Severe Thunderstorm Warning 44, NWS Phoenix, AZ

AZZ020>028-CAZ030>033-050600-

AREA FORECAST DISCUSSION...UPDATED AVIATION DISCUSSION
NATIONAL WEATHER SERVICE PHOENIX AZ
430 PM MST TUE SEP 4 2007

.SYNOPSIS...
AN INCREASE IN MOISTURE WILL SUPPORT ISOLATED THUNDERSTORMS MAINLY
OVER FAR SOUTHEAST CALIFORNIA AND SOUTHWEST ARIZONA THIS EVENING.
HURRICANE HENRIETTE...CURRENTLY NEAR THE SOUTHERN TIP OF BAJA
CALIFORNIA...WILL WEAKEN AND MOVE SLOWLY TOWARD THE NORTH DURING THE
NEXT COUPLE OF DAYS. AS THIS OCCURS...MOISTURE WILL BE ON THE
INCREASE OVER SOUTHWEST AND SOUTH-CENTRAL ARIZONA...WITH A CHANCE
FOR SHOWERS AND THUNDERSTORMS MAINLY OVER SOUTH-CENTRAL ARIZONA
WEDNESDAY EVENING THROUGH THURSDAY NIGHT. A SLIGHT CHANCE FOR A
SHOWER OR STORM WILL CONTINUE ON FRIDAY...BUT DRIER AND WARMER
WEATHER WILL RETURN TO THE REGION SATURDAY THROUGH MONDAY.

&&

.SHORT TERM...
TONIGHT THROUGH FRIDAY...
MAJOR FORECAST CHALLENGE CENTERS ON DEGREE OF MOIST ADVECTION AND
PRECIP CHANCES AS WEAKENING/DISSIPATING HENRIETTE PASSES TO THE
SOUTH AND EAST OF THE FORECAST AREA.

IMPRESSIVE LOW LEVEL MOIST ADVECTION FROM THE GULF OF CALIFORNIA HAS
BEEN ONGOING MAINLY OVER FAR SOUTHEAST CALIFORNIA AND SOUTHWEST
ARIZONA TODAY. KYUX VWP INDICATES MAIN PUSH OF MOISTURE HAD OCCURRED
IN THE LOWEST MILE AGL...WITH SFC DEW POINTS OVER AND WEST OF THE
LOWER COLORADO RIVER STILL IN THE UPPER 60S TO LOW 70S AS OF 3 PM.
COMBINED WITH STEEP LOW-MID LEVEL LAPSE RATE...TSTM DEVELOPMENT
OCCURRED MAINLY OVER HIGHER TERRAIN OF SOUTHWEST MARICOPA
COUNTY...CENTRAL LA PAZ COUNTY...NORTHERN BAJA CALIFORNIA...AND
HIGHER TERRAIN JUST WEST OF IMPERIAL COUNTY EARLIER THIS
AFTERNOON...WITH INTENSE STORMS PROPAGATING/DEVELOPING SLOWLY TOWARD
THE EAST OVER WESTERN IMPERIAL COUNTY AS OF 4 PM. HAVE BUMPED POP UP
A BIT OVER THE ENTIRE CWA FOR THIS EVENING...WITH BIGGEST INCREASE
OVER FAR SOUTHEAST CALIFORNIA.

HENRIETTE IS STILL FORECAST TO WEAKEN AND MOVE SLOWLY TOWARD THE
NORTH DURING THE NEXT COUPLE OF DAYS...WHILE A VIGOROUS TROUGH IN
THE WESTERLIES MOVES SLOWLY EAST ACROSS THE INTERMOUNTAIN WEST. NHC
FORECASTS REGARDING HENRIETTE HAVE BEEN VERY CONSISTENT...AS HAS
NUMERICAL GUIDANCE REGARDING HENRIETTE AND THE VIGOROUS TROUGH IN
THE WESTERLIES (LATEST INFORMATION REGARDING HENRIETTE WILL BE
PROVIDED BY THE NATIONAL HURRICANE CENTER (WWW.NHC.NOAA.GOV)).
INTERACTION BETWEEN THESE TWO SYSTEMS SHOULD RESULT IN A MOISTURE
INCREASE ACROSS THE EASTERN HALF OF THE CWA DURING THE NEXT 24-36
HRS...WITH AN INCREASED CHANCE FOR SHOWERS AND THUNDERSTORMS OVER
THE AZ PORTION OF THE CWA BY WEDNESDAY EVENING. OF COURSE...BIG WILD
CARDS CONTINUE TO BE THE DEGREE OF MOIST ADVECTION AND UPPER SUPPORT
OVER OUR CWA. ATTM...BEST CHANCE FOR SIGNIFICANT PRECIP APPEARS TO
BE OVER SOUTHEAST AZ...SOUTH AND EAST OF OUR CWA...THE AREA CLOSEST
TO THE TRACK OF HENRIETTE REMNANTS. FOR NOW...CHANCE POPS APPEAR
REASONABLE FOR SOUTH CENTRAL AZ WEDNESDAY EVENING THROUGH THURSDAY
EVENING. A DRYING TREND WILL COMMENCE BY FRIDAY...BUT A SLIGHT
CHANCE FOR A STORM WILL CONTINUE OVER SOUTH-CENTRAL AZ GIVEN
UNCERTAINTY REGARDING STABILITY/MOISTURE AVAILABILITY.

&&

.LONG TERM...
FRIDAY NIGHT THROUGH TUESDAY...
POPS AND CLOUDS WILL DECREASE FROM THE WEST OVER SOUTH-CENTRAL AZ
FRIDAY EVENING AS THE REMNANTS OF HENRIETTE MOVE EAST OF OUR AREA.
CONTINUED DRYING IS ON TAP SATURDAY INTO EARLY NEXT WEEK AS A
WESTERLY FLOW ALOFT MOVES INTO ARIZONA. AS SUCH POPS WILL DROP OFF
QUITE A BIT...AND HIGH TEMPERATURES WILL RISE TO SLIGHTLY ABOVE
NORMAL LEVELS...SUNDAY THROUGH TUESDAY.

&&

.AVIATION...
SEPTEMBER 4 2010 UTC (SEPTEMBER 4 1310 MST)

LOW TO MID LEVEL MOISTURE INCREASE FROM THE SOUTH THIS PAST 24 HOURS
HAS LEAD TO INCREASING INSTABILITY OVER THE SOUTH-CENTRAL DESERTS.
ISOLATED THUNDERSTORMS WILL CONTINUE TO DEVELOP OVER SOUTHWEST
MARICOPA COUNTY (40-50NM SW OF KPHX) THROUGH 0000 UTC...WITH A
SLIGHT CHANCE OF THUNDERSTORMS DEVELOPING CLOSER TO THE KPHX/KIWA
AIRFIELDS AFTER 0100 UTC. AS A MATTER OF FACT...GIVEN THE LOW LEVEL
INCREASE FROM SOUTHEAST CALIFORNIA TO SOUTHERN GILA COUNTY (ACROSS
OUR ENTIRE FORECAST AREA)...WE CANNOT RULE OUT THE SLIGHT CHANCE FOR
THUNDERSTORMS AT ANY OF THE FIVE TAF SITES. AT THIS TIME...
CONFIDENCE REMAINS LOW FOR DIRECT AIRFIELD IMPACT...SO WILL GO WITH
CB IN THE TAFS. WILL MONITOR CLOSELY AS AFTERNOON WEARS ON...AND
AMEND TAFS AS NECESSARY.

SEE TAFS PHXTAFPHX...PHXTAFIWA...PHXTAFYUM...LAXTAFBLH AND LAXTAFIPL
FOR MORE DETAILED INFORMATION.

AVIATION DISCUSSION IS NOT UPDATED FOR AMENDED TAFS.

&&

.FIRE WEATHER...
SEPTEMBER 4 2320 UTC (SEPTEMBER 4 430 PM MST)

QUITE A BIT OF UNCERTAINTY IN THE FORECAST LATE WEDNESDAY THROUGH
FRIDAY DUE TO POSSIBLE IMPACTS FROM THE REMNANTS OF A TROPICAL
SYSTEM. AT THIS TIME...IT APPEARS THAT CLOUD COVER...RH VALUES...AND
PRECIPITATION CHANCES WILL BEGIN TO INCREASE ACROSS THE EASTERN HALF
OF THE FORECAST AREA/MARICOPA COUNTY EAST/LATE WEDNESDAY... AND
REMAIN ELEVATED THROUGH FRIDAY...BUT THE BULK OF THE RAINFALL IS
EXPECTED TO IMPACT THE SOUTHEAST CORNER OF AZ. THE SYSTEM SHOULD BE
MOVING OFF TO THE EAST BY LATE FRIDAY. WEAK HIGH PRESSURE WILL BUILD
BACK OVER THE REGION OVER THE WEEKEND...RESULTING IN DECREASING RH
VALUES AND SLOWLY INCREASING TEMPERATURES.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...

AZ...NONE.

CA...NONE.

&&

NATIONAL WEATHER SERVICE PHOENIX IS ON THE INTERNET AT

WEATHER.GOV/PHOENIX

SHORT TERM...DG
LONG TERM...DG
AVIATION...WANEK
FIRE WX...INIGUEZ