Area Forecast Discussion
Issued by NWS Phoenix, AZ

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FXUS65 KPSR 051656
AFDPSR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
955 AM 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 WINDY WEATHER
TODAY...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...
OBJECTIVE ANALYSIS INDICATES H8 WINDS 30-40KT PERSISTING THROUGH FAR
SRN ARIZONA WITH VERTICAL MECHANICAL MIXING BEGINNING TO TRANSLATE
HIGHER MOMENTUM TO THE SFC. WHILE DEEPER MIXING INTO CNTRL ARIZONA
WILL BE MORE DELAYED AND THE LLJ AXIS WILL LIKELY WEAKEN SOMEWHAT
THIS AFTERNOON...IT STILL LOOKS LIKELY THAT A CORRIDOR OF GUSTS
APPROACHING 40 MPH WILL IMPACT AN AREA OF ERN YUMA/WRN
MARICOPA/PINAL COUNTIES THIS AFTERNOON. ALSO GIVEN THE SEASON OF
MANY FRESHLY PLOWED/HARVESTED FIELDS...LOCAL DENSE BLOWING DUST MAY
BECOME PROBLEMATIC AND HAVE PREEMPTIVELY ISSUED AN ADVISORY FOR
LATER TODAY. SIMILAR THINKING PREVAILS FOR MUCH OF IMPERIAL COUNTY
THIS EVENING AS THE ACTUAL COLD FRONT PASSES OVER THE SAN DIEGO
MOUNTAINS.

&&

.PREVIOUS DISCUSSION...
/750 AM MST THU MAY 5 2016/
A LARGE NEGATIVE HEIGHT ANOMALY CENTERED NEAR 33N 125W THIS MORNING
CONTINUES TO CHURN SLOWLY TOWARDS THE SRN CALIFORNIA COAST. TRENDS
IN CLOUD COVER PER SATELLITE IMAGERY SUGGESTS A SHEARED SHORTWAVE
AND UPPER LEVEL ASCENT EJECTING THROUGH THE NRN BAJA. CERTAINLY...A
PREFRONTAL TROUGH IS EVIDENT IN OBJECTIVE ANALYSIS...AND BOTH HRRR
AND 4KM WRF OUTPUT CAPTURE THIS EVOLUTION THROUGH WESTERN/CENTRAL
IMPERIAL COUNTY THIS MORNING. CORRESPONDINGLY...GUSTY WINDS AND SOME
LOFTED DUST HAVE ALREADY BEEN NOTED THROUGH IMPERIAL COUNTY...AND
THIS IS JUST THE PRECURSOR OF MORE WIDESPREAD SIMILAR WEATHER
CONDITIONS THIS AFTERNOON. ASIDE FROM REFINING SOME HOURLY DATA
TRENDS...HAVE ADDED MORE DUST MENTION THIS MORNING IN THE WRN CWA
WHILE ALSO ACCOUNTING FOR MORE AREAL AND TEMPORAL DETAILS IN CLOUD
COVERAGE.

/531 AM MST THU MAY 5 2016/
TODAY AND TONIGHT...
VERY INTERESTING WEATHER PATTERN WILL DEVELOP OVER THE REGION TODAY
THROUGH THE WEEKEND. A MASSIVE PACIFIC LOW PRESSURE SYSTEM OFF THE
CENTRAL AND SOUTHERN CA COAST WILL PARTIALLY MOVE INLAND TODAY.
500/300 HEIGHT FALL ORIENTATIONS THIS AFTERNOON SUGGEST A MODERATELY
STRONG VERTICAL MOTION FIELD DEVELOPING OVER SOUTHEAST CA AND
SOUTHERN NEVADA. LOW LEVEL WINDS WILL SUBSEQUENTLY RESPOND IN A BIG
WAY...BECOMING SOUTH 25 TO 40 MPH WITH AREAS OF ATTENDANT BLOWING
DUST. THE COMBINATION OF WIND...WARM TEMPS...AND DRY DESERT AND
MOUNTAIN BIO-FUELS HAVE ALSO PROMPTED A RED FLAG WARNING FOR HIGH
FIRE DANGER OVER A LARGE PART OF SOUTHWEST AND SOUTH CENTRAL ARIZONA.

DESPITE THE DEVELOPING VERTICAL MOTION FIELD...WEATHER BALLOON DATA
AND SATELLITE DERIVED PRECIPITABLE WATER FIELDS SHOW BONE DRY
CONDITIONS OVER OUR FORECAST AREA TODAY. THEREFORE NO PRECIP CHANCES
TODAY NOR TONIGHT.

THERE IS HOPE FOR MOISTURE THOUGH. NUMERICAL MODELS FOR DAYS NOW
HAVE BEEN FORECASTING A LONG FETCH OF NEAR GALE FORCE NORTHERLY
WINDS TO DEVELOP JUST OFF THE WEST COAST...EXTENDING FROM OFFSHORE
WASHINGTON/OREGON TO OFFSHORE SOUTHERN CA. ROUGH SEAS IN THE WIND
FETCH AREA SHOULD...AS USUAL...MECHANICALLY INJECT INCREASING
AMOUNTS OF MOISTURE INTO THE BOUNDARY LAYER. THIS LOW LEVEL
WIND/MOISTURE FETCH IS EXPECTED TO TURN INLAND AND OVER THE SOUTHERN
CA COASTAL RANGE...AND OVER THE NORTHERN/CENTRAL BAJA
MOUNTAINS...THEN BACK INTO AZ FROM THE SOUTH LATE TONIGHT AND
FRIDAY. MORE ABOUT THIS IN THE FRIDAY DISCUSSION BELOW.
OTHERWISE...DRY...WARM AND WINDY CONDITIONS ARE FORECAST TODAY AREA
WIDE.

FRIDAY THROUGH SUNDAY...
WE WILL CALL THIS PERIOD...UNSETTLED. SIGNIFICANT AMOUNTS OF PACIFIC
BOUNDARY LAYER MOISTURE WILL SWING INTO OUR FORECAST AREA LATE
THURSDAY NIGHT AND FRIDAY...GENERALLY FOLLOWING THE MASSIVE PACIFIC
LOW PRESSURE SYSTEM INLAND. THE GFS HINTS AT A MID LEVEL DISTURBANCE
TO ROTATE AROUND THE BASE OF THE LARGE CYCLONIC TROF AND INTO THE
IMPERIAL AND YUMA AREA FRIDAY AFTERNOON...THEN INTO SOUTH CENTRAL
ARIZONA INCLUDING PHOENIX FRIDAY NIGHT. ITS A LITTLE HARD TO SEE
THIS DISTURBANCE IN THE MODELED MID/UPPER WIND AND TEMP DATA... BUT
MODELED PRECIP FORECASTS...AS WELL AS HIGHER MOS GUIDANCE PRECIP
PROBABILITIES SUGGEST THIS IS THE BEST PERIOD FOR RAIN. A LOWER
CHANCE OF AFTERNOON INSTABILITY SHWRS AND TSTMS WILL FOLLOW ON
SATURDAY AND SUNDAY.

MUCH COOLER TEMPERATURES WILL SETTLE OVER THE REGION FRIDAY THROUGH
SUNDAY AS A LARGE BLOCKING TROF OVER THE EASTERN U.S. CAUSE OUR
SYSTEM TO BE A SLOW MOVER.

MONDAY THROUGH THURSDAY...
THE FORMER PACIFIC LOW PRESSURE SYSTEM IS FORECAST TO MOVE EAST AND
OUT OF THE REGION SUNDAY NIGHT...FOLLOWED BY DRY...STABLE...AND MUCH
WARMER WEATHER MON THROUGH THU. AFTERNOON DESERT TEMPERATURES WILL
BOUNCE BACK INTO THE 90S TUE THROUGH THU.

&&

.AVIATION...
SOUTH-CENTRAL ARIZONA INCLUDING KPHX...KIWA...AND KSDL...
AN APPROACHING DRY COLD FRONT WILL LEAD TO STRONG SOUTHERLY WINDS BY
MIDDAY/EARLY AFTERNOON WITH A SLOW TREND TOWARD SOUTHWESTERLY LATER
IN THE AFTERNOON. ANTICIPATE GUSTS OF 25-30 KTS AFT 18Z. WINDS WILL
SLOWLY WEAKEN...FAVORING SOUTHWEST DIRECTIONS...AFTER 02Z. NO
SIGNIFICANT CLOUDS THROUGH TONIGHT...JUST SOME MINOR CIRRUS.

SOUTHEAST CALIFORNIA/SOUTHWEST ARIZONA INCLUDING KIPL AND KBLH...
SOUTHERLY WINDS WILL BE FAVORED TODAY AND TONIGHT NEAR AND EAST OF
THE LOWER COLORADO RIVER VALLEY WITH STEADY STRENGTHENING DURING THE
DAY...GUSTS OF 25-30 KTS IN THE AFTERNOON. WEST OF THERE...WESTERLY
WINDS WILL BE FAVORED WITH SLOWER STRENGTHENING. NEAR AND WEST OF THE
IMPERIAL VALLEY...WINDS WILL PEAK AFTER 22Z WITH GUSTS TO 35-40 KTS
BTWN 23Z-05Z AND AREAS OF BLOWING DUST DUST AND SAND AT TIMES. WINDS
WILL SLOWLY WEAKEN OVERNIGHT. NO SIGNIFICANT CLOUDINESS.

AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SATURDAY THROUGH WEDNESDAY...
A LOW PRESSURE SYSTEM SETTLING OVER THE DESERT SOUTHWEST WILL KEEP
TEMPERATURES WELL BELOW NORMAL THIS WEEKEND WITH MINIMUM HUMIDITIES
NEAR OR ABOVE 20 PERCENT AND OVERNIGHT RECOVERY GOOD TO VERY GOOD.
RAIN CHANCES SATURDAY WILL BE SLIGHT...A BIT BETTER OVER NORTHERN
MARICOPA AND SOUTHERN GILA COUNTIES. THERE WILL ALSO BE A SLIGHT
CHANCE OF THUNDERSTORMS...MAINLY EAST OF THE LOWER COLORADO RIVER
VALLEY. ONLY SLIGHT CHANCES OF RAIN SUNDAY OVER THE HIGHER TERRAIN.
HIGH PRESSURE BUILDS IN NEXT WEEK FOR DRY CONDITIONS...WARMING
TEMPERATURES...AND DECREASING HUMIDITIES. WINDS WILL BE LIGHT THIS
WHOLE TIME PERIOD EXCEPT FOR MINOR AFTERNOON BREEZES.

&&

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

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...BLOWING DUST ADVISORY FROM 1 PM THIS AFTERNOON TO 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 FROM 4 PM THIS AFTERNOON TO 9 PM PDT THIS
     EVENING FOR CAZ033.

     WIND ADVISORY FROM 4 PM THIS AFTERNOON TO 10 PM PDT THIS
     EVENING FOR CAZ033.

&&

$$

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

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



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