000
FXUS65 KPSR 312141
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
240 PM MST SAT JUL 31 2010

.SYNOPSIS...
A VERY MOIST AND UNSTABLE AIR MASS IS EXPECTED TO CONTINUE THE
CHANCE OF SHOWERS AND THUNDERSTORMS...SOME WITH HEAVY RAIN...THROUGH
THE WEEKEND. IT WILL BE MUCH COOLER THAN AVERAGE FOR THIS TIME OF
YEAR IN SOUTH-CENTRAL ARIZONA THROUGH THE WEEKEND. DRIER AND WARMER
WEATHER IS EXPECTED NEXT WEEK WITH A DECREASE IN SHOWERS AND
THUNDERSTORMS. A SLIGHT CHANCE OF AFTERNOON AND EVENING SHOWERS AND
THUNDERSTORMS IS EXPECTED TO BE PUSHED EAST OF THE GREATER PHOENIX
AREA BY THE MIDDLE AND LATTER PARTS OF NEXT WEEK.

&&

.DISCUSSION...
VERY WET MONSOONAL PATTERN REMAINS IN FULL SWING ACROSS ARIZONA
EARLY THIS AFTERNOON. PWAT VALUES OVER THE CENTRAL DESERTS ARE IN
EXCESS OF 2 INCHES...850MB DEWPOINTS ARE GREATER THAN 16C...AND 2 PM
SURFACE DEWPOINTS WERE IN THE LOW TO MID 70S. EARLY AFTERNOON RADAR
SHOWED SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS OVER SOUTH
CENTRAL AZ...WITH SCATTERED CONVECTION SPREADING INTO THE SWRN
DESERTS. LOCALLY HEAVY RAINFALL HAS BEEN OCCURRING WITH THE
THUNDERSTORMS..RAINFALL RATES IN EXCESS OF 2 INCHES PER HOUR HAVE
BEEN COMMON. AS SUCH SEVERAL URBAN AND SMALL STREAM FLOOD ADVISORIES
HAVE BEEN ISSED TODAY FOR THE CENTRAL AZ DESERTS...INCLUDING ONE FOR
THE GREATER PHOENIX METRO AREA.

PROMINENT INVERTED TROF OVER FAR SERN AZ HAS BEEN SLOWLY EDGING TO
THE NORTHWEST TODAY...GENERATING DYNAMIC FORCING ON A VERY WET AND
MODERATELY UNSTABLE AIRMASS. STRONG DIFLUENCE/DEFORMATION ALOFT IS
NOTED IN THE UPPER LEVELS...PER THE VAPOR IMAGERY AND MODEL
200/300MB STREAMLINE FIELDS. SO...DESPITE VERY COOL HIGH
TEMPERATURES TODAY PUTTING A DAMPER ON POTENTIAL
INSTABILITY...FORCING IS SUFFICIENT TO SPIN UP WIDESPREAD
CONVECTION. WEAK ELY STEERING FLOW ALLOWING FOR SLOW STORM MOTION
WHICH AIDS THE HEAVY RAINFALL POTENTIAL. FLASH FLOOD WATCH WILL
CONTINUE THRU MIDNIGHT FOR MARICOPA COUNTY EAST.

PROGS ARE CONSISTENT THAT THE UPPER LOW WILL CONTINUE TO SLOWLY WORK
TO THE NORTHWEST OVER THE NEXT COUPLE OF DAYS...WITH THE LOW CENTER
MOVING INTO CENTRAL AZ BY SUNDAY AFTERNOON...AND THEN INTO FAR
NCNTRL AZ MONDAY AFTERNOON. THIS WILL KEEP OUR AIRMASS QUITE MOIST
AND UNSTABLE THRU THE WEEKEND WITH SOME DRYING STARTING TO WORK IN
BEHIND THE LOW BY MONDAY EVENING. A HIGH GRADE MONSOON FORECAST WILL
BE IN EFFECT TONIGHT THRU SUNDAY NIGHT...CHANCE TO LIKELY POPS IN
EFFECT EAST OF THE LOWER CO RIVER. DRIER AND MORE STABLE CONDITIONS
PERSIST OVER THE WESTERN ZONES...MAINLY OVER SERN CA...SO WE WILL
ONLY SEE A SLIGHT CHANCE FOR SHOWERS OR STORMS WEST OF THE RIVER
TONIGHT THRU SUNDAY NIGHT.

BY TUESDAY THE UPPER LOW WILL EXIT TO OUR NORTHEAST...WITH A DRIER
SWLY WINDFLOW SETTING UP OVER MOST OF OUR CWA. WE WILL CONTINUE TO
SEE DRYING FROM THE WEST...WITH ONLY A MODERATE GRADE FORECAST IN
EFFECT EAST OF THE RIVER. THAT IS...WE WILL SEE SLIGHT CHANCES OVER
THE CENTRAL DESERTS AND CHANCE POPS OVER THE HIGHER TERRAIN EAST OF
PHOENIX. AS THE AIRMASS DRIES...TEMPS WILL START TO WARM...AND HIGHS
BY TUESDAY SHOULD RETURN TO AROUND SEASONAL NORMALS.

PROGS AGREE THAT THE DRYING AND WARMING TREND WILL CONTINUE FOR THE
EXTENDED PORTION OF THE FORECAST. AN UPPER TROF ALONG THE CA COAST
WILL PROVIDE A SWLY WINDFLOW INTO SERN CA AND SWRN AND CENTRAL
ARIZONA...WHICH WILL CONTINUE TO PUSH MOISTURE OFF TO THE EAST AND
LEAD TO DECREASING POPS/WEATHER OVER THE CWA DAY BY DAY. FROM
WEDNESDAY THRU SATURDAY...THE THREAT FOR THUNDERSTORMS SHOULD BE
LIMITED MAINLY TO THE HIGHER TERRAIN EAST OF PHOENIX...ZONE 24. HIGH
TEMPS WILL BE ABOVE SEASONAL NORMALS EACH DAY...WITH SOME OF THE
HOTTER LOWER DESERTS TO REACH OR EXCEED 110 DEGREES.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX AND KIWA...SCATTERED SHOWERS
WITH ISOLATED T-STORMS WILL CONTINUE OVER THE AREA THIS AFTN/EVE.
LOCAL CIGS 5000FT AGL...DOWN TO 4000FT AGL IN HEAVIER SHOWERS. NO
STRONG OUTFLOWS EXPECTED TO AFFECT TAF SITES...THOUGH SUDDEN WIND
SHIFTS ARE POSSIBLE. IF CLOUD COVER THINS AND SURFACE HEATING
IMPROVES DURING THE AFTERNOON...COULD SEE INCREASE IN THUNDERSTORM
COVERAGE...SOME WITH LOCALLY HEAVY RAINFALL THAT COULD LOWER
VISIBILITY TO LESS THAN 2SM FOR BRIEF PERIODS OF TIME.

SOUTHEAST CA AND SOUTHWEST AZ...INCLUDING KBLH AND KIPL. EXPECT
SCT-BKN CLOUD BASES AOA 10 KFT THIS AFTERNOON AND EVENING. ISOLATED
STORMS POSSIBLE...ESPECIALLY NEAR/ALONG PORTIONS OF THE LOWER
COLORADO RIVER VALLEY...BUT UNCERTAINTY DICTATES USE OF CB IN TAFS
AT THIS TIME.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
ABOVE NORMAL PRECIP CHANCES WILL LINGER THROUGH THE WEEKEND AS A
MOIST AIRMASS REMAINS IN PLACE ACROSS THE DESERT SOUTHWEST. THIS
WILL RESULT IN AFTERNOON HUMIDITIES ONLY DROPPING INTO THE 20-30
PERCENT RANGE THROUGH THE WEEKEND WITH EXCELLENT OVERNIGHT RECOVERY
EXPECTED. DRIER AIR WILL BEGIN ARRIVING EARLY NEXT WEEK WITH PRECIP
CHANCES BECOMING CONFINED MAINLY TO THE HIGHER TERRAIN NORTHEAST OF
PHOENIX BY THE LATTER HALF OF NEXT WEEK. ACCORDINGLY...HUMIDITIES
WILL DROP SIGNIFICANTLY BUT OVERNIGHT VALUES WILL GENERALLY REMAIN
AT OR ABOVE 30 PERCENT ON THE LOWER ELEVATIONS.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...FLASH FLOOD WATCH UNTIL MIDNIGHT TONIGHT FOR SOUTH CENTRAL
     ARIZONA...ZONES 22...23...24...27...28.

CA...NONE.

&&

$$

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

DISCUSSION...CB/ELLIS
AVIATION...MEYERS
FIRE WEATHER...AJ/LEINS

NWS PSR Office Area Forecast Discussion