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000
FXUS65 KPSR 132246
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
345 PM MST THU MAR 13 2014

.SYNOPSIS...
A LOW PRESSURE SYSTEM MOVING THROUGH THE DESERT SOUTHWEST WILL BRING
AN INCREASED CHANCE OF SHOWERS AND EVEN ISOLATED THUNDERSTORMS TO
MAINLY THE HIGHER TERRAIN NORTH AND EAST OF PHOENIX THROUGH FRIDAY.
HOWEVER...TEMPERATURES WILL NOT COOL DOWN MUCH. HIGH PRESSURE WILL
BUILD IN OVER THE WEEKEND FOR SOME ADDITIONAL WARMING. ANTICIPATE A
GRADUAL COOLING TREND NEXT WEEK AS HIGH PRESSURE WEAKENS.

&&

.DISCUSSION...
REST OF TODAY THROUGH FRIDAY...
WATER VAPOR IMAGERY THIS AFTERNOON SHOWS THE MAIN VORT LOBE
ASSOCIATED WITH A POSITIVELY TILTED UPPER LOW ACROSS NEVADA AND
SOUTHERN CALIFORNIA NOW STARTING TO SWING EASTWARD TOWARD ARIZONA.
PVA ALREADY UNDERWAY WHICH HAS ENABLED VIRGA PRODUCING SHOWERS TO
DEVELOP AND THESE ARE SHOWING UP AS WEAK RADAR ECHOES. THIS WILL
CONTINUE OVER MAINLY THE NORTHEASTERN HALF OF ARIZONA TONIGHT AS THE
Q VECTOR BULLS-EYE TRACKS ACROSS THE STATE. PRECIP WILL STRUGGLE TO
REACH THE GROUND DUE TO DRY LOW LEVELS. THUS POPS ARE LIMITED TO
HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA AND NORTHEASTERN FRINGES OF
THE METRO PHOENIX AREA. EVAPORATIVE COOLING OF THE VIRGA COULD MAKE
FOR SOME VERY LOCALIZED AND SHORT LIVED GUSTINESS. LACK OF MOISTURE
ALSO KEEPS CAPE QUITE LIMITED BUT WITH THE FORCING...WARM BOUNDARY
LAYERS...AND SOME COOLING ALOFT...THERE IS A SLIGHT CHANCE OF
THUNDERSTORMS OVER THE AREA WHERE WE HAVE POPS. DURING THE DAY
FRIDAY AS THE LOW CENTER MOVES ACROSS...Q FORCING GOES AWAY BUT MID
LEVELS WILL BE COOLER AND MORE MOIST. MODELS DEPICT QPF TONIGHT AND
FRIDAY ONLY NIBBLING AT PORTIONS OF SOUTH-CENTRAL ARIZONA...MAINLY
SOUTHERN GILA COUNTY AND FAR NORTHERN MARICOPA COUNTY BUT OTHERWISE
STAYING NORTH OF OUR FORECAST AREA. LOCALLY BREEZY CONDITIONS CAN BE
EXPECTED FRIDAY NIGHT OVER SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA ON THE BACK SIDE OF THE DEPARTING SYSTEM. ANTICIPATE HIGH
TEMPS FRIDAY SLIGHTLY COOLER THAN TODAY...MORE NOTICEABLY OVER
SOUTH-CENTRAL ARIZONA.

SATURDAY AND SUNDAY...
A PACIFIC RIDGE BUILDS INTO WESTERN NORTH AMERICA SATURDAY FOR
SOMEWHAT WARMER TEMPERATURES. MEANWHILE...A DRY COOL FRONT WILL
SLIDE SOUTHWARD INTO NEW MEXICO AND PORTIONS OF ARIZONA LEADING TO
BREEZY TO WINDY CONDITIONS. ANTICIPATE LITTLE CHANGE IN TEMPERATURES
SUNDAY WITH PERHAPS SOME SUBTLE COOLING...MORE NOTICEABLY OVER THE
HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA. NOCTURNAL MIXING COULD KEEP
MIN TEMPS A BIT MORE MILD THAN THEY WOULD OTHERWISE BE.

MONDAY THROUGH THURSDAY...
THE RIDGE WEAKENS NEXT WEAK AS A TROUGH PASSES MAINLY TO THE NORTH.
THE ECWMF DIGS IT DEEPER INTO OUR AREA THAN THE GFS WHILE THE GEM
IS IN BETWEEN. THE GFS AGREES WELL WITH THE GEFS MEAN. TAKING A
CONSERVATIVE APPROACH...MADE ONLY MINOR DOWNWARD ADJUSTMENTS TO THE
TEMPS IN KEEPING WITH GFS SCENARIO. EVEN WITH THE MORE AGGRESSIVE
ECMWF SCENARIO WE WOULD STAY DRY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL... THE
PASSAGE OF A WEATHER DISTURBANCE WILL VEER SFC WINDS TO SWLY THIS
AFTERNOON...WITH PATCHY VIRGA ACCOMPANYING AN AC/AS DECK. WHILE
GENERAL SYNOPTIC WINDS WILL REMAIN AOB 10KT...LOCALIZED DOWNBURSTS
FROM EVAPORATION COOLING OF VIRGA WILL BE POSSIBLE THROUGHOUT CNTRL
ARIZONA THIS AFTERNOON. THIS MAY YIELD VERY ISOLATED INSTANCES OF
VARIABLE/SHIFTING 30KT WINDS...AND LOCALIZED WIND SHEAR DANGER TO
PILOTS SHOULD SUCH A DOWNBURST OCCUR NEAR A TERMINAL LOCATION.
OTHERWISE...CLOUD DECKS BETWEEN 12K-20K FT WILL BE COMMON THROUGH
TONIGHT...WITH A TENDENCY TOWARDS CLEARING AFTER SUNRISE FRIDAY.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
VARIABLE WINDS THIS AFTERNOON WILL BECOME PREDOMINANTLY WLY/NWLY BY
THIS EVENING WITH A WEAK FRONTAL PASSAGE...POTENTIALLY BECOMING
GUSTY FOR A BRIEF PERIOD AT KIPL. OTHERWISE...PERIODIC MID/HIGH
CLOUDS ABOVE 15K WILL GENERALLY CLEAR BY FRIDAY MORNING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
HIGH PRESSURE WILL BUILD EASTWARD INTO THE DESERT SOUTHWEST BRINGING
A WARMING TREND TO THE REGION INTO THE UPCOMING WEEKEND. BREEZY
CONDITIONS ARE EXPECTED ON SUNDAY AS A WEATHER SYSTEM SKIRTS BY JUST
TO THE EAST OF THE REGION. THE DRY CONDITIONS WILL PERSIST...BUT
EVEN DRIER AIR WILL SETTLE IN STARTING SATURDAY WITH MINIMUM
HUMIDITIES DROPPING INTO THE SINGLE DIGITS ACROSS THE LOWER DESERTS
SATURDAY THROUGH TUESDAY. NO MENTION OF PRECIPITATION CHANCES DURING
THIS TIME PERIOD.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...AJ
AVIATION...MO
FIRE WEATHER...CDEWEY