Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 280530 AAA
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
1030 PM MST THU AUG 27 2015

.UPDATE...AVIATION DISCUSSION.

&&

.SYNOPSIS...
HIGH PRESSURE SHIFTING TO THE SOUTHEAST OF THE REGION IS BEGINNING TO
BRING IN SOME DRIER CONDITIONS FROM THE WEST...BUT MODEST MONSOON
MOISTURE WILL STILL PERSIST FROM PHOENIX EASTWARD THROUGH FRIDAY.
THE DRIER AIR WILL PUSH FURTHER EAST THIS WEEKEND...CONFINING RAIN
CHANCES TO HIGHER TERRAIN AREAS EAST OF PHOENIX. TEMPERATURES THROUGH
THE WEEKEND WILL REMAIN ABOVE NORMAL WITH LOWER DESERT TEMPERATURES
AROUND 110 DEGREES ACROSS SOUTHWEST ARIZONA AND SOUTHEAST CALIFORNIA.

&&

.DISCUSSION... A RATHER ACTIVE LATE AFTERNOON/EARLY EVENING ACROSS
SOUTH-CENTRAL ARIZONA...AND TO A LESSER EXTENT ACROSS SOUTHWEST
ARIZONA. IN SPITE OF WESTERLY FLOW ALOFT...WHICH IS NORMALLY
UNFAVORABLE FOR MONSOON STORMS TO MOVE INTO THE LOWER DESERTS...THE
COMBINATION OF AMPLE MOISTURE (PWATS AOA 1.50 INCH) AND A WEAK
SHORTWAVE MOVING ACROSS ARIZONA HELPED TO TRIGGER SCATTERED
SHOWERS AND THUNDERSTORMS ACROSS THE REGION. THE STRONGEST STORMS
AFFECTED THE WEST VALLEY AND TEMPE...WHERE SEVERE STORMS PRODUCED
DAMAGING WINDS AND LOCALIZED FLOODING THIS AFTERNOON. THINGS ARE
MUCH QUIETER AT THIS HOUR...WITH THUNDERSTORMS ACTIVITY NOW BEING
CONFINED TO EXTREME SE AZ AND OVER PARTS OF NW AZ. AS FAR AS THE
FORECAST IS CONCERNED FOR THE REST OF TONIGHT...THERE IS JUST A
SLIGHT CHANCE OF AN ISOLATED STORM OVER THE LOWER DESERTS THROUGH
THE REST OF THIS EVENING. TOMORROW LOOKS TO BE MUCH QUIETER...DUE TO
WEAK SHORTWAVE RIDGING/SUBSIDENCE MOVING INTO THE REGION FROM THE
WEST AND A REDUCTION OF AVAILABLE MOISTURE (MIXING RATIOS FALLING
AOB 8 G/KG AT MOST LOCATIONS BY THURSDAY AFTERNOON).

&&

.PREVIOUS DISCUSSION... WITHIN JUST THE LAST TWO HOURS...FROM 1830Z
THROUGH 2030Z...CONVECTIVE ACTIVITY ACROSS NORTH-CENTRAL AND WESTERN
ARIZONA HAS POPULATED AND FILLED IN QUITE NICELY. KEEPING A CLOSE
WATCH ON A SUITE OF HIGH-RESOLUTION MODEL FORECASTS THIS
MORNING...ALL HINTED AT AFTERNOON CONVECTION FROM YAVAPAI COUNTY
STRETCHING SOUTHEAST THROUGH MARICOPA COUNTY INCLUDING PHOENIX AND
INTO SOUTHERN GILA COUNTY FOR THE REMAINDER OF THIS AFTERNOON.
TIMING WAS A BIT OFF WITH THE MODELS COMPARED TO WHAT WAS ACTUALLY
OCCURRING...AND WITH CLEAR SKIES THIS MORNING THE TEMPERATURES
CLIMBED A BIT FASTER THAN ANTICIPATED SO CONVECTIVE POTENTIAL WAS
REALIZED RATHER RAPIDLY. WITH A SHORT WAVE MOVING THROUGH CENTRAL
ARIZONA...THE HIGH RES MODELS PICKED UP ON THAT AND HAVE BEEN VERY
CONSISTENT. PER THE 12Z SOUNDING FOR PSR...A
-8C TEMPERATURE AT 500MB PAIRED WITH OVER 1.6 INCH OF PRECIPITABLE
WATER PROVIDES A GOOD ENVIRONMENT FOR HEAVY RAIN PRODUCING
THUNDERSTORMS. SOME DIFFLUENCE FROM 500-300MB ACROSS CENTRAL ARIZONA
WILL PROVIDE A GOOD BOUNDARY FOR THUNDERSTORM ACTIVITY. WHILE STILL
UNDER A WESTERLY FLOW ALOFT...STEERING FLOW IS RATHER WEAK.

AS THE UPPER LEVEL HIGH BETTER PLACES ITSELF SOUTH OF THE BORDER AND
SLIGHTLY MORE WEST...TOMORROW BOASTS ANOTHER CHANCE FOR HIGH TERRAIN
CONVECTION. ANOTHER DISTURBANCE IN THE FLOW FROM 500MB TO 300MB AND
MINIMAL DRYING IN THE MID LEVELS MAY PROVIDE JUST ENOUGH OF TRIGGER
FOR SOME CONVECTIVE ACTIVITY FRIDAY AFTERNOON. THROUGH TUESDAY OF
NEXT WEEK...AN APPROACHING TROUGH FROM THE WEST WILL SUPPORT
CONTINUED SOUTHWESTERLY FLOW ALOFT AND MID-LEVEL MIXING RATIO VALUES
ARE FORECAST TO DIP BELOW 8 G/KG. A SUBTLE DRYING TREND AND
AN UNFAVORABLE MONSOON PATTERN LOOKS TO SETTLE IN THROUGH MID-WEEK
NEXT WEEK. TEMPERATURES WILL TREND UPWARD THROUGH THE WEEKEND AND
THEN HOLD ON TO PERSISTENCE NEAR SEASONAL AVERAGE THROUGH THE WEEK
AHEAD.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...KSDL...AND

CURRENT BKN CIGS TO PREVAIL THROUGH FRIDAY MORNING...THEN BECOME
MAINLY SCT BY FRIDAY AFTERNOON AS SLIGHTLY DRIER AIR WORKS ITS WAY
IN FROM THE WEST...WITH CLOUD BASES IN THE 8-10K FT RANGE RISING
INTO THE 10-12K FT RANGE ON FRIDAY. SOUTHEASTERLY WINDS TONIGHT AND
EARLY FRIDAY TO BECOME WESTERLY BY FRIDAY AFTERNOON. THUNDERSTORM
ACTIVITY TO REMAIN MAINLY WELL TO THE EAST OF THE TERMINALS ON
FRIDAY.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...

FEW-SCT MID-LEVEL CIGS TO BECOME MAINLY CLR BY FRIDAY AFTERNOON.
WINDS TO REMAIN ON THE LIGHT SIDE...AOB 8KTS...MAINLY FOLLOWING
TYPICAL DIURNAL TRENDS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

SUNDAY THROUGH THURSDAY...DRIER AND WARMER WEATHER WILL SPREAD INTO
REGION FROM THE WEST...HOWEVER A SLIGHT CHANCE OF AFTERNOON AND
EVENING TSTMS IS STILL FORECAST FOR THE MOUNTAINS OF SOUTHERN GILA
COUNTY EACH DAY. HIGH TEMPERATURES THROUGH SUNDAY WILL BE WELL ABOVE
NORMAL WITH HOTTER DESERTS IN EXCESS OF 110...WITH SOME COOLING BACK
TOWARD NORMAL EARLY NEXT WEEK. MINIMUM RELATIVE HUMIDITIES WILL FALL
INTO THE 10 TO 15 PERCENT RANGE OVER THE WESTERN DESERTS BUT STAY
MOSTLY ABOVE 15 PERCENT ACROSS SOUTH CENTRAL ARIZONA EACH DAY WITH
VALUES REACHING 25 PERCENT IN SOUTHERN GILA COUNTY. AFTERNOON
SOUTHWEST WINDS WILL RANGE FROM 10 TO 20 MPH. GOOD OVERNIGHT
RECOVERY IS EXPECTED.


.SPOTTER INFORMATION STATEMENT...
SPOTTERS ARE ENCOURAGED TO REPORT 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...PERCHA
AVIATION...PERCHA
FIRE WEATHER...VASQUEZ


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