Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281650
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
950 AM MST FRI AUG 28 2015

.SYNOPSIS...
STRONG HIGH PRESSURE ALOFT WILL KEEP HIGH TEMPERATURES WELL ABOVE
SEASONAL NORMALS THROUGH SATURDAY WITH HOTTER LOWER DESERTS REACHING
OR EXCEEDING 110. THERE WILL BE SUFFICIENT MOISTURE EAST OF THE LOWER
COLORADO RIVER TO SUPPORT ISOLATED TO SCATTERED AFTERNOON AND EVENING
THUNDERSTORMS THROUGH SATURDAY. STARTING SUNDAY A DRIER SOUTHWEST
FLOW ALOFT WILL PUSH THE MOISTURE OFF TO THE EAST AND BY MONDAY STORM
CHANCES SHOULD BE CONFINED PRIMARILY TO HIGHER TERRAIN AREAS TO THE
EAST OF PHOENIX. THERE WILL BE A GRADUAL COOLING TREND STARTING
SUNDAY WITH CENTRAL DESERTS HIGH TEMPERATURES DROPPING TO AROUND
SEASONAL NORMALS BY THE MIDDLE OF NEXT WEEK.

&&

.DISCUSSION...
AFTER YESTERDAY`S ACTIVE MONSOON DAY...TODAY IS SHAPING UP TO BE
MUCH LESS ACTIVE. MOISTURE IS STILL PREVALENT AS MORNING RAOBS AND
SATELLITE DERIVED PWATS ARE STILL QUITE ELEVATED AT OR JUST ABOVE
1.50 INCHES. FLOW ALOFT CONTINUES TO BE WEAK...BUT HAS SHIFTED MORE
OUT OF THE NORTHWEST AND GUIDANCE INDICATES DECENT DRYING THROUGHOUT
THE DAY TODAY. THE BIGGEST INHIBITING FACTORS FOR WIDESPREAD SHOWERS
AND THUNDERSTORMS TODAY WILL BE THE DRYING NORTHWEST FLOW AND THE
MODESTLY WORKED OVER ATMOSPHERE FROM YESTERDAY`S ACTIVITY. AREA
TEMPERATURES ARE RUNNING ON AVERAGE 3-5 DEGREES COOLER THAN YESTERDAY
AND THUS NOT EXPECTING AN EARLY ONSET OF MOUNTAIN STORMS LIKE WE HAD
YESTERDAY. MID MORNING ML CAPES ARE HIGHEST OVER THE LOWER COLORADO
RIVER VALLEY WITH MUCH LESS INSTABILITY FROM PHOENIX EASTWARD.

CURRENT THINKING IS FIRST DEVELOPMENT WILL BE OVER HIGHER TERRAIN
AREAS OF SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA EARLY THIS
AFTERNOON AND THEN IN A MORE LIMITED CAPACITY OVER SOUTH-CENTRAL
ARIZONA. HI-RES MODEL OUTPUT SHOWS ONLY ISOLATED TO SCATTERED HIGH
TERRAIN ACTIVITY FOR THIS AFTERNOON WITH LITTLE TO NO STORMS OVER THE
LOWER DESERTS. POPS FOR TODAY ARE NEAR OR JUST ABOVE CLIMO AND MADE
SOME MINOR ADJUSTMENTS TO ADD IN SLIGHT CHANCES OVER HIGH TERRAIN
AREAS OF SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA WHILE LOWER POPS
OVER THE SOUTH-CENTRAL ARIZONA DESERTS. THE REST OF THE FORECAST
LOOKS TO BE IN GOOD SHAPE.

&&

.PREVIOUS DISCUSSION...
STRONG HIGH PRESSURE ALOFT REMAINS SITUATED ACROSS THE DESERT
SOUTHWEST THIS MORNING...WITH H5 HEIGHTS AROUND 594DM ACROSS THE
SOUTHERN DESERTS. THIS LED TO HOT TEMPERATURES OVER THE DESERTS
YESTERDAY WITH HIGHS REACHING 110 OVER THE HOTTER LOWER DESERTS.
DESPITE SOMEWHAT WEAK FLOW ALOFT...MOISTURE AND INSTABILITY WERE
SUFFICIENT YESTERDAY TO ALLOW FOR SCATTERED STRONG STORMS TO DEVELOP
ACROSS MUCH OF SOUTH CENTRAL ARIZONA. OUTFLOW BOUNDARY INTERACTIONS
WERE THE MAIN FORCING FEATURE FOR THE STRONG STORMS...NOT THE
PRESENCE OF A SIGNIFICANT INVERTED TROF/SHORT WAVE MOVING THROUGH THE
FLOW. YESTERDAYS CONVECTION ENDED LONG AGO AND AT 2 AM IR IMAGERY
SHOWED GENERALLY CLEAR SKIES FROM PHOENIX WESTWARD. SURFACE DEW
POINTS WERE ELEVATED AND WERE MOSTLY IN THE 60S WITH SOME LOW 70S
REPORTED.

THE TREND OF DRYING FROM THE WEST WILL BE PUT ON HOLD FOR THE NEXT
COUPLE OF DAYS OR SO...AND WE WILL BE LOOKING AT 2 MORE DAYS OF LOW
TO MODERATE GRADE MONSOON ACTIVITY ACROSS AREAS EAST OF THE LOWER
COLORADO RIVER. THE STRONG UPPER HIGH HAS BUILT WESTWARD A BIT AND
THE SOUTHWEST STEERING FLOW WILL BECOME MORE WEAK AND NONDESCRIPT
THROUGH SATURDAY...AS ARIZONA SITS UNDER THE CENTER OF THE STRONG
RIDGE. WITH MOISTURE REMAINING ELEVATED...PWAT VALUES ABOVE 1.5
INCHES IN MANY PLACES...PLENTY OF MLCAPE AVAILABLE...AND HIGH TEMPS
CLIMBING NEAR OF ABOVE 110 OVER THE HOTTER DESERTS...CONDITIONS ARE
SUITABLE FOR ISOLATED TO SCATTERED AFTERNOON AND EVENING STORMS
DEVELOPING TODAY AND SATURDAY. ONCE AGAIN...IT APPEARS THAT OUTFLOW
BOUNDARY INTERACTION WILL PLAY THE DOMINANT ROLE IN FORCING
CONVECTION AS MODELS DO NOT FORECAST ANY SIGNIFICANT
DISTURBANCES/INVERTED TROFS TO MOVE ACROSS THE AREA OVER THE NEXT 2
DAYS. POPS HAVE BEEN RAISED A BIT TODAY AND SATURDAY WILL STAY IN
THE SLIGHT CHANCE CATEGORY EAST OF THE LOWER CO RIVER...WITH CHANCE
VALUES OVER THE HIGHER TERRAIN EAST OF PHOENIX.

LATEST GFS AND ECMWF DETERMINISTIC GUIDANCE AS WELL AS ENSEMBLE
GUIDANCE REMAINS CONSISTENT IN CALLING FOR THE AFOREMENTIONED DRYING
TREND TO BEGIN SUNDAY AND CONTINUE THROUGH AT LEAST THE MIDDLE OF
NEXT WEEK. UPPER TROFFING IS FORECAST TO SET UP BOTH ALONG THE WEST
COAST AND INLAND OVER THE PAC NORTHWEST AND THIS WILL LEAD TO
STRENGTHENING SOUTHWEST FLOW ALOFT TO WORK INTO THE DESERT SOUTHWEST
AND GRADUALLY THIN OUT THE MOISTURE OVER SE CALIFORNIA AND THE LOWER
AZ DESERTS. BY NEXT MONDAY THUNDERSTORM CHANCES SHOULD BE CONFINED
PRIMARILY TO HIGHER TERRAIN AREAS EAST OF PHOENIX...ZONE 24 TO BE
EXACT. THERE WILL BE PERIODS OF HIGH CLOUDS MOVING THROUGH THE FLOW
BUT OVERALL DESERTS SHOULD RANGE FROM MOSTLY SUNNY TO PARTLY SUNNY
EACH DAY FROM MONDAY ONWARD. AS THE UPPER TROFFING DEVELOPS AND
HEIGHTS FALL...HIGH TEMPERATURES WILL STEADILY FALL OFF AND BY NEXT
MONDAY THE WARMER LOWER DESERTS WILL BE WELL UNDER 110. THE GREATER
PHOENIX AREA IS FORECAST TO DROP TO 105 ON MONDAY...AND EVENTUALLY
TO 103 ON WEDNESDAY AND THURSDAY. THE 103 DEGREE READINGS WILL EQUAL
THE CLIMATE NORMALS FOR THOSE DAYS.

&&

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

MOSTLY CLEAR SKIES AND LIGHT WINDS 10KT OR LESS EXPECTED AT ALL TAF
SITES. SKIES BECOME SCT-BKN AOA 10KFT ACROSS SOUTH-CENTRAL AZ...AND
THUNDERSTORM ACTIVITY WILL PICK UP AFTER 18Z OVER THE MOUNTAINS AND
HIGHER TERRAIN WELL EAST/NORTH OF PHOENIX...WITH SKIES REMAINING
MOSTLY CLEAR ACROSS SOUTHEAST CALIFORNIA. POSSIBLE FOR AN ISOLATED
STORM TO FORM OVER THE LOWER CENTRAL DESERTS AND GUSTY OUTFLOWS TO
IMPACT KPHX/KIWA/KSDL LATER THIS AFTERNOON AND EVENING.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...DRIER AND WARMER WEATHER WILL SPREAD INTO
REGION FROM THE WEST...HOWEVER A SLIGHT CHANCE OF AFTERNOON AND
EVENING TSTMS IS STILL FORECAST FOR THE MOUNTAINS OF SOUTHERN GILA
COUNTY EACH DAY. HIGH TEMPERATURES THROUGH SUNDAY WILL BE WELL ABOVE
NORMAL WITH HOTTER DESERTS IN EXCESS OF 110...WITH SOME COOLING BACK
TOWARD NORMAL EARLY NEXT WEEK. MINIMUM RELATIVE HUMIDITIES WILL FALL
INTO THE 10 TO 15 PERCENT RANGE OVER THE WESTERN DESERTS BUT STAY
MOSTLY ABOVE 15 PERCENT ACROSS SOUTH CENTRAL ARIZONA EACH DAY WITH
VALUES REACHING 25 PERCENT IN SOUTHERN GILA COUNTY. AFTERNOON
SOUTHWEST WINDS WILL RANGE FROM 10 TO 20 MPH. GOOD OVERNIGHT
RECOVERY IS EXPECTED.


.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT CONDITIONS ACCORDING TO STANDARD
OPERATING PROCEDURES.

&&

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

$$

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

DISCUSSION...KUHLMAN
PREVIOUS DISCUSSION...CB
AVIATION...MEYERS
FIRE WEATHER...VASQUEZ



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