Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 272156
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
255 PM MST SAT DEC 27 2014

.SYNOPSIS...
BELOW NORMAL TEMPERATURES ARE EXPECTED THIS WEEKEND AND EARLY NEXT
WEEK WITH OCCASIONAL HIGH CLOUDS. ANOTHER COLD AND POSSIBLY WET LOW
PRESSURE SYSTEM WILL MOVE INTO THE REGION BY MIDWEEK...WITH THE
POTENTIAL FOR DESERT RAIN AND MOUNTAIN SNOW. DRY BUT COOL WEATHER IS
EXPECTED TO RETURN BY NEXT WEEKEND.

&&

.DISCUSSION...
TAKING A CURRENT LOOK AT ARIZONA...TEMPERATURES ARE RANGING FROM 60F
IN YUMA TO 29F IN FLAGSTAFF AS OF 2150Z UNDER MOSTLY CLEAR SKIES
ASIDE FROM SOME SCATTERED CU ACROSS NAVAJO AND APACHE COUNTIES.
HEIGHTS ARE QUICKLY REBOUNDING AND ON THE RISE AS THE ELONGATED
TROUGH MOVES INTO WESTERN TEXAS TODAY...BUT ONLY FOR A FEW DAYS
BEFORE ANOTHER POSSIBLY MORE POTENT STORM SYSTEM MOVES
THROUGH...JUST IN TIME FOR THE END OF THE YEAR. IN THE SHORT
TERM...EXPECTING TO SEE ANOTHER ROUND OF COLD MORNING TEMPERATURES
ACROSS THE LOW LYING AREAS OF NORTHWEST PINAL COUNTY FOR SUNDAY AND
HAVE DECIDED TO KEEP A FREEZE WARNING FOR ONE MORE MORNING. OTHER
AREAS...JUST KEEPING A SPS TO HIGHLIGHT THE COLD AND NEAR FREEZING
TEMPERATURES.

LOOKING AHEAD INTO THIS WEEK...SEASONAL NORMAL HIGHS AND LOWS FOR
PHOENIX ARE 66F AND 44F RESPECTIVELY AND FOR YUMA 68F AND 46F
RESPECTIVELY. MENTION OF THIS TO KEEP IN MIND AS THE FORECAST
UNFOLDS THIS WEEK. MONDAY AND TUESDAY WILL BE PRETTY SEASONABLY
NORMAL BUT BY TUESDAY NIGHT SOME CHANGES WILL BE TAKING PLACE.
OPERATIONAL MODELS CONTINUE TO EVOLVE INTO BETTER AGREEMENT WITH A
VERY COLD UPPER LEVEL LOW PRESSURE SYSTEM MOVING SOUTH THROUGH THE
GREAT BASIN AND SWINGING OUT OVER THE PACIFIC JUST BEFORE PUSHING
BACK EAST ACROSS SOUTHEAST CALIFORNIA. BY THURSDAY THE MODELS BEGIN
TO DIFFER WITH HOW FAST THE SYSTEM WILL MOVE THROUGH...WITH THE GFS
TRENDING MORE PROGRESSIVELY AND THE ECMWF A BIT SLOWER. THIS WILL
PLAY A ROLE IN HOW MUCH PRECIP IS REALIZED AND WHERE...AND AT THIS
POINT IN THE FORECAST CONFIDENCE IS LOW TO MENTION ANY AMOUNTS.

ALL OF THIS TO SAY...ALONG WITH COLD AIR THERE WILL BE AN INCREASE
IN MOISTURE. SOUTHEAST CALIFORNIA WILL SEE THE FIRST WAVE OF COLD
AIR AND PRECIP CHANCES COME EARLY WEDNESDAY MORNING. 500HPA
TEMPERATURES BELOW -24C AND FALLING TIMED WITH THE BEST PRECIP
CHANCES ACROSS JOSHUA TREE AND EASTERN RIVERSIDE COUNTY WEDNESDAY
MORNING. SNOW LEVELS WILL DROP SUBSTANTIALLY AFTER 00Z
WEDNESDAY...DOWN TO 2200 FT BY 12Z WEDNESDAY...AND CONTINUE A
DOWNWARD HIKE BOTTOMING OUT BY THURSDAY MORNING. THE CORE OF COLD
AIR WILL MARCH EASTWARD BY LATE THURSDAY...700HPA TEMPS AT -10C OR
BELOW ACROSS LA PAZ...MARICOPA...AND INTO SOUTHERN GILA COUNTY. THE
THREAT FOR FREEZING TEMPERATURES AGAIN WILL BE IN PLACE.
HOWEVER...TIMING OF THE THICK CLOUD COVER AND ANY AMOUNT OF WIND MAY
HINDER THE CHANCES FOR TEMPERATURES TO GET BELOW FREEZING. THURSDAY
AND FRIDAY WILL SEE COLD DAYTIME TEMPERATURES...IN THE LOWER DESERTS
ONLY TOPPING OUT IN THE UPPER 40S AND LOW 50S.

WITH ALL OF THE MOISTURE IN THE LOWER ATMOSPHERE NEAR THE BOUNDARY
LAYER...THIS WILL BE AN UPSLOPE TYPE OF EVENT. EXTREMELY LITTLE TO
NO INSTABILITY TO WORK WITH AND POSITIVE LIFTED INDEX VALUES.
TERRAIN WILL PLAY A ROLE IN WHERE THE PRECIPITATION ACCUMULATES.
CLIMATOLOGICALLY SPEAKING...THIS SYSTEM IS NOT VERY ANOMALOUS AT ONE
TO TWO STANDARD DEVIATIONS BELOW NORMAL. BEING THIS TIME OF YEAR IS
OUR COLDEST...THIS SYSTEM IS NOT UNCOMMON. SNOW SHOWERS AND
RAIN-SNOW MIX WILL BE COMMON IN AREAS WHERE THE SNOW LEVELS DROP
SUBSTANTIALLY. LIGHT SNOW ACCUMULATION COULD BE SEEN AS LOW AS 2200
FEET ACROSS MARICOPA COUNTY...PLACING THIS IN THE NORTHWEST PORTION
OF THE COUNTY. OF COURSE AREAS OF HIGHER ELEVATION 3000 FT AND ABOVE
WHERE MARICOPA AND GILA COUNTY BORDER WILL BE LIKELY AS WELL.
ANALYZING THE MODELS TO SEE HOW THIS EVENT WILL UNFOLD WILL BE THE
CHALLENGE OVER THE NEXT FEW SHIFTS. ALL TO SAY...THE END OF 2014
SHOULD GO OUT WITH A POTENT STORM SYSTEM TO REMEMBER.

&&

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

CLEAR SKIES EXPECTED THROUGH THE EVENING ALTHOUGH HIGH CLOUDS WILL
BEGIN STREAMING IN FROM THE NORTH LATER TONIGHT. SHOULD BE OF LITTLE
IMPACT AVIATION-WISE. AS FOR WINDS...TYPICAL DIURNAL TRENDS EXPECTED
ALTHOUGH BLH WILL LIKELY STAY BREEZY UNTIL APPROX 00-02Z AROUND
SUNSET.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
DRY AND ABNORMALLY COOL WEATHER WILL PREVAIL MONDAY...WITH LIGHT
WINDS AND PERIODS OF HIGH CLOUDS. TUESDAY...ANOTHER STRONG LOW
PRESSURE SYSTEM QUICKLY DROPS SOUTH OUT OF CANADA AND CARVES OUT A
LARGE COLD TROUGH OVER THE WESTERN UNITED STATES...INCREASING THE
POTENTIAL FOR STRONGER WINDS ACROSS SOUTHEAST CALIFORNIA AND THE
LOWER COLORADO RIVER VALLEY...BUT ALSO THE CHANCES FOR MOUNTAIN SNOW
AND VALLEY RAIN SHOWERS TO AFFECT THE DISTRICTS INTO FRIDAY NEXT
WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 9 AM MST SUNDAY AZZ028.

CA...NONE.

&&

$$

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

DISCUSSION...DEWEY
AVIATION...LEINS
FIRE WEATHER...MEYERS








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