Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 100935
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
235 AM MST THU JUL 10 2014

.SYNOPSIS...
MONSOON FLOW WILL BE DISRUPTED SOMEWHAT THIS WEEKEND WITH LESS
THUNDERSTORM ACTIVITY THAN SEEN THE PAST WEEK. WITH THIS TEMPORARY
LULL IN MONSOON ACTIVITY...TEMPERATURES ACROSS THE REGION WILL WARM
WELL INTO THE ABOVE NORMAL CATEGORY. MOISTURE SHOULD BEGIN TO SURGE
BACK NORTH EARLY NEXT WEEK ALLOWING MORE PERVASIVE THUNDERSTORMS TO
DEVELOP WHILE TEMPERATURES FALL BACK TOWARDS THE SEASONAL NORMAL.

&&

.DISCUSSION...
THE LARGEST FORECAST CHALLENGE FOR THE NEXT SEVERAL DAYS WILL BE
DIAGNOSING THE IMPACT AND MAGNITUDE OF A SUBTLE SHIFT IN THE FLOW
PATTERN ALOFT ACROSS THE REGION. THE PRIMARY SUBTROPICAL HIGH CENTER
WILL DRIFT EASTWARD INTO THE CNTRL/SRN PLAINS OVER THE NEXT 24-48
HOURS WHILE LOWER HEIGHTS...AT LEAST TWO SHORTWAVES...AND
PREDOMINANT SWLY FLOW EDGE ONTO THE CALIFORNIA COAST. THIS
CONFIGURATION WILL ALLOW DRIER AIR TO ADVECT EASTWARD ACROSS MUCH OF
THE FORECAST AREA...SIGNIFICANTLY LIMITING INSTABILITY AND BRINGING
A MORE INACTIVE CONVECTIVE PERIOD TO THE REGION. EVENTUALLY...AS THE
AFOREMENTIONED SHORTWAVES LIFT NORTH INTO THE PACIFIC NORTHWEST BY
THE END OF THE WEEKEND...HIGH PRESSURE ALOFT WILL RETROGRADE BACK
INTO THE GREAT BASIN PROVIDING A PATTERN OF DEEP SOUTHEASTERLY FLOW
MUCH MORE CONDUCIVE FOR WIDESPREAD THUNDERSTORMS.

EARLY MORNING WV IMAGERY DEPICTS TWO DISTINCT MCV CENTERS ROTATING
NORTH ALONG THE LOWER COLORADO RIVER ON THE WESTERN PERIPHERY OF THE
SUBTROPICAL HIGH CIRCULATION. IN ALL LIKELIHOOD...THERE ARE MORE
SUCH VORTICITY CENTERS SPINNING OVER THE REGION...HOWEVER THE LACK
OF STORMS/OUTFLOW THE PAST 24 HOURS HAS MADE IDENTIFICATION MORE
DIFFICULT. NEVERTHELESS...WITH NO LARGER EASTERLY WAVES IMPACTING
THE REGION TODAY AND DEVELOPING SOUTHWESTERLY FLOW ACROSS THE EAST
PACIFIC PINCHING THE SUBTROPICAL RIDGE AND YIELDING CONFLUENT FLOW
ALOFT...THERE IS SOME QUESTION AS TO THE AMOUNT OF THUNDERSTORM
ACTIVITY THAT COULD DEVELOP AND SURVIVE INTO THE FORECAST AREA THIS
AFTERNOON/EVENING. UNLIKE YESTERDAY...SFC HEATING SHOULD BE MORE
EFFICIENT (ALTHOUGH SOME DEBRIS CLOUDS WILL STILL PREVAIL) ALLOWING
MLCAPES AROUND 500 J/KG TO BE REALIZED...HOWEVER FORECAST SOUNDINGS
ALREADY BEGIN TO SHOW THE ENTRAINMENT OF DRY AIR INTO THE BOUNDARY
LAYER WITH LOW LEVEL MIXING RATIO STARTING TO DECREASE CLOSER TO 10
G/KG THIS AFTERNOON. THEREFORE...BELIEVE STORMS DEVELOPING OVER
HIGHER TERRAIN WILL PROPAGATE TOWARDS THE CWA...BUT TEND TO DROP
CORES BEFORE REACHING LOWER ELEVATIONS RESULTING IN MORE
WIND/BLOWING DUST THREAT THAN ACTUAL RAINFALL. THUS...HAVE TRENDED
POPS LOWER ALTHOUGH HAVE YET TO EXCLUSIVELY MENTION BLOWING DUST IN
THE FORECAST GRIDS UNTIL BETTER CONFIDENCE IN THIS OUTCOME CAN BE
DETERMINED.

MODEL GUIDANCE CONTINUES TO POINT TOWARDS LITTLE TO NO STORM
ACTIVITY IMPACTING THE FORECAST AREA FRIDAY AND SATURDAY AS DRY AIR
PUNCHES EAST THROUGHOUT MUCH OF THE REGION. FORECAST SOUNDING DATA
REMAINS CONSISTENT IN PORTRAYING BOUNDARY LAYER MIXING RATIOS
FALLING STEEPLY INTO A 5-8 G/KG RANGE BY FRIDAY EVENING WITH TOTAL
COLUMN PWATS DESCENDING TO AROUND ONE INCH. AS A
RESULT...INSTABILITY PARAMETERS ARE ALMOST COMPLETELY ABSENT SANS
THE HIGHER TERRAIN OF SRN GILA COUNTY...AND MOST POPS WERE
SIGNIFICANTLY REDUCED FOR THE PHOENIX METRO AND POINTS WESTWARD. ONE
CONSEQUENCE OF THIS DRIER REGIME WILL BE NOTABLE WARMING OF THE
SFC-H7 LAYER...SPECIFICALLY WITH H8 TEMPERATURES REACHING NEAR 30C
AND AFTERNOON HIGHS BACK AROUND THE 110F THRESHOLD.

THIS CONVECTIVELY INACTIVE WEEKEND PERIOD SHOULD BE FAIRLY SHORT
LIVED AS 596DM HIGH PRESSURE ALOFT RETROGRADES BACK INTO THE GREAT
BASIN BY EARLY NEXT WEEK...ALLOWING PRONOUNCED DEEP SOUTHEASTERLY
FLOW TO RETURN TO THE FORECAST AREA. WHILE MODEL UNCERTAINTY
REGARDING THE TIMING OF MOISTURE SURGING BACK NORTH EXISTS...THE
OVERALL PATTERN STRONGLY SUPPORTS WIDESPREAD CONVECTION AND
POTENTIALLY SEVERAL VERY ACTIVE DAYS NEXT WEEK. MORE ROBUST ACTIVITY
MAY BEGIN AS EARLY AS SUNDAY WITH THE INTRODUCTION OF AN EASTERLY
WAVE...HOWEVER THIS WAVE MAY JUST BE THE INITIAL IMPETUS FOR
MOISTURE RETURN WITH SUBSEQUENT PERTURBATIONS DELIVERING THE
NECESSARY LIFT IN AN INCREASINGLY UNSTABLE ENVIRONMENT. STARTED
RAMPING POPS UP MONDAY AFTERNOON...WITH THE EXPECTATION OF STRONGER
WORDING WITH BETTER CONFIDENCE ATTAINED BY THE WEEKEND TIME FRAME.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...KSDL...
DEEP PLUME OF MONSOON MOISTURE CONTINUES TO RUN SOUTH TO NORTH OVER
ARIZONA EVEN AS TODAY WAS MORE OF A DOWN DAY IN STORM ACTIVITY. FOR
TONIGHT...EXPECT DEBRIS CLOUDS TO DRIFT IN FROM THE SOUTH MOSTLY
REMAINING SCT-BKN IN NATURE RANGING FROM 10-15KFT OR SO. EVEN
MOISTURE REMAINS IN THE ATMOSPHERE THAT SOME OF THE THICKER CLOUDS
COULD GENERATE SOME LIGHT PASSING SHOWERS...BUT NOT WIDESPREAD OF
FREQUENT ENOUGH TO INCLUDE IN THE TAFS OVERNIGHT. WEST TO SOUTHWEST
WINDS TO HOLD OVERNIGHT...POSSIBLY BACKING TO THE EAST CLOSER TOWARDS
SUNRISE. SPEEDS SHOULD REMAIN 12KTS OR LESS THROUGH THURSDAY AM.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
ISOLATED STORM ACTIVITY TO THE NORTHEAST AND EAST OF KBLH WILL LINGER
OVER THE NEXT HOUR OR TWO BEFORE DISSIPATING. SHOWERS/STORMS NOT
EXPECTED TO IMPACT THE KBLH TERMINAL...SO OUTSIDE OF SOME VARIABLE
OUTFLOW WINDS...SHOULD BE QUIET NIGHT FOR KBLH AND KIPL. DRIER AIR
ALOFT HAS GRADUALLY TRANSITION INTO SOUTHEAST CA...KEEPING THE
THICKER DEBRIS CLOUDS AT BAY AND STORM CHANCES VERY LOW FOR THURSDAY.
STRONG MOISTURE SURGE FROM THE GULF OF CALIFORNIA WILL MAINTAIN WIND
HEADINGS VARYING FROM SOUTH THROUGH EAST WITH SPEEDS 10-15KTS AT
TIMES.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
A TYPICAL MONSOONAL PATTERN WILL REMAIN IN PLACE ACROSS THE DESERT
SOUTHWEST DURING THE PERIOD...WITH ELEVATED HUMIDITY LEVELS...
ESPECIALLY ACROSS SOUTH CENTRAL ARIZONA. AFTERNOON HIGH TEMPERATURES
ARE EXPECTED TO REMAIN NEAR SEASONAL NORMALS EACH DAY...ALTHOUGH
THEY COULD LOWER TO BELOW NORMAL VALUES SHOULD SIGNIFICANT MONSOON
RAINS DEVELOP. ISOLATED AFTERNOON AND EVENING THUNDERSTORMS ARE ON
TAP EACH DAY MAINLY EAST OF THE LOWER COLORADO RIVER VALLEY...WITH
SCATTERED STORMS TO MOVE ACROSS THE HIGHER TERRAIN EAST OF PHOENIX.
WINDS WILL BE ON THE LIGHT SIDE EACH DAY...FAVORING NORMAL DIURNAL
SPEEDS AND DIRECTIONS...HOWEVER STRONG GUSTY AND VARIABLE WINDS WILL
ACCOMPANY ANY THUNDERSTORMS THAT DEVELOP.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO
AVIATION....DEWEY
FIRE WEATHER...VM/LEINS





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