002 FXUS65 KPSR 191112 AFDPSR AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE PHOENIX AZ 410 AM MST TUE MAR 19 2013 .SYNOPSIS... WELL ABOVE NORMAL TEMPERATURES WILL CONTINUE THROUGH THURSDAY BEFORE A COOLING TREND TAKES PLACE LATE THIS WEEK. A DRY COLD FRONT IS EXPECTED TO BRING NOTICEABLY COOLER TEMPERATURES SATURDAY WITH DESERT HIGHS IN THE MID TO UPPER 70S. ANTICIPATE SIMILAR TEMPERATURES SUNDAY BEFORE A WARMING TREND BEGINS MONDAY. && .DISCUSSION... TODAY THROUGH THURSDAY...WATER VAPOR IMAGERY SHOWS A SHORT WAVE RIDING OVER THE NORTHEAST PACIFIC RIDGE MOVING INTO THE GREAT BASIN. THE FEATURE WILL BRUSH OUR AREA TODAY AND IS ALREADY SPREADING HIGH CLOUDS AHEAD OF IT. MODEL TEMPERATURE GUIDANCE INDICATES THERE WILL BE LITTLE OR NO IMPACT ON HIGH TEMPS TODAY. IN FACT SOME DEPICT EVEN WARMER HIGHS THAN YESTERDAY. GIVEN MORE HIGH CLOUDINESS AROUND ANTICIPATE LITTLE OR NO CHANGE...ALTHOUGH MIN TEMPS THIS MORNING WILL BE STARTING A LITTLE HIGHER THAN YESTERDAY. ANTICIPATE A SIMILAR SITUATION WEDNESDAY WITH HIGH CLOUDS AHEAD OF ANOTHER SHORT WAVE. HOWEVER...A TRANSIENT RIDGE WILL MOVE ACROSS SO THERE MAY ACTUALLY BE VERY SUBTLE WARMING BUT REALLY NO CHANGE. PERHAPS VERY SUBTLE COOLING THURSDAY BEHIND THE SHORT WAVE BUT AGAIN...VERY LITTLE CHANGE IN TEMPS. EXPECT MORE NOTICEABLE AFTERNOON AND EVENING BREEZES WEDNESDAY...ESPECIALLY SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA. FRIDAY THROUGH MONDAY...GFS...ECMWF...AND GEM ALL DEPICT VARYING AMOUNTS OF NORTHEAST PACIFIC RIDGING AND CONUS TROUGHING DURING THIS TIME. THERE IS GOOD AGREEMENT ON A TROUGH DEEPENING OVER THE WESTERN STATES FRIDAY AND SATURDAY WITH A HIGH AMPLITUDE RIDGE UPSTREAM. THIS LEADS TO A DRY COLD FRONT MOVING SOUTHWARD THROUGH OUR AREA EARLY SATURDAY WITH AN UPPER LOW CENTER MOVING ACROSS THE 4 CORNERS. PREVIOUS RUNS OF THE GFS AND ECMWF HAD WEAKER SYSTEMS BUT HAVE COME AROUND TO WHAT THE GEM WAS SHOWING ON IT/S PREVIOUS 00Z RUN. THE ECMWF HAD BEEN THE MOST MILD NOW IT IS ON THE COLDER END FOR OUR AREA. THE EC ENSEMBLE MEAN AND GEFS MEAN SUPPORT THE SCENARIO OF A COLDER SYSTEM. THUS LOWERED PREVIOUS FORECAST MAX TEMPS BY SEVERAL DEGREES SATURDAY AND SUNDAY MAX TEMPS...INTO THE MID AND UPPER 70S ON THE LOW DESERTS WHICH IS A LITTLE BELOW NORMAL. ANTICIPATE WINDY CONDITIONS IN THE VICINITY OF THE LOWER COLORADO RIVER VALLEY LATE FRIDAY NIGHT INTO SATURDAY. THE OVERLAND TRAJECTORY OF THE SYSTEM AND THE UPPER LOW CENTER TRACKING NORTH AND EAST...THE SYSTEM WILL BE DRY FOR OUR AREA. THE ECMWF DEPICTS FOLLOW ON SHORT WAVES KEEPING TEMPERATURES FROM REBOUNDING MUCH BUT THE GFS AND GEM ARE SHOWING MORE RIDGING. THE EC ENSEMBLE MEAN DOES NOT LEND A LOT OF SUPPORT TO THE SCENARIO OF LINGERING TROUGHING OVER THE INTERIOR WEST. THUS SHOW MODEST WARMING ON MONDAY. && .AVIATION... SOUTH-CENTRAL AZ INCLUDING KPHX...KIWA AND KSDL...AND SOUTHEAST CA AND SOUTHWEST AZ INCLUDING KIPL AND KBLH... CIGS AOA 20K FT WILL PREVAIL ACROSS THE REGION THROUGH TUESDAY MORNING...WITH MORE SCT COVERAGE EXPECTED INTO TUESDAY AFTERNOON. SFC WINDS WILL GENERALLY FOLLOW THE TYPICAL DIURNAL DIRECTIONAL TRENDS...ALTHOUGH WITH A MORE N/NW COMPONENT FOR SERN CALIFORNIA AERODROMES THAN EXPERIENCED THE PAST COUPLE DAYS. WHILE A FEW HIGHER WIND GUSTS MAY OCCUR...SPEEDS SHOULD GENERALLY REMAIN AOB 10KT YIELDING NO SIGNIFICANT AVIATION IMPACTS. AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. && .FIRE WEATHER... WEDNESDAY THROUGH SUNDAY... BEGINNING WEDNESDAY AND CONTINUING INTO THE WEEKEND...A DEEP AND RATHER STRONG AREA OF LOW PRESSURE WILL DEVELOP OVER THE NORTH CENTRAL CONUS...CENTERED WELL TO THE NORTH OF ARIZONA. THIS WILL LEAD TO INCREASED WIND ACROSS THE AREA EACH DAY WITH BREEZY OR EVEN LOCALLY WINDY CONDITIONS DEVELOPING DURING THE AFTERNOON AND EVENING HOURS. THE ATMOSPHERE WILL BE DRY EACH DAY WITH THE ONLY CHANCE FOR PRECIPITATION BEING A SLIGHT CHANCE FOR SHOWERS ACROSS THE HIGHER TERRAIN EAST OF PHOENIX ON WEDNESDAY. MINIMUM HUMIDITIES WILL BE MOSTLY IN THE TEENS WEDNESDAY AND THURSDAY...BUT DRIER AIR WILL SPREAD IN FROM THE NORTHWEST STARTING FRIDAY LEADING TO SINGLE DIGIT HUMIDITIES THROUGH THE WEEKEND. AT THIS TIME...DESPITE THE RATHER DRY CONDITIONS...WINDS ARE EXPECTED TO REMAIN A BIT BELOW CRITICAL FIRE WEATHER THRESHOLDS THIS WEEK. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...NONE. CA...NONE. && $$ VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX DISCUSSION...AJ AVIATION...MO FIRE WEATHER...CB