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000
FXUS65 KPSR 240401
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
900 PM MST THU MAY 23 2013

.SYNOPSIS...
LOW PRESSURE CENTER OVER THE PACIFIC NORTHWEST IS EXPECTED TO KEEP
THE REGION UNDER DRY SOUTHWESTERLY FLOW ALOFT...WITH BREEZY TO WINDY
CONDITIONS AT TIMES THE REST OF THIS WEEK AND INTO NEXT WEEK.
ANTICIPATE LITTLE CHANGE IN TEMPERATURES THROUGH SATURDAY. NEXT
WEEK...THE TROUGH ALONG THE WEST COAST IS ANTICIPATED TO DEEPEN
WHICH WILL LEAD TO SOME MODEST COOLING SUNDAY AND MONDAY WITH SOME
MORE NOTICEABLE COOLING TUESDAY AND WEDNESDAY.

&&

.DISCUSSION...
UNDER MOSTLY CLEAR SKIES TODAY...THE SOUTHWEST DESERTS AGAIN WARMED
INTO THE UPPER 90S TO LOW 100S. 8 PM MST OBSERVATIONS FROM AROUND
THE AREA ARE SIMILAR TO READINGS FROM LAST NIGHT...WITH UPPER 80 TO
LOW 90 DEGREE TEMPERATURES AND PERSISTENTLY ELEVATED WEST TO
SOUTHWEST BREEZINESS. LARGE UPPER LOW AND TROUGHING CONTINUES TO
EXPAND AND SETTLE ACROSS THE PACIFIC NW AND DOWN INTO THE GREAT
BASIN. MOSTLY DRY SOUTHWEST FLOW ALOFT REMAINS OVER THE DESERTS. AS
THIS LOW FEATURE REMAINS SOMEWHAT STATIONARY...WITH INDIVIDUAL
SHORTWAVES EMBEDDED THROUGH THE FLOW...AFTERNOON BREEZES WILL
CONTINUE WHILE TEMPERATURES WILL BEGIN A SLIGHT COOL DOWN THROUGH
MEMORIAL DAY HOLIDAY WEEKEND. FOR TONIGHT...EXPECT CONTINUED CLEAR
SKIES WITH ELEVATED WEST-SOUTHWEST WINDS PERSISTING ACROSS SOUTHEAST
CALIFORNIA. BACK INTO THE SOUTH CENTRAL DESERTS...WINDS WILL SLOWLY
RELAX BECOMING MORE VARIABLE IN NATURE OVERNIGHT BEFORE PICKING UP
TYPICAL EAST DRAINAGE FLOW BY SUNRISE. NO UPDATES PLANNED FOR THE
GRID PACKAGE THIS EVENING.

&&

.PREVIOUS DISCUSSION /ISSUED AT 250 PM MST/PDT/...
REST OF TODAY THROUGH MEMORIAL DAY...
TEMPERATURES EARLY THIS AFTERNOON ARE RUNNING A BIT COOLER THAN 24
HOURS AGO...ESPECIALLY OVER SOUTHEAST CALIFORNIA WHICH IS CLOSER TO
AXIS OF THE UPPER TROUGH CENTERED ALONG THE WEST COAST. THE ENHANCED
SOUTHWESTERLY FLOW ALOFT COMBINED WITH GOOD MIXING DUE TO SURFACE
HEATING WILL KEEP AFTERNOONS AND EARLY EVENINGS BREEZY THROUGH THE
WEEKEND. THERE WILL BE DAY TO DAY FLUCTUATIONS IN THE STRENGTH OF
THE BREEZINESS AS VORT MAXES MOVE THROUGH THE TROUGH...PASSING
MAINLY TO THE NORTH OF OUR FORECAST AREA. THERE WILL BE MINOR
FLUCTUATIONS IN HIGH TEMPERATURES THROUGH SATURDAY WITH READINGS ON
THE LOW DESERTS IN THE MID 90S TO NEAR 100. BEGINNING SUNDAY...THE
MODELS SHOW THE SOUTHERN END OF THE TROUGH DEEPENING IN RESPONSE TO
UPSTREAM LOW PRESSURE SYSTEMS OVER THE PACIFIC. IN ESSENCE...THERE
WILL BE A SERIES OF SHORT WAVES THAT WILL LEAD TO SOME MODEST
COOLING. SKIES WILL BE CLEAR EXCEPT FOR THICKER HIGH CLOUDINESS ON
MONDAY.

TUESDAY THROUGH THURSDAY...
THE GFS/ECMWF/GEM ALL SHOW A SPLIT IN THE FLOW ON THE UPSTREAM SIDE
OF THE TROUGH WHICH LEADS TO A SIZABLE SHORT WAVE IN THE SOUTHERN
BRANCH THAT MOVES THROUGH THE DESERT SOUTHWEST IN THE LATE MONDAY
THROUGH WEDNESDAY TIME FRAME. HOWEVER...THERE ARE CONSIDERABLE
DIFFERENCES IN TIMING AND DEPTH OF THE FEATURE. THE ECMWF IS DEEPEST
AND SLOWEST. THE GEM IS WEAKEST AND FASTEST. THE GFS IS IN BETWEEN
BUT CLOSER TO THE GEM SOLUTION. THE GEFS MEAN SUPPORTS THE GFS
PRETTY WELL. THE ECMWF ENSEMBLE OUTPUT SUGGESTS THAT THE OPERATIONAL
RUN IS TOO DEEP AND A BIT SLOW. HOWEVER...THERE IS CONSIDERABLE
SPREAD AMONGST THE INDIVIDUAL ENSEMBLE MEMBERS. MADE SOME SUBTLE
DOWNWARD ADJUSTMENTS TO TEMPS BUT NOT AS AGGRESSIVE AS WHAT ECMWF
WOULD SUGGEST. KEEPING THINGS DRY FOR NOW AS THERE WILL NOT BE MUCH
MOISTURE AVAILABLE WITH THE SYSTEM PLUS THE TIME OF YEAR INDICATES
LOW PROBABILITY FOR PRECIP. BEHIND THE SYSTEM...TEMPS START TO WARM
UP. THE STRENGTH AND TIMING OF THE SYSTEM WILL ALSO INFLUENCE THE
STRENGTH OF THE SURFACE WINDS. ANTICIPATE AT LEAST BREEZY CONDITIONS
AT TIMES WITH THE PASSAGE OF THE SYSTEM.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA...INCLUDING KPHX...KIWA...KSDL...SOUTHEAST
CALIFORNIA/SOUTHWEST ARIZONA...INCLUDING KIPL AND KBLH...

THE TERMINAL FORECASTS WILL FAVOR PERSISTENCE THE NEXT FEW DAYS AS
DRY SOUTHWEST FLOW ALOFT REMAINS OVER THE SOUTHWEST. THIS WILL
CONTINUE MOSTLY CLEAR SKIES AND PERIODS OF ELEVATED WINDS. FOR KIPL
AND KBLH...WEST-SOUTHWEST BREEZES WILL PERSIST BEFORE BECOMING MORE
VARIABLE AT AND AFTER SUNRISE. THE PHX METRO TERMINALS WILL ALSO SEE
A DECREASE IN WESTERLY BREEZES BEFORE VRBING OUT AND GOING EAST
BEFORE SUNRISE. AFTN/EVE BREEZES WILL REDEVELOP FRIDAY...BEGINNING
TYPICALLY BY EARLY/MID AFTERNOON AND CONTINUING THRU MID EVENING.
GUSTS IN EXCESS OF 20KT ARE LIKELY AT ALL AIRFIELDS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
LOW PRESSURE IS EXPECTED TO REMAIN ALONG THE WEST COAST FROM SUNDAY
INTO MONDAY...THEN MOVE INLAND ON TUESDAY AND WEDNESDAY...KEEPING
ARIZONA AND SOUTHEAST CALIFORNIA UNDER A DRY SOUTHWEST TO WEST FLOW
ALOFT THROUGH THE PERIOD. BREEZY TO WINDY CONDITIONS WILL DEVELOP
DURING THE AFTERNOON AND EVENING HOURS EACH DAY...WITH PEAK WIND
GUSTS IN EXCESS OF 25 MPH POSSIBLE. SINGLE DIGIT MINIMUM HUMIDITIES
WILL CONTINUE THROUGH MONDAY...WITH SLIGHTLY HIGHER VALUES TUESDAY
INTO THURSDAY. OVERNIGHT RECOVERY WILL BE POOR OVER SOUTH-CENTRAL
ARIZONA AND POOR TO FAIR OVER SOUTHWEST ARIZONA AND SOUTHEAST
CALIFORNIA. HIGH TEMPERATURES WILL REMAIN NEAR OR A BIT BELOW
SEASONAL NORMALS THROUGH MONDAY...WITH COOLER TEMPERATURES POSSIBLE
ON TUESDAY AND WEDNESDAY AS THE LOW PRESSURE MOVES INLAND INTO THE
DESERT SOUTHWEST. DRY WESTERLY FLOW ALOFT WILL FOLLOW THURSDAY ALONG
WITH SLIGHTLY WARMER HIGH TEMPERATURES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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DISCUSSION...NOLTE
PREVIOUS DISCUSSION...AJ
AVIATION...NOLTE
FIRE WEATHER...CB/PERCHA