FXUS65 KPSR 231730
AFDPSR

AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE PHOENIX AZ
1030 AM MST WED DEC 23 2009

.UPDATE...UPDATED AVIATION DISCUSSION...

&&

.SYNOPSIS...
THE LOW PRESSURE SYSTEM OVER EASTERN ARIZONA WILL CONTINUE TO MOVE 
EAST TODAY...WITH SHOWERS ENDING OVER THE MOUNTAINS OF SOUTH CENTRAL 
ARIZONA. CLEAR SKIES ARE EXPECTED ELSEWHERE ACROSS SOUTHEAST 
CALIFORNIA AND SOUTHWEST ARIZONA TODAY. A HIGH PRESSURE SYSTEM WILL 
SLOWLY BUILD INTO THE REGION FOR SUNNY SKIES THURSDAY AND CHRISTMAS 
DAY. DRY WEATHER WILL CONTINUE THIS WEEKEND...HOWEVER ANOTHER PACIFIC
COLD FRONT IS EXPECTED MONDAY...WITH INCREASING CLOUDS AND A SLIGHT 
CHANCE OF SHOWERS TO MOST AREAS. 

&&

.DISCUSSION...
THE COLD LOW PRESSURE SYSTEM OVER EASTERN ARIZONA THIS MORNING WILL 
MOVE QUICKLY EAST INTO NEW MEXICO BY AFTERNOON. SOME WRAP AROUND 
CLOUDS AND SNOW FLURRIES WERE NOTED OVER THE MOUNTAINS OF SOUTHERN 
GILA COUNTY THIS MORNING...BUT SHOULD QUICKLY BE ENDING BY NOON. THE 
WINTER WEATHER ADVISORY FOR SOUTHERN GILA COUNTY EXPIRED AT 9 AM 
LOCAL TIME. 

OTHERWISE...CLEARING SKIES AND DRY WEATHER WILL SPREAD ACROSS THE 
ENTIRE FORECAST AREA BY AFTERNOON. DRY NORTHWEST FLOW ALOFT...
WITH BELOW NORMAL TEMPERATURES ARE EXPECTED THURSDAY AND CHRISTMAS 
DAY.

CURRENT FORECASTS LOOK OK. SOME MINOR MORNING UPDATES WERE MADE
TO ACCOUNT FOR CLEARING TRENDS IN SOUTH CENTRAL AZ BY AFTERNOON. NO 
ADDITIONAL UPDATES ARE EXPECTED.  PORTIONS OF PREVIOUS DISCUSSION 
BELOW STILL APPLIES.

PORTIONS OF PREVIOUS DISCUSSION...
COLD OVERNIGHT LOWS WILL BE THE NEXT CONCERN FOR THE REMAINDER OF 
THE WEEK. GFS/NAM BOTH SHOW THE COLD CORE LOW THRU NEW MEXICO BY 
24/06Z WITH A GOOD CLEARING TREND CONTINUING. H5 HEIGHTS RISE 
GRADUALLY THROUGH CHRISTMAS EVE AS A DRIER AIRMASS WILL TAKES OVER. 
LATEST MEX GUIDANCE IS SIMILAR TO OLDER DATA...AND THE OVERNIGHT 
LOWS ARE LIKELY TO DROP OFF INTO THE UPPER 20S IN THE COLDER VALLEY 
LOCATIONS FOR CHRISTMAS MORNING AND SATURDAY MORNING. FREEZE WARNING 
MAY BE NEEDED AS THIS WILL BE THE COLDEST PERIOD SO FAR THIS SEASON 
FOR THE VALLEY OF THE SUN.

ECMWF/GFS GENERALLY AGREE ON THE STRENGTH AND LOCATION OF UPPER 
RIDGE THIS WEEKEND...AND THE LOCATION OF THE DEVELOPING UPPER LOW 
THAT FORMS IN THE EASTERN PACIFIC LATE SUNDAY. WILL GO ALONG WITH A 
MORE PROGRESSIVE SOLUTION AND INCREASE THE CHANCES OF PRECIP BY 
ABOUT MONDAY. STILL TOO EARLY TO SAY WHAT PRECIP AMOUNTS THIS ONE 
WILL BRING US...AND LATER SHIFTS WILL BETTER DEFINE COVERAGE OF THE 
SHOWERS AS WELL AS AMOUNTS.
 
&&

.AVIATION...
THE MID-LEVEL CENTER OF CIRCULATION...CURRENTLY POSITIONED OVER 
CENTRAL NEW MEXICO...WILL CONTINUE ITS EASTWARD MIGRATION. THUS THE 
CLEARING TREND WILL CONTINUE THROUGH TODAY FROM WEST TO EAST AS HIGH 
PRESSURE SLOWLY BUILDS OVER THE REGION. SKIES ARE ALREADY CLEAR OVER 
THE WESTERN TAF SITES...KIPL/KBLH...WITH CLEARING OVER KPHX/KIWA 
ANTICIPATED BY LATE THIS AFTERNOON. WINDS COULD BE GUSTY OUT OF THE 
NORTHWEST TODAY AT ALL SITES...ESPECIALLY KBLH...BUT NOT AS STRONG 
AS YESTERDAY. WINDS WILL BECOME LIGHT AND CONFORM TO MORE TYPICAL 
DIURNAL PATTERNS GENERALLY AFTER 06Z THURSDAY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. 

&&

.FIRE WEATHER...
FRIDAY THROUGH TUESDAY...
MUCH LOWER HUMIDITY SPREADING ACROSS THE REGION FROM THE NORTH. 
OTHERWISE DRY WEATHER WITH BELOW NORMAL TEMPERATURES THROUGH THE 
WEEKEND. RH WILL INCREASE EARLY NEXT WEEK AS LOW PRESSURE APPROACHES 
THE REGION FROM THE WEST.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...VASQUEZ/SIPPLE
AVIATION...PADDOCK
FIRE WEATHER...LEINS