Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 300343
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
840 PM MST TUE JUL 29 2014

.SYNOPSIS...
THERE WILL BE A BREAK IN THE MONSOON THROUGH THURSDAY...WITH
DECREASED CHANCES OF SHOWERS AND THUNDERSTORMS. MOISTURE WILL TREND
DOWNWARD OVER THE NEXT FEW DAYS...AND THE DRIER AIR WILL BRING ABOUT
WARMER DAYTIME TEMPERATURES...ONCE AGAIN FLIRTING WITH EXCESSIVE
HEAT RANGING FROM 112 TO 115 DEGREES FOR THE LOWER DESERTS ON
WEDNESDAY. A RETURN TO A MORE TYPICAL MONSOON REGIME IS EXPECTED
LATE FRIDAY INTO THE WEEKEND AS SHOWERS AND THUNDERSTORMS ARE ONCE
AGAIN EXPECTED ACROSS THE REGION.

&&

.DISCUSSION...
BASED ON CURRENT WV IMAGERY AND OBJECTIVE ANALYSIS...THE CENTER OF
THE SUBTROPICAL 594DM ANTI-CYCLONE HAS SHIFTED INTO SERN ARIZONA
WITH VERTICAL MOTIONS SUPPORTIVE FOR DEEP CONVECTION LIMITED TO THE
PERIMETER OF THE CIRCULATION THROUGH NRN MEXICO...AS WELL AS THE
FOUR CORNERS REGION. 00Z SOUNDING DATA INDICATED PREVAILING LIGHT
WESTERLY FLOW HAS BROUGHT PWATS BELOW 1.25 INCHES WHILE BOUNDARY
LAYER MIXING RATIOS HAVE FALLEN BELOW 9 G/KG...ESSENTIALLY
PROHIBITING FREE CONVECTION. LITTLE TO NO CHANGE WAS MADE TO
FORECAST GRIDS...AS PREVAILING CONDITIONS WERE ALREADY WELL
CAPTURED. BIGGEST WEATHER HIGHLIGHTS OVER THE NEXT 48 HOURS WILL BE
WARMER THAN NORMAL CONDITIONS...BEFORE MONSOON MOISTURE BEGINS TO
RETURN ON FRIDAY.

&&

.PREVIOUS DISCUSSION...
/230 PM MST TUE JUL 29 2014/
THERE IS A CHANGE TO SOME OF THE FORECAST THINKING THIS HOUR AS IT
PERTAINS TO TEMPERATURES. IN SHORT...WITH THE DRIER NATURE OF THE
ATMOSPHERE...AND SITTING ALMOST RIGHT UNDER A 594DM HIGH FOR THE
NEXT DAY OR TWO...DAYTIME TEMPERATURES ARE GOING TO BE WARMER THAN
PREVIOUSLY FORECAST. AGGRAVATING THE WARMTH WAS THE VERY WARM START
TO THE MORNING/DAY...WITH 92 DEGREES OBSERVED AT PHOENIX SKY HARBOR
AIRPORT...WHICH WILL SET RECORD HIGH MINIMUM FOR THE DAY IF TEMPS
DONT COOL OFF BELOW THAT BEFORE MIDNIGHT.

ADJUSTING TEMPERATURES UPWARDS A FEW DEGREES FOR WHAT IS SHOWN IN
THE WARMEST GUIDANCE...NAMELY THE THE ECMWF...THE FORECAST DAYTIME
HIGH FOR WEDNESDAY IS NOW FLIRTING WITH EXCESSIVE HEAT THRESHOLDS
FOR PHOENIX AND YUMA AT 111 AND 113 DEGREES RESPECTIVELY. WILL BE
ISSUING A SPECIAL WEATHER STATEMENT TO DISCUSS THE VERY HOT
TEMPERATURES THIS SHIFT TO ALERT EVERYONE TO THIS HAZARD.
TEMPERATURES FOR THURSDAY ARE STILL ADVERTISED TO BE A FEW DEGREES
COOLER...BACK INTO THE 107-110 DEGREE RANGE FOR OUR EASTERN
ZONES/LOWER AZ DESERTS... POSSIBLY DUE TO SOME MID-LEVEL MOISTURE
SEEPING BACK INTO THE STATE. TEMPS OUT ACROSS SOUTHEAST CALIFORNIA
AND ALONG THE LOWER COLORADO RIVER VALLEY WILL STILL BE QUITE
HOT...RANGING 110-113 DEGREES MOST SITES. OTHER THAN THIS IMPORTANT
CHANGE TO TEMPERATURES...THE PREVIOUS FORECAST DISCUSSION CONCERNING
THE CONVECTIVE POTENTIAL AND RETURN OF MONSOON MOISTURE STILL
APPLIES.

THE LARGE UPPER LEVEL ANTICYCLONE WILL CONTINUE TO DOMINATE OUR
MONSOON WEATHER PATTERN. HOWEVER...WITH WEST-NORTHWESTERLY 700-300MB
FLOW ALOFT AND DRIER AIR IN THE MID LEVELS...THERE WILL BE A BREAK
IN THUNDERSTORM ACTIVITY FOR THE NEXT FEW DAYS...MODELS IN THE
SHORT TERM CONTINUE TO SHOW REDUCTIONS IN ATMOSPHERIC MOISTURE...
PRECIPITABLE WATER DECREASING WITH TIME...WITH ONLY A NARROW BAND OF
MOISTURE LINGERING OVER THE MOUNTAINS OF EASTERN ARIZONA EACH DAY.
WITH NO DISCERNIBLE STORM TRIGGERS NOTED FROM ANY OF THE OPERATIONAL
MODELS OR ENSEMBLES THROUGH THURSDAY...PRECIPITATION CHANCES FOR
SOUTHEAST CALIFORNIA...SOUTHWEST AND SOUTH-CENTRAL ARIZONA ARE NIL.
THE DESERTS WILL STAY DRY...WITH ONLY SLIGHT CHANCE POPS AT BEST
OVER THE HIGHER TERRAIN OF SOUTHERN GILA COUNTY/ZONE 24...WELL EAST
AND NORTH OF PHOENIX.

THE ECMWF/GFS SUGGEST THE RETURN OF A MORE MOIST SOUTH-SOUTHEASTERLY
FLOW BY FRIDAY...WITH SOME DIFFERENCES IN THE AMOUNT AND ARRIVAL OF
THE MOISTURE...AND COOLER TEMPERATURES FOR THE WEEKEND. WILL
NEED TO MONITOR AS THINGS GET CLOSER BUT LOOKING AT THE BIG
PICTURE...FRIDAY COULD SEE DISTANT STORMS TO THE SOUTHEAST ALONG
WITH THE POTENTIAL FOR BLOWING DUST...WHEREAS THE WEEKEND COULD SEE
CONVECTION DEVELOP OVERHEAD ACROSS THE LOWER DESERTS. WILL MAINTAIN
THE IDEA OF ELEVATED POPS FRIDAY THROUGH THE WEEKEND BUT THE FINER
DETAILS WILL NEED TO BE WORKED OUT AS WE GET FURTHER INTO THE WEEK.
UNFORTUNATELY THERE ARE VARYING SOLUTIONS ON WHAT HAPPENS FROM
MONDAY ONWARD WITH EQUAL CHANCES OF WESTERLY FLOW RETURNING OR A
CONTINUED SOUTHEASTERLY FETCH. GOING WITH CLIMO FOR NOW.



&&

.AVIATION...
SOUTH-CENTRAL AND SOUTHWEST ARIZONA AND SOUTHEAST
CALIFORNIA...INCLUDING KPHX...KIWA...KSDL...KIPL...AND KBLH...

NO AVIATION IMPACTS THROUGH WEDNESDAY AFTERNOON AS ONLY FEW/SCT MID
AND HIGH CLOUDS DEVELOP MAINLY OVER HIGH TERRAIN REMOVED FROM
TERMINAL SITES. LARGEST FORECAST CHALLENGE WILL BE TIMING OF WIND
SHIFTS...AND MUCH LIKE THE PAST 24 HOURS...TYPICAL DIRECTIONAL
CHANGES MAY BE DELAYED OR ABSENT. EVEN PROLONGED PERIODS OF VARIABLE
WINDS WILL BE POSSIBLE...WITH PEAK WINDS GENERALLY AOB 12KT.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
THURSDAY THROUGH MONDAY...
DRIER THAN NORMAL CONDITIONS CONTINUE THURSDAY. STORM CHANCES
WILL BE SLIGHT AND WILL BE LIMITED TO THE HIGHER TERRAIN OF EASTERN
ARIZONA. FRIDAY AND OVER THE WEEKEND WEEKEND...AN INCREASE IN
MOISTURE AND ASSOCIATED HUMIDITIES IS ANTICIPATED. THIS WILL LEAD TO
BETTER STORM CHANCES OVER THE HIGHER TERRAIN OF SOUTH-CENTRAL
ARIZONA AND STORM CHANCES...THOUGH SLIGHT...EXPANDING WESTWARD TO
THE LOWER ELEVATIONS. HIGH TEMPERATURES TREND DOWNWARD AS WELL.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

$$

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

DISCUSSION...MO/MEYERS/LEINS
AVIATION...MO
FIRE WEATHER...AJ





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