000
FXUS65 KPSR 101649
AFDPSR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
948 AM MST FRI OCT 10 2008
SOUTH-CENTRAL AND SOUTHWEST ARIZONA...AND SOUTHEAST CALIFORNIA
FORECAST DISCUSSION
.SYNOPSIS...
AN INTENSE UPPER LEVEL LOW PRESSURE SYSTEM WILL MOVE ACROSS THE
SOUTHWEST STATES TODAY AND SATURDAY USHERING IN WINDY AND MUCH
COOLER WEATHER. MOISTURE ENTERING THE REGION FROM MEXICO WILL ALSO
GIVE A CHANCE OF SHOWERS TO PARTS OF SOUTH-CENTRAL ARIZONA TONIGHT
THROUGH SATURDAY...MAINLY FROM THE PHOENIX AREA EASTWARD. THERE WILL
BE LESS WIND ON SUNDAY AS THE LOW PRESSURE SYSTEM WEAKENS...WITH
COOL TEMPERATURES REMAINING. HIGHER PRESSURE ALOFT NEXT WEEK WILL
RESULT IN DRY AND WARMER WEATHER.
&&
.DISCUSSION...
WEATHER ACROSS THE REGION IS NOW RAPIDLY CHANGING AS THE WELL
ADVERTISED PAC NW TROUGH DIPS INTO THE SOUTHWEST. OVERALL MODELS
APPEAR TO BE HANDLING THE SITUATION RELATIVELY WELL AND FORECAST
TRENDS ARE STILL LOOKING ON TARGET.
ONE NOTICEABLE CHANGE THOUGH IS THAT WINDS WILL BE STRONGER TODAY
THAN PREVIOUSLY THOUGHT AS THE H5 SYSTEM IS MOVING IN A BIT QUICKER.
NAM/GFS BOTH DEVELOP A 30-40KT SW/NE H85 JET THIS AFTERNOON OVER
PIMA/PINAL/GILA COUNTIES. THOSE AREAS COULD FLIRT WITH WINDY
ADVISORY CRITERIA THIS AFTERNOON AND EVENING /SUSTAINED 30 MPH OR
GUST 40 MPH/ BUT FEEL THAT IT WILL ONLY BE ISOLATED AREAS AND
MOUNTAIN TOPS THAT ACTUALLY REACH CRITERIA AND WILL THEREFORE HOLD
OFF. WE DID ADD AREAS OF BLOWING SAND/DUST TO SW MARICOPA AND NW
PINAL COUNTIES THIS AFTERNOON...AND MOST AREAS ALONG AND WEST OF THE
LOWER CO RIVER FOR THIS AFTERNOON INTO THE OVERNIGHT HOURS. WILL
ALSO HAVE TO ASCERTAIN HOW STRONG WINDS WILL BE ACROSS SE CA THIS
EVENING/TONIGHT AS FROPA WILL ENHANCE ALREADY STRONG WINDS THERE. A
WINDY ADVISORY MAY BE REQ/D.
WILL HAVE TO LOOK AT WINDY ADVISORY AND FIRE WX WATCH THAT IS
CURRENTLY IN EFFECT FOR SATURDAY. FASTER PROGRESSION OF THE SYSTEM
MAY INDICATE THAT WINDS WILL BE A BIT WEAKER ACROSS MARICOPA/NW
PINAL COUNTIES THAN PREVIOUSLY INDICATED AND MAY BE SLIGHTLY BELOW
WIND ADVISORY/RED FLAG CRITERIA. DECISION ON THESE TWO PRODUCTS WILL
BE MADE WITH AFTN PACKAGE. WILL ALSO FINE-TUNE POPS FOR TONIGHT AND
TOMORROW. STILL APPEARS THAT MOST OF THE PRECIP WILL BE OUT OF OUR
CWA BY SAT EVENING.
WEB FORECAST UPDATED...ZONES OUT SHORTLY.
PREVIOUS DISCUSSION...
WV IMAGERY SHOWING THE STRONG TROUGH DEVELOPING OVER THE WRN US AS
UPPER RIDGE BUILDS OVER THE ERN PAC NEAR 140W. MODELS IN VERY GOOD
AGREEMENT NOW WITH THE EXPECTED INTENSIFYING AND MOVING OF THIS
TROUGH/UPPER LOW OVER THE NEXT COUPLE OF DAYS. AS TROUGH DROPS SWD...
IT WILL BEGIN TO TAP SOME OF NORBERT/S LOW/MID LEVEL MOISTURE IN
DEVELOPING SELY AGEOSTROPHIC FLOW. DYNAMICS WILL BE STRONG ENOUGH TO
LIFT THIS MOISTURE AND GIVE INCREASING THREAT OF SHOWERS TO OUR FAR
ERN CWA LATER TONIGHT AND THRU MUCH OF SATURDAY. IT APPEARS THAT THE
GREATER PHX AREA WILL BE ON THE FAR WRN EDGE OF PRECIP SHIELD...WITH
MOST OF THE SIGNIFICANT QPF AMOUNTS STAYING OVER ZONE 24. COULD
EASILY SEE ONE QUARTER TO ONE HALF INCH OF PRECIP FROM ABOUT GLOBE
EWD WITH THIS EVENT. BY SATURDAY AFTERNOON...VERY DRY AIR WILL WRAP
NEWD INTO THE LOW CIRCULATION...THEREBY CUTTING OFF PRECIP OVER ALL
BUT EXTREME ERN CWA BY SATURDAY AFTERNOON.
TO BE SURE...WIND WILL BE THE MAIN WEATHER FEATURE TO CONTEND WITH
NEXT 24 TO 48 HOURS. AS HEIGHT/PRESSURE GRADIENTS TIGHTEN ACROSS THE
REGION WITH THE LOW TO OUR N...WE SHOULD SEE A MARKED INCREASE IN
WIND SPEEDS BY AFTERNOON...ESPECIALLY OVER HIGHER TERRAIN AREAS OF
FAR WRN CWA. DECIDED TO HOIST A WIND ADVISORY FOR JOSHUA TREE NP
FROM 21Z-04Z. AND...SINCE HUMIDITIES WILL BE NEAR 15 PCNT HAVE ALSO
ISSUED A RED FLAG WARNING SAME AREA TODAY. ON SATURDAY AS THE COLD
FRONT SWEEPS ACROSS THE AREA...WE SHOULD SEE STRONGEST WIND SPEEDS
SHIFT TO SCNTRL AZ ZONES...WITH SOME GUSTS TO NEAR 40 MPH POSSIBLE.
WIND ADVISORY HAS THEREFORE BEEN ISSUED FOR THESE AREAS LATE SAT
MORNING INTO EARLY SATURDAY EVENING. IN ADDITION...MUCH DRIER AIR
ADVECTING INTO THE REGION ON SATURDAY WILL GIVE LOCALIZED SURFACE
HUMIDITIES LESS THAN 15 PCT OVER THE ENTIRE CWA EXCEPT FOR ZONE 24.
HAVE ISSUED FIRE WEATHER WATCH TO ACCOUNT FOR THIS.
BY SUNDAY...THE UPPER LOW WILL BEGIN LIFTING NEWD INTO THE NRN
ROCKIES...LEAVING BEHIND GENERAL TROUGHINESS ACROSS THE AREA THAT
WILL PERSIST THROUGH MONDAY. WILL BE BREEZY ON SUNDAY...BUT MUCH
LESS WIND THAN SATURDAY. MAIN FOCUS AREA FOR WIND WILL BE DOWN THE
LOWER CO RIVER VALLEY BOTH MONDAY AND TUESDAY. MUCH COOLER AIRMASS
THAT WILL SETTLE IN OVER THE REGION OVER THE WEEKEND WILL GRADUALLY
MODIFY BACK TO NEAR OR SLIGHTLY ABOVE NORMAL VALUES BY THE MIDDLE OF
NEXT WEEK UNDER HIGHER PRESSURE ALOFT AND INCREASING THICKNESSES.
&&
.AVIATION...
KPHX AND KIWA AIRFIELDS...CLEAR SKIES AND LIGHT SFC WINDS EXPECTED
THROUGH 16Z...WITH MUCH STRONGER WINDS OF 20-30 KTS THRU 2 THSD FT
AGL. LOCAL AREAS OF LOW LEVEL WIND SHEAR OF 20 KTS IS POSSIBLE THIS
MORNING. INCREASING MOISTURE IS ALSO UNDERWAY...DEW POINTS RAMPING
UP ACROSS MOST OF SOUTHERN AZ...WILL LEAD TO SCT CLOUDS...OCNL BKN
IN EASTERN PORTIONS. SLGT CHC OF -SHRA TO THE EAST OF KIWA AFTER
0200Z. SHARP COLD FRONT EXPECTED TO SWEEP THRU THE PHOENIX AREA
SATURDAY FOR STRONGER WEST WINDS...BUT NOT CONFIDENT ENUF TO
INTRODUCE ANY BLWG DUST AND LOWER VSBYS IN KPHX OR KIWA TAFS.
SOUTHEAST CA AND THE COLORADO RIVER VALLEY...INCLUDING KIPL...KNYL
AND KBLH...A SHARP COLD FRONT...NEAR LAS VEGAS AT 12Z WILL SWEEP
INTO THE SOUTHEAST CALIFORNIA AREA BY THIS AFTERNOON...AND STRONG
GUSTY SFC WINDS...POSSIBLY SOME PATCHY BLWG DUST...IS EXPECTED.
MOSTLY CLEAR SKIES ARE ALSO FORECAST THIS PERIOD.
AVIATION DISCUSSION NOT UPDATED FOR AMENDED TAFS.
&&
.FIRE WEATHER...
AN APPROACHING COLD FRONT WILL LEAD TO WINDY CONDITIONS THIS
AFTERNOON AND EVENING...ESPECIALLY IN SOUTHEAST CALIFORNIA. THE
COMBINATION OF WINDS...LOW HUMIDITIES...AND FUEL CONDITIONS HAS
PROMPTED THE ISSUANCE OF A RED FLAG WARNING FOR JOSHUA TREE NATIONAL
PARK FROM 2 PM TO 9 PM. THE DRY FRONT IS EXPECTED TO MOVE FROM
SOUTHEAST CALIFORNIA LATE TONIGHT AND ACROSS SOUTHWEST AND
SOUTH-CENTRAL ARIZONA SATURDAY. THUS A FIRE WEATHER WATCH IS IN
EFFECT FOR ALL ZONES DURING THE DAY SATURDAY EXCEPT AZ133...SOUTHERN
GILA COUNTY AND FAR NORTHEAST MARICOPA COUNTY. AZ133 IS ANTICIPATED
TO HAVE HIGH ENOUGH HUMIDITIES TO AVOID CRITICAL THRESHOLDS. IN FACT
THERE WILL BE A SLIGHT CHANCE OF SHOWERS AND THUNDERSTORMS IN THAT
ZONE TODAY AND TONIGHT...INCREASING TO A CHANCE SATURDAY. THERE WILL
ALSO BE A SLIGHT CHANCE OF SHOWERS IN FAR EASTERN PORTIONS OF
AZ132...SPECIFICALLY THE PHOENIX METRO AREA AND NORTHWEST PINAL
COUNTY...TONIGHT AND SATURDAY MORNING BEFORE THE FRONT PUSHES
THROUGH AND BRINGS IN MUCH DRIER AIR FOR THE AFTERNOON SUFFICIENT TO
PRODUCE CRITICAL THRESHOLDS.
SUNDAY THROUGH TUESDAY...
WINDS WILL DECREASE IN ALL ZONES ON SUNDAY AS THE UPPER LOW MOVES
THROUGH THE ROCKIES AND HIGH PRESSURE FILTERS INTO CALIFORNIA. LOW
RH IS EXPECTED TO CONTINUE SUNDAY INTO TUESDAY...MAINLY ACROSS THE
DESERTS. GENERALLY CLEAR SKIES WILL PREVAIL DURING THE PERIOD. WINDS
ARE EXPECTED TO REMAIN BELOW CRITICAL FIRE WEATHER THRESHOLDS.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...FIRE WEATHER WATCH FROM SATURDAY MORNING THROUGH SATURDAY
AFTERNOON FOR AZZ131-132.
WIND ADVISORY FROM 10 AM TO 6 PM MST SATURDAY FOR
AZZ022>024-027-028.
CA...FIRE WEATHER WATCH FROM SATURDAY MORNING THROUGH SATURDAY
AFTERNOON FOR CAZ230>232.
RED FLAG WARNING FROM 2 PM THIS AFTERNOON TO 9 PM PDT THIS
EVENING FOR CAZ230.
WIND ADVISORY FROM 2 PM THIS AFTERNOON TO 9 PM PDT THIS EVENING
FOR CAZ030.
&&
$$
NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT
WEATHER.GOV/PHOENIX
DISCUSSION...INIGUEZ/ESTLE
AVIATION...SIPPLE
FIRE WEATHER...SIPPLE
