Severe Thunderstorm Warning 89, NWS Salt Lake City, UT

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
443 PM MDT WED SEP 22 2010

.SYNOPSIS...A PACIFIC TROUGH WILL CROSS THE REGION TONIGHT. DRIER
WESTERLIES WILL SPREAD BACK INTO THE AREA THURSDAY. HIGH PRESSURE
WILL BUILD THROUGH THE WEEKEND AND REMAIN DOMINANT THROUGH MUCH OF
NEXT WEEK.

&&

.DISCUSSION...PACIFIC TROUGH CARVING THROUGH THE GREAT BASIN
TODAY IS JUST NOW REACHING THE WESTERN FRINGES OF THE STATE. A
WEAK COLD FRONT THAT HAS REMAINED NEARLY STATIONARY FOR THE LAST
SEVERAL HOURS OVER NORTHWESTERN UTAH HAS SLOWLY STARTED TO SURGE
SOUTHEAST ALONG THE WASATCH FRONT THIS AFTERNOON. THE MID
LEVEL TROUGH AXIS AND ASSOCIATED COLD POOL HAS NOSED INTO THE
WESTERN DESERTS AND WILL REACH THE INTERSTATE 15 CORRIDOR BY MID
EVENING.

CONVECTION BLEW RAPIDLY EARLIER TODAY WITHIN MOIST AIRMASS THAT
WAS PULLED NORTH AHEAD OF THE APPROACHING TROUGH. UTAH HAS BEEN
IN THE SWEET SPOT FOR CONVECTION TODAY...WITH NUMEROUS STRONG
THUNDERSTORMS DEVELOPING FROM ROUGHLY OGDEN SOUTH TO UTAHS DIXIE
AND POINTS EAST. INTENSE RAINFALL RATES AND TRAINING OF STORMS
WAS SUFFICIENT TO WARRANT SEVERAL FLASH FLOOD WARNINGS ACROSS
GRAND STAIRCASE/ESCALANTE NATIONAL MONUMENT AND WITHIN CAPITOL
REEF NATIONAL PARK...WITH ONE VERIFIED EVENT REPORTED ALREADY.
PRESENCE OF SHEAR EVEN ALLOWED FOR BORDERLINE SEVERE THUNDERSTORM
ORGANIZATION...WITH HAIL UP TO NICKLE SIZE REPORTED IN LEHI AND
ALPINE JUST SHY OF MIDDAY.

SURFACE DEWPOINTS HAVE BEEN CRASHING ACROSS THE WESTERN DESERTS
AND UTAH DIXIE THROUGHOUT THE AFTERNOON...WITH MANY SITES THAT
WERE PREVIOUSLY IN THE UPPER 40S NOW FALLING INTO THE 30 DEGREE
RANGE. ADDITIONALLY...A MID LEVEL DRY TONGUE HAS SURGED INTO THE
WESTERN HALF OF THE STATE ALLOWING A BIT OF DRY ENTRAINMENT INTO
CONVECTION THAT CONTINUES TO PERSIST AT THIS TIME. RESULT IS
SHALLOWER CONVECTIVE CELLS LESS INTENSE IN NATURE ACROSS CENTRAL
AND NORTHERN UTAH. FURTHER EAST...BREADTH OF MOISTURE CONTINUES
TO FUEL STRONGER CELLS WITH INTENSE PRECIP RATES...SOME EXHIBITING
WEAK ORGANIZATION. ANTICIPATE THESE TRENDS IN ACTIVITY TO CONTINUE
INTO THE OVERNIGHT HOURS WITH A GRADUAL EASTWARD SHIFT OF
AFOREMENTIONED DRY SLOT. ALLOWING GOING FLASH FLOOD WATCH TO
CONTINUE THROUGH 10PM ACROSS SOUTHCENTRAL/SOUTHEASTERN UTAH...BUT
HAVE CANCELLED WATCH FOR UTAHS DIXIE DUE TO ABOVE STATED REASONING.

MID LEVEL COLD POOL ASSOCIATED WITH TROUGH PASSAGE TRACKING
THROUGH NORTHERN UTAH SHOULD INCREASE AREAL COVERAGE OF PRECIP
EARLY THIS EVENING AFTER A BRIEF LULL IN ACTIVITY...BUT
AGAIN...RAINFALL RATES SHOULD BE ON THE LIGHTER SIDE AND MORE
SYNOPTIC IN NATURE.

THE TROUGH WILL PROGRESS RAPIDLY EAST THROUGH THE STATE OVERNIGHT.
PRECIP TO WANE WEST TO EAST RATHER SHARPLY IN SUBSIDENT
ENVIRONMENT AND A DRIER WESTERLY FLOW ALOFT THROUGH THE LATTER
HALF OF THE NIGHT.

TEMPS STATEWIDE WILL FALL TO SEASONAL NORMS THURSDAY IN WAKE OF
TROUGH...WITH PLEASANT EARLY FALL CONDITIONS DOMINATING. RIDGING
WILL AMPLIFY NORTHWARD THIS WEEKEND AND REMAIN IN PLACE THROUGH
MUCH IF NOT ALL OF NEXT WEEK ALLOWING TEMPS TO SURGE WELL ABOVE
NORMAL ONCE AGAIN.

&&

.AVIATION...RAIN SHOWERS WILL CONTINUE TO MOVE ACROSS THE SLC
TERMINAL AND VICINITY THROUGH AROUND 06Z. ISOLATED THUNDERSTORMS
WILL BE EMBEDDED IN THESE SHOWERS...AND THERE IS A 20 PERCENT CHANCE
OF THUNDERSTORMS DIRECTLY IMPACTING THE SLC TERMINAL. PREVAILING
CIGS WILL BE ABOVE 7000FT AGL...BUT WILL OCCASIONALLY DROP BELOW
7000FT NEAR SHOWERS. SKIES WILL GRADUALLY CLEAR AFTER MIDNIGHT AS A
DRIER AIRMASS SPREADS INTO THE AREA. NORTH WINDS HAVE SURGED ACROSS
THE TERMINAL AND WILL LIKELY BE MAINTAINED THROUGH 06-08Z WHEN
SOUTHERLY DRAINAGE WINDS ARE EXPECTED TO RETURN.

&&

.FIRE WEATHER...A BROAD TROUGH WILL CONTINUE TO MOVE ACROSS THE
REGION OVERNIGHT AND EXIT THE STATE BY THURSDAY MORNING. RAINFALL
TODAY HAS HELPED FIRE CONDITIONS AND ITS EFFECTS WILL LINGER INTO
THURSDAY. COOLER AND MORE STABLE AIR WILL MOVE INTO THE REGION FOR
THURSDAY AND FRIDAY. HIGH PRESSURE ALOFT WILL BUILD THIS
WEEKEND...ALLOWING FOR A GRADUAL WARMING AND DRYING TREND...WITH
FIRE WEATHER THREATS INCREASING ONCE AGAIN THROUGH EARLY NEXT
WEEK.

&&

.SLC WATCHES/WARNINGS/ADVISORIES...
UT...RED FLAG WARNING UNTIL 9 PM MDT THIS EVENING FOR
     UTZ420>427-431>441.

     FLASH FLOOD WATCH UNTIL 10 PM MDT THIS EVENING FOR
     UTZ013-019>021-518.

WY...NONE.
&&

PUBLIC...MERRILL
FIRE WEATHER...SAR
AVIATION...CHENG

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

FOR FREQUENTLY ASKED QUESTIONS ABOUT THE AREA FORECAST DISCUSSION
VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY/GENERAL/AFD_FAQS.PHP (ALL LOWER CASE)

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
626 PM MDT WED SEP 22 2010

UTZ001>016-019>021-517-518-WYZ021-231200-
CACHE VALLEY/UTAH PORTION-NORTHERN WASATCH FRONT-
SALT LAKE AND TOOELE VALLEYS-SOUTHERN WASATCH FRONT-
GREAT SALT LAKE DESERT AND MOUNTAINS-WASATCH MOUNTAIN VALLEYS-
WASATCH MOUNTAINS I-80 NORTH-WASATCH MOUNTAINS SOUTH OF I-80-
WESTERN UINTA MOUNTAINS-WASATCH PLATEAU/BOOK CLIFFS-
WESTERN UINTA BASIN-CASTLE COUNTRY-SAN RAFAEL SWELL-
SANPETE/SEVIER VALLEYS-WEST CENTRAL UTAH-SOUTHWEST UTAH-
UTAHS DIXIE AND ZION NATIONAL PARK-SOUTH CENTRAL UTAH-
GLEN CANYON RECREATION AREA/LAKE POWELL-CENTRAL MOUNTAINS-
SOUTHERN MOUNTAINS-SOUTHWEST WYOMING-
626 PM MDT WED SEP 22 2010

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE WESTERN TWO THIRDS OF
UTAH AND FAR SOUTHWEST WYOMING.

.DAY ONE...TONIGHT

MOISTURE WILL REMAIN ACROSS THE NORTHERN AND EASTERN PORTIONS OF
THE OUTLOOK AREA INTO TONIGHT THEN BEGIN TO SHIFT EAST AFTER
MIDNIGHT. THIS WILL KEEP SHOWERS AND THUNDERSTORMS ACTIVE THROUGH
THE EVENING BEFORE WINDING DOWN LATE TONIGHT.

HEAVY RAIN WILL STILL BE POSSIBLE WITH SOME OF THESE STORMS...
PARTICULARLY EAST OF INTERSTATE 15.

GUSTY WINDS AND A THREAT OF LIGHTNING WILL CONTINUE TO BRING A
FIRE WEATHER HAZARD TO MOST OF THE AREA THROUGH MID EVENING.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

DRY WEATHER WITH TEMPERATURES NEAR SEASONAL NORMALS ARE EXPECTED
THURSDAY. IT WILL REMAIN DRY WITH A WARMING TREND FRIDAY THROUGH
EARLY NEXT WEEK AS HIGH PRESSURE DOMINATES THE REGION.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS ARE ENCOURAGED TO REPORT SIGNIFICANT WEATHER
CONDITIONS ACCORDING TO STANDARD OPERATING PROCEDURES.

FOR MORE INFORMATION FROM NOAA/S NATIONAL WEATHER SERVICE VISIT...
HTTP://WEATHER.GOV/SALTLAKECITY (ALL LOWER CASE)

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE SALT LAKE CITY UT
405 PM MDT WED SEP 22 2010

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0230 PM     FLASH FLOOD      1 NE BIG WATER          37.08N 111.65W
09/22/2010                   KANE               UT   PARK/FOREST SRVC

            FLASH FLOODING ALONG WAHWEAP CREEK NEAR BIG WATER. 4 TO 6
            FEET DEEP AND 100 FEET WIDE AT THE PEAK. LOGS AND OTHER
            DEBRIS REPORTED.

&&

CRK

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