Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 050427
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
925 PM MST SAT JUL 4 2015

.SYNOPSIS...
RELATIVELY HIGH MONSOON HUMIDITY AND UNSETTLED SOUTHERLY FLOW ALOFT
WILL CONTINUE THE CHANCE OF SHOWERS AND THUNDERSTORMS OVER PORTIONS
OF SOUTHWEST AND SOUTH CENTRAL ARIZONA THIS AFTERNOON AND EVENING.
THE THREAT FOR SHOWERS ON SUNDAY WILL SHIFT INTO CENTRAL AND EASTERN
ARIZONA...WITH A MORE DRIER AND STABLE AIRMASS NEXT WEEK.

&&

.DISCUSSION... UPPER LEVEL LOW PRESSURE SYSTEM TAKING SHAPE ALONG
THE CALIFORNIA COAST HAS STARTED TO PUSH THE UPPER HIGH FUTHER TO
THE EAST...AND HAS SET UP A SOUTH/SOUTHWEST STEERING FLOW ACROSS
MUCH OF ARIZONA AND SOUTHEAST CALIFORNIA. DRIER AIR HAS BEEN
SPREADING INTO OUR WESTERN DESERTS...AND IR IMAGERY AT 8 PM SHOWED
GENLY CLEAR SKIES WEST OF MARICOPA COUNTY. SURFACE DEWPOINTS OVER
THE CENTRAL DESERTS WERE A BIT ON THE LOW SIDE AND WERE RUNNING
MOSTLY IN THE MID 50S THIS EVENING. CONVECTION DURING THE AFTERNOON
ADN EVENING ACROSS SOUTH CENTRAL ARIZONA...AND SOUTHEAST AZ...HAS
BEEN VERY MINIMAL AND THE CLOUD FIELD AS SEEN IN IR IMAGERY LOOKED
RATHER WARM TOPPED AND STABLE. A LOOK AT THE PHOENIX AND TUCSON
SOUNDINGS SHED SOME LIGHT ON THIS AS THEY BOTH SHOWED A PROMINENT
UPPER CAP AND VERY LOW CAPE VALUES.

RADAR AT 8 PM SHOWED JUST A FEW STRUGGLING SHOWERS MAINLY SOUTH OF
THE GREATER PHOENIX AREA AND NO THUNDERSTORMS WERE POISED TO MOVE
INTO THE CENTRAL DESERTS OR SRN GILA COUNTY. FOR THE REST OF
TONIGHT...BOTH THE NAM AND THE GFS SUGGEST THERE MAY BE A WEAK
WAVE/DISTURBANCE EMBEDDED IN THE SOUTHERLY FLOW ALOFT THAT WILL MOVE
NORTH AND INTO SOUTH CENTRAL AZ AFTER MIDNIGHT. THIS FEATURE IS HARD
TO DETECT ON THE PLOT OR VAPOR IMAGERY SO CONFIDENCE IN IT IS NOT
HIGH. STILL...GIVEN THE SIGNIFANT CONVECTION SEEN SOUTHEAST OF
TUCSON...OVER NWRN MEXICO...AND THE TENDENCY FOR LATE NIGHT
CONVECTION OVER THE DESERTS OVER THE PAST WEEK...DECIDED TO KEEP
POPS AOA 20 PERCENT OVER THE CENTRAL DESERTS FOR THE REST OF
TONIGHT. WE MAY WELL SEE THICKENING OF THE MID LEVEL CLOUD FIELD
AFTER MIDNIGHT WITH EMBEDDED SHOWERS...AND POSSIBLY A
THUNDERSTORM...ALTHOUGH GIVEN THE STABLE CHARACTER OF THE AIRMASS
PER THE EVENING SOUNDINGS...ANY STORM THAT DEVELOPS WILL LIKELY BE
WEAK AND LOW TOPPED. FORECASTS HAVE BEEN UPDATED TO REFLECT THIS
THINKING AND LOOK TO BE IN GOOD SHAPE.

.PREVIOUS DISCUSSION...

.TONIGHT AND SUNDAY...LOOKING AT WATER VAPOR
SATELLITE THE UPPER LEVEL HIGH CONTINUES TO REPOSITION...THE
300/250MB CENTER HAS ELONGATED WITH THE AXIS POSITIONED ACROSS
WESTERN NEW MEXICO THIS AFTERNOON. MODELS CONTINUE TO INDICATE THAT
THE CENTER WILL FINALLY CONSOLIDATE AND TAKE UP RESIDENCE SOMEWHERE
NEAR EL PASO BY SUNDAY MORNING. AS THE FLOW HAS
TRANSITIONED...AFTERNOON SATELLITE IMAGERY AND REGIONAL RADAR MOSAIC
REVEAL SHOWERS AND THUNDERSTORMS THAT HAVE BLOSSOMED IN THE WHITE
MOUNTAINS IN EASTERN AZ...AND ALONG PORTIONS THE RIM COUNTRY IN
NORTHERN AZ. A DEFORMATION ZONE OVER NORTHEAST AZ CURRENTLY SUPPORTS
THE STORM DEVELOPMENT IN THAT AREA. LATER THIS EVENING... ANOTHER
DEFORMATION ZONE WILL OPEN UP ACROSS SOUTHEAST AZ FOR INCREASED
STORM ACTIVITY...SO THE BEST THREAT OF AFTERNOON/EVENING SHOWERS AND
THUNDERSTORMS WILL BE OVER THE SOUTHEAST QUARTER OF THE
STATE...INCLUDING EASTERN PORTIONS OF GILA COUNTY/ZONE 24.

THE ONE FEATURE THAT HAS THE POTENTIAL TO EXTEND THE SHOWER AND
THUNDERSTORM THREAT FURTHER NORTH AND WEST INTO MARICOPA/PINAL
COUNTIES THIS EVENING...IS THE MCV THAT HAS DRIFTED NORTHWARD OUT OF
SONORA MEXICO AND IS NOW CENTERED NEAR NOGALES. SOME THUNDERSTORMS
HAVE ALREADY FIRED UP ALONG THE NORTHERN PERIPHERY IF THE MCV...BUT
THESE STORMS ARE STRUGGLING TO MOVE NORTHWARD IN TO THE DRIER MORE
SUBSIDENT ENVIRONMENT NOW IN PLACE OVER THE CENTRAL DESERTS. SURFACE
DEW POINTS ACROSS SOUTH-CENTRAL ARIZONA HAVE DROPPED OFF A BIT THIS
AFTERNOON...CURRENTLY IN THE LOW TO MID 50S AT MANY SITES...BUT
THERE IS STILL PLENTY OF MID LEVEL MOISTURE THAT REMAINS THAT CAN
AID CONVECTION LATER ON THIS EVENING.

MODELS STILL HOLD ONTO A MID-LEVEL DISTURBANCE THAT MOVES NORTHWARD
IN THE ANTICYCLONIC FLOW LATER THIS EVENING...SO WILL CONTINUE TO
HOLD ONTO THE CHANCE POPS FOR SOUTH-CENTRAL ARIZONA...MAINLY
MARICOPA COUNTY EASTWARD. THERE WILL BE LITTLE TO NO ACTIVITY
WESTWARD TOWARD THE COLORADO RIVER AND INTO SOUTHEAST CALIFORNIA
BASED ON THE DRIER SOUTHWESTERLY/CYCLONIC FLOW THAT IS NOW OVER OUR
WESTERN ZONES...ALL DUE TO THE UPPER LEVEL LOW NEAR 35N 130W IN
THE EASTERN PACIFIC.

THE FLOW ALOFT ON SUNDAY IS FORECAST TO BECOME MORE SOUTHWESTERLY
AND LAMINAR A DAY EARLIER THAN PREVIOUS MODEL RUNS SUGGESTED...
RESULTING IN A LOW GRADE SLIGHT CHANCE OF SHOWER FORECAST IN SOUTH
CENTRAL AZ...WITH SLIGHTLY HIGHER PRECIP PROBABILITIES IN THE
MOUNTAINS OF SOUTHERN GILA COUNTY.

MONDAY THROUGH FRIDAY...FOR THE MOST PART UPPER LEVEL FLOW BECOMES
MORE WEST SOUTH-WESTERLY ALOFT...WITH THE DEEPEST MONSOON MOISTURE
SLOWLY SHIFTING INTO EASTERN AZ. THIS PATTERN IS QUASI-
STABLE...HOWEVER SOME UNCERTAINTY WILL EXIST AROUND MIDWEEK...NAMELY
THE EASTERN PACIFIC TROF IS FORECAST TO SHIFT INLAND CREATING BROAD
DIFLUENT FLOW ALOFT OVER THE SOUTHWESTERN STATES AND MAYBE SOME
POTENTIAL FOR RENEWED STORMINESS WEDNESDAY.

WARMER AIR ALOFT WILL SHIFT INTO AZ FROM THE SOUTHWEST DIRECTION
THURSDAY AND FRIDAY AND LIKELY STABILIZE THE AIRMASS AGAIN.


SATURDAY AND SUNDAY...AS THE WEST COAST TROF WEAKENS...MUCH STRONGER
SOUTHEASTERLY MID/UPPER LEVEL WINDS FROM MEXICO ARE FORECAST SHIFT
BACK INTO THE SOUTHEAST QUARTER OF AZ...INCREASING MONSOON MOISTURE
ALONG WITH A FEW HARD TO TIME INVERTED TROFS. IN OTHER WORDS...AN
INCREASING THREAT FOR SHOWERS AND THUNDERSTORMS OVER SOUTHEAST
AZ...INCLUDING OUR PORTIONS OF SOUTH CENTRAL AZ FROM PHOENIX
EASTWARD.

$$

.AVIATION...

SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...

STEERING FLOW HAS BECOME SOUTH-SOUTHWEST...WHICH IS NOT FAVORABLE
FOR MOVING STORMS INTO THE CENTRAL DESERTS...AND A LOOK AT THE
LATEST EVENING SOUNDINGS SHOWED RATHER STABLE CONDITIONS. THUS THE
THREAT OF THUNDER FOR THE REST OF TONIGHT IS VERY LOW. HOWEVER
GUIDANCE SUGGESTS THAT WE MAY SEE A WEAK DISTURBANCE MOVE NORTH AND
INTO THE DESERTS AFTER MIDNIGHT...CONTINUING INTO SUNDAY MORNING
WHICH MAY BRING THICKER AND LOWER CLOUDS ALONG WITH EMBEDDED
SHOWERS. THUS WILL DROP MENTION OF VCTS BUT REPLACE WITH VCSH AND
KEEP THIS IN THE AREA TAFS THROUGH AT LEAST 11Z...WITH POTENTIAL FOR
LINGERING SHOWERS TO EXTEND INTO THE MORNING HOURS. CIGS SHOULD STAY
GENLY AOA 8K FEET OVERNIGHT AND INTO THE DAY SUNDAY.

WINDS TO BACK AROUND TO THE SOUTHEAST AFTER MIDNIGHT WITH SPEEDS
MOSTLY BELOW 10KT...THEN RETURN TO THE SOUTH/SOUTHWEST AFTER 18Z
SUNDAY.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

LITTLE IN TERMS OF AVIATION IMPACTS EXPECTED NEXT 24 HOURS AS FLOW
ALOFT HAS BECOME A DRIER SOUTHWESTERLY DIRECTION. SKIES TO BE MOSTLY
CLEAR THROUGH SUNDAY AFTERNOON AT LEAST WITH ONLY A FEW MID/HI
CLOUDS TO MOVE THROUGH AT TIMES. WINDS TO FAVOR THE SOUTH AT
KBLH...LOCALLY GUSTY DURING THE AFTERNOON ON SUNDAY. WINDS SHOULD
FAVOR THE SOUTHEAST MOST OF THE TAF PERIOD AT KIPL BUT MAY SWITCH
BRIEFLY TO THE SOUTHWEST THROUGH 09Z OR SO TONIGHT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
TUESDAY THROUGH SATURDAY...
ATMOSPHERIC FLOW WILL BECOME MORE WESTERLY/SOUTHWESTERLY NEXT
WEEK...ALLOWING DEEP MOISTURE AND THUNDERSTORM CHANCES TO BE
DISPLACED WELL TO THE EAST OF PHOENIX OVER HIGHER TERRAIN LOCATIONS.
EVEN THE TYPICALLY ACTIVE REGIONS IN SOUTHERN GILA COUNTY MAY LACK
THUNDERSTORM DEVELOPMENT AND COVERAGE FOR MUCH OF THE WEEK.
AFTERNOON HUMIDITY LEVEL WILL RETREAT BACK INTO A 10-15 PERCENT
RANGE ACROSS LOWER ELEVATIONS WITH FAIR TO GOOD OVERNIGHT RECOVERY.
HIGHER HUMIDITY VALUES WILL BE EXPERIENCED IN MOUNTAIN LOCATIONS.
GENERALLY LIGHT AND DIURNALLY DRIVEN WINDS SPEEDS AND DIRECTIONS
WILL PREDOMINATE ALL WEEK...WITH SOMEWHAT MORE AFTERNOON UPSLOPE
GUSTINESS THAN IS TYPICAL DURING MONSOON SEASON.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT ANY SIGNIFICANT WEATHER 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
PREVIOUS DISCUSSION...MEYERS/VASQUEZ
AVIATION...CB
FIRE WEATHER...MO


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