Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 172012
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
115 PM MST WED DEC 17 2014

&&

.SYNOPSIS...
THE LAST TWO IN A SERIES OF FAST MOVING WEATHER SYSTEMS MOVING
THROUGH THE WESTERN STATES WILL KEEP PRECIPITATION CHANCES ELEVATED
THROUGH THURSDAY. THE BEST CHANCES FOR SHOWERS ARE EXPECTED THIS
EVENING...AND AGAIN DURING THE DAY ON THURSDAY...MAINLY ACROSS
SOUTHWEST AND SOUTH-CENTRAL ARIZONA. DRY WEATHER IS EXPECTED TO
RETURN BY THE END OF THE WEEK...WITH A GRADUAL WARMING TREND
ANTICIPATED FROM THE WEEKEND ONWARD INTO THE MIDDLE OF NEXT
WEEK...BEFORE A POSSIBLE CHANGE TO MUCH COLDER WEATHER BY THE END OF
NEXT WEEK.

&&

.DISCUSSION...
TONIGHT THROUGH THURSDAY...

AFTER A WET EARLY MORNING ACROSS SOUTH-CENTRAL ARIZONA...WHICH SAW
RAINFALL AMOUNTS RANGING FROM AROUND 0.05 INCH TO AS MUCH AS 0.25
INCH...ANOTHER AREA OF SHOWERS IS NOW PROGRESSING EASTWARD AT THIS
TIME ACROSS SOUTHWEST AND SOUTH-CENTRAL AZ...AS ANOTHER IN A SERIES
OF WEAK...BUT RATHER MOIST SHORTWAVES MOVES ACROSS OUR CWA. IT NOW
APPEARS THAT THE SHOWERS...WHICH ARE NOW MOVING INTO THE WESTERN
PORTION OF THE GREATER PHOENIX AREA...WILL CONTINUE THROUGH THE
EVENING HOURS BEFORE TAPERING OFF LATE TONIGHT AS THE UPPER TROF
MOVES OFF TO THE EAST. DUE TO THE PROGRESSIVE NATURE OF THIS SYSTEM
AND THE LACK OF ANY GOOD FORCING...RAINFALL AMOUNTS ARE EXPECTED TO
REMAIN ON THE LIGHT SIDE...RANGING FROM AROUND 0.10 OF A INCH ACROSS
THE PHOENIX AREA UP TO 0.25 OF AN INCH ACROSS THE HIGHER TERRAIN OF
SOUTHERN GILA COUNTY. ONCE AGAIN...SNOWFALL...IF ANY...IS EXPECTED
TO BE MAINLY CONFINED TO ELEVATIONS ABOVE 6000FT...WITH MAYBE A
DUSTING AT MOST ON THE HIGHEST PEAKS. THE COMBINATION OF A MOIST
BOUNDARY LAYER...LIGHT WINDS...AND PERHAPS SOME CLEARING LATER
TONIGHT COULD ALSO ALLOW AREAS OF FOG TO FORM AS WELL.

THURSDAY WILL LIKELY SEE ONE LAST SHOT OF LIGHT RAINFALL AS THE
FINAL SHORTWAVE IN THE SERIES...WHICH EARLIER HAD BEEN EXPECTED TO
TRACK WELL TO OUR SOUTH ACROSS MEXICO...MOVES ACROSS SOUTH-CENTRAL
ARIZONA. RAINFALL AMOUNTS WITH THIS SHORTWAVE ARE EXPECTED TO REMAIN
QUITE LIGHT...RANGING FROM A FEW HUNDREDTHS OF AN INCH ACROSS THE
PHOENIX AREA UP TO AROUND 0.10 OF AN INCH OVER THE HIGHER TERRAIN
NORTH AND EAST OF PHOENIX. THE CLOUDS AND RAINFALL WILL LIKELY ONCE
AGAIN KEEP HIGH TEMPERATURES SLIGHTLY BELOW NORMAL ON
THURSDAY...MAINLY IN THE LOW TO MID 60S ACROSS THE LOWER DESERTS.

FRIDAY THROUGH WEDNESDAY...
DRY WEATHER IS FORECAST TO RETURN BY FRIDAY...THEN CONTINUE INTO AT
LEAST THE MIDDLE PART OF NEXT WEEK AS RIDGING BUILDS BACK EASTWARD
OVER THE REGION. ALTHOUGH LATEST MODEL RUNS CONTINUE TO BRING
ANOTHER WEAK SHORTWAVE ACROSS OUR CWA FRIDAY NIGHT AND
SATURDAY...THEY CONTINUE TO KEEP IT COMPLETELY DRY...WITH JUST AN
INCREASE IN CLOUDINESS ASSOCIATED WITH IT. AS FAR AS TEMPERATURES
ARE CONCERNED...AFTER HIGHS IN THE LOW TO MID 60S FROM FRIDAY INTO
SUNDAY...THEY ARE EXPECTED TO RISE INTO THE LOW TO MID 70S BY
TUESDAY AND WEDNESDAY OF NEXT WEEK AS HIGH PRESSURE RIDGING ALOFT
STRENGTHENS OVER THE DESERT SOUTHWEST. AS FAR AS THE FORECAST FOR
THE END OF NEXT WEEK...EVEN THOUGH IT IS STILL WELL OUT IN THE
EXTENDED PERIOD...MODEL CONSENSUS IS BUILDING TOWARD THE IDEA OF A
CHANGE TO MUCH COLDER WEATHER...AS THE EURO AND GFS NOW BOTH DIG A
VERY DEEP...AND COLD LOW-WAVE TROF SOUTHWARD INTO THE WESTERN STATES
DURING THIS PERIOD.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
THE NEXT ROUND OF SHOWERS TO IMPACT THE PHOENIX AREA TAF SITES
SHOULD ARRIVE BETWEEN 21Z AND 02Z. WINDS SHOULD NOT BE MUCH OF A
HAZARD...WITH MOSTLY LIGHT WIND SPEEDS AT OR BELOW 10 KTS...HOWEVER
CIGS WILL BE THE MAIN CAUSE FOR CONCERN. EXPECTING MOSTLY 5K FEET
CIGS AND VISIBILITY DUE TO RAIN/MIST TO STAY 6 TO 8 MILES DURING THE
EVENING RUSH HOURS AT THE TAF SITES...NOT TO RULE OUT 2K CIGS AT
KSDL AND KIWA ALONG THE HIGHER TERRAIN. IN THE MOUNTAINS EAST OF
PHOENIX 6K TO 10K FEET CLOUD DECKS ARE EXPECTED ON APPROACH TO KPHX.
EXPECT CIGS AND VISIBILITY TO IMPROVE GREATLY AFTER 05Z THURSDAY
BEFORE THE NEXT ROUND OF SHOWERS IS EXPECTED ACROSS THE CENTRAL
PHOENIX AIR FIELDS 15Z THROUGH 21Z.

ONE LAST NOTE...CANNOT COMPLETELY RULE OUT THE POSSIBILITY OF
THUNDER AT SOME POINT TODAY...BUT ANY STORMS THAT FORM WILL MOST
LIKELY STAY SOUTH OF OUR AREA AND NOT AFFECT THE TAF SITES.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA...INCLUDING KIPL/KBLH...
UNSETTLED CONDITIONS WILL PERSIST ACROSS THE WESTERN DESERTS
TONIGHT. CIGS MAY DROP NEAR OR BELOW 4K FEET AT TIMES AT BOTH TAF
SITES AND MAYBE DOWN NEAR 3K FEET AT DUE TO FOG/MIST. COULD SEE
BRIEF DROP IN VSBYS BELOW 5SM IN FOG/MIST THIS EVENING OR EARLY
THURSDAY MORNING. EXPECTING CLEARING FROM THE WEST THURSDAY
MORNING...AS THE LAST CHANCE FOR SHOWERS ENDS. NO WIND ISSUES NEXT
24 HOURS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
THE WET WEATHER PATTERN EXPERIENCED DURING THE MIDDLE OF THE WEEK
WILL CHANGE TO A WARMER AND DRIER PATTERN AS DRIER NORTHWEST FLOW
ALOFT STARTS TO BUILD INTO THE AREA FROM THE WEST STARTING ON
FRIDAY. A WEAK WEATHER DISTURBANCE PASSES ACROSS THE AREA FROM THE
NORTHWEST SATURDAY BUT BRINGS LITTLE IF ANY CHANCE FOR RAIN. SUNDAY
INTO THE MIDDLE OF NEXT WEEK A LARGE AREA OF HIGH PRESSURE BUILDS
INTO THE DESERT SOUTHWEST LEADING TO GRADUALLY DRIER AND WARMER
CONDITIONS. EXPECT HIGH TEMPERATURES NEAR NORMAL THROUGH SATURDAY...
WITH WARMING STARTING ON SUNDAY AND CONTINUING THROUGH TUESDAY. BY
NEXT TUESDAY...HIGH TEMPERATURES WILL REACH INTO THE LOW TO MIDDLE
70S OVER THE WARMER LOWER DESERTS. MINIMUM HUMIDITY VALUES WILL STAY
ELEVATED THROUGH THE 5 DAY PERIOD...BUT WILL GRADUALLY LOWER DAY TO
DAY AS BOTH DRIER AIR WORKS IN FROM THE WEST AND TEMPERATURES CLIMB.
DESPITE THE DRYING MINIMUM RH VALUES WILL RANGE MOSTLY BETWEEN 20
AND 30 PERCENT NEXT MONDAY AND TUESDAY. WINDS WILL NOT BE AN ISSUE
DURING THE PERIOD...REMAINING ON THE LIGHT SIDE AND FOLLOWING NORMAL
DIURNAL PATTERNS EACH DAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...PERCHA
AVIATION...DEWEY
FIRE WEATHER...CB




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