Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 061156 AAA
AFDPSR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE PHOENIX AZ
455 AM MST WED MAY 6 2015

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

&&

.SYNOPSIS...
DRIER AND BREEZY CONDITIONS WILL OCCUR THROUGH THURSDAY BEFORE A
STRONG EASTERN PACIFIC WEATHER SYSTEM MOVES INTO THE REGION BY
FRIDAY. THIS SYSTEM WILL BRING EVEN COOLER TEMPERATURES...CONTINUED
GUSTY WINDS...AND MORE PRECIPITATION CHANCES INTO SATURDAY. A SLOW
WARMING TREND COMMENCES THROUGH THE WEEKEND INTO EARLY NEXT WEEK AS
HIGH PRESSURE GRADUALLY REBUILDS OVER THE DESERT SOUTHWEST.

&&

.DISCUSSION...
DRY AIR IN THE LOW LEVELS WILL CONTINUE TO WORK INTO THE DESERT
SOUTHWEST TODAY. THIS WILL KEEP THINGS DRY ACROSS THE ENTIRE AREA
TODAY EVEN THOUGH A WEAK SHORTWAVE TROUGH WILL TRAVERSE THE REGION
THROUGH TONIGHT. CURRENT WATER VAPOR IMAGERY SHOWS THE VORTICITY MAX
JUST OFF THE SOUTHERN CALIFORNIA COAST WITH MODEST MID LEVEL MOISTURE
OUT AHEAD. THIS IS CAUSING A DECENT AMOUNT OF MID LEVEL CLOUDS
SPREADING EASTWARD ACROSS ARIZONA. THE SHORTWAVE TROUGH AND THE
CLOUDS WILL EXIT THE AREA BY LATE THIS EVENING BEFORE ANOTHER MORE
POTENT SYSTEM MOVES IN FOR FRIDAY. DAYTIME WINDS WILL BE QUITE BREEZY
TODAY AND THURSDAY UNDER A MODEST SURFACE PRESSURE GRADIENT. MAY SEE
SOME GUSTS IN THE 30-40 MPH RANGE ACROSS SOUTHEAST CALIFORNIA AND
20-30 MPH OVER SOUTH-CENTRAL ARIZONA. CAN/T RULE OUT THE POSSIBILITY
OF SOME BLOWING DUST...BUT AT THIS TIME FEEL IT WILL BE ISOLATED.

MODELS ARE IN EXCELLENT AGREEMENT WITH THE UPCOMING STRONG UPPER LOW
MOVING SOUTHWARD THROUGH CALIFORNIA ON THURSDAY AND INTO THE DESERT
SOUTHWEST ON FRIDAY. THIS WILL DEFINITELY BRING COOLER TEMPERATURES
INTO THE REGION...POTENTIALLY AS LOW AS 15 DEGREES BELOW NORMAL ON
FRIDAY...BUT THERE IS SOME DOUBT ON HOW MUCH MOISTURE WILL RETURN
AHEAD OF THE SYSTEM. UP TO THIS POINT MODELS HAVE BEEN SUGGESTING
THIS SYSTEM WILL BE MOSTLY DRY WITH LITTLE CHANCES FOR ANY RAIN...BUT
THE LATEST 00Z RUNS ARE STARTING TO SHOW SOME HIGHER MOISTURE LEVELS
AND FEEL THIS IS STILL PROBABLY TOO PESSIMISTIC. AM THINKING MOISTURE
LEVELS WILL ACTUALLY BE HIGHER THAN CURRENTLY DEPICTED...THUS OUR
RAIN CHANCES WILL BE BETTER AND THIS IS SHOWN ON THE LATEST SREF RUN.
HAVE INCREASED RAIN CHANCES ON FRIDAY AND SATURDAY...BUT WILL LIKELY
HAVE TO INCREASE THOSE FURTHER BEFORE THE EVENT OCCURS. STORM
DYNAMICS WILL BE FAIRLY ROBUST AS IT MOVES THROUGH CALIFORNIA...BUT
BY THE TIME THE UPPER LOW MOVES INTO THE DESERT SOUTHWEST IT WILL BE
FILLING AND FORCED ASCENT WILL BE WEAKENING.

UNSEASONABLY COOL AIR WILL MOVE IN WITH THE STORM SYSTEM WITH 850MB
TEMPERATURES DROPPING TO AROUND 12C ON FRIDAY. HAVE LOWERED OUR
FORECAST HIGHS ON FRIDAY FURTHER WITH LOWER DESERT HIGHS MAINLY ONLY
IN THE LOW TO MID 70S. THE UPPER LOW WILL STILL AFFECT ARIZONA INTO
EARLY SATURDAY WITH A TRAILING VORTICITY LOBE FORECAST TO SWING
THROUGH SOUTH-CENTRAL AND EASTERN ARIZONA BETWEEN 12-18Z. THIS WILL
LIKELY SPARK OFF ADDITIONAL SHOWERS AND POTENTIALLY SOME
THUNDERSTORMS UNDER STEEP MID LEVEL LAPSE RATES. AFTER 18Z
SATURDAY...SUBSIDENCE ALOFT WILL QUICKLY TAKE OVER FROM WEST TO EAST
WITH SKIES CLEARING AND ONLY A SLIGHT CHANCE OF SOME LINGERING
SHOWERS OVER OUR EASTERN HIGH TERRAIN AREAS.

SUNDAY INTO EARLY NEXT WEEK WILL TRANSITION BACK INTO MORE NORMAL
CONDITIONS WITH WEAK RIDGING ALOFT TAKING OVER AND TEMPERATURES
WARMING BACK TOWARD NORMAL STARTING NEXT MONDAY. WILL BE WATCHING
ANOTHER POTENTIAL STORM SYSTEM FOR THE MIDDLE OF NEXT WEEK DROPPING
OUT OF THE NORTHERN PACIFIC...BUT AT THIS TIME BOTH THE GFS AND
EUROPEAN KEEP IT WELL TO OUR NORTH.

&&

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

WEAK AREA OF LOW PRESSURE DEVELOPING OVER SERN CA TODAY WILL LEAD TO
DRY CONDITIONS NEXT 24 HOURS...ALONG WITH LOCALLY BREEZY SOUTH TO
SOUTHWEST WINDS THIS AFTERNOON AND EARLY EVENING. VARIABLE AMOUNTS
OF CIRRUS THIS MORNING SHOULD DECREASE AS THE DAY PROGRESSES.
ALSO...FEW-SCT MID DECKS MAY LINGER THROUGH THE MORNING WITH BASES
MOSTLY AOA 10K FEET. KIPL WILL SEE WINDS MOSTLY FROM THE WEST TODAY
INCREASING AND BECOMING GUSTY LATER THIS AFTERNOON...WITH PEAK GUSTS
TO AT LEAST 25KT AFTER 22Z...AND THRU AROUND MIDNIGHT TONIGHT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

FRIDAY THROUGH TUESDAY...AN AREA OF LOW PRESSURE MOVING ACROSS THE
DESERT SOUTHWEST WILL USHER IN AN INCREASING THREAT FOR SHOWERS TO
THE AREA FRIDAY THROUGH SATURDAY...AND WILL ALSO CAUSE HIGH
TEMPERATURES TO FALL WELL BELOW SEASONAL NORMALS WITH MOST DESERT
READINGS FALLING INTO THE 70S ON FRIDAY. BREEZY TO WINDY SOUTHWEST
TO WEST WIND CAN BE EXPECTED FRIDAY AFTERNOON AND EVENING...
ESPECIALLY OVER SOUTHEAST CALIFORNIA. ELEVATED HUMIDITY LEVELS
FRIDAY WILL OFFSET THE GUSTY WINDS...AS MINIMUM RH VALUES WILL RANGE
MOSTLY FROM 20 TO 30 PERCENT...HIGHEST OVER THE WESTERN DESERTS. FOR
SUNDAY THROUGH TUESDAY...HIGH PRESSURE ALOFT WILL BUILD BACK INTO
THE AREA FROM THE WEST...RESULTING IN A DRYING AND WARMING TREND
ALONG WITH LESS WIND. MINIMUM RH VALUES WILL LOWER INTO THE TEENS
SUNDAY...THEN FALL BELOW 15 PERCENT EARLY NEXT WEEK WITH THE DRIER
DESERTS SEEING SOME AREAS WITH SINGLE DIGIT HUMIDITIES. HIGH
TEMPERATURES OVER THE DESERTS MONDAY AND TUESDAY WILL RISE MOSTLY
INTO THE LOWER 90S.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...NONE.
CA...NONE.
&&

$$

VISIT US ON FACEBOOK...TWITTER...AND AT WEATHER.GOV/PHOENIX

DISCUSSION...KUHLMAN
AVIATION...CB
FIRE WEATHER...CB


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