FXUS65 KPSR 260940
AFDPSR

AREA FORECAST DISCUSSION 
NATIONAL WEATHER SERVICE PHOENIX AZ
245 AM MST SCT DEC 26 2009

.SYNOPSIS...
DRY CONDITIONS AND BELOW NORMAL TEMPERATURES WILL CONTINUE THROUGH 
THE WEEKEND...BEFORE ANOTHER PACIFIC LOW PRESSURE SYSTEM APPROACHES 
THE AREA MONDAY. THIS NEXT SYSTEM WILL BRING A SLIGHT CHANCE OF 
SHOWERS TO MAINLY SOUTH-CENTRAL ARIZONA EARLY NEXT WEEK. A DRIER 
PATTERN WILL RETURN TO THE REGION LATE NEXT WEEK.
 
&&

.DISCUSSION...
TODAY AND SUNDAY...
CLEAR AND COLD NORTHWESTERLY FLOW ALOFT OF RECENT DAYS WILL 
TRANSITION INTO A MORE WESTERLY FLOW ALOFT LATER TODAY AND SUNDAY. 
INCREASING WESTERLY FLOW MARKS AN APPROACHING STORM TRACK. AS A 
RESULT...A SMALL UPPER LEVEL DISTURBANCE WILL RACE ACROSS THE AREA 
LATE TONIGHT/EARLY SUNDAY FOR INCREASING MID AND HIGH CLOUDS. THIS 
SLIGHTLY MORE HUMID AIRMASS ALOFT SHOULD LIFT SUNDAY MORNING MINIMUM 
TEMPERATURES A FEW DEGREES...AND OUT OF FREEZE WARNING CRITERIA FOR 
SOUTH CENTRAL DESERTS...INCLUDING PHOENIX AND VICINITY.

MONDAY AND TUESDAY...
THE STORM TRACK WILL SETTLE OVER THE REGION. ALL MEDIUM RANGE MODELS 
ARE IN AGREEMENT IN MOVING A PACIFIC DISTURBANCE INTO THE AREA 
MONDAY AND TUESDAY. ALTHOUGH MOST UPPER LEVEL DYNAMICS WILL REMAIN 
OVER NORTHWEST MEXICO...A VERY SATURATED MID/UPPER LEVEL AIRMASS 
WILL SPREAD WEST TO EAST ACROSS THE FORECAST AREA MONDAY AND 
TUESDAY. FORECAST SOUNDINGS INDICATE ENOUGH MOISTURE FOR POSSIBLE 
AREAS OF LIGHT SHOWERS.  THEREFORE WE WILL CONTINUE WITH A SLIGHT 
CHANCE OF SHOWERS AREA-WIDE MONDAY AND TUESDAY.

WEDNESDAY...
MODELS ARE IN DISAGREEMENT WITH A SECONDARY FOLLOW SHORTWAVE ACROSS 
CENTRAL AND EASTERN ARIZONA WEDNESDAY. NO SUCH FEATURE IS SEEN IN 
THE EUROPEAN MODEL. SINCE THE STORM TRACK IS OVER THE AREA...WE WILL 
OPT TO CONTINUE WITH A THREAT FOR SHOWERS OVER MOUNTAINOUS ZONE 24 
SOUTHERN GILA COUNTY ON WEDNESDAY.

THURSDAY THROUGH SATURDAY...
HIGH PRESSURE BUILDING OVER THE AREA WILL RESULT IN DRY WEATHER THIS 
PERIOD.

  &&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX AND KIWA...ANTICIPATE EASTERLY 
WINDS AROUND 15 KT JUST ABOVE THE SURFACE SAT MORNING NEAR 
KPHX...POSSIBLY MIXING DOWN TO THE SURFACE IN THE FORM OF 10 KT 
SUSTAINED WINDS AROUND 18Z...THEN BECOMING LIGHT AND VARIABLE AFTER 
21Z. OTHERWISE SKIES WILL BE CLEAR WITH INCREASING CIRRUS SATURDAY 
AFTERNOON.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. EXPECT LINGERING 
NORTHERLY WINDS DOWN THE LOWER COLORADO RIVER VALLEY UP TO 10 KTS... 
LIGHT AND VARIABLE ELSEWHERE. SKIES WILL BE CLEAR BEFORE THICK HIGH 
CLOUDS MOVE IN SATURDAY AFTERNOON.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. 

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
GENERALLY INCREASING RH THROUGH THE PERIOD. THERE WILL BE A SLIGHT
CHANCE OF SHOWERS ON MONDAY AND TUESDAY AS A PACIFIC LOW PRESSURE 
SYSTEM MOVES ONSHORE AND DRIFTS EAST. A CLEARING TREND WILL SWEEP 
FROM WEST TO EAST ON WEDNESDAY WITH A SLOW WARMING TREND BY 
THURSDAY.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FREEZE WARNING IN EFFECT UNTIL TO 10 AM THIS MORNING FOR 
     AZZ023 AND AZZ028. 

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...VASQUEZ
AVIATION...AJ
FIRE WEATHER...SIPPLE