Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 201534
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
835 AM MST SAT SEP 20 2014


.SYNOPSIS...
LINGERING MOISTURE ACROSS THE REGION AND LOW PRESSURE APPROACHING
FROM THE WEST WILL KEEP AT LEAST SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS FOR TODAY. DRIER AIR WILL GRADUALLY FILTER
INTO THE REGION SUNDAY AND MONDAY FOR A DECLINE IN STORM CHANCES.
SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS WILL BE CONFINED TO THE
HIGHER MOUNTAINS OF SOUTH-CENTRAL ARIZONA DURING THE MIDDLE OF NEXT
WEEK WITH SLIGHTLY ABOVE NORMAL TEMPERATURES. AN APPROACHING
PACIFIC WEATHER SYSTEM LATE NEXT WEEK WILL LEAD TO AN INCREASE IN
STORM CHANCES.

&&

.DISCUSSION...
ANOTHER HUMID MORNING AS YOU WALK OUTSIDE. CURRENT DEWPOINT READINGS
ACROSS PHOENIX METRO RANGE FROM THE MID 60S TO MID 70S AND ACROSS
SOUTHEAST CALIFORNIA 60S TO 70S AS WELL WITH SOME DRIER AIR FARTHER
NORTH INTO JOSHUA TREE NATIONAL PARK AND SAN BERNARDINO COUNTY. THE
STRONG UPPER LEVEL LOW CONTINUES TO SPIN OFF SHORE OF SOUTHERN
CALIFORNIA WHILE HIGH PRESSURE REMAINS ACROSS SOUTHERN NEW MEXICO
AND WEST TEXAS...GIVING WAY TO A SOUTHERLY FETCH OF MOISTURE
STREAMING INTO ARIZONA. THIS SHOULD REMAIN IN PLACE THE REMAINDER OF
TODAY...CREATING DIFLUENT CONDITIONS FROM THE LOWER COLORADO RIVER
VALLEY UP THROUGH EASTERN NEVADA AND WESTERN UTAH WHERE CONDITIONS
SHOULD BE MORE FAVORABLE FOR THUNDERSTORM ACTIVITY. THE FORECAST IS
IN GOOD SHAPE FROM THE PREVIOUS SHIFT SO NO UPDATES NEEDED AT THIS
TIME AND THE PREVIOUS DISCUSSION STILL APPLIES.

.PREVIOUS DISCUSSION.../ISSUED 248 AM MST/PDT 20 SEPT 2014/...
MONSOON MOISTURE WILL STILL BE A FACTOR OVER THE NEXT WEEK...BUT
MAINLY ACROSS EASTERN PORTIONS OF ARIZONA. IN THE NEAR TERM...A
CUT-OFF UPPER LOW CENTERED OFF THE SOUTHERN CALIFORNIA COAST IS
ALLOWING FOR AN INCREASE IN SOUTHERLY FLOW ACROSS THE AREA...THUS
TAPPING INTO ADDITIONAL MOISTURE OVER NORTHERN MEXICO. CURRENT IR
IMAGERY HINTS AT SOME OF THIS MOISTURE ADVECTION IN THE FORM OF
ACCAS CLOUDS ACROSS SOUTHERN ARIZONA. HI-RES MODELS DO INDICATE SOME
LIGHT SHOWERS WILL BE PRESENT ACROSS YUMA COUNTY AFTER 12Z THIS
MORNING IN THE MAIN MOISTURE ADVECTION AREA. HAVE INTRODUCED SOME
SLIGHT CHANCE POPS ACROSS YUMA AND SOUTHERN MARICOPA COUNTIES
STARTING AROUND 12Z AND THEN EXPANDING AS THE DAY PROGRESSES.

THE UPPER LOW WILL REMAIN NEARLY STATIONARY UNTIL THIS EVENING WHEN
GOOD MODEL AGREEMENT SHOWS IT FINALLY LIFTING NORTHEASTWARD INTO THE
GREAT BASIN. A FAIRLY STRONG UPPER JET MAX ACROSS SOUTHEAST
CALIFORNIA WILL ALLOW FOR A FAVORABLE AREA OF ASCENT TODAY MAINLY
FOCUSED ACROSS WESTERN ARIZONA. COULD SEE SOME ISOLATED SHOWERS AND
THUNDERSTORMS ACROSS ALL BUT THE IMPERIAL VALLEY THIS AFTERNOON WITH
THE BEST CHANCES ACROSS LA PAZ COUNTY CLOSER TO THE FAVORED ASCENT
AREA AND ACROSS THE HIGHER TERRAIN OF GILA COUNTY. ACTIVITY SHOULD
REMAIN FAIRLY ISOLATED AS INSTABILITY WILL BE SOMEWHAT LIMITED BASED
ON FORECAST SOUNDINGS. THERE WILL BE SOME POTENTIAL FOR STRONG GUSTY
WINDS TODAY...MAINLY ACROSS SOUTHWEST ARIZONA WHERE MID LEVEL WINDS
WILL BE 15-25 KNOTS. DON/T FEEL THERE WILL BE MUCH OF A FLOOD THREAT
TODAY WITH A SOUTHERLY STEERING FLOW AT 10-20 KNOTS AND PRECIPITABLE
WATER VALUES OF 1.25-1.50 INCHES.

AS THE UPPER LOW LIFTS INTO THE GREAT BASIN ON
SUNDAY...SOUTHWESTERLY MID AND UPPER LEVEL FLOW WILL BRING IN DRIER
AIR FROM THE SOUTHWEST. THE LOW LEVELS WILL REMAIN FAIRLY MOIST FROM
MARICOPA COUNTY EASTWARD ALLOWING FOR A CONTINUED SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS FOR SUNDAY MAINLY OVER THE HIGHER TERRAIN
NORTH AND EAST OF PHOENIX. FURTHER DRYING WILL TAKE PLACE EARLY NEXT
WEEK...CONFINING ANY SLIGHT CHANCE POPS ONLY ACROSS HIGHER TERRAIN
AREAS EAST OF PHOENIX ON MONDAY AND TUESDAY. UPPER LEVEL RIDGING
TAKES OVER STARTING MONDAY WITH 500MB HEIGHTS BUILDING TO AROUND
590DM. GIVEN THE HIGH HEIGHTS AND FORECAST 850MB TEMPERATURES OF
23-25C...FEEL CONFIDENT THAT LOWER DESERT LOCATIONS WILL TOP OUT
ABOVE 100 STARTING MONDAY. DURING THE MIDDLE OF NEXT WEEK...THE
UPPER RIDGE WILL AMPLIFY AHEAD OF A DEEPENING UPPER TROUGH OFF THE
PACIFIC NORTHWEST. THIS WILL KEEP TEMPERATURES ON THE WARM
SIDE...AROUND 3-5 DEGREES ABOVE NORMAL...AT LEAST THROUGH THURSDAY
AND LIMIT ANY SHOWER AND THUNDERSTORM ACTIVITY TO FAR EASTERN GILA
COUNTY.

ATTENTION THEN TURNS TO A POSSIBLE SEASONAL TRANSITION SYSTEM FOR
LATE NEXT WEEK INTO NEXT WEEKEND. CONFIDENCE IS STILL NOT VERY HIGH
ON THE SPECIFICS OF THE SYSTEM...BUT THE 00Z MODEL RUNS CAME INTO
FAIRLY GOOD AGREEMENT THAT A DEEP PACIFIC TROUGH WILL SLIDE THROUGH
CALIFORNIA ON FRIDAY AND POSSIBLY AS FAR SOUTH AS ARIZONA SOMETIME
NEXT WEEKEND. WIDESPREAD SLIGHT CHANCE POPS ARE IN THE FORECAST FOR
FRIDAY...AND MAY NEED TO RAMP UP POPS OVER THE NEXT FEW DAYS IF THE
TROUGH LOOKS LIKE IT WILL DIG FAR ENOUGH SOUTH INTO OUR AREA. EITHER
WAY IT IS FAIRLY LIKELY THIS LOW WILL USHER IN COOLER AND MUCH DRIER
AIR...AND POTENTIALLY ENDING OUR MONSOON SEASON.

&&

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

AN UPPER LOW CENTERED OFF THE COAST OF SOUTHERN CALIFORNIA WILL PULL
MONSOON MOISTURE NORTHWARD TODAY FOR SCT-BKN080-100 WITH SCATTERED
SHOWERS AND THUNDERSTORMS OVER THE HIGHER TERRAIN NORTH...EAST...AND
SOUTH...OF THE PHOENIX AREA AND ISOLATED ELSEWHERE. ONSET OF SHOWERS
POSSIBLE BEFORE 18Z. CONFIDENCE TOO LOW AN ANY GIVEN TAF SITE TO
INSERT TEMPO SHWRS/TSTMS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
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...MAINLY EAST OF THE LOWER COLORADO RIVER VALLEY. IN
ADDITION...COOLER TEMPERATURES 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...DEWEY
PREVIOUS DISCUSSION...KUHLMAN
AVIATION...AJ
FIRE WEATHER...AJ






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