Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 280343
AFDPSR

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

.SYNOPSIS...
BELOW NORMAL TEMPERATURES ARE EXPECTED THROUGH THE REST OF 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.

&&

ANOTHER CHILLY NIGHT IS ON TAP ACROSS THE REGION...BUT NOT QUITE
LIKE THE LOWS SEEN FROM LAST NIGHT. AN UPPER LEVEL RIDGE IS QUICKLY
PUSHING SOUTHEASTWARD INTO ARIZONA FROM THE GREAT BASIN ALLOWING FOR
INCREASING THICKNESSES AND IS EXPECTED TO BRING IN SOME SCATTERED
HIGH CLOUDS LATE TONIGHT. CURRENT TEMPERATURES ARE RUNNING A COUPLE
DEGREES WARMER COMPARED TO THIS TIME YESTERDAY...AND WHEN
CONSIDERING THE DECENT POTENTIAL FOR HIGH CLOUDS MOVING IN FROM THE
NORTH AFTER MIDNIGHT...LOWS TONIGHT SHOULD GENERALLY END UP IN THE
LOWER TO MIDDLE 30S. THE COLDEST SPOTS...LIKELY ACROSS NORTHERN
PINAL COUNTY...SHOULD AGAIN DIP BELOW 30 DEGREES FOR SEVERAL HOURS
WHICH PROMPTED ANOTHER FREEZE WARNING. NO APPRECIABLE CHANGES WERE
NEEDED TO THE CURRENT FORECAST.

&&

.PREVIOUS DISCUSSION...
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 REST OF THE EVENING...WHILE HIGH
CLOUDS WILL BEGIN STREAMING IN FROM THE NORTH LATER TONIGHT WITH
SKIES BECOMING BROKEN AT 18-20K FEET BY LATE SUNDAY MORNING. WINDS
WILL REMAIN LIGHT...LESS THAN 10 KTS...THROUGH SUNDAY AND FOLLOW
TYPICAL DIURNAL DIRECTIONS.

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...KUHLMAN
PREVIOUS DISCUSSION...DEWEY
AVIATION...KUHLMAN
FIRE WEATHER...MEYERS










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