Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 071048
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
348 AM MST TUE JUL 7 2015

.SYNOPSIS...
TODAY WILL BE THE LAST OPPORTUNITY FOR THUNDERSTORMS ON THE LOWER
ELEVATIONS FOR THE NEXT SEVERAL DAYS AS DRIER SOUTHWESTERLY FLOW
DEVELOPS ACROSS THE REGION. RAINFALL CHANCES WILL PRIMARILY BE
RELEGATED TO THE MOUNTAINS OF NORTHERN AND EASTERN ARIZONA. DESPITE
THE LACK OF STORM ACTIVITY...TEMPERATURES WILL REMAIN SLIGHTLY BELOW
NORMAL. DURING THIS UPCOMING WEEKEND...HIGH PRESSURE WILL BEGIN TO
STRENGTHEN LEADING TO WARMER TEMPERATURES AND POSSIBLY AN INCREASE IN
MOISTURE.

&&

.DISCUSSION...
TODAY AND WEDNESDAY...
MOISTURE CONTINUES TO BE SLOWER TO DECLINE THAN PREVIOUSLY
ANTICIPATED AND THUS REINTRODUCED SLIGHT CHANCE POPS ON THE LOWER
DESERTS TODAY EAST OF THE LOWER COLORADO RIVER VALLEY. ANOTHER FACTOR
IS THE POTENTIAL FOR SUBTLE PERTURBATIONS WITHIN THE SOUTHWESTERLY
FLOW TO POSSIBLY ENHANCE THE CAPE THAT IS LEFT. THERE MAY ALSO BE A
LITTLE BIT OF DIFFLUENCE OVER OUR AREA BUT NOT NEARLY TO THE SAME
DEGREE AS IS OVER VEF CWA. HOWEVER...WOULD ANTICIPATE LESS STORM
COVERAGE THAN WAS SEEN ON MONDAY AS THERE WILL BE SOME FURTHER
DRYING. THE SOUTHWESTERLY FLOW OVER OUR AREA IS PART OF A REX PATTERN
OVER THE NORTHEAST PACIFIC WITH AN UPPER LOW...CENTERED OFF THE
NORTHERN CALIFORNIA COAST...TRAPPED UNDER NARROW RIDGE WITH THE MAIN
ANTICYCLONIC CENTER NEAR THE B.C. CANADA COAST. MODELS CONTINUE TO
DEPICT THE LOW ADVANCING SLOWLY EASTWARD LEADING TO AN EASTWARD
RETREAT OF DEEPER MOISTURE WITH STORM CHANCES CONFINED TO EASTERN
ARIZONA WITH JUST OUR HIGHER TERRAIN ZONE HAVING ANY POPS. OF NOTE IS
THAT STRONGER FLOW ALOFT ALSO MOVES OVER THE DESERT SOUTHWEST WHICH
COULD BE A PLAYER FOR AREAS THAT HAVE THE MOISTURE.

THURSDAY AND FRIDAY...
AS THE UPPER LOW CENTER MOVES OVER SRN CALIFORNIA THURSDAY...A
DEEPER SOUTHERLY FLOW TEMPORARILY INCREASES MOISTURE OVER SOUTHEAST
ARIZONA...WITH A SHARP DROP OFF IN MOISTURE OVER CENTRAL ARIZONA.
DURING THE DAY THURSDAY...THE LOW SWINGS A VORT LOBE THROUGH
SOUTHEAST CALIFORNIA AND WESTERN ARIZONA...BRUSHING EASTERN ARIZONA.
ASSOCIATED DYNAMICAL FORCING LOOKS TO BE LESS THAN ROBUST OVER THE
AREAS WHERE THE MOISTURE WILL BE WITH THE JET AXIS REMAINING TO THE
WEST. HOWEVER...NUDGED UP THE POPS OVER ZONE 24 AS EVEN SUBTLE
INFLUENCES CAN MAKE A DIFFERENCE THIS TIME OF YEAR. THE LOW QUICKLY
SHIFTS OFF AND WEAKENS BUT IS REPLACED BY RENEWED TROUGHING WHICH
KEEPS A JET IN PLACE OVER SOUTHEAST CALIFORNIA AND NORTHERN ARIZONA
FRIDAY. VERTICAL WIND SHEAR PEAKS ON THURSDAY AND FRIDAY SO ANY
STORMS THAT CAN SURVIVE COULD BE POTENT. ANTICIPATE TEMPS TO BE
BELOW NORMAL WITH THIS THE PASSAGE OF THE LOW.

SATURDAY THROUGH MONDAY...
MODELS CONTINUE TO  DEPICT A WESTWARD EXPANSION OF THE HIGH CENTERED
TO OUR EAST WITH MOISTURE IMPROVING OVER THE LOWER DESERTS. THE GFS
CONTINUES TO BE MORE GENEROUS WITH THE MOIST ADVECTION THAN THE
ECMWF. THIS IS LIKELY DUE IN PART TO HOW THE GFS HAS MORE OF A
SOUTHERLY COMPONENT TO THE FLOW WITH DEEPER COASTAL TROUGHING.
ACCORDINGLY IT ALSO SHOWS STRONGER WINDS ALOFT OVER OUR FORECAST
AREA. IN ADDITION...IT SHIFTS THE TROUGH NORTHEASTWARD SUNDAY WITH A JET
MOVING THROUGH CALIFORNIA AND INTO THE GREAT BASIN WITH THE ENTRANCE
REGION OVER OUR FORECAST AREA FOR A BRIEF TIME. TAKING CONSERVATIVE
APPROACH DUE TO INHERENT UNCERTAINTIES...GOING WITH ONLY SLIGHT
CHANCE POPS OVER THE SOUTH-CENTRAL DESERTS SUNDAY WHICH IS AN
WESTWARD EXPANSION COMPARED TO PRECEDING DAYS. THERE IS AN EVEN
GREATER DIFFERENCE BETWEEN GFS AND ECMWF IN MOISTURE FOR MONDAY AS
THE ECMWF HOLDS ON TO THE WEST COAST TROUGHING AND NUDGES IT FURTHER
EAST FOR MORE DRYING. THE GFS MEANWHILE EXPANDS THE HIGH FURTHER WEST
FOR A BIT OF ADDITIONAL WARMING ALOFT. BOTH OF THOSE
SCENARIOS...ESPECIALLY ECMWF...COULD HAVE A NEGATIVE IMPACT ON STORM
POTENTIAL AND SO PULLED BACK POPS FROM THE LOWER ELEVATIONS OF
SOUTH-CENTRAL ARIZONA MONDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
WINDS SHOULD REMAIN OUT OF THE WEST THROUGH EARLY MORNING HOURS
TUESDAY...BEFORE SWITCHING EASTERLY. CLOUDS SHOULD REMAIN AT OR ABOVE
10K FT AND BEGIN LIFTING BY 15Z TUESDAY. ANOTHER CHANCE OF AFTERNOON
AND EARLY EVENING TSRA SHOULD REMAIN CONFINED MAINLY WELL NORTH AND/OR
EAST OF THE TERMINALS.


SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
NO AVIATION IMPACTS UNDER MOSTLY CLEAR SKIES. WINDS WILL GENERALLY
RETAIN A SOUTHERLY COMPONENT THROUGH THE PERIOD...THOUGH COULD
BECOME VARIABLE AT TIMES TOWARDS SUNRISE. OCCASIONAL AFTERNOON GUSTS
MAY ALSO BE POSSIBLE.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
ATMOSPHERIC FLOW WILL REMAIN SOUTHWESTERLY HEADING INTO THE
WEEKEND...KEEPING THUNDERSTORM CHANCES WELL TO THE EAST OF PHOENIX
OVER HIGHER TERRAIN LOCATIONS. EVEN THE TYPICALLY ACTIVE REGIONS IN
SOUTHERN GILA COUNTY MAY LACK THUNDERSTORMS DURING THE END OF THE
WEEK. MOISTURE MAY RETURN BY THE BEGINNING OF NEXT WEEK BRINGING
BACK MORE EXTENSIVE STORMS. AFTERNOON HUMIDITY LEVELS WILL RETREAT
BACK INTO A 10-15 PERCENT RANGE ACROSS LOWER ELEVATIONS WITH FAIR TO
GOOD OVERNIGHT RECOVERY. SOMEWHAT 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...AJ
AVIATION...DEWEY/MO
FIRE WEATHER...MO


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