Area Forecast Discussion
Issued by NWS Tucson, AZ

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000
FXUS65 KTWC 231555
AFDTWC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE TUCSON AZ
900 AM MST TUE SEP 23 2014

.SYNOPSIS...LIMITED COVERAGE OF SHOWERS AND THUNDERSTORMS TODAY AND
WEDNESDAY...MAINLY NEAR THE MOUNTAINS. THE CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL THEN INCREASE THURSDAY THROUGH SATURDAY AS A
FRONT APPROACHES THE AREA FROM THE NORTHWEST. MUCH DRIER AND SEVERAL
DEGREES COOLER LATE THIS WEEKEND INTO EARLY NEXT WEEK.

&&

.DISCUSSION...STILL DECENT MOISTURE OUT THERE FOR LATE SEPTEMBER
WITH 1.1 TO 1.3 INCHES PRECIPITABLE WATER...BUT THE 12Z SOUNDING WAS
SHOWING ALMOST NO FLOW AND WEAK POTENTIAL STORM STRUCTURE AWAY FROM
TERRAIN INFLUENCES. WE UPDATED TO TWEAK MOUNTAIN COVERAGE UP TO THE
20-30 PERCENT RANGE THIS AFTERNOON BUT THEY WILL NOT TEND TO WANT TO
WANDER FAR AWAY FROM THE MOUNTAINS...COVERAGE IN VALLEY LOCATIONS
WILL BE SPOTTY AT BEST AND NON EXISTENT IN THE DRIER WESTERN AREAS.
WE WILL PROBABLY SEE A FEW MOUNTAIN STORMS AROUND THE AREA AGAIN
WEDNESDAY AFTERNOON. MINOR TWEAKS TO REFLECT THIS...OTHERWISE
CURRENT FORECAST TRENDS LOOK SOLID. PLEASE SEE PREV DISCUSSION
SECTION BELOW FOR ADDITIONAL DETAILS.

&&

.AVIATION...VALID THRU 24/18Z.
EXPECT ISOLD SHRA/TSRA FROM KTUS EASTWARD BETWEEN 23/19Z AND 24/04Z.
STORMS WILL EXHIBIT VERY SLOW MOVEMENT AND MAY HAVE TROUBLE MOVING
OFF THE MOUNTAINS. SURFACE WIND GENERALLY LESS THAN 10 KTS. AVIATION
DISCUSSION NOT UPDATED FOR TAF AMENDMENTS.

&&

.FIRE WEATHER...THERE IS A SLIGHT CHANCE OF SHOWERS AND
THUNDERSTORMS TODAY FROM TUCSON EASTWARD AND MAINLY OVER THE
MOUNTAINS. ON WEDNESDAY...ANY STORMS THAT DO DEVELOP SHOULD BE
CONFINED TO MOUNTAINS NEAR THE NEW MEXICO BORDER. INCREASING CHANCES
FOR SHOWERS AND THUNDERSTORMS WILL THEN OCCUR THURSDAY THROUGH
SATURDAY FOLLOWED MUCH DRIER CONDITIONS EARLY NEXT WEEK. BRIEF GUSTY
OUTFLOWS WILL OCCUR WITH THE STRONGER THUNDERSTORMS.
OTHERWISE...20-FOOT WINDS WILL GENERALLY BE LESS THAN 15 MPH THIS
WEEK.

&&

.PREV DISCUSSION...WATER VAPOR IMAGERY THIS MORNING SHOWED AN UPPER
LOW MOVING OUT OF WYOMING...A STRONG TROF MOVING TOWARD THE PACIFIC
NORTHWEST...AND ELONGATED RIDGE OF HIGH PRESSURE EXTENDING FROM SRN
UTAH SW TO WELL WEST OF BAJA CALIFORNIA. DRIER SW FLOW ALOFT OVER
SRN ARIZONA THIS MORNING WITH BLENDED PRECIPITABLE WATER VALUES
RANGING FROM 1" OVER WRN PIMA COUNTY TO 1.25" ALONG AZ/NM BORDER.
GPS VALUES WERE SLIGHTLY HIGHER...ESPECIALLY FROM TUCSON EAST. 00Z
MODELS SUGGESTED A VERY LIMITED THUNDERSTORM DAY HOWEVER 06Z NAM HAS
INCREASED POPS ALONG INTERNATIONAL BORDER FROM SANTA CRUZ COUNTY
EAST TO THE NEW MEXICO BOOT WITH THE SRN MOUNTAINS OF COCHISE COUNTY
GETTING INTO THE MIX. NAM INCREASED PW VALUES IN THESE AREAS TO OVER
1.50". SOME ADDITIONAL HR GUIDANCE ALSO SUGGESTING WE SHOULD HAVE
HIGHER POPS DOWN SOUTH. WITH THAT IN MIND...HAVE INCREASED POPS A
BIT FROM NOGALES EAST AND UP INTO THE WHITES...MAINLY IN THE LOW
SLIGHT CHANCE AREA. HIGHS TODAY WILL BE AT OR SLIGHTLY WARMER THAN
MONDAY.

WEDNESDAY...UPPER RIDGE EXTENDS FROM NRN BAJA NNE INTO WRN ND WITH
CENTER OVER NRN AZ. N-NE FLOW OVER THE AREA WITH LIMITED MOISTURE
OVER THE AREA. VERY SLIGHT CHANCE OF STORMS OVER THE HIGHER TERRAIN
E AND S OF TUCSON. HIGHS AT OR SLIGHTLY WARMER THAN TODAY.

THURSDAY...UPPER RIDGE STRETCHES NE INTO THE GREAT LAKES AS STRONG
PACIFIC TROF APPROACHES PAC NW/NRN CA. NE-E FLOW OVER THE AREA WITH
MID-LEVEL TEMPERATURES COOLING TO BETWEEN -5C AND -6C VIA 00Z GFS
WHILE 06Z NAM HAS -6C TO -8C. EITHER WAY THE BEST CHANCES FOR STORMS
WILL BE IN THE WHITES AND THE MOUNTAINS E AND S OF TUCSON. HIGHS
SLIGHTLY COOLER THAN WEDNESDAY.

FRIDAY AND SATURDAY...MODELS HAVE SLOWED THE MOVEMENT OF THE PACIFIC
UPPER TROF INTO THE WESTERN CONUS. YESTERDAY I MENTIONED THAT FRIDAY
COULD SEE AN INCREASED CHANCE FOR SEVERE STORMS. NOW IT APPEARS THAT
THIS MAY OCCUR ON SATURDAY...ESPECIALLY FROM TUCSON NORTH. HIGH
TEMPERATURES ON SATURDAY WILL BE 2-7 DEGREES COOLER THAN FRIDAY WITH
BIGGEST CHANGE OCCURRING FROM TUCSON EAST. LOCALLY BREEZY ON
SATURDAY ALSO.

SUNDAY...UPPER LEVEL TROFINESS HANGING OVER THE STATE WITH DRIER AIR
WORKING INTO THE WESTERN AREAS. MODEL HANG ON TO MOISTURE TO WARRANT
THE SLIGHT CHANCE TO CHANCE OF STORMS...MAINLY FROM TUCSON EAST.

MONDAY...2014 MONSOON DONE.

&&

.TWC WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

VISIT US ON FACEBOOK...TWITTER...YOUTUBE...AND AT WEATHER.GOV/TUCSON

MEYER/DROZD




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