Weather Service Report


301 
FXUS65 KPSR 270403
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
903 PM MST FRI DEC 26 2014

.SYNOPSIS...
EXPECT CLEAR SKIES AND COLD TEMPERATURES TONIGHT AND THROUGH THE 
WEEKEND. NEAR NORMAL TEMPERATURES WILL START THE WEEK OFF. ANOTHER 
LOW PRESSURE SYSTEM IS EXPECTED TO MOVE INTO THE REGION NEXT 
WEDNESDAY AND THURSDAY...WITH A SLIGHT CHANCE OF SHOWERS.

&&

.DISCUSSION...
THIS EVENING STARTED OFF RATHER CHILLY WITH HIGHS THIS AFTERNOON NOT 
MAKING IT OUT OF THE 50S ACROSS THE LOWER DESERTS. TEMPERATURES HAVE 
COOLED OFF FAIRLY QUICKLY ALREADY WITH SOME LOCATIONS ACROSS THE 
SOUTH-CENTRAL ARIZONA DESERTS DIPPING INTO THE UPPER 30S. THE 
CURRENT FORECAST CALLING FOR FREEZING TEMPERATURES TONIGHT LOOKS TO 
BE ON TRACK. WOULD NOT BE SURPRISED IF SOME LOCATIONS END UP 
BOTTOMING IN THE MIDDLE 20S...BUT IN GENERAL LOWS IN THE UPPER 20S 
AND LOWER 30S WILL BE MOST COMMON. THE CLEAR SKIES...SURFACE DEW 
POINTS IN THE TEENS AND 20S...AND ALREADY LIGHT TO CALM WINDS WILL 
ALLOW FOR VERY EFFICIENT RADIATIONAL COOLING OVERNIGHT. A GRADUAL 
IMPROVEMENT IN TEMPERATURES IS EXPECTED THIS WEEKEND AS THICKNESSES 
QUICKLY RECOVER...BUT SATURDAY NIGHT SHOULD END UP RATHER CHILLY 
WITH SOME LOCATIONS AGAIN SEEING FREEZING TEMPERATURES. 

&&

.PREVIOUS DISCUSSION...
MOSTLY CLEAR SKIES HAVE PREVAILED ACROSS SOUTHEAST CALIFORNIA AND
SOUTH-CENTRAL ARIZONA TODAY...AS CLOUDS COVER THE NORTHEAST CORNER
AND SOUTHEAST CORNER OF THE STATE. THE STRONG COLD LOW PRESSURE
SYSTEM IS MOVING THROUGH THE FOUR CORNERS AREA TODAY BRINGING SNOW TO
MUCH OF SOUTHERN COLORADO AND NORTHERN NEW MEXICO AMONG OTHER
LOCATIONS. OVERCOME WITH COLD AIR...MANY LOCATIONS ACROSS THE CENTRAL
DESERTS SAW TEMPERATURES IN THE LOW 30S AND SOME AREAS HAD READINGS
IN THE UPPER 20S. THE COLD SYSTEM WILL PROGRESS SLOWLY EASTWARD
LEAVING BEHIND COLD AIR FOR ANOTHER MORNING OR TWO. LOW
DEWPOINTS...CLEAR SKIES AND MOSTLY LIGHT WINDS WILL ALLOW THE
TEMPERATURE TO DROP A HANDFUL MORE DEGREES FOR SATURDAY MORNING. MANY
LOCATIONS WILL REACH OR DIP JUST BELOW FREEZING AND AS SUCH A FREEZE
WARNING IS IN EFFECT FOR SATURDAY MORNING. SUNDAY WILL SEE
TEMPERATURES RISE JUST A FEW DEGREES AND SAME THING MONDAY...AS THE
PATTERN TURNS TO A NORTHERLY FLOW AHEAD OF THE NEXT STRONG LOW
PRESSURE SYSTEM.

EARLY IN THE WEEK HIGH CLOUDS WILL STREAM IN AS TEMPERATURES REMAIN
BELOW SEASONAL NORMAL (NORMAL HIGH TEMPS FOR PHOENIX 65...YUMA 67
DEGREES). OPERATIONAL MODELS HAVE COME INTO BETTER AGREEMENT...GFS
AND ECMWF...ABOUT THE MIDWEEK STORM SYSTEM TIMING AND LOCATION. A
COLD CANADIAN LOW WILL DROP DOWN THROUGH THE GREAT BASIN AND SLIGHTLY
RETROGRADE OVER THE SOUTHERN CALIFORNIA COAST...ADDING SOME MOISTURE
INTO THE MIX. MODELS DEPICT ANY CHANCES FOR PRECIPITATION TO BE
INTRODUCED TUESDAY EVENING OR EARLY WEDNESDAY MORNING. WITH THE
STRONG HEIGHT FALLS AND TIGHT PRESSURE GRADIENT...SIMILAR COLD 
TEMPERATURES...TO WHAT WE SEE THIS WEEKEND...ALOFT (500HPA AND 
700HPA) ARE FORECAST BY LATE NEXT WEEK.

CONTINUING TO WATCH HOW THIS SYSTEM EVOLVES OVER THE NEXT MODEL RUNS.
WITH A DIVERSE SYSTEM INCLUDING VERY COLD AIR AND MOISTURE...TIMING
FOR SNOWFALL AND RAINFALL AS WELL AS ANOTHER ROUND OF NEAR FREEZING
TEMPERATURES IS ON TAP FOR THE END OF THE YEAR. SNOW LEVELS MAY DROP
LOW ENOUGH TO ALLOW SNOW ACCUMULATION IN PORTIONS OF SOUTHEAST
CALIFORNIA (JOSHUA TREE NATIONAL PARK). AT THIS TIME IT IS DIFFICULT
TO PIN POINT ANYTHING SOLID...THUS KEEPING THE SLIGHT CHANCE MENTION
OF SHOWERS IN THE FORECAST. 


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

CLEAR OR MOSTLY CLEAR SKIES ARE FORECAST AT ALL SITES THROUGH AT 
LEAST SATURDAY EVENING. WINDS WILL BE LIGHT AND FAVOR TYPICAL 
DIURNAL TRENDS...ALTHOUGH SOME EARLY MORNING BREEZINESS IS POSSIBLE 
DOWN THE COLORADO RIVER VALLEY AT BLH AFTER 12Z SATURDAY. 

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER... 
SUNDAY THROUGH THURSDAY... 
DRY AND ABNORMALLY COOL WEATHER WILL PREVAIL SUNDAY AND MONDAY... 
WITH GENERALLY LIGHT WINDS AND PERIODS OF HIGH CLOUDS. BY 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 AFFECTING THE 
DISTRICTS THROUGH THE MIDDLE OF NEXT WEEK. 

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FREEZE WARNING FROM MIDNIGHT TONIGHT TO 8 AM MST SATURDAY 
     AZZ021>023-026>028.

CA...NONE.

&&

$$

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






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