Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 181238
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
538 AM MST THU DEC 18 2014

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS...

&&

.SYNOPSIS...
A FAST MOVING TROUGH WILL SWEEP THROUGH THE AREA TODAY...ONCE AGAIN
BRINGING A CHANCE OF SHOWERS TO THE REGION. DRY WEATHER WILL RETURN
ON FRIDAY AND A GRADUAL WARMING TREND WILL COMMENCE THROUGH THE
WEEKEND. DRY WEATHER WITH ABOVE NORMAL TEMPERATURES ARE EXPECTED
THROUGH NEXT WEEK...BEFORE A POSSIBLE CHANGE TO MUCH COLDER WEATHER
BY NEXT FRIDAY.

&&

.DISCUSSION...
SHORTWAVE TROUGH IS EVIDENT ON WATER VAPOR IMAGERY OVER SOUTHEAST
CALIFORNIA THIS MORNING AS OF 08Z...YET REGIONAL RADAR MOSAIC
SUGGESTS ONLY INDICATES VERY WIDELY SCATTERED SHOWERS ACROSS THE
AREA. STARTING TO SEE SOME MODEST CLOUD TOP COOLING ON IR SATELLITE
IMAGERY...MEANWHILE SURFACE OBS ACROSS THE REGION ARE BEGINNING TO
SHOW LOWERING CEILINGS. NEARLY ALL SITES ACROSS THE PHOENIX METRO
HAVE SEEN CLOUDS THICKEN UP QUITE A BIT SINCE LATE WEDNESDAY
EVENING. MEANWHILE DEWPOINTS REMAIN SOMEWHAT ELEVATED IN THE MID 40S.

THE FORECAST FOR TODAY REMAINS ON TRACK...THE LOW WILL MOVE THROUGH
THE AREA THIS MORNING WITH SHOWERS BECOMING MORE WIDESPREAD AROUND
12Z. DESPITE THE INCREASE IN COVERAGE...AMOUNTS WILL BE
LIGHT...GENERALLY A FEW HUNDREDTHS TO A TENTH OF AN INCH. PRECIP
WILL SHIFT INTO THE MOUNTAINS NORTH/EAST OF PHOENIX THIS AFTERNOON
AND THERE COULD BE A FEW WRAP-AROUND SHOWERS LATER THIS AFTERNOON IF
SKIES CLEAR AND THE ATMOSPHERE DESTABILIZES. LOCAL WRF ENSEMBLE AND
SPC SSEO SUGGEST AFTERNOON SHOWERS WOULD BE CONFINED MORE TO THE
HIGHER TERRAIN NORTH/EAST OF PHOENIX AND THIS MATCHES THE INHERITED
FORECAST CLOSELY.

NORTHWESTERLY FLOW BEHIND THE DEPARTING TROUGH WILL COMMENCE ON
FRIDAY ALTHOUGH A FEW VERY WEAK SHORTWAVES ARE EXPECTED WITHIN THE
FLOW. SHOULD HAVE A NEGLIGIBLE IMPACT ON OUR WEATHER THIS WEEKEND
ALTHOUGH VARYING AMOUNTS OF HIGH CLOUDS ARE EXPECTED. NORTHWESTERLY
FLOW WILL GRADUALLY GIVE WAY TO STRONG 500MB RIDGING ON MONDAY WHICH
WILL ALLOW THE REAL WARM-UP TO BEGIN. TEMPS SHOULD EASILY CLIMB INTO
THE LOWER 70S FOR MUCH OF THE UPCOMING WEEK ALONG WITH NIL CHANCES
OF PRECIPITATION.

LOOKING JUST BEYOND THE FORECAST PERIOD TO NEXT FRIDAY...THERE ARE
SOME PRETTY NOTEWORTHY DIFFERENCES BETWEEN THE GFS AND THE EUROPEAN
MODELS. WHILE BOTH MODELS INDICATE TROUGHING OVER THE WEST...THE GFS
IS MUCH MORE PROGRESSIVE WHEREAS THE EUROPEAN BRINGS A CLOSED
CIRCULATION OVER ARIZONA WITH SUBSTANTIALLY COLDER TEMPERATURES OVER
THE REGION. CONSEQUENTLY PRECIP CHANCES ARE MUCH HIGHER COURTESY OF
THE EUROPEAN. ENSEMBLE GUIDANCE SUGGESTS A MIDDLE OF THE ROAD
APPROACH...NOT AS PROGRESSIVE AS THE GFS BUT NOT NEARLY AS DEEP AS
THE EUROPEAN. WILL SORT OUT THE DETAILS AS WE GET CLOSER TO THE END
OF NEXT WEEK BUT THIS WILL CERTAINLY WARRANT WATCHING.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...

A WEAK TROUGH WILL MOVE THROUGH THIS MORNING BRINGING ISOLATED TO
SCATTERED LIGHT SHOWERS THROUGH AROUND NOON WITH THE MAJORITY OF THE
SHOWERS CONFINED ACROSS HIGHER TERRAIN AREAS NORTH OF PHOENIX. CIGS
FOR THE MOST PART WILL BE IN THE LOW VFR RANGE THIS MORNING...BUT A
FEW BRIEF PERIODS OF MVFR CIGS ARE POSSIBLE...ESPECIALLY IF
ANY SHOWERS MOVE OVERHEAD. WILL BEGIN TO SEE BREAKS IN THE CLOUDS BY
LATE MORNING AND CLOUD DECKS SHOULD MAINLY BE SCATTERED STARTING
THIS AFTERNOON. WINDS WILL REMAIN LIGHT AND GENERALLY FOLLOW TYPICAL
DIURNAL PATTERNS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA...INCLUDING KIPL AND
KBLH...
CLEARING SKIES WILL OCCUR FROM WEST TO EAST THIS MORNING WITH CLEAR
TO MOSTLY CLEAR SKIES DOMINATING AFTER 18Z. WINDS WILL REMAIN LIGHT
THROUGH THE PERIOD.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
UPPER LEVEL RIDGING WILL TAKE OVER STARTING LATE SATURDAY WITH
WARMING TEMPERATURES AND SLIGHTLY DRIER CONDITIONS. HIGHS WILL WARM
TO ABOVE NORMAL STARTING SUNDAY WITH LOWER DESERT HIGHS IN THE LOW
TO MID 70S FOR LATE IN THE PERIOD. HUMIDITIES WILL REMAIN FAIRLY
HIGH THROUGH THE PERIOD WITH MINIMUM VALUES STAYING ABOVE 25
PERCENT. WINDS WILL REMAIN LIGHT FOR THE MOST PART WITH THE
EXCEPTION OF OCCASIONAL AFTERNOON BREEZINESS MAINLY CONFINED TO
SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA SUNDAY THROUGH TUESDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...LEINS
AVIATION...KUHLMAN
FIRE WEATHER...KUHLMAN








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