315
FXUS65 KPSR 050008 AAA
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
508 PM MST SAT JUL 4 2009
UPDATE
UPDATED AVIATION DISCUSSION.
SYNOPSIS
A LESS HUMID...MORE STABLE...AND WARMER AIRMASS WILL BUILD INTO THE
AREA FROM THE WEST AND SOUTHWEST THE NEXT FEW DAYS. FOR THE PERIOD
SUNDAY THROUGH TUESDAY...EXPECT ONLY A SLIGHT CHANCE FOR AFTERNOON
AND EVENING STORMS OVER THE HIGHER TERRAIN OF SOUTH-CENTRAL
ARIZONA...WITH DRY CONDITIONS OVER THE LOWER DESERT. MONSOON
MOISTURE FROM MEXICO WILL BEGIN TO SHIFT NORTH INTO THE REGION AGAIN
BY THE MIDDLE OF NEXT WEEK...AND INCREASE THE THREAT FOR AFTERNOON
AND EVENING THUNDERSTORM ACTIVITY MAINLY OVER SOUTH CENTRAL ARIZONA.
DISCUSSION
THE FLOW PATTERN IS BEGINNING TO CHANGE TOWARD A MORE DRIER AND
STABLE ONE.
12Z PLOT DATA HOWEVER CONTINUED TO SHOW A RATHER HUMID AIRMASS IN
PLACE...WITH THE MONSOON MOISTURE BOUNDARY ... I.E. 800/850 MB
DEWPOINT AT 8 DEGREES C ...LOCATED ALONG A LINE FROM YUMA...TO
BETWEEN PHOENIX AND FLAGSTAFF...THEN EAST TOWARD SHOWLOW AND
THE WHITE MOUNTAINS. IN OTHER WORDS SOUTHERN AZ WAS STILL IN THE
SOUP. HOWEVER...THE UPPER LEVEL FLOW PATTERN - 300/250 MB - IS
BEGINNING TO CHANGE DIRECTIONS FROM RECENT DAYS...WHICH WAS OUT OF
THE SOUTH INCLUDING PERIODS OF UPPER DEFORMATION/DIVERGENCE TO
SUPPORT LARGE THUNDERSTORM OUTBREAKS...TO A MORE WEST AND
SOUTHWESTERLY CONVERGENT FLOW THIS EVENING THROUGH TUESDAY. THIS
UPPER LEVEL WIND PATTERN IS LESS FAVORABLE TO SUPPORT TALLER AND
MORE WIDESPREAD THUNDERSTORMS. ALSO...A DRIER AIRMASS FROM THE WEST
WILL OVER-SPREAD SOUTHWEST AND SOUTH CENTRAL AZ BEGINNING SUNDAY...
PUSHING THE MONSOON MOISTURE BOUNDARY SOUTH TO THE MEXICAN BORDER BY
MONDAY AFTERNOON.
FOR TONIGHT...THE ONLY THREAT FOR SHOWERS WILL BE OVER THE HIGHER
TERRAIN IN SOUTH CENTRAL AZ...I.E. FAR TO THE NORTH THROUGH EAST OF
THE GREATER PHOENIX AREA. NO THUNDERSTORMS IN THE GREATER PHOENIX
AREA TONIGHT.
SUNDAY THROUGH TUESDAY...
THE UPPER LEVEL WIND PATTERN - 300/250 MB - IS FORECAST TO INCREASE
AND CHANGE DIRECTION...BECOMING MORE WEST AND SOUTHWESTERLY...AND
CONFLUENT. AND...IN COMBINATION WITH A DRIER AIRMASS FROM THE
WEST...WILL LIMIT AFTERNOON THUNDERSTORM ACTIVITY ONLY TO THE
MOUNTAINS OF SOUTHERN GILA COUNTY.
ADDITIONALLY...AFTERNOON TEMPERATURES ARE FORECAST TO INCREASE
SUBSTANTIALLY INTO THE 110 TO 114 DEGREE RANGE DUE TO A DRIER
AIRMASS.
WEDNESDAY THROUGH SATURDAY...
THE MONSOON MOISTURE BOUNDARY IS EXPECTED TO SHIFT NORTH AGAIN INTO
CENTRAL AZ THIS PERIOD. WINDS ALOFT -300/250 MB - ARE FORECAST TO
BECOME MORE SOUTHERLY AGAIN...PERHAPS SUPPORTING A FEW DISTURBANCES
COMING OUT OF MEXICO. THIS WILL SUPPORT AN INCREASING THREAT...
ALTHOUGH NOT A BIG ONE AT THE MOMENT...OF TYPICAL AFTERNOON AND
EVENING THUNDERSTORM ACTIVITY MAINLY OVER SOUTH CENTRAL AZ.
AVIATION
KPHX/KIWA AND SURROUNDING AIRFIELDS...
STORMS SHOULD REMAIN OVER THE HIGHER TERRAIN WELL EAST AND NORTH OF
THE AIRFIELDS THIS EVENING. WEST-NORTHWEST FLOW 10-15 KT IN
SFC-10KFT LAYER SHOULD RESULT IN WESTERLY COMPONENT TO SFC WIND
UNTIL WELL AFTER MIDNIGHT. TYPICAL LIGHT EASTERLY FLOW FROM NEAR
DAWN TO MID-MORNING SUNDAY...WITH WESTERLY COMPONENT REASSERTING
ITSELF BY EARLY AFTERNOON. PERSISTENT WESTERLY FLOW SUGGESTS DRIER
CONDITIONS AND LESS THUNDERSTORM ACTIVITY ON SUNDAY.
KIPL/KBLH AND SURROUNDING AIRFIELDS...
DRY CONDITIONS WITH TYPICAL DIURNAL WIND PATTERN THROUGH PERIOD.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
FIRE WEATHER
TUESDAY THROUGH SATURDAY...
HIGH PRESSURE WILL DRIFT SOUTH AND EAST OF THE AREA...AND A DRIER
WESTERLY FLOW ALOFT WILL PREVAIL. ONLY ZONE 133 WILL EXPECT SLIGHT
CHANCES OF WETTING RAIN THROUGH THE WEEK. HIGH TEMPS WILL BE HOT AND
MINIMUM RH VALUES WILL DROP INTO THE TEENS ACROSS THE LOWER DESERTS.
SOUTHWEST WINDS MAY BECOME GUSTY AT TIMES...BUT SHOULD REMAIN BELOW
CRITICAL FIRE WEATHER THRESHOLDS.
PSR WATCHES/WARNINGS/ADVISORIES
AZ...NONE.
CA...NONE.
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...VASQUEZ/ESTLE
AVIATION...DG
FIRE WEATHER...INIGUEZ
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