PHXAFDPSR (10/08/08 0402)


FXUS65 KPSR 081055
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
345 AM MST WED OCT 8 2008

SOUTH-CENTRAL AND SOUTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA 
FORECAST DISCUSSION

.SYNOPSIS...
HIGH PRESSURE WILL RESULT IN SUNNY SKIES AND WARM WEATHER TODAY. A 
STRONG LOW PRESSURE SYSTEM WILL MOVE ACROSS THE WESTERN UNITED 
STATES THURSDAY THROUGH SATURDAY. EXPECT LOCALLY BREEZY CONDITIONS 
THURSDAY AFTERNOON...AND BREEZY TO WINDY WEATHER FRIDAY AND SATURDAY 
ACROSS THE REGION. TEMPERATURES WILL COOL SIGNIFICANTLY OVER THE 
WEEKEND AND WILL BE WELL BELOW AVERAGE FOR EARLY OCTOBER BY SUNDAY. 
HIGH PRESSURE WILL REBUILD EARLY NEXT WEEK FOR A GRADUAL WARMING 
TREND. 

&&

.DISCUSSION...
IR SATELLITE IMAGERY REVEALS CLEAR SKIES OVER THE STATE AT THIS 
HOUR...SOME HIGH LEVEL CLOUDS STREAMING ACROSS THE NORTHERN TIER OF 
THE CONUS IN A PROGRESSIVE ZONAL FLOW...SUGGESTING THAT THE RIDGE OF 
HIGH PRESSURE THAT HAS BEEN OVER THE SOUTHWEST IS BEGINNING TO 
WEAKEN-FLATTEN-ERODE. THE RIDGE AXIS SHIFTS EASTWARD TODAY IN 
ADVANCE OF A STRONG PACIFIC LOW PRESSURE SYSTEM AND TROF PROGGED TO 
MOVE INTO-THROUGH THE GREAT BASIN LATE THURSDAY AND FRIDAY...AND  
EVENTUALLY DEEPEN AND CENTER OVER SOUTHERN NV AND NORTHWEST AZ 
SATURDAY. 

FOR TODAY...AS HEIGHTS BEGIN TO DROP...THICKNESSES SHOW LITTLE 
CHANGE AND 850 MB TEMPERATURES STAY WARM...SO EXPECT MAX TEMPS WILL 
ONCE AGAIN BE IN THE UPPER 90S TO NEAR 100 DEGREES AT MOST DESERT 
LOCALES. A COOLING TREND BEGINS THURSDAY AS HEIGHTS CONTINUE TO 
FALL...AND SOUTHWEST WINDS ARE EXPECTED TO INCREASE AS THE GRADIENT 
TIGHTENS. MODELS ARE IN GOOD AGREEMENT THAT THE STRONG CLOSED LOW 
WILL PUSH SOUTH THROUGH NEVADA FRIDAY...AND THAT THE CONTINENTAL 
TRAJECTORY WILL LIMIT MOISTURE AVAILABILITY...KEEPING THE SYSTEM DRY 
FOR SOUTHEAST CALIFORNIA AND SOUTH-CENTRAL ARIZONA.

THE CURRENT GFS AND THE ECMWF TRACK HURRICANE NORBERT TO MOVE NORTH 
AND CROSS OVER THE SOUTHERN BAJA PENINSULA SATURDAY. THE HURRICANE 
QUICKLY WEAKENS AS MOISTURE IS SHEARED OFF AND TRANSPORTED TO THE NE 
INTO THE GREAT PLAINS AHEAD OF THE STRONG LOW/TROF MOVING THROUGH 
THE WESTERN CONUS. SO...ANY MOISTURE THAT MAKES ITS WAY INTO EASTERN 
PORTIONS OF ARIZONA AHEAD OF THE TROF WILL BE LIMITED AND CONFINED 
TO OUR FAR EASTERN ZONES (SOUTHERN GILA COUNTY) WHERE A SLIGHT 
CHANCE FOR SHOWERS IS IN THE FORECAST SATURDAY. MEANWHILE... 
SIGNIFICANTLY DRIER AIR WILL MOVE INTO SOUTHEAST CA AND ALONG THE 
LOWER COLORADO RIVER VALLEY SATURDAY...AND COUPLED WITH THE 
BREEZY/WINDY CONDITIONS...HAZARDOUS FIRE WEATHER CONDITIONS ARE 
POSSIBLE OVER THE WEEKEND.

AS FOR TEMPS...HIGHS ACROSS THE WARMEST DESERTS LOCALES WILL COOL TO 
NEAR AVERAGE FRIDAY BEFORE LOWERING TO THE LOW TO MID 80S BY SUNDAY 
AND MONDAY. OVERNIGHT LOWS SUN/MON WILL BE AS LOW AS WE HAVE SEEN 
SINCE MAY...MID 50'S TO NEAR 60 ACROSS THE WARMEST DESERT FLOORS AND 
RIGHT AROUND FREEZING AT THE HIGHEST ELEVATIONS OF ZONE 24/SOUTHERN 
GILA COUNTY. 

&&

.AVIATION...
HIGH PRESSURE ALOFT TO GIVE REGIONAL AIRFIELDS ANOTHER DAY OR TWO OF 
GENLY CLR SKIES...UNRESTRICTED VSBYS AND LIGHT...DIURNAL WINDS. NO 
AVIATION CONCERNS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
FRIDAY THROUGH SUNDAY...
A DEEP UPPER LEVEL LOW PRESSURE SYSTEM WILL TAKE SHAPE OVER THE WRN 
STATES ON FRIDAY AND BE NEARLY STATIONARY OVER THE WEEKEND. THIS 
SYSTEM WILL BE MAINLY DRY FOR SCNTRL AZ THRU SE CA...WITH PRECIP 
EXPECTED TO BE CONFINED TO HIGHEST TERRAIN AREAS WELL TO THE N AND E 
OF THE PHX METRO. WINDS AND COOLER TEMPS WILL BE THE MAIN RESULT...
WITH 20 FOOT WIND SPEEDS POSSIBLY NEAR CRITICAL THRESHOLDS FOR A FEW 
HRS ON SATURDAY. HOWEVER...SURFACE HUMIDITIES APPEAR AS IF THEY MAY 
REMAIN JUST ABOVE CRITICAL VALUES OF 15 PCT DURING THIS EVENT AT 
MOST LOCALES. 

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&



NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...MEYERS/WANEK
AVIATION...ESTLE
FIRE WEATHER...ESTLE