS SYSTEM...MOVING ACROSS THE DESERT SOUTHWEST IN A SIMILAR FASHION THIS WEEKEND. THE LOW WILL BEHAVE MUCH LIKE TODAYS LOW...WITH MOST OF THE MOISTURE AND PRECIPITATION CONFINED TO THE NORTHERN HALF OF THE STATE KEEPING THE MOST SIGNIFICANT PRECIP IN OUR AREA CONFINED TO THE NORTHERN DESERTS AND HIGHER TERRAIN NORTH AND EAST OF PHOENIX. IT WILL BE BREEZY ONCE AGAIN BUT MOST LIKELY THE WINDS WILL STAY BELOW WIND ADVISORY THRESHOLDS. AFTER A MODEST WARMUP SATURDAY THAT WILL NOT EVEN REACH SEASONAL NORMALS...COOLING WILL FOLLOW ONCE AGAIN ON SUNDAY ALTHOUGH BEST PERFORMING GRIDDED GUIDANCE DOES NOT COOL THE DESERTS DOWN AS LOW AS TODAYS READINGS...MOST DESERTS WILL STAY IN THE LOW TO MID 80S. ENSEMBLE GUIDANCE AS WELL AS OPERATIONAL RUNS FROM THE GFS AND ECMWF ARE PRETTY CONSISTENT WITH THE HANDLING OF THIS NEXT LOW OVER THE WEEKEND AND CONFIDENCE IN THE PRECIP...WIND AND TEMPERATURE FORECASTS IS RELATIVELY HIGH. UPPER LOW SHIFTS OFF TO THE NORTHEAST MONDAY AS HIGH PRESSURE ALOFT BUILDS IN ALONG THE SRN CA COAST AND DRIER SUBSIDENT NORTHWEST FLOW ALOFT OVERSPREAD THE LOWER DESERTS. EXPECT HIGHS MONDAY TO RISE INTO THE MID 80S TO LOW 90S UNDER SUNNY SKIES. SOME RESIDUAL MOISTURE WILL REMAIN OVER THE HIGHER TERRAIN EAST OF PHOENIX AND AN ISOLATED INSTABILITY SHOWER OR THUNDERSTORM IS POSSIBLE MAINLY ACROSS AREAS EAST OF GLOBE. TUESDAY THROUGH LATE NEXT WEEK... DETERMINISTIC AND ENSEMBLE MODEL AGREEMENT IS FAIRLY GOOD FOR THE MEDIUM TO EXTENDED RANGE PERIOD WITH HIGH AMPLITUDE RIDGING OVERTAKING MUCH OF THE INTERMOUNTAIN WEST/ROCKIES EARLY TUESDAY AND LINGERING THROUGH THURSDAY. INCREASING THICKNESSES AND RECOVERING ATMO THERMAL PROFILE WILL ALLOW FOR NEAR TO ABOVE AVERAGE TEMPERATURES WITH MANY LOWER DESERT SITES RETURNING TO THE 90S BY TUESDAY. 500MB HEIGHTS HEAD INTO THE LOW 580 DAM RANGE EASILY PEAKING SURFACE TEMPERATURES INTO THE MID-90S BY THE MIDDLE PORTION OF THE WEEK. SOME OF THE WARMEST DESERT LOCALES...SUCH AS TACNA AND EL CENTRO...COULD FLIRT WITH THE TRIPLE-DIGIT READINGS...BUT THE CLIMATE STATIONS OF PHOENIX AND YUMA STILL ARE IN THE CLEAR WITH THE LATEST GUIDANCE. LATE WEDNESDAY INTO THURSDAY THE UPPER RIDGE WILL CLEAR EAST OF THE AREA AS A PACIFIC TROUGH APPROACHES THE WEST COAST. MORE OCEANIC TRACK AND SOUTHERLY REACHES OF THIS TROUGH COULD SPELL INCREASING HUMIDITIES INTO THE REGION ALONG WITH A COOLING TREND FOR TEMPERATURES FOR THE WEEKEND AFTER NEXT.
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&& .AVIATION...
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SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA AND KSDL... AS A FAIRLY DRY COLD FRONT EXITS THE REGION EXPECT OCCASIONALLY VERY BREEZY WEST TO SOUTHWESTERLY WIND GUSTS UP TO 20 TO 25KTS FOR MOST OF THE AFTERNOON TOGETHER WITH MOSTLY CLEAR SKIES. WEST WINDS WILL BECOME LIGHT THIS EVENING ALONG WITH SOME MID LEVEL CIGS MOVING THROUGH AND EXITING LATER TONIGHT. EASTERLY COMPONENT OR LIGHT AND VARIABLE WINDS SHOULD BEGIN IN THE VERY EARLY MORNING HOURS. SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH... AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. EXPECT VERY BREEZY TO OCCASIONALLY WINDY WEST TO SOUTHWEST WINDS WITH GUSTS UP TO 25 TO 33 KTS DURING THE AFTERNOON. SOME OCCASIONAL MID LEVEL CIGS AT 7 TO 8K FT COULD MOVE TROUGH KBLH ALONG WITH SOME ISOLATED RAIN SHOWERS IN THE VICINITY DURING THE AFTERNOON AND INTO THE EARLY EVENING. LATER TONIGHT WESTERLY COMPONENT WINDS SHOULD BECOME LIGHT AS THE SKIES BECOME MOSTLY CLEAR. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
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&& .FIRE WEATHER...
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SUNDAY THROUGH THURSDAY... AS A DRIER LOW PRESSURE SYSTEM MOVES THROUGH SUNDAY AND EARLY MONDAY EXPECT SIGNIFICANTLY LOWER THAN NORMAL HIGH TEMPERATURES ON SUNDAY ...IN THE LOW 80S...TO INCREASE TO SLIGHTLY BELOW NORMAL ON TUESDAY AND THEN TO TO NEAR NORMAL ON WEDNESDAY WHEN HIGH PRESSURE AND DRIER AIR BUILDS IN. IN ADDITION...THERE WILL BE NO CHANCE OF WETTING RAIN WITH SUNDAY`S SYSTEM. MINIMUM RELATIVE HUMIDITIES ON SUNDAY WILL BE DRY IN THE UPPER TEENS TO MID 20 PERCENT RANGE AND WILL BECOME VERY DRY BY TUESDAY AND WEDNESDAY IN THE MID SINGLE DIGITS TO LOWER TEENS. OVERNIGHT RECOVERIES ARE EXPECTED TO BE GOOD TO EXCELLENT ON SUNDAY NIGHT...FAIR TO GOOD ON MONDAY NIGHT AND FAIR BY TUESDAY NIGHT. WINDS WILL BE BE LIGHT EXCEPT FOR SOME BREEZY CONDITIONS SUNDAY AFTERNOON IN THE TONTO FOOTHILLS AND SOUTHERN GILA COUNTY AS WELL AS ON WEDNESDAY AFTERNOON IN SW AZ...THE LOWER COLORADO RIVER VALLEY AND SE CA.
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&& .SPOTTER INFORMATION STATEMENT... SPOTTER ACTIVATION IS NOT EXPECTED. && .PSR WATCHES/WARNINGS/ADVISORIES...
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AZ...NONE. CA...NONE.
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&& $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...CB/NOLTE AVIATION...SAWTELLE FIRE WEATHER...SAWTELLE

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