907 FXUS65 KPSR 271020 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 320 PM MST MON APR 27 2009 .SYNOPSIS... CLOUDS WILL BE ON THE INCREASE TODAY AS A WEAK AREA OF LOW PRESSURE OFF THE SOUTHERN CALIFORNIA COAST MOVES EAST ACROSS THE FORECAST AREA. WARMER CONDITIONS ARE EXPECTED DESPITE THE CLOUDS WITH HIGH TEMPERATURES IN THE UPPER 80S. THE WARMING TREND WILL CONTINUE THROUGH THE WEEK...WITH THE WARMEST TEMPERATURES EXPECTED THU OR FRI AS HIGH PRESSURE BUILDS ACROSS THE INTERMOUNTAIN WEST. && .DISCUSSION... ONE SHORT WAVE TROUGH ACROSS CO WILL EJECT NORTHEASTWARD TODAY WHILE ANOTHER DIVES SOUTH ALONG THE PACIFIC NORTHWEST COAST. IN BETWEEN THESE TWO SYSTEMS...HEIGHT RISES NEAR THE FOUR CORNERS WILL EQUATE TO ROUGHLY A 5 DEGREE INCREASE (COMPARED TO SUN) IN MAX TEMPS. MEANWHILE IN THE SOUTHERN STREAM...A JET MAX OFF THE SOUTHERN CA COAST WILL PRODUCE AN INCREASE IN CIRRUS THROUGHOUT THE DAY. WARMING TREND WILL CONTINUE THROUGH THE WEEK AS A SERIES OF VORTS ACROSS THE PACIFIC NORTHWEST EVOLVE INTO A LARGER VORTEX...GENERATING A WARM DRY WESTERLY FLOW ACROSS THE DESERT SOUTHWEST. THIS LOW WILL ULTIMATELY FILL WHILE SLIDING EASTWARD LATE IN THE WEEK. WARMEST DAY LOOKS TO BE THU OR FRI WITH THE MODELS (PREFERENCE AGAIN TOWARDS THE ECMWF) DEPICTING A RIDGE BUILDING ACROSS THE WESTERN CONUS. MEX TEMPS IN THE EXTENDED HAVE BOUNCED AROUND SOMEWHAT OVER THE PAST FEW DAYS...THOUGH LATEST RUN APPEARS REASONABLE WITH HIGH TEMPS PEAKING IN THE MID 90S IN THE LOWER DESERTS...OR ROUGHLY 5 DEGREES ABOVE AVERAGE. CONFIDENCE IS INCREASING FOR NEXT WEEKEND WITH A TROUGH MOVING EAST OFF THE PACIFIC. IT IS UNLIKELY THIS SYSTEM WILL HAVE A SIGNIFICANT IMPACT THIS FAR SOUTH. NEVERTHELESS...LATEST FCST REFLECTS A SLIGHT INCREASE IN POPS...ALBEIT LESS THAN 10 PERCENT. && .AVIATION... SOUTH-CENTRAL DESERTS INCLUDING KPHX AND KIWA... WINDS GENLY FROM THE WEST THIS EVENING LESS THAN 15 KTS...BECOMING LIGHT DIURNAL BY MIDNIGHT. EXPECT WINDS TO BECOME SLY BY LATE MORNING THEN BACK TO THE SW OR W 6-10 KTS BY 21Z MONDAY. CLEAR SKIES ON TAP THIS EVENING WITH SOME INCREASE IN HIGH CLOUDS BY SUNRISE. INCREASING AND THICKENING HIGH CLOUDS MONDAY...WITH SOME OVC CIGS AOA 20K FEET BY AFTERNOON. VFR CONDITIONS ALL AIRFIELDS NEXT 24 HOURS. KIPL... WIND EXPECTED TO GENERALLY BE FROM THE WEST TONIGHT THRU LATE MONDAY MORNING...GENLY LESS THAN 10 KTS. COULD SEE WINDS BACK AROUND TO THE SOUTHEAST AFTER 19Z MONDAY...AT 6-10KT. CLEAR SKIES THIS EVE...BUT THEN INCREASING HIGH CLOUDS AFTER MIDNIGHT...WITH BKN TO OVC CIGS AOA 20K FEET BY MID DAY MONDAY. VFR CONDITIONS NEXT 24 HOURS. KBLH... WINDS SHOULD TEND TO FAVOR THE SOUTH LESS THAN 10KT THIS EVE...THEN BECOME LIGHT VARIABLE AFTER MIDNIGHT. WINDS WILL PICK UP AGAIN FROM THE SOUTH OR SOUTHEAST BY 18Z MONDAY...WITH SOME AFTERNOON GUSTS TO 18KT POSSIBLE. EXPECT CLEAR SKIES THIS EVE...THEN GRADUALLY INCREASING HIGH CLOUDS AFTER MIDNIGHT WITH BKN-OVC CIGS AOA 20K FEET BY 18Z MONDAY. VFR CONDITIONS NEXT 24 HOURS. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... WEDNESDAY THROUGH SUNDAY... VERY DRY WEATHER IS EXPECTED TO CONTINUE WITH MINIMUM AFTERNOON RELATIVE HUMIDITY GENERALLY BELOW 15 PERCENT...AND IN THE SINGLE DIGITS IN ALL BUT THE HIGHEST TERRAIN THROUGH FRIDAY. TEMPERATURES ARE ANTICIPATED TO CLIMB ABOVE AVERAGE WITH HIGHS IN THE 90S IN THE LOWER ELEVATIONS. TYPICAL AFTERNOON BREEZINESS CAN BE EXPECTED... EXCEPT WINDS FROM THE SOUTHWEST MAY INCREASE SATURDAY AFTERNOON AS THE DRY SOUTHERN END OF A PACIFIC LOW PRESSURE SYSTEM MOVES INTO THE AREA. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT WEATHER.GOV/PHOENIX DISCUSSION...HIRSCH AVIATION...CB FIRE WEATHER...ELLIS