Blowing Dust Advisory 25, NWS Phoenix, AZ

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
359 PM MST FRI AUG 10 2012

.SYNOPSIS...
STRONG HIGH PRESSURE WILL CONTINUE OVER THE DESERT SOUTHWEST THROUGH
THE END OF THE WEEKEND AND INTO EARLY NEXT WEEK...RESULTING IN WELL
ABOVE NORMAL TEMPERATURES AND PERIODS OF EXCESSIVE HEAT. MONSOON
MOISTURE WILL SLOWLY SPREAD BACK INTO THE REGION...RESULTING IN A
CHANCE OF AFTERNOON THUNDERSTORM ACTIVITY OVER SOUTHEAST CALIFORNIA
AND SOUTHWEST ARIZONA ON SATURDAY...SPREADING ACROSS THE ENTIRE AREA
SUNDAY AND EARLY NEXT WEEK.

&&

.DISCUSSION...
QUICK ADJUSTMENT TO INTRODUCE ISOLATED SHOWERS AND THUNDERSTORMS
ACROSS SW AZ AND SE CA PER CURRENT RADAR/SATELLITE IMAGERY. STORMS
SHOULD DIE OFF AFTER SUNSET. MAINTAINED DRY FORECAST AFTER 06Z.

&&

.PREVIOUS DISCUSSION...

NOTE: THE HEAT WAVE WILL CONTINUE OVER THE LOWER DESERTS OF
SOUTHEAST CA...SOUTHWEST AND SOUTH CENTRAL ARIZONA...AND THE
EXCESSIVE HEAT WARNING HAS BEEN EXTENDED THROUGH MONDAY.

TONIGHT THROUGH SUNDAY...
MORNING REGIONAL WEATHER BALLOON SOUNDINGS SHOWED DRY AIR FROM NEW
MEXICO HAD SPREAD QUICKLY WEST ACROSS ARIZONA OVERNIGHT. MONSOON
MOISTURE HAS BEEN SHOVED WEST INTO SOUTHERN CA WHERE THE SAN DIEGO
SOUNDING DETECTED EXCESSIVE MOISTURE AMOUNTS...WITH A PRECIP WATER
VALUE OF 1.88 INCHES OR 184 PERCENT OF NORMAL.  DRY AIR AND
UNFAVORABLE WINDS ALOFT SHOULD RESULT IN DRY CONDITIONS ACROSS OUR
FORECAST AREA...SOUTHEAST CA TO SOUTH CENTRAL AZ TONIGHT.

HOWEVER FOR SATURDAY AND SUNDAY...MODELS ARE STILL FORECASTING A
SIGNIFICANT MEXICAN INVERTED TROF TO MOVE FROM THE GULF OF CA THIS
AFTERNOON /SEE WATER VAPOR IMAGERY/ INTO SOUTHEAST CA AND SOUTHWEST
AZ SATURDAY AND SUNDAY. INTERESTING IS THE MODEL REFLECTION OF THIS
INVERTED TROF AT THE 300 AND 250 MB LEVEL. IT RANGES FROM A CLOSED
LOW NEAR YUMA SATURDAY AND SUNDAY WITH THE EUROPEAN MODEL...TO AN
OPEN WAVE WITH THE GFS SOLUTION ON SATURDAY...WHICH QUICKLY
DISSIPATES SUNDAY. QUITE A DIFFERENCE. CONCERNS WITH EITHER MODEL
FOR SATURDAY AFTERNOON AND EVENING INCLUDE POSSIBLE STRONG
THUNDERSTORMS IN SOUTHEAST CA AND SOUTHWEST AZ. THEREFORE THE
PROBABILITY OF SHWRS/TSTMS HAVE BEEN INCREASED IN THIS AREA. LATEST
PRECIP WATER SATELLITE IMAGERY ALSO SHOWED A SLOW MIGRATION OF
MONSOON MOISTURE BACK INTO AZ.

A SLIGHT CHANCE OF AFTERNOON OR EVENING THUNDERSTORMS IS FORECAST
ACROSS THE ENTIRE FORECAST AREA ON SUNDAY.

FURTHERMORE...FORECAST LOWER ATMOSPHERIC TEMPERATURES AND
ATMOSPHERIC THICKNESS VALUES CHANGE VERY LITTLE THROUGH THE WEEKEND.
THEREFORE THE EXCESSIVE HEAT WARNING HAS BEEN EXTENDED THROUGH
MONDAY. ALTHOUGH AFTERNOON FORECAST TEMPERATURES FOR SOUTHEAST CA
AND THE COLORADO RIVER VALLEY FALL A FEW DEGREES BELOW HEAT WARNING
CRITERIA OF 114 DEGREES F...HUMIDITY VALUES ARE EXPECTED TO MAKE THE
HEAT INDEX RISE ABOVE OUR THRESHOLD OF 110 DEGREES.

MONDAY THROUGH THURSDAY...
MODELS FORECAST MONSOON MOISTURE TO SLOWLY SPREAD BACK INTO THE
REGION. A NUMBER OF HARD TO TIME UPPER LEVEL DISTURBANCES FROM THE
SOUTHWEST DIRECTION SHOULD START TO INCREASE THE THREAT OF AFTERNOON
SHOWERS AND THUNDERSTORMS...MAINLY OVER PORTIONS OF SOUTHWEST AND
SOUTH CENTRAL AZ...INCLUDING PHOENIX.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
MOSTLY CLEAR SKIES AND LIGHT WINDS WILL PREVAIL AT ALL SITES THROUGH
SATURDAY AFTERNOON.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
GENERALLY LIGHT WINDS AT ALL SITES. SOME INCREASING HIGH CLOUDS
POSSIBLE DUE TO DISTANT CONVECTION. VCTS POSSIBLE AT BLH THROUGH 01Z
BASED ON CURRENT TRENDS. OTHERWISE CONDITIONS SHOULD BE QUIET AND
DRY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
MONDAY THROUGH FRIDAY...
AN AREA OF HIGH PRESSURE WILL CONTINUE TO DOMINATE ACROSS THE DESERT
SOUTHWEST...RESULTING IN WELL ABOVE NORMAL TEMPERATURES THROUGH
EARLY NEXT WEEK. AS THE WEEK PROGRESSES...THIS HIGH PRESSURE WILL
SLOWLY SLIDE EAST...ALLOWING SOME SLIGHT COOLING AND INTRODUCTION OF
MONSOON MOISTURE BACK INTO THE REGION. PRIMARILY DRY CONDITIONS WILL
REMAIN INTO EARLY NEXT WEEK WITH AFTERNOON RELATIVE HUMIDITY
VALUES GENERALLY DROPPING INTO THE TEENS EACH DAY...WITH GOOD
OVERNIGHT RECOVERIES. THUNDERSTORM ACTIVITY WILL BE MOSTLY CONFINED
TO THE HIGHER ELEVATIONS NORTH AND EAST OF PHOENIX THROUGH MONDAY
BEFORE EXPANDING ACROSS THE LOWER DESERTS AND INTO THE COLORADO
RIVER VALLEY BY THE MIDDLE OF NEXT WEEK.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...EXCESSIVE HEAT WARNING UNTIL 8 PM MST MONDAY
     AZZ020>023...025>028.

CA...EXCESSIVE HEAT WARNING UNTIL 8 PM PDT MONDAY
     CAZ031>033.

&&

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DISCUSSION...VASQUEZ
AVIATION...DEWEY
FIRE WEATHER...DEWEY