000 
FXUS65 KPSR 290043 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
540 PM MST TUE APR 28 2009

.UPDATE...UPDATED AVIATION SECTION.

&&

.SYNOPSIS...
HIGH PRESSURE BUILDING OVER THE EASTERN PACIFIC WILL GRADUALLY MOVE 
EAST OVER THE WESTERN UNITED STATES WITH A WARMING TREND THROUGH 
FRIDAY. MOSTLY CLEAR NIGHTS AND SUNNY DAYS ARE EXPECTED THROUGH 
THURSDAY. CONSIDERABLE HIGH CLOUDINESS IS EXPECTED TO MOVE EAST OVER 
OUR AREA FRIDAY AND FRIDAY NIGHT AHEAD OF A PACIFIC LOW PRESSURE 
SYSTEM. THIS SYSTEM IS EXPECTED TO WEAKEN AND MOVE EAST ACROSS THE 
WESTERN UNITED STATES...AND CAUSE TEMPERATURES TO DROP BACK SOMEWHAT 
THIS WEEKEND ALONG WITH AN INCREASE IN AFTERNOON BREEZINESS.

&&

.DISCUSSION...
HIGH CLOUDINESS SOUTHEAST AND EAST OF THE GREATER PHOENIX AREA WAS 
CLEARING FROM THE WEST EARLY THIS AFTERNOON WITH ONLY A LITTLE THIN 
HIGH CLOUDINESS FOLLOWING OVER THE REST OF THE AREA. THUS...SKIES 
WERE MOSTLY SUNNY WITH TEMPERATURES 2 TO 4 DEGREES WARMER EARLY THIS 
AFTERNOON COMPARED WITH THE SAME TIME YESTERDAY. OTHER THAN THE HIGH 
CLOUDINESS...OUR AREA WAS UNDER A GENERALLY DRY FLOW OF AIR ALOFT 
FROM THE SOUTHWEST TODAY.

A LOW PRESSURE SYSTEM WAS CENTERED NEAR THE OREGON COAST THIS 
AFTERNOON. THE SOUTHERN END OF THIS SYSTEM OVER SOUTHERN CALIFORNIA 
WAS RESULTING IN GUSTY WINDS FROM THE WEST OF 20 TO 35 MPH IN 
SOUTHEAST CALIFORNIA THIS AFTERNOON. THESE WINDS ARE EXPECTED TO 
CONTINUE THIS EVENING THEN DECREASE LATE TONIGHT. IT WAS BREEZY FROM 
THE SOUTHWEST GENERALLY 10 TO 20 MPH ACROSS THE REST OF THE AREA 
EARLY THIS AFTERNOON.

THE LOW PRESSURE SYSTEM NEAR THE OREGON COAST WILL UNWIND AND 
ELONGATE FROM WEST TO EAST AS THE CENTER OF THE LOW MOVES EAST OVER 
OREGON WEDNESDAY AND OVER IDAHO THURSDAY. AS THIS HAPPENS...OUR AREA 
WILL COME UNDER A GENERALLY DRY FLOW ALOFT FROM THE WEST AND MORE 
UNDER THE INFLUENCE OF HIGHER PRESSURE ALOFT FROM THE PACIFIC WITH 
LESS AFTERNOON WIND WEDNESDAY AND THURSDAY.

AN AXIS OR RIDGE OF HIGH PRESSURE ALOFT WAS LOCATED OVER THE EASTERN 
PACIFIC WEST OF BAJA CALIFORNIA AND CALIFORNIA BETWEEN 130 AND 140 
DEGREES WEST LONGITUDE THIS AFTERNOON. THIS SYSTEM WILL CONTINUE 
MOVING EAST AND WILL BE NEAR THE CALIFORNIA COAST LATE THURSDAY AND 
MOVE ACROSS OUR AREA THURSDAY NIGHT AND FRIDAY. AS A RESULT...MOSTLY 
CLEAR NIGHTS AND SUNNY DAYS ARE EXPECTED THROUGH THURSDAY. IT IS 
ALSO EXPECTED TO BECOME SOMEWHAT WARMER EACH DAY THROUGH FRIDAY.

CONSIDERABLE HIGH CLOUDINESS IS EXPECTED TO MOVE EAST OVER OUR AREA 
FRIDAY ESPECIALLY LATE FRIDAY AND FRIDAY NIGHT AHEAD OF A PACIFIC 
LOW PRESSURE SYSTEM THAT WAS LOCATED SOUTH OF THE ALEUTIAN ISLANDS 
THIS AFTERNOON. ALSO...SOME INCREASE IN BREEZINESS FROM THE WEST IS 
EXPECTED IN SOUTHEAST CALIFORNIA FRIDAY AFTERNOON AS THE WEAKENING 
LOW PRESSURE SYSTEM APPROACHES OUR AREA.

PREVIOUS DISCUSSION...
GFS/ECMWF ARE IN FAIR AGREEMENT FOR THE WEEKEND...DEPICTING A 
SOUTHERN STREAM TROUGH MOVING OFF THE PACIFIC AND EAST ACROSS THE 
AREA. HOWEVER...THIS SYSTEM WILL BE MOVING INTO AN AMPLIFIED 
LONGWAVE RIDGE SO ITS IMPACT IS EXPECTED TO BE MINIMAL. MOISTURE AND 
BEST DYNAMICS WILL REMAIN CONFINED TO THE UPPER 
ATMOSPHERE...GENERATING A SIGNIFICANT AMOUNT OF MID AND HIGH CLOUDS. 
MEX TEMPS APPEAR TO WARM GIVEN THE EXPECTED CIRRUS CANOPY AND THE 
OFFICIAL FORECAST IS WEIGHTED MORE TOWARDS THE COOLER ECMWF.

NEXT SYSTEM OF NOTE IS EXPECTED TO ARRIVE EARLY NEXT WEEK AS A PIECE 
OF A NORTHERN PACIFIC TROUGH MOVES INTO THE GREAT BASIN...POSSIBLY 
BECOMING CUT OFF (IF THE ECMWF IS CORRECT). POP FORECAST AT THIS 
TIME IS NON-ZERO FOR MON NIGHT-TUE.

&&

.AVIATION...
KPHX...KIWA...AND SURROUNDING AIRFIELDS...
HIGH CLOUDS WILL PUSH E OF THE AREA THIS EVENING WITH SKC EXPECTED 
BY AROUND 06Z. WLY EVENING SUSTAINED WINDS GENLY LESS THAN 10KTS...
WITH ISOLD GUSTS TO NEAR 18KTS...WILL GRADUALLY BECOME E/SELY AFT 
06Z WITH SPEEDS LESS THAN 8KTS. EXPECT A TURN BACK TO WLY DIRECTIONS 
AFTER 20Z WED WITH SPEEDS UNDER 10KTS FOR THE MOST PART. 

KIPL...KBLH...AND SURROUNDING AIRFIELDS...
SKC ANTICIPATED AROUND THE REGION THRU 00Z THU. W/SWLY WINDS GUSTING 
TO 25-30KTS WILL DECREASE RAPIDLY AFTER SUNSET TO GENLY LESS THAN 
10KTS. LIGHTER WIND IS ANTICIPATED WEDNESDAY. 

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
A WARMING TREND WILL CONTINUE THROUGHOUT ALL ZONES INTO FRIDAY 
BEFORE ANOTHER WEAK LOW PRESSURE SYSTEM MOVES THROUGH. ALONG WITH 
THE WARMER WEATHER...EXPECT DRY CONDITIONS WITH MINIMUM RH VALUES 
DROPPING BELOW 15 PERCENT IN ALL ZONES...WITH POOR OVERNIGHT 
RECOVERY. A DIURNAL TREND ON THE WINDS CAN BE EXPECTED...WITH SPEEDS 
WELL BELOW CRITICAL FIRE WEATHER THRESHOLDS. 

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...ELLIS/HIRSCH
AVIATION...ESTLE
FIRE WEATHER...SIPPLE