Severe Thunderstorm Warning 19, NWS Grand Junction, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
302 PM MDT TUE SEP 17 2013

.SHORT TERM...(TONIGHT THROUGH WEDNESDAY NIGHT)
ISSUED AT 302 PM MDT TUE SEP 17 2013

SOUTHERLY FLOW IN ADVANCE OF STRONG WEST COAST TROUGH HAS TAPPED
INTO LOWER LEVEL MONSOONAL MOISTURE. FIRST LINE OF SHOWERS AND
THUNDERSTORMS CURRENTLY MOVING ACROSS NW COLORADO AT 19Z/20Z TIME
FRAME. FARTHER UPSTREAM...STORMS THAT HAVE FIRED OVER THE UTAH
SPINE HAVE SPREAD INTO THE WRN UINTA BASIN. STORMS ON RADAR
LOOKING STRONG WITH SOME ROTATION. WITH SHEAR AXIS AHEAD OF THE
WEST COAST TROUGH ENHANCING DEEP LAYERED SHEAR...AGREED WITH THE
SEVERE THUNDERSTORM WATCH FOR THE NRN PORTION OF THE FORECAST
AREA THROUGH 03Z THIS EVENING.

STRONG THUNDERSTORM POSSIBLE SOUTH OF THE WATCH AREA...INCLUDING
THE VICINITY OF THE SAN JUAN MOUNTAINS LATER THIS AFTERNOON GIVEN
MONSOONAL MOISTURE THAT PERSISTS ACROSS THIS AREA. ENERGY ALOFT
DRAGS ACROSS SW COLORADO THIS EVENING...THEREFORE SHOWERS AND
STORMS MAY PERSIST BEYOND MIDNIGHT TONIGHT ACROSS THE SAN JUAN
MOUNTAINS AND ADJACENT LOWER VALLEYS (DURANGO TO PAGOSA SPRINGS).

STRONG TROUGH AXIS MOVING ACROSS THE NRN AND CENTRAL ROCKIES WILL
BE LIFTING NORTHEAST. LOWER LEVEL MONSOONAL MOISTURE REMAINS IN
PLACE ACROSS THE WESTERN SLOPE FOR AFTERNOON CONVECTION. PWATS
WILL BE LOWER FOR LOWER CAPE VALUES...BUT STILL SUFFICIENT MOISTURE FOR
ISOLATED STRONG THUNDERSTORMS THAT GENERATE GUSTY WINDS ACROSS
SOUTHWEST COLORADO GIVEN GRADIENT FLOW. CONVECTION DIES OUT FAIRLY
QUICKLY WEDNESDAY EVENING FOR CLEARING SKIES ACROSS THE ENTIRE REGION.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 302 PM MDT TUE SEP 17 2013

A PROGRESSIVE SERIES OF PACIFIC TROUGHS WILL BRING A ROLLER
COASTER RIDE OF SUNNY MILD WEATHER WITH BREEZY SHOWERS MIXED IN
OVER THE WEEKEND AND AGAIN NEXT WEDNESDAY.

THE DRY AND COOL AIR MASS WILL SETTLE OVER THE FORECAST AREA ON
THURSDAY. THE WEST TO EAST COOL FRONT LOOKS TO BE ORIENTED CLOSE
TO THE HIGHWAY 50 LINE. THIS WILL BRING 10 DEGREES OF COOLING TO
THE NORTH WITH LITTLE CHANGE SOUTH. FLOW ALOFT VEERS TO WNW.
THURSDAY NIGHT A RIDGE PROGRESSES INTO UTAH. UNDER CLEAR SKIES AND
LIGHT WINDS OVERNIGHT INVERSIONS WILL BECOME STRONG. LOW
TEMPERATURES WILL BE WELL BELOW NORMAL WITH NEAR FREEZING
TEMPERATURES IN THE CRAIG AREA.

FRIDAY THE UPPER RIDGE PASSES...FLOW BACKS TO SW... AND
TEMPERATURES RECOVER TO NEAR NORMAL. MOISTURE THAT WAS LURKING JUST
BELOW THE FOUR CORNERS BEGINS TO FLOW BACK INTO THE SOUTHERN ZONES
FOR A CHANCE OF CONVECTIVE SHOWERS SATURDAY. SW GRADIENT WINDS
INCREASE SATURDAY AFTERNOON AND OVERNIGHT. TEMPERATURES CLIMB
ABOVE NORMAL.

SUNDAY THE NEXT PACIFIC TROUGH PASSES TO THE NORTH. THE LATEST
MODEL GUIDANCE PRODUCES MORE SHOWERS AND STORMS THAN IN PREVIOUS
MODEL RUNS. THE ASSOCIATED COOL FRONT WITH THIS TROUGH IS
CURRENTLY PROGGED TO WEAKEN AND STAY WELL WEST OF THIS FORECAST AREA.

ANOTHER PACIFIC TROUGH WILL THREATEN THE AREA NEXT WEDNESDAY.
UNTIL THEN SW FLOW ALOFT WILL KEEP BREEZY AND MILD EARLY FALL WEATHER.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 302 PM MDT TUE SEP 17 2013

SCATTERED SHOWERS AND STORMS WILL CONTINUE TO 03Z THIS EVENING.
STORM MOTION WILL BE TO THE NORTHEAST AT 20KTS SOUTH...35KTS
NORTH. THERE IS A SLIGHT CHANCE OF SEVERE THUNDERSTORMS FROM
STRONG WIND GUSTS AND HAIL ACROSS NE UTAH AND FAR NW COLORADO
INCLUDING KVEL. SOME BRIEF MVFR VISIBILITIES ARE POSSIBLE DUE TO
LOW VIS IN HEAVIER SHOWERS AND STORMS AT ALL AREA AIRPORTS. EXPECT
ISOLATED STORMS AND SHOWERS TO CONTINUE BEYOND MIDNIGHT. LOW LEVEL
WIND SHEAR IS POSSIBLE THROUGH WEDNESDAY MORNING AS STRONG SW
WINDS CONTINUE AT AND ABOVE MOUNTAIN TOP LEVEL. WEDNESDAY
SCATTERED CONVECTION WITH LOCAL MVFR CIGS WILL CONTINUE... MAINLY
ALONG THE COLORADO SPINE...AHEAD OF THE COOL FRONT. EXPECT
MODERATE TURBULENCE IN STRONG SW GRADIENT WINDS WEDNESDAY
AFTERNOON.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...NONE.

UT...NONE.

&&

SHORT TERM...PF
LONG TERM...JOE
AVIATION...JOE

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
927 AM MDT TUE SEP 17 2013

COZ001>014-017>023-UTZ022>025-027>029-181300-
LOWER YAMPA RIVER BASIN-CENTRAL YAMPA RIVER BASIN-
ROAN AND TAVAPUTS PLATEAUS-ELKHEAD AND PARK MOUNTAINS-
UPPER YAMPA RIVER BASIN-GRAND VALLEY-DEBEQUE TO SILT CORRIDOR-
CENTRAL COLORADO RIVER BASIN-GRAND AND BATTLEMENT MESAS-
GORE AND ELK MOUNTAINS/CENTRAL MOUNTAIN VALLEYS-
CENTRAL GUNNISON AND UNCOMPAHGRE RIVER BASIN-
WEST ELK AND SAWATCH MOUNTAINS-FLATTOPS-
UPPER GUNNISON RIVER VALLEY-UNCOMPAHGRE PLATEAU AND DALLAS DIVIDE-
NORTHWEST SAN JUAN MOUNTAINS-SOUTHWEST SAN JUAN MOUNTAINS-
PARADOX VALLEY/LOWER DOLORES RIVER-
FOUR CORNERS/UPPER DOLORES RIVER-ANIMAS RIVER BASIN-
SAN JUAN RIVER BASIN-SOUTHEAST UTAH-EASTERN UINTA MOUNTAINS-
EASTERN UINTA BASIN-TAVAPUTS PLATEAU-ARCHES/GRAND FLAT-
LA SAL AND ABAJO MOUNTAINS-CANYONLANDS/NATURAL BRIDGES-
927 AM MDT TUE SEP 17 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EASTERN UTAH AND WESTERN
COLORADO.

.DAY ONE...TODAY AND TONIGHT

STRONG THUNDERSTORM WILL BE POSSIBLE THIS AFTERNOON AND EARLY
EVENING...ESPECIALLY ACROSS THE NORTHERN AREAS. STRONG GUSTY WINDS
TO 50 MPH WILL BE THE MAIN THREAT...BUT ISOLATED STORMS MAY
PRODUCE PEA TO MARBLE SIZED HAIL. ISOLATED SHOWERS AND
THUNDERSTORMS WILL CONTINUE THROUGH THE NIGHT.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

A DRY COLD FRONT WILL MOVE THROUGH THE AREA WEDNESDAY AFTERNOON
AND EVENING BRINGING A SLIGHT CHANCE FOR SOME SHOWERS AND STORMS
MAINLY UP NORTH. ONCE IT PASSES...EXPECT CLEAR SKIES AS HIGH
PRESSURE BUILDS IN WITH COOL TEMPERATURES EXPECTED THURSDAY
BEFORE A WARM UP STARTS FOR THE WEEKEND.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS POSSIBLE TODAY. SPOTTERS ARE ENCOURAGED TO
REPORT EXCESSIVE WIND OR HAIL TO THE GRAND JUNCTION FORECAST
OFFICE.

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