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