Area Forecast Discussion
Issued by NWS Phoenix, AZ

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KPSR 191541
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
840 AM MST FRI SEP 19 2014


.SYNOPSIS...
LINGERING MOISTURE ACROSS THE REGION AND LOW PRESSURE APPROACHING
FROM THE WEST WILL KEEP AT LEAST SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS IN THE FORECAST TODAY THROUGH SATURDAY. DRIER AIR WILL
GRADUALLY FILTER INTO THE REGION SUNDAY FOR A DECLINE IN STORM
CHANCES. SOME ADDITIONAL DRYING MONDAY...WITH LITTLE CHANGE THROUGH
WEDNESDAY...WILL KEEP STORM CHANCES VERY SLIGHT AND LIMITED TO THE
HIGHER MOUNTAINS OF SOUTH-CENTRAL ARIZONA. TEMPERATURES WILL BE
WARMER AS WELL. AN APPROACHING PACIFIC WEATHER SYSTEM LATE NEXT WEEK
WILL LEAD TO AN INCREASE IN STORM CHANCES OVER THE HIGHER TERRAIN OF
SOUTH-CENTRAL ARIZONA.

&&

.DISCUSSION...
QUITE A BIT OF MOISTURE STILL PRESENT ACROSS THE LOWER DESERTS THIS
MORNING. DEWPOINTS FROM FAR SOUTHEAST ARIZONA TO NORTH-CENTRAL
ARIZONA IN THE UPPER 50S TO LOW 70S...AND EVEN ACROSS SOUTHERN
CALIFORNIA FROM THE COAST TO THE LOWER DESERTS WITH SIMILAR VALUES.
CLOUD COVER REMAINING THROUGH THE OVERNIGHT HOURS WITH BASES 8-10K
FT AS DEPICTED BY THE 12Z PSR SOUNDING...A VERY MOIST LAYER AND
COLUMN WITH OVER 1.7 INCHES OF PRECIPITABLE WATER AND WEAK WIND
PROFILE. NOTABLE BOUNDARY OF MOISTURE FROM SOUTH-CENTRAL ARIZONA
STRETCHING NORTHEAST TOWARDS FOUR-CORNERS AREA...WITH AN APPROACHING
TROUGH MOVING ON TO THE WEST COAST THIS WEEKEND. FOR
TODAY...ISOLATED SHOWER CHANCES SHOULD REMAIN VERY SLIGHT AND MOSTLY
TERRAIN DRIVEN AS DEPICTED IN LOCAL HIGH-RES MODEL FORECASTS. NO
UPDATES NEEDED FOR THE FORECAST PACKAGE AT THIS TIME.


.PREVIOUS DISCUSSION.../ISSUED 410 AM MST/PDT FRIDAY 19 SEPT/...
TODAY THROUGH SUNDAY...
SATELLITE IMAGERY EARLY THIS MORNING SHOWS A FAIR AMOUNT OF CLOUD
COVER OVER ARIZONA...INCLUDING OUR FORECAST AREA. PHOENIX AREA
METARS HAVE THE BASES AT 8-10 KFT AGL. MOST OF THE CLOUD TOPS ARE
AROUND...OR WARMER THAN...0 DEG C. SOME OF THE CLOUDINESS IS COLDER
THAN THAT WHICH INDICATES A DEEPER CLOUD AND BETTER POTENTIAL TO
PRODUCE PRECIP. WATER VAPOR LOOP INDICATES THERE WERE A COUPLE OF
VORT MAXES THAT HAVE SHIFTED EASTWARD INTO NEW MEXICO. IT ALSO SHOWS
A TROUGH CENTERED ROUGHLY ALONG THE CALIFORNIA COAST WITH MULTIPLE
VORT MAXES MOVING THROUGH AND STRONGER SOUTHWESTERLY FLOW ALOFT
APPROACHING THE FORECAST AREA. BLENDED TPW IMAGERY SHOWS A FAIRLY
SHARP MOISTURE GRADIENT OVER FAR WESTERN ARIZONA. LATEST MODELS HAVE
ALL BEEN DEPICTING QPF OVER EASTERN PORTIONS OF THE FORECAST AREA
THIS MORNING. HOWEVER...MOST OF THEM GENERATED QPF BETWEEN 0-6Z
WHICH DID NOT HAPPEN AT ALL. THEY SHOWED EVEN MORE BETWEEN 6-12Z
WHICH HAS NOT HAPPENED YET. IT MAY BE A REFLECTION OF A
JETLET...AHEAD OF A STRONGER JET CLOSER TO THE MAIN TROUGH
AXIS...FORECAST TO MOVE INTO ARIZONA AND WEAKEN LATER TODAY. OF
NOTE...MODELS ARE GENERALLY SHOWING MORE QPF IN THE 12-18Z TIME
FRAME THAN 18Z-00Z...LIKELY DUE TO DRIER AIR MOVING IN. LOCAL WRF
HAS BEEN THE MOST CONSERVATIVE IN TERMS OF AREAL COVERAGE AND THUS
IT APPEARS TO BE DOING BETTER THAN MANY OTHER MODELS. EVEN
STILL...IT GENERATES SOME LARGE QPF BULLSEYES OVER THE MAZATZALS AND
FOUR PEAKS WHICH LOOKS OVERDONE. HELD OFF ON EXPANDING THE SLIGHT
CHANCE AREA FOR THIS MORNING DUE TO DISCONNECT BETWEEN OBSERVED
CONDITIONS AND MODEL FORECAST. HOWEVER...HELD ON TO SLIGHT CHANCE
THIS AFTERNOON OVER OUR EASTERN AREAS AS SURFACE HEATING WILL BE
BETTER.

MODELS ARE IN AGREEMENT THAT A VORT MAX WITHIN THE PACIFIC TROUGH
WILL BECOME THE MAIN CIRCULATION CENTER AND BECOMES A CUTOFF LOW FOR
A SHORT TIME. MEANWHILE...AN ANTICYCLONE BECOMES CENTERED OVER
COLORADO. IN TURN...MOISTURE PUSHES WEST AND NORTHWARD...A REVERSAL
OF THE PREVIOUS DRY ADVECTION. A JET STREAK TRACKS ACROSS SOUTHEAST
CALIFORNIA AND ARIZONA SATURDAY INTO SUNDAY...SLOWLY WEAKENING IN
THE PROCESS AS THE LOW TRACKS NORTHEASTWARD IN RESPONSE TO A LARGE
UPSTREAM TROUGH. BEST DYNAMICAL LIFT LOOKS TO BE WHERE MOISTURE IS
MORE LIMITED AND THE CONVERSE IS TRUE. THUS POPS REMAIN CONSERVATIVE
THOUGH SOME SUBTLE UPWARD ADJUSTMENTS WERE MADE SATURDAY. WITH DRIER
AIR MOVING IN SUNDAY...POPS TREND DOWNWARD.

TEMPS LOOK TO BE SLIGHTLY COOLER TODAY DUE TO INFLUENCE FROM THE
NEARBY TROUGH. ANTICIPATE ADDITIONAL COOLING OVER OUR WESTERN AREAS
SATURDAY FOR THE SAME REASON BUT SOME WARMING OVER OUR EASTERN AREAS
DUE TO LESS CLOUDINESS. LITTLE CHANGE SUNDAY.

MONDAY THROUGH THURSDAY...
WITH RIDGING BEGINNING TO BUILD IN MONDAY ALONG WITH SOME ADDITIONAL
DRYING...TEMPS WILL BE A BIT WARMER AND POPS WILL BE LIMITED TO LOW
END SLIGHT CHANCE OVER THE HIGHER MOUNTAINS OF SOUTH-CENTRAL
ARIZONA. LOOK FOR SLIGHT ADDITIONAL WARMING TUESDAY WITH LITTLE
CHANGE WEDNESDAY ALONG WITH  LITTLE CHANGE IN POPS. BY THURSDAY...A
PACIFIC TROUGH MOVES INLAND AND DRAWS SOME MOISTURE NORTHWARD.
SLIGHT CHANCE AREA WAS BROADENED BUT STILL CONFINED TO THE HIGHER
TERRAIN OF SOUTH-CENTRAL ARIZONA.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...CURRENT
SCT-BKN 7-8K FT CIGS TO BECOME FEW-SCT BY THIS AFTERNOON AS SOMEWHAT
DRIER AIR FILTERS INTO THE REGION FROM THE WEST. SCT-BKN MID-LEVEL
CIGS TO RETURN AFTER MIDNIGHT TONIGHT AS SOUTHERLY FLOW ALOFT PUSHES
MOISTURE BACK NORTHWARD INTO THE PHX AREA. WINDS TO MAINLY FOLLOW
THE USUAL DIURNAL TRENDS...WHILE REMAINING ON THE LIGHT
SIDE...MAINLY AOB 10KTS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
CURRENT WESTERLY WINDS AT KIPL...AND SOUTHERLY WINDS AT KBLH...THAT
ARE NOW AROUND 10KTS...ARE EXPECTED TO DIMINISH TO AROUND...OR BELOW
5KTS BY MID-LATE MORNING. MAINLY CLEAR SKIES TO PREVAIL THROUGH THE
TAF PERIOD AT BOTH OF THE SE CA TERMINALS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
RATHER DRY WESTERLY FLOW TO KEEP SKIES MAINLY CLEAR THROUGH THE
FORECAST PERIOD AT MOST LOCATIONS ACROSS THE REGION...WITH THE
EXCEPTION OF THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX...WHERE
LINGERING MOISTURE MAY ALLOW ISOLATED SHOWERS/THUNDERSTORMS TO
DEVELOP EACH AFTERNOON/EARLY EVENING. MINIMUM RELATIVE HUMIDITIES TO
FALL INTO THE 20 TO 30 PERCENT RANGE EACH AFTERNOON...WITH GOOD TO
EXCELLENT OVERNIGHT RECOVERIES. WINDS TO REMAIN MAINLY ON THE LIGHT
SIDE...MAINLY IN THE 5 TO 15 MPH RANGE...WITH THE USUAL DIURNAL
TRENDS TO PREVAIL AT MOST LOCATIONS.


&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...DEWEY
PREVIOUS DISCUSSION...AJ
AVIATION...PERCHA
FIRE WEATHER...PERCHA






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.