Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 281233 AAA
AFDPSR

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

.UPDATE...UPDATED AVIATION DISCUSSION.

&&

.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... 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...CB
AVIATION...MEYERS
FIRE WEATHER...VASQUEZ


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