Area Forecast Discussion
Issued by NWS Phoenix, AZ

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000
FXUS65 KPSR 251637
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
937 AM MST FRI JUL 25 2014

.SYNOPSIS...
A NOTICEABLE INCREASE IN MONSOON ACTIVITY IS EXPECTED TO COMMENCE
TODAY AND CONTINUE INTO THE WEEKEND. THE HIGH PRESSURE CENTER THAT
BROUGHT THE REGION VERY HOT TEMPERATURES THE LAST FEW DAYS WILL
WEAKEN AND SHIFT FURTHER OFF TO THE EAST...ALLOWING MOISTURE THAT IS
NOW OVER MEXICO TO SURGE NORTHWARD INTO THE REGION. SUFFICIENT
MONSOONAL MOISTURE WILL THEN REMAIN AROUND THE REGION TO SUPPORT
AFTERNOON AND EVENING STORM CHANCES THROUGH AT LEAST THE MIDDLE OF
THE COMING WEEK...WITH THE BEST FOCUS FOR STORMS LIKELY OVER THE
HIGHER TERRAIN OF SOUTH-CENTRAL ARIZONA. DAYTIME TEMPERATURES WILL
STILL HOLD ABOVE SEASONAL NORMALS...BUT ARE EXPECTED TO FALL BACK
FROM THEIR NEAR-RECORD READINGS.

&&

.DISCUSSION...
VASTLY DIFFERENT FORECAST SET-UP HAS TAKEN SHAPE WHEN LOOKING OVER
THE LAST 24 HOURS OVER THE SOUTHWEST DESERTS. THIS TIME THURSDAY
MORNING WE WERE OBSERVING A SLIGHT DRYING TREND FROM THE EAST WITH
ISOLATED CONVECTIVE ACTIVITY RESULTING IN THE AFTERNOON/EVE ACROSS
THE WESTERN AZ DESERTS. WITH THE UPPER HIGH NOW WEAKENING AND
DRIFTING EASTWARD THIS MORNING...MEAN ATMOSPHERIC FLOW HAS
CONSOLIDATED TO BROAD SOUTHERLY HEADINGS TRANSPORTING A DEEPER
MOISTURE SURFACE IN FROM NORTHERN MEXICO AND THE GULF OF CALIFORNIA.
GULF SURGE CONDITIONS CONTINUE THIS MORNING ALONG THE COLORADO RIVER
VALLEY WHERE YUMA HAS HELD PERSIST GUSTY SOUTHERLY WINDS WITH THEIR
DEWPOINTS NOW CLIMBING INTO THE 70S. DEWPOINTS FURTHER "INLAND" HAVE
SIGNIFICANTLY INCREASED INTO MID AND UPPER 60 DEGREE READINGS.

OVERNIGHT LOOP OF THE WATER VAPOR IMAGERY SHOWED SOME SUBTLE INVERTED
WAVE FEATURE TRAVELING ACROSS NORTHERN OLD MEXICO/SOUTHERN NEW
MEXICO THAT IS NOW MOVING AZ THIS MORNING. THERE IS SOME WEAK BROAD
CIRCULATION TO IT...WITH ONLY A FEW OF THE HI-RES AND THE LATEST NAM
SHOWING IT WEAKLY AROUND 700MB. IN ADDITION...UPPER JET SUPPORT
REMAINS TO OUR NORTHWEST ACROSS SOUTHERN NV/CENTRAL UT...WHICH
COULD BE AN AIDE FOR STORM DEVELOPMENT FURTHER IN THE DAY. GIVEN THE
RETURN OF DEEP MONSOON MOISTURE...INCLUDING AT 850/700MB WHERE
READINGS ARE AVERAGING 10C AND 6C OR SO DEGREES ACROSS THE
STATE...AND THE DYNAMICS/INSTABILITY IN PLACE...CONFIDENCE STILL
REMAINS HIGH FOR AN ACTIVE MONSOON DAY. WE WILL LIKELY SEE THE
BLOWING DUST/OUTFLOW IMPACTS IN THE AFTERNOON HOURS FIRST...WITH
STORM DEVELOPMENT ALONG THOSE BOUNDARIES AS THEY MOVE OVER THE LOWER
DESERTS. ANTICIPATORY BLOWING DUST ADVISORY WAS ISSUED BY THE
PREVIOUS SHIFT AND IS IN GOOD SHAPE. OUTSIDE OF SOME MINOR SKY AND
DEWPOINT GRID TWEAKS...NO MAJOR UPDATES PLANNED THIS AM.

&&

.PREVIOUS DISCUSSION /ISSUED AT 215 AM MST/PDT/...
A SIGNIFICANT CHANGE TO A MORE ACTIVE MONSOON REGIME
NOW APPEARS TO BE TAKING PLACE ACROSS THE REGION TODAY. THE VERY
STRONG UPPER HIGH CENTER THAT BROUGHT US THE VERY HOT WEATHER OVER
THE LAST FEW DAYS IS NOW SHIFTING OFF TO THE EAST...OVER NM AND WEST
TEXAS. THIS IS ALLOWING A DEEP SOUTHERLY FLOW TO DEVELOP OVER THE
REGION THIS MORNING. CHANGES CAN ALREADY BE SEEN AT THE
SURFACE...WITH YUMA NOW EXPERIENCING A SOUTHERLY SURGE THAT HAS
BROUGHT 20+MPH WINDS AND RAISED THE DEWPOINT TO 71F AS OF 1AM THIS
MORNING. THE PHX AREA ALSO SAW A SURGE ON DEWPOINTS AS WELL LATE
YESTERDAY EVENING...FROM THE UPPER 30S AND LOW 40S UP INTO THE LOW
60S WHEN THE WINDS SHIFTED TO A WESTERLY DIRECTION. THE LATEST GFS
AND EURO MODEL OUTPUT HAS GREATLY INCREASE POPS ACROSS SOUTH-CENTRAL
AZ AS THEY NOW BOTH PUSH A WEAK DISTURBANCE NORTHWARD ACROSS THE
REGION...WITH PWATS RISING AS HIGH AS 2.0 INCHES BY LATE THIS EVENING
AND MUCAPES SHOOTING ABOVE 1000 J/KG. GIVEN THE FACT THAT THERE WILL
LIKELY BE EVEN MORE TS ACTIVITY TO OUR SOUTH...OVER PIMA AND SOUTHERN
PINAL COUNTIES...IT APPEARS THAT IT IS QUITE LIKELY THAT WE WILL SEE
AT LEAST SOME BLOWING DUST FROM STORM OUTFLOWS.

SATURDAY LOOKS LIKE IT MAY BE SIMILAR TO TODAY...WITH SIMILAR
MOISTURE AND MUCAPE VALUES BEING FORECASTED ACROSS THE REGION.
HOWEVER...IF TODAY TURNS OUT TO BE QUITE ACTIVE...THE WORKED-OVER
ATMOSPHERE MAY HOLD TS ACTIVITY DOWN SOMEWHAT ON SATURDAY. THE
INCREASING MOISTURE AND CLOUDINESS...ALONG WITH LOWER 500MB
HEIGHTS...IS EXPECTED TO END OUR EXCESSIVE HEAT...WITH HIGHS AROUND
110F TODAY AND THE 105-109F RANGE ON SATURDAY. SATURDAY COULD TURN
OUT TO BE EVEN COOLER IF THERE IS WIDESPREAD RAINFALL TODAY/THIS
EVENING.

SUNDAY THROUGH THURSDAY...
IT APPEARS THAT A LOW-MID GRADE MONSOON WILL LIKELY PREVAIL THROUGH
THE EXTENDED PERIOD AS WEAK SOUTHERLY FLOW ALOFT CONTINUES TO PULL
MOISTURE INTO THE REGION...WITH THE GFS SHOWING A MORE ACTIVE
PATTERN AS IT KEEPS THE UPPER HIGH CENTER OFF TO OUR EAST...AND THE
EURO SHOWING A DRIER ONE AS IT ATTEMPTS TO REPOSITION THE UPPER
HIGH CENTER WESTWARD BACK OVER THE REGION.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...MOISTURE
INCREASING OVER THE REGION TODAY WILL MEAN A GREATER THREAT OF
THUNDERSTORMS THIS AFTERNOON AND EVENING. THIS ACTIVITY HAS A GOOD
CHANCE OF IMPACTING THE KPHX...KIWA...AND KSDL TERMINALS BETWEEN 22Z
AND 06Z. VARIABLE AND GUSTY WINDS AND CLOUD BASES LOWERING AOA 5 KFT
ARE POSSIBLE DURING THIS PERIOD. OTHERWISE EXPECT SCT TO BKN MID AND
HIGH CLOUDS AND PREVAILING SOUTH TO SOUTHWEST WINDS AT AROUND 10 KTS.

SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
EXPECT SCT MID AND HIGH CLOUDS THROUGH TODAY WITH BASES AOA 15 KFT.
AT KIPL...WINDS WILL REMAIN OUT OF THE SOUTHEAST AT AROUND 10 KTS.
ALONG THE COLORADO RIVER VALLEY...INCLUDING KBLH...WINDS WILL
INCREASE THROUGH THE DAY OUT OF THE SOUTH...WITH EXPECTED GUSTS TO
AROUND 25KTS AFTER 16Z.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SUNDAY THROUGH THURSDAY...
SLIGHTLY COOLER AFTERNOON TEMPERATURES ARE EXPECTED ALONG WITH
HIGHER HUMIDITY. MINIMUM RELATIVE HUMIDITY LEVELS WILL RANGE FROM 15
TO 25 PERCENT. A TYPICAL MONSOON DAILY THREAT OF AFTERNOON AND
EVENING THUNDERSTORMS ARE EXPECTED WITH THE HIGHEST PROBABILITIES IN
THE MOUNTAINS EAST OF PHOENIX. TYPICAL AFTERNOON AND EVENING
SOUTHWEST WINDS ARE EXPECTED WITH GOOD RECOVERY AT NIGHT.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...BLOWING DUST ADVISORY FROM 2 PM THIS AFTERNOON TO 9 PM MST THIS
     EVENING AZZ022-023-027-028.

CA...NONE.

&&

$$

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

DISCUSSION...NOLTE
PREVIOUS DISCUSSION...PERCHA
AVIATION....MCLANE
FIRE WEATHER...VASQUEZ




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