Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 052147
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
215 PM MST THU MAY 5 2016

.SYNOPSIS...
A LARGE PACIFIC LOW PRESSURE SYSTEM WILL MOVE INTO THE DESERT
SOUTHWEST THROUGH THE WEEKEND. THIS SYSTEM WILL BRING BREEZY WEATHER
TO THE REGION THIS EVENING...FOLLOWED BY MUCH COOLER CONDITIONS AND
A THREAT OF SHOWERS AND THUNDERSTORMS FRIDAY AND SATURDAY. THE LOW
PRESSURE SYSTEM WILL BEGIN TO MOVE EAST SUNDAY...FOLLOWED BY DRY AND
MUCH WARMER WEATHER NEXT WEEK.

&&

.DISCUSSION...
A LARGE NEGATIVE HEIGHT ANOMALY CENTERED NEAR 32N 124W THIS
AFTERNOON CONTINUES TO CHURN SLOWLY TOWARDS THE SRN CALIFORNIA COAST
WITH A LEADING STRONG MERIDIONAL JET LIFTING INTO SRN NEVADA. AN
INITIAL LEAD WAVE ON THIS JET NOSE WAS QUICKLY PROGRESSING NORTH
WITH AN ASSOCIATED SFC PREFRONTAL TROUGH LOSING DEFINITION AND
UPSTREAM GRADIENT OVER THE LOWER COLORADO RIVER VALLEY.
MEANWHILE...A LLJ ALONG THE H9-H7 THERMAL GRADIENT THROUGH SRN/CNTRL
ARIZONA WAS STEADILY MIXING HIGHER MOMENTUM AIR TO THE SFC WITH
GUSTS OVER 30 MPH AND THE FIRST VESTIGES OF LOFTED DUST ON AREA WEB
CAMERAS.

WHILE THE LLJ VELOCITIES WERE SLOWLY DECREASING PER OBJECTIVE
ANALYSIS...A MORE PRONOUNCED LOW LEVEL FRONTAL BOUNDARY WILL PUSH
THROUGH SERN CALIFORNIA LATER THIS AFTERNOON/EARLY EVENING
EFFECTIVELY REINFORCING THE PRESSURE GRADIENT. THE STRONGEST
SUNDOWNER WINDS THROUGH IMPERIAL COUNTY SHOULD STILL MATERIALIZE
SUFFICIENTLY STRONG TO JUSTIFY BOTH THE WIND ADVISORY AND BLOWING
DUST ADVISORY. FURTHER TO THE EAST...PARTIAL DECOUPLING SHOULD LIMIT
THE FULL GUST POTENTIAL AS THE LLJ RE-INTENSIFIES AND FEEL THE
GREATEST IMPACTS WILL WANE BY LATER IN THE EVENING.

THE AFOREMENTIONED LARGE NEGATIVE HEIGHT ANOMALY WILL TRANSLATE
ONSHORE FRIDAY WITH MODEST HEIGHT FALLS PROGRESSING INTO THE
MAJORITY OF THE FORECAST AREA. WHILE THE STEEPER FRONTAL BOUNDARY
AND WARM SFC AIRMASS MOVES IN NEW MEXICO BY EARLY AFTERNOON...ONE
NOTABLE VORTICITY MAXIMUM CURRENTLY EVIDENT IN WV IMAGERY AND
SAMPLED WELL BY 12Z MODELS WILL SWING THROUGH THE SRN PERIPHERY OF
THE CIRCULATION INTO SWRN ARIZONA. FAIRLY DECENT COOLING ALOFT ALONG
A WEAK MIDTROPOSPHERIC FRONT AND WITHIN THE OVERALL CYCLONIC FLOW
WILL SUPPORT LARGE SCALE ASCENT AS MOISTURE SEEPS INTO THE REGION.

12Z KNKX SOUNDING DATA SAMPLED A VERY DEEP MARINE LAYER THROUGH H8
AND PART OF THIS 5-8 G/KG LOW LEVEL MOISTURE PROFILE WILL BE PULLED
INTO MUCH OF SE CALIFORNIA/ARIZONA FRIDAY AFTERNOON. AS A
RESULT...FORECAST SOUNDINGS RESOUNDINGLY SUPPORT MLCAPES INCREASING
TO A 200-400 J/KG RANGE BY LATE AFTERNOON...AND BOTH SREF
PROBABILITIES AND HIGH RESOLUTION ENSEMBLE OUTPUT YIELD AN AXIS OF
BETTER 30-50 PERCENT CHANCES. ENSEMBLE MEAN QPF IS NOT TERRIBLY HIGH
(NOT SURPRISING GIVEN THE SCT COVERAGE) THOUGH BRIEF MODERATE/HEAVY
RAIN WILL BE POSSIBLE IN ANY MORE ORGANIZED CELLS. UNLIKE THIS PAST
SATURDAY...CLOUD BASES MAY BE MUCH LOWER AND EVAPORATIONAL COOLING
LESS EFFECTIVE IN PRODUCING STRONGER WIND GUSTS...AND FEEL IMPACTS
WILL BE MORE LIMITED WITH THIS ROUND OF SHOWERS/STORMS.

THE COLD CORE ALOFT WILL GRADUALLY PROPAGATE ACROSS THE REGION OVER
THE WEEKEND WITH OTHER SMALL SHORTWAVES ROTATING WITHIN THE
CIRCULATION ENVELOPE. WHILE A FEW SHOWERS COULD SPRING UP THROUGH
LOWER ELEVATION LOCATIONS OF SOUTHERN AND CENTRAL ARIZONA...IT MAY
BE MORE A COMBINATION OF SYNOPTIC ASCENT AND OROGRAPHIC HELP TO GET
SHOWERS FORMING OVER HIGHER TERRAIN OF NORTHEAST MARICOPA/SRN GILA
COUNTIES SATURDAY AND SUNDAY. FORECAST CARRIES SOMEWHAT LOWER
CONFIDENCE DURING THIS TIME FRAME...AND HAVE TAILORED FORECASTS
HEAVILY TOWARDS SREF MEANS ACCOUNTING FOR MODEL VARIABILITY.

MONDAY THROUGH THURSDAY...
THE FORMER PACIFIC LOW PRESSURE SYSTEM WILL MOVE EAST AND OUT OF THE
REGION SUNDAY NIGHT...FOLLOWED BY DRY...STABLE...AND MUCH WARMER
WEATHER MON THROUGH THU. AFTERNOON DESERT TEMPERATURES WILL EASILY
REBOUND BACK INTO THE 90S TUE THROUGH THU AS H5 HEIGHTS RECOVER TO
NEAR 580DM. IT IS CERTAINLY CONCEIVABLE (AND ALMOST EXPECTED) THAT
FURTHER INCREASES TO HEIGHTS ALOFT BY THE END OF NEXT WEEK WILL
YIELD THE NEXT ROUND OF AFTERNOON HIGHS ABOVE 100F.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
AS A SLOW MOVING COLD FRONT APPROACHES FROM THE WEST...EXPECT STRONG
SOUTHERLY TO SOUTHWESTERLY WINDS WITH GUSTS OF 22 TO 35 KTS ALONG
WITH SOME LOFTED BLOWING DUST THAT COULD REDUCE SLANT RANGE
VISIBILITIES THROUGH EARLY EVENING. BY 04Z TO 05Z...WINDS WILL
BECOME LIGHTER AT 6 TO 10 KTS AND FAVOR A SOUTHERLY COMPONENT.
OTHERWISE...SKIES WILL BE PARTLY TO OCCASIONALLY MOSTLY CLOUDY WITH
HIGH CLOUD CIGS UNTIL ABOUT 10Z OR 11Z WHEN BKN CIGS SHOULD MOVE IN
AT ABOUT 8 TO 10K FT.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
STRONG WESTERLY WINDS WITH GUSTS OF 25 TO 35 KTS ALONG WITH SOME
LOFTED BLOWING DUST THAT COULD REDUCE SLANT RANGE VISIBILITIES ARE
EXPECTED AT KIPL THROUGH TONIGHT. LIGHT WEST TO NORTHWESTERLY WINDS
WILL BEGIN LATE TONIGHT WITH OCCASIONAL HIGH CIGS LOWERING TO ABOUT
10K FT. AT KBLH...EXPECT STRONG SOUTHERLY TO SOUTHWESTERLY WINDS
WITH GUSTS OF 23 TO 28KTS THROUGH TONIGHT. LIGHT SOUTHWESTERLY WINDS
ARE EXPECTED LATE TONIGHT WITH PARTLY CLOUDY SKIES WITH OCCASIONAL
LOW TO MID LEVEL CLOUDS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...

SUNDAY THROUGH THURSDAY...

WITH A BROAD LOW PRESSURE SYSTEM SLOW TO EXIT EXPECT A SLIGHT CHANCE
OF RAIN SHOWERS AND ISOLATED THUNDERSTORMS SUNDAY AND WELL BELOW
NORMAL AFTERNOON HIGH TEMPERATURES NEAR 80 ON SUNDAY...AND IN THE
MID 80S ON MONDAY. EXPECT MINIMUM RELATIVE HUMIDITIES IN THE UPPER
TEENS TO MID 20 PERCENT RANGE SUNDAY. OCCASIONALLY BREEZY SOUTHWEST
WINDS CAN BE EXPECTED EACH AFTERNOON THROUGH MONDAY...ESPECIALLY IN
THE TONTO FOOTHILLS AND S GILA COUNTY. WARMER AND DRIER CONDITIONS
MOVE IN BEGINNING TUESDAY AS TEMPERATURES INCREASE TO NEAR NORMAL ON
TUESDAY AND THEN ABOVE NORMAL THROUGH THURSDAY. OTHERWISE...EXPECT
MINIMUM RELATIVE HUMIDITIES IN THE 10 TO 15 PERCENT RANGE.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...BLOWING DUST ADVISORY UNTIL 8 PM MST THIS EVENING FOR
     AZZ021>023-026>028.

     RED FLAG WARNING UNTIL 8 PM MST THIS EVENING FOR AZZ132-133.

CA...BLOWING DUST ADVISORY UNTIL 9 PM PDT THIS EVENING FOR CAZ033.

     WIND ADVISORY UNTIL 10 PM PDT THIS EVENING FOR CAZ033.

&&

$$

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

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



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