Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 220308
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
810 PM MST SUN SEP 21 2014

.SYNOPSIS...
DRIER AIR WILL GRADUALLY FILTER INTO THE REGION THROUGH MID WEEK
LEADING TO DRASTIC DECLINE IN STORM CHANCES. SLIGHT CHANCES FOR
SHOWERS AND THUNDERSTORMS WILL BE CONFINED TO THE HIGHER MOUNTAINS
OF SOUTH-CENTRAL ARIZONA THROUGH MONDAY. SLIGHTLY ABOVE NORMAL
TEMPERATURES ARE ANTICIPATED THROUGH THE MIDDLE OF THIS WEEK. AN
APPROACHING PACIFIC WEATHER SYSTEM LIKELY AFFECTING THE DESERT
SOUTHWEST ON FRIDAY AND SATURDAY WILL LEAD TO AN INCREASE IN STORM
CHANCES AND COOLER TEMPERATURES.

&&

.DISCUSSION...
THE VIGOROUS PACIFIC TROF OVER CENTRAL AND SOUTHERN CA YESTERDAY
CONTINUED ITS NORTHEASTWARD TRACK INTO NORTHEAST NV TODAY. IN ITS
WAKE AT OUR LATITUDE...A DRIER BOUNDARY LAYER AND MORE STABLE UPPER
LEVEL WINDS MOVED INTO MOST OF SOUTHWEST AND SOUTH CENTRAL AZ FOR
NEARLY CLEAR SKIES. THE EXCEPTION WAS IN EASTERN AZ...INCLUDING THE
FAR PORTIONS OF OUR ZONE 24 SOUTHERN GILA COUNTY WHERE A FEW MTN
TSTMS DEVELOPED IN REMNANT MONSOON MOISTURE. CONVECTIVE THREATS WILL
END OVER SOUTHERN GILA COUNTY IN A FEW HOURS. OTHERWISE DRY AND
WARMER DAYS ARE EXPECTED THROUGH TUESDAY.

MINOR UPDATES TO FIRST PERIOD FORECASTS WERE SENT EARLIER. PREVIOUS
DISCUSSION BELOW STILL APPLIES.


.PREVIOUS DISCUSSION...245 PM MST...
EARLY AFTERNOON RADAR IMAGERY FILLING IN WITH THUNDERSTORMS ALONG
THE EASTERN HALF OF ARIZONA IN THE WHITE MOUNTAINS FROM COCHISE
COUNTY NORTH THROUGH PORTIONS OF COCONINO COUNTY AND NORTHERN
PORTIONS OF MOHAVE COUNTY. FROM SOUTHEAST CALIFORNIA THROUGH THE
EAST VALLEY OF THE GREATER PHOENIX METRO MOSTLY CLEAR SKIES HAVE
BEEN THE STORY TODAY WITH STEADY OR FALLING DEWPOINT VALUES. AS OF
215 PM MST/PDT THE DEWPOINT AT SKY HARBOR IS SITTING AT 49F
/9C/...SO IT IS EVIDENT THERE IS A BOUNDARY OF DRY AIR WORKING INTO
ARIZONA AND SLOWLY PUSHING EAST. DO NOT EXPECT SHOWERS IN THE METRO
AREA OR CENTRAL DESERTS THIS EVENING WITH A WESTERLY FLOW AND
MINIMAL MOISTURE /1000-700 MB MIXING RATIOS BELOW 8 G/KG/.

GRADUAL RISING HEIGHTS THROUGH MOST OF THE WEEK...UNDER A 591 DM
RIDGE OF HIGH PRESSURE AND DOMINATING WESTERLY FLOW ALOFT...WILL
ALLOW TEMPERATURES TO RISE A DEGREE OR TWO EACH DAY BY THURSDAY.

FOR THE EXTENDED PART OF THE FORECAST LATER THIS WEEK...A LARGE
PACIFIC TROUGH WILL MOVE ON SHORE FROM THE GULF OF ALASKA BRINGING A
COOLER AND DRIER AIR MASS DOWN THROUGH THE GREAT BASIN AND INTO THE
DESERT SOUTHWEST. MODEL RUN TO RUN CONSISTENCY HAS BEEN DECENT WITH
OPERATIONAL MODELS IN GOOD AGREEMENT THIS FAR OUT IN THE EXTENDED.
MINOR DIFFERENCES IN TIMING AND STRENGTH...BUT THE OVERALL PLACEMENT
AND TIMING LOOKS GOOD. PRECIP CHANCES WILL BEGIN A RAMP UP STARTING
FRIDAY AFTERNOON THROUGH EARLY SUNDAY...SO MADE UPWARD TREND CHANGES
TO THE FORECAST AT THIS TIME. BY SUNDAY THOUGH MODELS BEGIN TO
DRASTICALLY DIFFER...WITH THE GFS TAKING THE TROUGH EASTWARD ACROSS
THE ROCKIES AND THE ECMWF KEEPING THE CUT OFF LOW CENTERED OVER
WESTERN NEVADA WITH SLOW FORWARD PROPAGATION. THESE DIFFERENCES
COULD MEAN CHANGES TO PRECIP FOR THE SOUTHWEST SO CONFIDENCE IS
PRETTY LOW THAT FAR OUT.

&&

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

DRIER WESTERLY FLOW ALOFT WILL RESULT IN MOSTLY CLEAR SKIES AND
LIGHT WIND THROUGH AT LEAST 19Z MONDAY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
WEDNESDAY THROUGH SUNDAY...
MOISTURE RETREAT DUE TO WESTERLY FLOW WILL KEEP STORM CHANCES
MINIMAL THROUGH THURSDAY AND LIMITED TO THE HIGHER MOUNTAINS OF
SOUTH-CENTRAL ARIZONA. MEANWHILE...TEMPERATURES NUDGE UPWARD A FEW
DEGREES ABOVE NORMAL. HUMIDITIES ON THE LOWER DESERTS DROP BELOW 15
PERCENT THOUGH MAX HUMIDITIES REMAIN FAIR. NO STRONG WINDS ARE
EXPECTED DURING THIS TIME FRAME. ON FRIDAY...A PACIFIC WEATHER
SYSTEM WILL PULL MOISTURE NORTHWARD OVER THE REGION FOR A RETURN OF
STORM CHANCES INTO NEXT WEEKEND...MAINLY EAST OF THE LOWER COLORADO
RIVER VALLEY. IN ADDITION...COOLER TEMPERATURES...HIGHER
HUMIDITIES...AND BREEZY TO LOCALLY WINDY CONDITIONS CAN BE EXPECTED
AS WELL.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...VASQUEZ/DEWEY
AVIATION...VASQUEZ
FIRE WEATHER...MEYERS/AJ









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