Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 101559
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
900 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...
FOR THE MOST PART THIS MORNING THE WEATHER HAS BEEN RATHER QUIET
ACROSS THE LOWER DESERTS...WITH THE EXCEPTION OF A CLUSTER OF
THUNDERSTORMS THAT DEVELOPED ALONG THE LOWER COLORADO RIVER VALLEY
EARLIER THIS MORNING. THE CLUSTER WAS LOCATED OVER THE NORTHERN
PORTION OF THE COLORADO RIVER...FROM BLYTHE NORTHWARD. IT WAS BEING
KICKED OFF BY AN UPPER LEVEL VORT LOBE OVER SERN CA...ROTATING
NORTHWARD ALONG A PROMINENT MOISTURE BOUNDARY CLEARLY SEEN IN THE
VAPOR IMAGERY. UPPER DIFLUENCE AHEAD OF THIS VORT LOBE WAS HELPING
TO SUPPORT THE THUNDERSTORM DEVELOPMENT...AND THESE STORMS SHOULD
CONTINUE TO PUSH NORTH THIS MORNING AND EVENTUALLY DISSIPATE AND OR
MOVE OUT OF OUR AREA.

OTHERWISE...ACROSS THE CENTRAL AZ DESERTS...THERE WAS A LOT OF MID
LEVEL DEBRIS CLOUDS THIS MORNING...AND EVEN A BIT OF VIRGA....BUT
OTHERWISE NO SIGNIFICANT SHOWERS OR CONVECTION. A STRONGER SLY FLOW
ALOFT WAS NOTED IN THE PLOT AND SOUNDING DATA...AND MOISTURE VALUES
REMAINED QUITE HIGH AS THE DEEP MONSOONAL MOISTURE PLUME REMAINED IN
PLACE OVER MOST OF THE STATE. SOUNDINGS ALSO SHOWED DECENT AMOUNTS
OF INSTABILITY/CAPE AS WELL. DESPITE THE LACK OF WELL DEFINED
FORCING FEATURES/DISTURBANCES IN THE UPPER FLOW PATTERN...AND RATHER
LAMINAR STREAMLINE FIELDS...THE ELEVATED MOISTURE AND INSTABILITY IN
THE ATMOSPHERE SHOULD ALLOW FOR AT LEAST ISOLATED THUNDERSTORMS TO
DEVELOP ACROSS SOUTH CENTRAL AZ LATER THIS AFTERNOON AND EVENING...
AND WE WILL RAISE OUR POPS SLIGHTLY TO REFLECT THIS. WE STARTED WITH
MORNING LOW TEMPS THAT WERE SEVERAL DEGREES HIGHER THAN YESTERDAY
AND HIGH TEMPS WILL ALSO RISE A FEW DEGREES SO THIS SHOULD HELP
INCREASE INSTABILITY A BIT AND INCREASE OUR CHANCES FOR AFTERNOON
CONVECTION. FORECASTS HAVE BEEN TWEAKED TO REFLECT CURRENT SKY AND
WEATHER TRENDS AND NO ADDITIONAL UPDATES ARE PLANNED FOR NOW.

.PREVIOUS FORECAST...
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...
EXPECT TO SEE MID TO HIGH LEVEL BROKEN DECK GRADUALLY BREAK UP
SOMEWHAT BY LATE MORNING. SHOWERS AND THUNDERSTORMS WILL MAINLY
AFFECT HIGHER TERRAIN AREAS THIS AFTERNOON WITH THE POTENTIAL FOR A
FEW STORMS TO MAKE THEIR WAY INTO THE PHOENIX AREA THIS
EVENING...ALBEIT A SMALL CHANCE. THERE WILL BE BETTER CHANCES OF
THUNDERSTORM OUTFLOW WINDS TO AFFECT AREA TERMINALS EARLY TO MID
EVENING WITH THE HIGHEST PROBABILITY COMING OUT OF THE SOUTHEAST.
DRY AIR WILL BEGIN TO SLIDE IN FROM THE WEST LATE TONIGHT LEADING TO
A QUIETER COUPLE MONSOON DAYS HEADING INTO THE WEEKEND.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
DRIER AIR ALOFT WILL GRADUALLY FILTER IN FROM THE WEST TODAY...BUT
THERE REMAINS A VERY SMALL CHANCE OF A STRAY SHOWER OR THUNDERSTORM
AFFECTING KBLH THIS AFTERNOON. BY TONIGHT...THE DRY AIR WILL
VIRTUALLY CUT OFF ANY CHANCE FOR STORMS THROUGH SATURDAY.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
A RETREAT OF MONSOON MOISTURE ON FRIDAY AND SATURDAY WILL RESULT IN
ONLY SMALL CHANCES OF STORMS ACROSS HIGH TERRAIN AREAS FOR THIS
WEEKEND AND MINIMUM HUMIDITIES IN THE TEENS ACROSS THE DESERTS.
AFTERNOON HIGH TEMPERATURES ARE EXPECTED TO REMAIN NEAR SEASONAL
NORMALS MOST DAYS...EXCEPT FOR SATURDAY WHEN HIGHS OF AROUND 110
SHOULD BE FAIRLY WIDESPREAD. A MOISTURE SURGE IS EXPECTED SUNDAY
NIGHT INTO MONDAY LEADING TO SLIGHTLY COOLER AFTERNOON
HIGHS...INCREASED CHANCES OF SHOWERS AND THUNDERSTORMS...AND HIGHER
HUMIDITIES FOR EARLY NEXT WEEK. GRADIENT 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...CB
PREVIOUS DISCUSSION...MO
AVIATION....KUHLMAN
FIRE WEATHER...KUHLMAN











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