Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 311615 CCA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
915 AM MST THU JUL 31 2014

.SYNOPSIS...
ANTICIPATE ANOTHER HOT DAY TODAY...THOUGH THERE WILL BE MORE
CLOUDINESS AROUND. A SLIGHT CHANCE OF STORMS RETURNS TO PORTIONS OF
SOUTH-CENTRAL ARIZONA TODAY. EXPECT AN UPTREND IN THUNDERSTORM
CHANCES EXPANDING FROM EAST TO WEST FRIDAY THROUGH SUNDAY.
ACCORDINGLY...TEMPERATURES WILL NOT BE AS HOT. NEXT WEEK...A
DOWNTREND IS ANTICIPATED AS DRIER AIR FILTERS IN.


&&

.DISCUSSION...
UPPER HIGH REMAINS CENTERED TO OUR SOUTH THIS MORNING...KEEPING A
LIGHT AND SOMEWHAT DRIER SOUTHWEST/WESTERLY FLOW ALOFT IN PLACE
ACROSS OUR LOWER DESERTS THIS MORNING. A DECAYING MCS THAT FORMED
OVER NWRN MEXICO LAST NIGHT SENT CONSIDERABLE DEBRIS CLOUDS ALONG
WITH A FEW SHOWERS INTO SERN AZ AND PORTIONS OF SOUTH CENTRAL AZ
DURING THE MORNING...AND LATEST 9 AM IR IMAGERY SHOWED PARTLY TO
MOSTLY CLOUDY SKIES EAST OF THE LOWER CO RIVER VALLEY. MOST OF THE
DISSIPATING SHOWERS WERE LOCATED TO THE SOUTHEAST OF THE GREATER
PHOENIX AREA...AND OVER THE HIGHER TERRAIN OF ZONE 24...AND THEY
SHOULD CONTINUE TO DISSIPATE AS THE MORNING WEARS ON. OF
COURSE...THE CLOUD COVER WILL ACT TO SUPPRESS OUR HIGH TEMPS
TODAY...AND WITH THE PREVIOUS FORECAST ALREADY BARELY AT HEAT
WARNING THRESHOLDS...WE NOW EXPECT HIGHS TO COME UP A FEW DEGREES
SHORT. AS SUCH WE HAVE CANCELLED THE EXCESSIVE HEAT WARNING FOR ALL
AREAS EAST OF THE LOWER CO RIVER VALLEY. LOCAL ANALYSIS OF THE AREA
SOUNDINGS SUGGEST CHANCES FOR STORMS ARE MEAGER TODAY...AND POPS
WILL STAY IN THE SINGLE DIGITS EXCEPT FOR ZONE 24 WHERE SLIGHT
CHANCES WILL REMAIN. AT 9 AM DEWPOINTS AT YUMA AND IMPERIAL JUMPED
TO 66...A RESULT OF OUTFLOWS MOVING IN FROM THE DECAYING MCS.
INCREASING HUMIDITY MAY LEAD TO TEMPS NOT REACHING HEAT WARNING
THRESHOLDS OUT WEST...SO WE MAY NEED TO DROP THE WARNING FOR THE FAR
WESTERN ZONES...BUT WILL WAIT UNTIL LATER IN THE MORNING TO MAKE
THAT CALL. OTHERWISE...FORECASTS NOW APPEAR TO BE IN GOOD SHAPE AND
NO ADDITIONAL UPDATES ARE PLANNED ATTM.

.PREVIOUS DISCUSSION...
OVERNIGHT TEMPS RUNNING WARMER AT MOST LOCATIONS IN THE FORECAST
AREA COMPARED TO 24 HRS AGO. THIS SHOULD HELP KEEP MAX TEMPS RATHER
WARM TODAY. HOWEVER...AN X FACTOR IN THE MAX TEMPS TODAY IS AN MCS
CURRENTLY OVER SONORA. ANTICIPATE DEBRIS CLOUDS FROM THAT TO SPREAD
OVER A GOOD DEAL OF THE FORECAST AREA TODAY. IT REMAINS TO BE SEEN
JUST HOW THICK THEY WILL BE. ANTICIPATE EASTERN HALF OF CWA TO SEE
MORE THAN WESTERN HALF. ACCORDINGLY...NUDGED MAX TEMPS DOWN IN
EASTERN AREAS BY 2-3 DEGREES COMPARED TO YESTERDAY. ANOTHER WAY THAT
THE MCS COULD AFFECT TEMPERATURES TODAY IS WITH LONG LIVED OUTFLOW.
06Z NAM INDICATES A SHALLOW SURGE MOVING INTO MOSTLY SOUTHWEST
ARIZONA DURING THE DAY. SOME WEAK SHOWER DEVELOPMENT NORTH OF THE
MEXICO BORDER EARLY THIS MORNING WILL NEED TO BE MONITORED AS IT IS
POSSIBLE WE COULD SEE SOME ISOLATED NUISANCE STUFF IN OUR AREA THIS
MORNING. FOR NOW...HAVE HELD OFF ON POPS UNTIL THIS AFTERNOON. WOULD
NOT BE SURPRISED TO SEE SOME DUST OVER PINAL COUNTY TODAY FROM
STORMS EMANATING FROM FURTHER SOUTH...BUT LINGERING CLOUD COVER
THERE COULD INHIBIT STORM ACTIVITY.

FRIDAY THROUGH SUNDAY...
LATEST MODELS DEPICT AN OVERALL UPTREND IN MOISTURE AND QPF FROM
EAST TO WEST FRIDAY AND SATURDAY AND CONTINUING SUNDAY. THE BASIC
SCENARIO IS THE ANTICYCLONE...CURRENTLY CENTERED NEAR THE MEXICO
BORDER...BREAKING UP INTO TWO MAIN ANTICYCLONIC CIRCULATIONS WITH A
DEFORMATION ZONE IN BETWEEN. MEANWHILE AN UPPER LOW...CURRENTLY
CENTERED NOT FAR WEST OF SOUTHERN BAJA...WILL SLOWLY MOVE
NORTHWESTWARD AND A VORT LOBE ON THE EASTERN PERIPHERY WILL MOVE UP
THROUGH WESTERN SONORA. THE GFS AND EC INDICATE THIS FEATURE HELPING
TO REIGNITE SONORA CONVECTION LATER TONIGHT. EVENTUALLY...AN
INVERTED TROUGH MOVES NORTHWESTWARD FROM SOUTHEAST ARIZONA INTO THE
MOHAVE DESERT OVER THE WEEKEND. THERE MAY EVEN BE SOME SHORT WAVE
ENERGY FROM THE WESTERLIES WHICH BREAKS OFF FROM NEW MEXICO THAT
COMES INTO PLAY. A BACKDOOR FRONT ALREADY OVER NEW MEXICO MAY ALSO
BE AN AID IN THE UPWARD MOISTURE TREND. OF NOTE...THERE ARE
SIGNIFICANT DIFFERENCES IN THE DETAILS BETWEEN THE MODELS. IN
GENERAL...THE EC IS SLOWER THAN THE GFS WITH THE PASSAGE OF THE
INVERTED TROUGH. FORECASTS REFLECT THE WESTWARD ADVANCE OF STORM
CHANCES...OVERSPREADING THE ENTIRE FORECAST AREA BY SATURDAY. WITH
MORE CLOUDINESS AND OUTFLOW AIR AROUND...TEMPERATURES TREND DOWNWARD.

MONDAY THROUGH WEDNESDAY...
THE FIRST HALF OF THE NEXT WORKWEEK CONTINUES TO LOOK LIKE A
DOWNTREND IN STORM ACTIVITY AS THE INVERTED TROUGH DEPARTS AND DRIER
AIR MOVES INTO THE REGION...AT FIRST FROM WESTERLY FLOW THEN
NORTHERLY. ACCORDINGLY...POPS RETREAT EASTWARD AND TEMPS SLOWLY
CLIMB.


&&

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

STARTING TO SEE SOME THICKER CLOUDS AND ISOLATED SHOWERS MOVING INTO
SOUTHEAST ARIZONA ON THE LEADING EDGE OF A DECAYING MCS. NOT
ANTICIPATING ANY PRECIP AT ANY OF THE TERMINALS BUT CLOUDS WILL
CERTAINLY THICKEN UP THIS MORNING...POSSIBLY LINGERING ALL THE WAY
INTO THE AFTERNOON. BKN150-BKN250 WILL BE COMMON AT ALL PHOENIX
SITES AND TO A LESSER EXTENT AT IPL/BLH AS WELL. OTHERWISE NO MAJOR
WEATHER IMPACTS EXPECTED. WINDS WILL FAVOR TYPICAL DIURNAL TRENDS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
MOISTURE WILL RETURN TO THE AREA BY THE WEEKEND WITH SHOWERS AND
THUNDERSTORMS EXPECTED. DAY TO DAY TIMING AND PLACEMENT OF STORMS IS
HARD TO PIN DOWN BUT IT LOOKS LIKE A DECENT CHANCE OF A WETTING RAIN
EVEN ACROSS SOME DESERT LOCATIONS. HUMIDITY VALUES WILL STEADILY
INCREASE WITH MINIMUM VALUES BETWEEN 20 AND 30 PERCENT EXPECTED
ACROSS THE DESERTS SATURDAY INTO THE EARLY PART OF NEXT WEEK.
CORRESPONDINGLY...HIGH TEMPERATURES WILL FALL OFF...DROPPING FROM
AROUND SEASONAL NORMALS FRIDAY TO WELL BELOW NORMAL VALUES ON
SUNDAY. SLIGHT WARMING WILL RETURN BY NEXT TUESDAY AS HUMIDITY
VALUES LOWER SOMEWHAT. STRONG WINDS ARE NOT EXPECTED DURING THE FIVE
DAY PERIOD...AND THEY SHOULD TYPICALLY FAVOR SOUTH TO SOUTHWEST
DIRECTIONS DURING THE AFTERNOON AND EVENING HOURS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...EXCESSIVE HEAT WARNING TODAY UNTIL 8 PM MST AZZ020...025.

CA...EXCESSIVE HEAT WARNING TODAY UNTIL 8 PM PDT CAZ031>033.

&&

$$

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

DISCUSSION...CB
PREVIOUS DISCUSSION...AJ
AVIATION...LEINS
FIRE WEATHER...LEINS










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