000 FXUS65 KPSR 181550 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 850 AM MST TUE NOV 18 2008 .SYNOPSIS... STRONG HIGH PRESSURE ALOFT WILL YIELD MOSTLY CLEAR COOL NIGHTS AND SUNNY WARM DAYS THROUGH WEDNESDAY...WITH NEAR RECORD HIGH READINGS LIKELY OVER THE WARMEST DESERTS TODAY. THE HIGH WILL WEAKEN AND MOVE WELL EAST OF OUR AREA BY LATE IN THE WEEK. AS IT DOES SO... TEMPERATURES WILL LOWER SOMEWHAT AND THERE WILL BE A SLIGHT INCREASE IN CLOUDINESS. EVEN WITH THE SLIGHT COOLING EXPECTED... TEMPERATURES WILL REMAIN ABOVE AVERAGE FOR LATE NOVEMBER. && .DISCUSSION... OBSERVATIONAL DATA AS WELL AS 06Z AND INCOMING 12Z MODEL DATA ALL INDICATE NO SIGNIFICANT CHANGES REQUIRED TO THE GOING FORECAST. THEREFORE ONLY MINOR TWEAKS MADE TO THE DIGITAL DATABASE. STILL EXPECTING RECORD/NEAR-RECORD HIGHS CWA-WIDE TODAY AS VERY ANOMALOUSLY STRONG H5 RIDGE DRIFTS OVERHEAD /PLUS-2 ST DEV FROM CLIMO/. PREVIOUS DISCUSSION... STRONG HIGH PRESSURE ALOFT CONTINUES OVER THE WESTERN STATES...WITH 589DM H5 HEIGHTS SEEN OVER NRN AZ PER THE RECENT 00Z PLOT DATA. AIRMASS VERY DRY WITH PWAT VALUES BELOW 0.10 INCHES...AND IR IMAGERY EARLY THIS MORNING SHOWED CLEAR SKIES OVER SRN CA AND AZ. PROGS AGREE THAT THE RIDGE WILL REMAIN STRONG OVERHEAD TODAY...AND UNDER SUNNY SKIES MAX TEMPS SHOULD AGAIN BE ABLE TO REACH TO NEAR RECORD VALUES. PHOENIX REACHED A RECORD OF 87 YESTERDAY...AND SHOULD HIT ANOTHER RECORD OF 87 TODAY. RIDGE FORECAST TO WEAKEN SLIGHTLY WEDNESDAY AS A PACIFIC SHORTWAVE APPROACHES THE PAC NW COAST. AS HEIGHTS FALL ALOFT TEMPS SHOULD LOWER SLIGHTLY TO BELOW RECORD VALUES...BUT REMAIN IN THE LOW TO MID 80S OVER WARMER LOCALES. GFS AND EUROPEAN CONTINUE TO AGREE THAT THE RIDGE WILL FLATTEN FURTHER ON THURSDAY AS THE STRONG SHORTWAVE MOVES INLAND THRU THE PAC NW. DESPITE HEIGHT FALLS ALOFT THICKNESS VALUES CHANGE LITTLE AND TEMPS WILL REMAIN WELL ABOVE SEASONAL NORMALS...AND IN THE LOW TO MID 80S OVER THE LOWER DESERTS. AS THE RIDGE FLATTENS IT WILL BECOME SOMEWHAT DIRTY AND ALLOW VARIABLE HIGH CLOUDS TO SPREAD THRU IT. STILL...EXPECT SKIES TO BE ON THE MOSTLY SUNNY SIDE. FOR FRIDAY INTO SATURDAY...ALTHOUGH HEIGHTS/THICKNESSES CONTINUE TO FALL AS THE RIDGE ERODES...MAIN STORM TRACK REMAINS NORTH OF OUR AREA AND DRY CONDITIONS WILL PERSIST. HOWEVER A WEAK UPPER LOW IS FORECAST TO DEVELOP OFF NRN BAJA. THIS FEATURE SHOULD NOT DO MUCH OTHER THAN TO CONTINUE TO SPREAD MAINLY HIGH CLOUDS ACROSS THE AREA...AND LEAD TO PARTLY CLOUDY SKIES AT TIMES. WITH ADDITIONAL CLOUD COVER... TEMPERATURES WILL CONTINUE TO SLOWLY LOWER AND BY SATURDAY...MAX TEMPS OVER THE LOWER DESERTS SHOULD FALL INTO THE UPPER 70S IN MANY PLACES. FOR THE LATTER PORTION OF THE EXTENDED FORECAST...SUNDAY THROUGH MONDAY...FORECAST CONFIDENCE REMAINS QUITE LOW AS MEDIUM RANGE MODEL SOLUTIONS REALLY DIVERGE YET AGAIN. GFS ENSEMBLE MEMBERS SHOW SUBSTANTIAL SPREAD IN THIS TIME FRAME...AND DPROG/DT COMPARISONS OF THE GFS ON MONDAY SHOW WIDELY DIVERGENT SOLUTIONS OVER THE PAST SEVERAL MODEL RUNS. FOR NOW WILL KEEP JUST CLIMO POPS IN THE FORECAST DURING THIS PERIOD...AS IT APPEARS THAT THE NEXT SIGNIFICANT PRECIP PRODUCER SHOULD STILL BE BEYOND DAY 7. WILL CONTINUE THE TEMP TRENDS THAT WERE ALREADY IN THE FORECAST... LOWERING MAX TEMPS WITH TIME...AND BY NEXT MONDAY WE SHOULD SEE MAX VALUES FINALLY APPROACH SEASONAL NORMALS. && .AVIATION... ANOTHER DAY OF STRONG HIGH PRESSURE MEANS LIGHT WIND AND CLEAR SKIES FOR ALL AIRFIELDS. KPHX/KIWA SHOULD EXPERIENCE AN EASTERLY WIND THROUGH 12Z. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... THE STRONG HIGH PRESSURE BEGINS TO WEAKEN BY THE END OF THE WEEK AND TEMPERATURES WILL BEGIN TO COOL. WINDS WILL REMAIN LIGHT WHILE MINIMUM RH VALUES ARE EXPECTED TO INCREASE SLIGHTLY BY THE WEEKEND. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT WEATHER.GOV/PHOENIX DISCUSSION...INIGUEZ/CB AVIATION...PADDOCK FIRE WEATHER...PADDOCK