673 
FXUS65 KPSR 191240 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
540 AM MST TUE MAR 19 2013

.UPDATE...UPDATED AVIATION AND FIRE WEATHER DISCUSSIONS.

&&

.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...

RATHER FLAT UPPER RIDGE WILL BE IN PLACE ACROSS THE AREA TODAY INTO 
WEDNESDAY...ALLOWING VARIABLE AMOUNTS OF MAINLY HIGH CLOUDS TO 
SPREAD THROUGH IT AND ACROSS THE AIRFIELDS. BASES GENLY AOA 15K FEET 
WITH CIGS AOA 20K FEET AT TIMES. WINDS LIGHT AND FAVORING NORMAL 
DIURNAL SPEEDS AND DIRECTIONS FOR THE MOST PART THROUGH WEDNESDAY 
MORNING. NO AVIATION CONCERNS. VFR CONDITIONS AT ALL AIRFIELDS NEXT 
24 HRS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS. 

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
BEGINNING THURSDAY AND CONTINUING INTO THE WEEKEND...A DEEP AND 
RATHER STRONG AREA OF LOW PRESSURE WILL DEVELOP OVER THE WEST AND 
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 STRONGEST WINDS WILL LIKELY BE FRIDAY AND SATURDAY. THE 
ATMOSPHERE WILL BE DRY THROUGH THE PERIOD WITH NO CHANCE FOR 
PRECIPITATION. MINIMUM HUMIDITIES WILL BE MOSTLY IN THE TEENS 
THURSDAY...BUT COOLER AND DRIER AIR WILL SPREAD IN FROM THE 
NORTHWEST STARTING FRIDAY LEADING TO SINGLE DIGIT HUMIDITIES THROUGH 
THE WEEKEND ALONG WITH HIGH TEMPERATURES FALLING TO AROUND SEASONAL 
NORMALS. 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...CB
FIRE WEATHER...CB