Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 211218 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
520 AM MST SUN SEP 21 2014

.UPDATE...
UPDATED AVIATION AND FIRE WEATHER SECTIONS.

&&

.SYNOPSIS...
DRIER AIR WILL GRADUALLY FILTER INTO THE REGION TODAY AND MONDAY
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...
AS THE UPPER LOW WHICH IS NOW CENTERED OVER CENTRAL CALIFORNIA
CONTINUES TO LIFT NORTHWARD...DRIER SOUTHWESTERLY MID AND UPPER
LEVEL FLOW IS TAKING OVER ACROSS SOUTHWEST AND MUCH OF SOUTH-CENTRAL
ARIZONA. THIS DRIER AIR IS EXPECTED TO PUSH AS FAR EAST AS PHOENIX
BY THIS AFTERNOON...ESSENTIALLY CUTTING OFF ANY RAIN CHANCES EXCEPT
FOR HIGHER TERRAIN AREAS EAST OF PHOENIX. THE UPPER LOW IS FORECAST
TO MOVE INTO THE GREAT BASIN BY THIS EVENING WITH THE UPPER RIDGE TO
OUR SOUTH CREEPING NORTHWARD INTO ARIZONA. GOOD MODEL AGREEMENT
SHOWS THE RIDGE BUILDING OVER THE DESERT SOUTHWEST THE NEXT FEW DAYS
WITH HEIGHTS MAXING OUT IN THE 590-592DM RANGE ON TUESDAY AND
WEDNESDAY. ANY LINGERING LOW LEVEL MOISTURE OVER EAST-CENTRAL
ARIZONA WILL LIKELY GET PUSHED OUT OF THE AREA WHICH SHOULD END ANY
SLIGHT CHANCES FOR RAIN ACROSS THE HIGHER TERRAIN ON TUESDAY AND
WEDNESDAY. THE HIGH HEIGHTS AND DRIER AIR WILL ALLOW FOR SOME
WARMING OVER THE NEXT FEW DAYS WITH LOWER DESERT LOCATIONS PEAKING
OUT IN THE 100-105 RANGE...OR ROUGHLY 3-5 DEGREES ABOVE SEASONAL
NORMALS.

BY LATE IN THE WEEK...THE NEXT WEATHER SYSTEM WILL SLOWLY MOVE
SOUTHEASTWARD INTO THE PACIFIC NORTHWEST AND GREAT BASIN. A GOOD
AMOUNT OF UNCERTAINTY REMAINS WITH THIS SYSTEM WITH LONG RANGE
MODELS STRUGGLING A BIT WITH THE TIMING AND HOW FAR SOUTH THE MAIN
SHORTWAVE WILL GO. LATEST RUNS SHOW A FASTER AND LESS DIGGING TROUGH
FROM THE GFS WHILE THE EUROPEAN DIGS THE TROUGH AS FAR SOUTH AS
SOUTHERN CALIFORNIA WHILE BRIEFLY CUTTING THE LOW OFF FROM THE POLAR
JET STREAM. THE TIMING DOES SEEM TO BE PUSHED BACK FROM YESTERDAY/S
MODEL RUNS...SO THE BEST RAIN CHANCES HAVE SHIFTED FROM FRIDAY TO
SATURDAY. THIS IS REFLECTED IN THE FORECAST BY DECREASING POPS
SLIGHTLY ON FRIDAY AND INCREASING POPS ON SATURDAY. THE AMOUNT OF
MOISTURE THAT WILL GET DRAWN UP AHEAD OF THE SYSTEM IS ALSO
PROBLEMATIC AS THE DEEPER EUROPEAN BRINGS IN SUBSTANTIALLY MORE
MOISTURE THAN THE GFS. FOR NOW...KEEPING WITH A FAIRLY WIDESPREAD
10-20 POPS ON BOTH DAYS. TEMPERATURES WILL BEGIN TO DECREASE
STARTING FRIDAY WITH LOWER DESERT HIGHS LIKELY ONLY IN THE LOWER 90S
FOR NEXT WEEKEND.

&&

.AVIATION...
SOUTH-CENTRAL AND SOUTHWEST ARIZONA INCLUDING KPHX...KIWA...KSDL...
STORM CHANCES OVER SOUTHERN ARIZONA TODAY WILL BE EAST OF A LINE
FROM WICKENBURG TO SELLS WITH ONLY SLIGHT CHANCES OVER PHOENIX
METRO. THUS HELD OFF ON INSERTING TEMPO SHWRS/TSTMS IN TAFS.
OUTFLOWS FROM DISTANT STORMS MAY LEAD TO WIND SHIFTS LATER
TODAY...BUT LESS LIKELY THAN YESTERDAY. ANTICIPATE SLOWER ARRIVAL OF
WESTERLY WINDS AT KPHX TODAY THAN YESTERDAY.

SOUTHEAST CALIFORNIA INCLUDING KIPL...AND KBLH...
SOUTH AND SOUTHEASTERLY WINDS WILL BE FAVORED ONCE AGAIN...LESS SO
OVER IMPERIAL VALLEY WITH WESTERLY FAVORED. OTHERWISE CLEAR SKIES.


AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
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...KUHLMAN
AVIATION...AJ
FIRE WEATHER...AJ













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