Flash Flood and Hail in Colorado, September 5, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
407 AM MDT WED SEP 5 2007

.SHORT TERM (TODAY THROUGH THURSDAY NIGHT)...
A MAJOR SHIFT IN THE WEATHER PATTERN IS UNDERWAY AS A VIGOROUS
TROUGH MOVES INTO THE GREAT BASIN THIS MORNING. STRONG DYNAMIC
FORCING WITH THIS SYSTEM AND AN ASSOCIATED COLD FRONT WILL ACT ON
DEEP MOISTURE IN PLACE AND PRODUCE STRONG THUNDERSTORMS ACROSS
EASTERN UTAH AND WESTERN COLORADO. FAST MOVING ORGANIZED CONVECTION
LIKELY TO TAKE SHAPE THIS AFTERNOON AND EVENING WITH POTENTIAL FOR
STRONG DAMAGING WINDS AND SOME LARGE HAIL. AREAS UNDER THE GREATEST
THREAT FOR SEVERE STORMS ARE UINTAH AND DAGGETT COUNTIES IN NORTHEAST
UTAH AND RIO BLANCO AND MOFFAT COUNTIES IN NORTHWEST COLORADO.
ALTHOUGH STORMS WILL BE MOVING QUICKLY...THE THREAT OF LOCALIZED
FLOODING WILL NEED TO BE MONITORED ESPECIALLY IN AREAS OF TRAINING
STORMS CELLS.

THE COLD FRONT WILL MARCH ACROSS THE AREA TONIGHT WITH A LINE OF
CONVECTION LIKELY TO ACCOMPANY IT. INSTABILITY AND STRONG FORCING
PROGGED TO CONTINUE THROUGH THE OVERNIGHT PERIOD...WITH MOST OF THE
CONVECTION CLEARING EASTERN UTAH AROUND MIDNIGHT BUT CONTINUING
ACROSS WESTERN COLORADO THROUGH EARLY THURSDAY MORNING AND LINGERING
INTO THE DAYLIGHT HOURS ALONG THE CONTINENTAL DIVIDE. STORMS WILL BE
LOSING SOME PUNCH THROUGH THE LATE NIGHT HOURS.

THE UPPER TROUGH AXIS WILL PUSH EAST OF THE AREA THURSDAY
AFTERNOON WITH MUCH DRIER AND MORE STABLE AIR ADVECTING ACROSS THE
AREA BEHIND IT IN WEST FLOW. THE ABOVE NORMAL TEMPERATURES WE HAVE
BEEN EXPERIENCING WILL CEASE WITH THIS SYSTEM AND WE WILL SETTLE INTO
A SEASONAL PATTERN THROUGH THE END OF THE WEEK.

.LONG TERM...FRIDAY THROUGH WEDNESDAY...
UPPER LEVEL WINDS BECOME WESTERLY ON FRIDAY IN THE WAKE OF THE UPPER
TROUGH AND HELP PUSH MOISTURE EAST OF THE CWA. MOST OF THE SUB
TROPICAL MOISTURE FROM THE REMNANTS OF HENRIETTE ARE WELL SOUTH AND
EAST BY FRIDAY. TEMPERATURES WILL INCREASE ON FRIDAY ALTHOUGH NOT TO
WHAT THEY WERE DURING THE BEGINNING OF THE WEEK AND PRECIPITATION
SHOULD BE LIMITED. UPPER PATTERN JUST SOUTH OF UT AND CO TURNS
SOUTHWEST AND COULD BRING A SLIGHT INCREASE OF MID AND UPPER LEVEL
MOISTURE TO THE SOUTHERN PORTION OF THE CWA BY MID WEEKEND. A FEW
WEAK SHORTWAVES ALSO TRACK OVERHEAD DURING THE WEEKEND SO WILL KEEP
THE DRY BIAS WITH THE SLIGHT CHC POPS MAINLY OVER THE HIGHER
TERRAIN. SHOWER AND THUNDERSTORM COVERAGE WILL INCREASE...ALTHOUGH
ONLY SLIGHTLY...FROM SATURDAY TO SUNDAY. GFS AND DGEX MODELS HAVE
KEPT THE UPPER CLOSED LOW DEVELOPING OVER THE PAC NORTHWEST EARLY
MONDAY. IF THIS WORKS OUT THE TROUGH WILL INDUCE A RIDGE AND
INCREASED HEIGHTS AND WARMING THE FIRST PART OF THE WEEK.
SOUTHWESTERLY FLOW ALOFT WOULD BRING A PLUME OF SUB TROPICAL
MOISTURE OVER THE CWA BY LATE TUESDAY AND WEDNESDAY. DID INCREASE
MTN POPS FOR THE SAN JUANS SLIGHTLY TUESDAY AND CONTINUED THAT TREND
OVER THE HIGHER TERRAIN FOR WEDNESDAY. IF MODELS CONTINUE WITH THE
CURRENT PATTERN WILL HAVE TO CONTINUE TO TREND POPS IN THE UPWARD
DIRECTION FOR MID WEEK NEXT.

&&

.AVIATION...
MVFR TO LOCAL IFR CONDITIONS EXPECTED TODAY AND TONIGHT ASSOCIATED
WITH STRONG FAST MOVING THUNDERSTORMS ALONG AND AHEAD OF A COLD
FRONT. HEAVY RAIN...HAIL...AND STRONG GUSTY WINDS IN EXCESS 50
MPH WILL ACCOMPANY SOME STORMS. INCREASING SOUTHWEST GRADIENT FLOW
WILL LIKELY YIELD AREAS OF LOW LEVEL WIND SHEAR.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
.CO...NONE.
.UT...NONE.

SHORT TERM...TAL
LONG TERM...AS
AVIATION...TAL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
607 AM MDT WED SEP 5 2007

COZ001>014-017>023-UTZ022>025-027>029-061200-
ANIMAS RIVER BASIN-ARCHES/GRAND FLAT-CANYONLANDS/NATURAL BRIDGES-
CENTRAL COLORADO RIVER BASIN-
CENTRAL GUNNISON AND UNCOMPAHGRE RIVER BASIN-
CENTRAL YAMPA RIVER BASIN-DEBEQUE TO SILT CORRIDOR-
EASTERN UINTA BASIN-EASTERN UINTA MOUNTAINS-
ELKHEAD AND PARK MOUNTAINS-FLAT TOPS-
FOUR CORNERS/UPPER DOLORES RIVER-
GORE AND ELK MOUNTAINS/CENTRAL MOUNTAINS-GRAND AND BATTLEMENT MESAS-
GRAND VALLEY-LA SAL AND ABAJO MOUNTAINS-LOWER YAMPA RIVER BASIN-
NORTHWEST SAN JUAN MOUNTAINS-PARADOX VALLEY/LOWER DOLORES RIVER-
ROAN AND TAVAPUTS PLATEAUS-SAN JUAN RIVER BASIN-SOUTHEAST UTAH-
SOUTHWEST SAN JUAN MOUNTAINS-TAVAPUTS PLATEAU-
UNCOMPAHGRE PLATEAU AND DALLAS DIVIDE-UPPER GUNNISON RIVER VALLEY-
UPPER YAMPA RIVER BASIN-WEST ELK AND SAWATCH MOUNTAINS-
607 AM MDT WED SEP 5 2007

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED THUNDERSTORMS WILL OCCUR TODAY...ESPECIALLY THIS AFTERNOON
AND EVENING AS A STRONG LOW PRESSURE SYSTEM MOVES INTO THE AREA.
DAMAGING WINDS AND LARGE HAIL MAY ACCOMPANY SOME STORMS...ESPECIALLY
ACROSS NORTHEAST UTAH AND NORTHWEST COLORADO. HEAVY DOWNPOURS
CAN BE EXPECTED WITH THUNDERSTORMS...POTENTIALLY CAUSING LOCALIZED
FLOODING...AND ROCK OR MUD SLIDES IN STEEP TERRAIN.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY

THE CHANCE OF SHOWERS AND THUNDERSTORMS WILL CONTINUE ON THURSDAY...
ESPECIALLY IN THE MORNING. THERE WILL BE A SLIGHT CHANCE OF
AFTERNOON THUNDERSTORMS EACH DAY FRIDAY THROUGH TUESDAY...MAINLY OVER
THE MOUNTAINS.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON AND EVENING.
SPOTTERS ARE ENCOURAGED TO REPORT HAIL SIZE...STRONG WINDS...
RAINFALL AMOUNTS...ANY FLOODING...AND ANY WEATHER RELATED
PROPERTY DAMAGE TO THE NATIONAL WEATHER SERVICE OFFICE IN GRAND
JUNCTION.