Flash Flood Warning 57, NWS Grand Junction, CO

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
451 PM MDT SUN SEP 22 2013

.UPDATE...
ISSUED AT 450 PM MDT SUN SEP 22 2013

THE SITUATION HAS TRANSITIONED FROM STRONG-SEVERE TYPE
THUNDERSTORMS TO WIDESPREAD RAIN WITH EMBEDDED THUNDERSTORMS.
THEREFORE THE SEVERE THUNDERSTORM WATCH HAS BEEN CANCELLED. WE
STILL MAY SEE AN ISOLATED STRONG STORM OVER FAR SOUTHWEST
COLORADO THROUGH THE NEXT HOUR OR SO AS CELLS MOVE NORTH ACROSS
THE BORDER FROM NEW MEXICO. OTHERWISE THE CONVECTIVE ACTIVITY HAS
CONGEALED INTO A LARGE AREA OF MODERATE RAIN WITH EMBEDDED HEAVIER
THUNDERSTORMS...MAINLY OVER THE CENTER OF THE FORECAST AREA.
THEREFORE THE RISK OF FLOODING AND MUD SLIDES WILL CONTINUE. SO
FOR NOW THERE WILL BE NO CHANGE TO THE FLASH FLOOD WATCH.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY NIGHT)
ISSUED AT 243 PM MDT SUN SEP 22 2013

VIGOROUS STORM SYSTEM WILL CONTINUE TO PASS OVER THE AREA THIS
EVENING. THIS SYSTEM HAS RESULTED IN SEVERAL SEVERE THUNDERSTORMS
ALREADY TODAY...AS WELL AS A FEW REPORTS OF FLASH FLOODING. THIS
POTENTIALLY STRONG ACTIVITY IS EXPECTED TO CONTINUE FOR A FEW MORE
HOURS BEFORE THE MAIN BEST LIFT/DYNAMICS SHIFT EAST.

SHOWERS AND THUNDERSTORMS WILL BEGIN TO WIND DOWN BETWEEN 6 AND 7
PM MDT THIS EVENING...WITH SOME STRONG STORMS POSSIBLE UNTIL THEN.
THE ONGOING SEVERE THUNDERSTORM WATCH WILL CONTINUE UNTIL 7 PM
MDT. THIS CONTINUES TO LOOK LIKE GOOD TIMING AS THE SURFACE FRONT
SHOULD BE TO OUR EAST BY THEN. THE POSSIBILITY OF HEAVY RAIN MAY
PERSIST A LITTLE LONGER AS THE UPPER TROUGH PASSES OVERHEAD AND
THEN ACROSS THE DIVIDE BY MIDNIGHT. THIS ALONG WITH THE LOSS OF
DAYTIME HEATING SHOULD ALLOW THE CHANCE FOR HEAVY RAIN TO ALSO
DIMINISH BY LATE EVENING. AS FIRST THE FRONT THE THE UPPER TROUGH
PASS THE WIND WILL SHIFT TO THE WEST.

THEN LATE TONIGHT BEHIND THE TROUGH THE FLOW BECOMES NORTHWEST. IT
ALSO LOOKS LIKE THERE WILL BE A MINI-SHOT OF MOISTURE...MAINLY
OVER THE EASTERN HALF. THIS WILL KEEP SHOWERS ONGOING OVER THE
MOUNTAINS INTO MONDAY MORNING...FAVORING THE NORTHWEST-NORTH
FACING SLOPES...ESPECIALLY FROM THE VAIL AREA NORTHWARD. COLD
ADVECTION WILL LOWER SNOW LEVELS TO AROUND 9500 FEET BY MONDAY
MORNING. HOWEVER MODELS KEEP THE 700MB TEMPERATURES ABOVE ZERO C
THROUGH THE DURATION. SO I DO NOT EXPECT MUCH IN THE WAY OF
ACCUMULATIONS. THE HIGHER PASSES MAY SEE A COUPLE INCHES AT
BEST...WITH MORE OVER THE HIGHEST PEAKS. OTHERWISE THE DRIER
NORTHWEST FLOW WILL RESULT IN CLEARING SKIES FROM THE WEST LATE
TONIGHT.

SHOWERS WILL LINGER ALONG THE NORTHERN DIVIDE THROUGH MONDAY
MORNING...MOSTLY ENDING BY NOON. A COOL BUT BLUEBIRD DAY WILL BE
IN STORE WITH VALLEY TEMPERATURES MOSTLY IN THE 60S...AND MID 40S
TO LOWER 50S IN THE MOUNTAINS. THE LOWER UT VALLEYS ARE THE ONLY
PLACES THAT WILL REACH INTO THE 70S.

MON NIGHT PROMISES TO BE COLDER DUE TO THE DRIER AIR MASS. THE
NORTHERN VALLEYS AND THE UPPER GUNNISON BASIN MAY SEE BELOW
FREEZING TEMPERATURES. WILL WAIT FOR ANOTHER MODEL RUN OR TWO TO
SEE IF FREEZE HIGHLIGHTS WILL BE NEEDED.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 243 PM MDT SUN SEP 22 2013

DRY CONDITIONS CONTINUE INTO TUESDAY AND WEDNESDAY AS THE RIDGE
BEGINS TO SHIFT TO THE EAST. HIGHS WILL PUSH BACK TO THE NORMAL
MARK BY TUESDAY WITH SOUTHWEST FLOW DOMINATING. THIS RIDGE WILL BE
MOVING DOWNSTREAM AS A BROAD UPPER TROUGH DROPS INTO THE
INTERMOUNTAIN WEST AGAIN ON WEDNESDAY NIGHT. GFS AND ECMWF SHOW
PIECES OF ENERGY SHEARING NORTHEAST AS THE TROUGH WEAKENS CROSSING
THE CENTRAL ROCKIES. COULD HAVE ANOTHER ACTIVE WEATHER DAY LATE
WED NIGHT AND/OR THURSDAY AHEAD OF THIS TROUGH. SNOW LEVELS COULD
FALL TO NEAR 8000 FEET FRIDAY MORNING BUT CONFIDENCE IS LOW ON THE
EXACT STRENGTH OF THE TROUGH AT THIS TIME AND HOW MUCH SNOW COULD
BE HAD AT HIGHER ELEVATIONS.

BOTH THE GFS AND ECMWF AGREE THAT A RIDGE WILL BUILD INTO THE AREA
SATURDAY...LEAVING ANOTHER CRISP AUTUMN MORNING IN THE WAKE OF THE
TROUGH GIVING WAY TO SUNSHINE AND GRADUALLY INCREASING TEMPS OVER
THE WEEKEND.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 243 PM MDT SUN SEP 22 2013

POTENTIALLY DANGEROUS CONDITIONS WILL CONTINUE FOR A SHORT TIME
INTO THE EVENING WITH THE MAIN HAZARDS OF LOCAL +TSRAGS WITH
STRONG GUSTS OF 35 TO 45 KTS POSSIBLE. THESE STRONGER STORMS
SHOULD DIMINISH BY AROUND 01Z. HOWEVER THE THREAT OF HEAVY RAIN
WILL PERSIST A LITTLE LONGER...ENDING BY AROUND 03-04Z. OCCASIONAL
TO WIDESPREAD IFR/MVFR VIS/CIGS WITH PASSING SHOWERS AND
THUNDERSTORMS ARE EXPECTED. IMPROVING CONDITIONS AFTER 03Z AS
-SHRA/-TSRA DECREASE FROM THE WEST. HOWEVER SNOW SHOWERS WILL
DEVELOP ALONG THE CONTINENTAL DIVIDE AFTER 03Z. THESE SHOWERS WILL
CONTINUE INTO MONDAY MORNING...LINGERING LONGEST FROM THE VAIL
AREA NORTHWARD. MOUNTAIN OBSCURATIONS WILL BE POSSIBLE FROM THESE
SHOWERS.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...FLASH FLOOD WATCH UNTIL 9 PM MDT THIS EVENING FOR COZ003-006-007-
     009-011-012-014-017>023.

UT...FLASH FLOOD WATCH UNTIL 9 PM MDT THIS EVENING FOR UTZ022-025-
     027>029.

&&

UPDATE...EH
SHORT TERM...EH
LONG TERM...JAM
AVIATION...EH

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
450 PM MDT SUN SEP 22 2013

COZ001>014-017>023-UTZ022>025-027>029-232300-
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-
450 PM MDT SUN SEP 22 2013

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

.DAY ONE...TONIGHT

A POWERFUL WEATHER SYSTEM WILL CONTINUE MOVING ACROSS THE REGION
TONIGHT AND WIDESPREAD MODERATE TO HEAVY RAIN AND A FEW
THUNDERSTORMS.

HEAVY RAIN SHOWERS...ESPECIALLY ACROSS THE SOUTH WILL BRING A
THREAT OF FLASH FLOODING...MUD DEBRIS FLOWS...AND ROCKSLIDES IN
STEEP TERRAIN.

LATE TONIGHT...LIGHT SNOW ACCUMULATIONS MAY RESULT IN SLUSHY
CONDITIONS OVER THE MOUNTAIN PASSES.

FOR SPECIFIC DETAILS OF HAZARDOUS WEATHER TODAY AND TONIGHT...SEE
THE FLASH FLOOD WATCH AND SPECIAL WEATHER STATEMENTS THAT PROVIDE
SPECIFIC DETAILS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

THE NEXT CHANCE FOR PRECIPITATION WILL BE WEDNESDAY NIGHT THROUGH
FRIDAY AS ANOTHER COLD FRONT MOVES THROUGH. SNOW WILL BE POSSIBLE
OVER THE MOUNTAIN PASSES ACROSS WESTERN COLORADO.

ON FRIDAY AND SATURDAY MORNING...FREEZING TEMPERATURES MAY RESULT
IN SEASON ENDING KILLING FROST IN THE HIGHER VALLEYS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL NOT BE NEEDED.

CC

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