Area Forecast Discussion
Issued by NWS Phoenix, AZ

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683
FXUS65 KPSR 042139
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
235 PM MST WED MAY 4 2016

.SYNOPSIS...
A SLOW MOVING LOW PRESSURE SYSTEM WILL MOVE INTO THE SOUTHWEST
DURING THE REMAINDER OF THE WEEK YIELDING MUCH COOLER WEATHER.
AFTERNOON HIGHS IN THE MIDDLE 70S TO LOWER 80S WILL BE COMMON
THROUGH THE WEEKEND. BREEZY CONDITIONS WILL ALSO PREVAIL THURSDAY
AND FRIDAY WITH LOCALIZED BLOWING DUST. ALONG WITH THE COOLER
TEMPERATURES...THERE WILL ALSO BE CHANCES FOR LIGHT RAIN LATE FRIDAY
AND SATURDAY ALONG WITH A SLIGHT CHANCE OF THUNDERSTORMS.


&&

.DISCUSSION...
SHORTWAVE RIDGING CONTINUES TO HOLD OVER THE SWRN CONUS AS A SLOW
MOVING NEGATIVE HEIGHT ANOMALY EASES TOWARDS SRN CALIFORNIA. 12Z
KTWC SOUNDING DATA INDICATED HEIGHTS AND TEMPERATURES ALOFT BETWEEN
THE 75TH AND 90TH PERCENTILE WHICH HAS EQUATED TO WIDESPREAD
AFTERNOON HIGHS ECLIPSING THE 100F THRESHOLD (YET SEVERAL DEGREES
SHORT OF RECORD TERRITORY). WITH CLEAR SKIES AND LOW DEWPOINTS
PREVAILING THROUGH THE OVERNIGHT...ONLY SOMEWHAT ELEVATED WIND
SPEEDS NEAR THE BOUNDARY LAYER AND WARMER ANTECEDENT CONDITIONS WILL
KEEP MORNING LOWS SLIGHTLY HIGHER THAN PERSISTENCE.

THE NORTH AMERICAN FLOW PATTERN WILL REMAIN LARGELY STALLED AND
CHARACTERIZED BY AN OMEGA BLOCK THROUGH THE WEEKEND WITH ARIZONA
SITUATED UNDER THE UPSTREAM NEGATIVE HEIGHT ANOMALY. WITH THE SLOW
FORWARD PROGRESSION OF FEATURES OVER THE NEXT SEVERAL DAYS...HEIGHTS
WILL ONLY GRADUALLY COLLAPSE THURSDAY AFTERNOON YIELDING A LARGER
THAN TYPICAL THERMAL GRADIENT ACROSS THE FORECAST AREA...AND CENTRAL
ARIZONA ONLY 4-7F COOLER THAN TODAY. FAR MORE PRONOUNCED COOLING
WILL SPREAD ACROSS THE ENTIRE REGION FRIDAY-SUNDAY UNDER THE COLD
CORE ALOFT WITH HIGHS SOME 15F BELOW AVERAGE.

HOWEVER...THE GREATEST IMPACTS THURSDAY WILL RESULT FROM INCREASED
WIND GUSTS ALONG A TIGHTENED H8 GRADIENT/FRONTAL BOUNDARY. A NARROW
CORRIDOR OF SOUTHERLY GUSTS 30-35 MPH WILL BE POSSIBLE FOR A SHORT
PERIOD LATE THURSDAY AFTERNOON ACROSS CNTRL/WRN ARIZONA WITH THE
USUAL BLOWING DUST LOCATIONS EXPERIENCING SOME REDUCED VISIBILITIES.
MAY NEED SOME LOCAL DUST ADVISORIES ONCE STRONGER WINDS ARE
MANIFESTED...BUT AT THIS POINT WIND SPEEDS ONLY FLIRT WITH WIND
ADVISORY CRITERIA. THE LARGEST IMPACT WILL LIKELY BE FIRE WEATHER
CONCERNS AS HUMIDITY VALUES FALL TOWARDS SINGLE DIGITS WITH FUELS
CONTINUING TO DRY.

THERE WILL ALSO BE A SERIES OF VORT LOBES ROTATING ABOUT LARGER
CIRCULATION CENTER. THE BEST OPPORTUNITY FOR SHOWERS CONTINUES TO
OCCUR ON FRIDAY NIGHT AND SATURDAY AS COOLER AIR ALOFT COMBINES WITH
SOME MODEST DYNAMICAL LIFT/MIDLEVEL FRONTOGENESIS. MODELS SUGGEST
SOME MODEST INSTABILITY (MLCAPES 100-200 J/KG) YIELDING A SLIGHT
CHANCE OF THUNDERSTORMS. THE FINAL VORTICTY LOBE ROTATES THROUGH
CNTRL ARIZONA SUNDAY THOUGH PREVAILING DEEP WESTERLY FLOW WILL
LIKELY DEFLECT THE BEST SHOWER OPPORTUNITY INTO HIGHER TERRAIN NORTH
AND EAST OF PHOENIX.

MONDAY THROUGH WEDNESDAY...
HIGH PRESSURE BUILDS IN DURING THE FIRST HALF OF THE NEXT WORKWEEK.
THIS WILL LEAD TO TEMPERATURES A FEW DEGREES ABOVE NORMAL BY
NEXT WEDNESDAY.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
WITH AN EASTERN PACIFIC LOW SLOWLY APPROACHING FROM THE WEST...VERY
BREEZY SOUTHEASTERLY TO SOUTHERLY WINDS WITH GUSTS OF 20 TO 25 KTS
WILL TURN TO THE SOUTHWEST AND WESTERLY DIRECTIONS DURING MID TO
LATE AFTERNOON WITH SOME STRONG WIND GUSTS PERSISTING INTO THE EARLY
EVENING. WEST WINDS WILL BECOME MOSTLY LIGHT BY 03 TO 04Z BEFORE
CHANGING TO AN EASTERLY DIRECTION AROUND 05 TO 06Z. OTHERWISE EXPECT
SKIES TO REMAIN CLEAR TO MOSTLY CLEAR.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
VERY BREEZY SOUTHERLY COMPONENT WINDS WITH OCCASIONAL GUSTS UP TO 20
TO 25 KTS DURING THE AFTERNOON WILL BECOME MORE SOUTHWESTERLY TO
WESTERLY TONIGHT WITH AT ABOUT 10 TO 12 KTS AT KIPL AND 5 TO 7 KTS
AT KBLH. CLEAR TO MOSTLY CLEAR SKIES CAN ALSO BE EXPECTED.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.


&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
WITH A COOL LOW PRESSURE SYSTEM STILL IN PLACE...EXPECT A SLIGHT
CHANCE OF RAIN SHOWERS SATURDAY MORNING AND WELL BELOW NORMAL
AFTERNOON HIGH TEMPERATURES ONLY IN THE UPPER 70S THROUGH
SUNDAY...AND INTO THE MID 80S ON MONDAY. EXPECT MINIMUM RELATIVE
HUMIDITIES IN THE 22 TO 28 PERCENT RANGE ON SATURDAY AND FALLING TO
THE UPPER TEENS TO LOW 20 PERCENT RANGE SUNDAY AND TO THE MID TO
UPPER TEENS BY MONDAY. OCCASIONALLY BREEZY SOUTHWEST WINDS CAN BE
EXPECTED EACH AFTERNOON THROUGH MONDAY...ESPECIALLY IN THE TONTO
FOOTHILLS AND S GILA COUNTY. ON TUESDAY AND WEDNESDAY...WARMER AND
DRIER WEATHER WILL PREVAIL WITH TEMPERATURES INCREASING TO NEAR
NORMAL OR SLIGHTLY ABOVE NORMAL AND MINIMUM RELATIVE HUMIDITIES
SETTLING INTO THE LOW TO MID TEENS BY WEDNESDAY.

&&

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION IS NOT EXPECTED.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...RED FLAG WARNING FROM 11 AM TO 8 PM MST THURSDAY FOR AZZ132-133.
CA...NONE.

&&

$$

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

DISCUSSION...MO/AJ
AVIATION...SAWTELLE
FIRE WEATHER...SAWTELLE



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