Flash Flood in Colorado, August 25, 2009

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
227 PM MDT TUE AUG 25 2009

.SHORT TERM...TONIGHT THROUGH THURSDAY...
ANOTHER FAIRLY ACTIVE DAY TODAY WITH WIDESPREAD SMALLISH
THUNDERSTORMS FORMING OVER JUST ABOUT ALL RIDGES. ABOUT 25 PERCENT OF
THEM ARE REMAINING ALIVE FOR A BIT AS THEY MOVE OFF THE MOUNTAINS.
THE INTENSITY IS LOW AND MOST ARE FAIRLY SHORT-LIVED. THE MOISTURE
WAS A BIT HIGHER THIS MORNING IN GJT AND SLC SOUNDINGS AND THE CAPE
WAS HIGHER AS WELL. THE WIND SHEAR ALOFT WAS A GOOD BIT WEAKER THAN
YESTERDAY AND THERE ARE NO SMALL SHORTWAVES MOVING THROUGH...ALL
RESULTING IN DECREASED TSTM STRENGTH. THE REMNANTS OF THE GREAT BASIN
TROUGH IS WEAKENING IN THE RUC AND IN SATELLITE IMAGERY AS IT MOVES
OVER NORTHERN UT. THE NAM AND RUC CARRY THIS FEATURE OVER NE UT AND
NW CO THIS EVENING WITHIN AN ERODING MOISTURE FIELD. BELIEVE IT WILL
ONLY HAVE A MINOR AFFECT ON CONVECTION AND EXTEND THE TSTMS ONLY AN
HOUR OR SO BEYOND SUNSET...AND ONLY OVER NW CO AND NE UT.

WEDNESDAY THROUGH THURSDAY...HIGH PRESSURE WILL BUILD OVER THE GREAT
BASIN AND MUCH DRIER AIR WILL ADVECT IN. THE FLOW ALOFT WILL BECOME
PROGRESSIVELY MORE NNW TO NNE. THIS WILL HOLD DOWN THE WARMING TREND
A BIT THAT WOULD NORMALLY BE EXPECTED FROM MOSTLY SUNNY SKIES.

&&

.LONG TERM...THURSDAY NIGHT THROUGH TUESDAY...
THE PERIOD STARTS OUT DRY AS HIGH PRESSURE STRENGTHENS OVER THE
WESTERN U.S. THROUGH FRIDAY...WITH NORTHWEST FLOW OVER THE FORECAST
AREA. JUST ENOUGH MOISTURE LINGERS OVER THE DIVIDE TO KEEP ISOLATED
CONVECTION IN PLACE FRIDAY AFTERNOON AND EVENING...OTHERWISE A DRY
DAY IS EXPECTED WITH TEMPS 3 TO 5 DEGREES ABOVE NORMAL. A PACIFIC
WAVE MOVES INTO THE NORTHWEST ON FRIDAY NIGHT...WHICH WILL ACT TO
FLATTEN THE RIDGE...BREAKING IT DOWN BY THE WEEKEND.

THE 12Z GFS BRINGS THE WEAKENED LOW INTO THE NORTHERN GREAT BASIN
LATE IN THE WEEKEND....ACROSS THE FORECAST AREA ON TUE.  THIS WILL
ALLOW MOISTURE TO CREEP INTO THE FORECAST AREA FROM THE SOUTH. MADE
JUST SLIGHT ADJUSTMENTS TO THE FORECAST AS THE TREND FOR A INCREASED
POPS HAS BEEN HANDLED WELL. CONFIDENCE BEGINS TO DROP BY THE WORK
WEEK AS THE ECMWF SOLUTION INITIALLY IS MUCH SLOWER AND MORE
WESTERLY. THE EC ALSO SHOWS A MORE NORTHERLY TRACK AS IT TAKES THE
WEAKENED LOW ACROSS THE NORTHERN ROCKIES ON TUE...FOR A DRIER
RESULT.

&&

.AVIATION...
VFR CONDITIONS EXPECTED OVER THE VALLEYS AND PREDOMINATE AT THE TAF
SITES. THUNDERSTORMS THE REST OF THIS AFTERNOON THROUGH ABOUT 04Z
THIS EVENING WILL CAUSE ISOLATED AND BRIEF MVFR CIGS AND VSBY...
ESPECIALLY OVER ASE AND EGE. WEDNESDAY WILL BRING MUCH LESS
THUNDERSTORM DEVELOPMENT AS HIGH PRESSURE AND DRIER AIR MOVE IN FROM
THE WEST.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

.CO...NONE.
.UT...NONE.

SHORT TERM.....CJC
LONG TERM......JDC/EH
AVIATION.......CJC

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
521 AM MDT TUE AUG 25 2009

COZ001>014-017>023-UTZ022>025-027>029-261121-
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-
521 AM MDT TUE AUG 25 2009

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

.DAY ONE...TODAY AND TONIGHT...

DISTURBANCES WILL CONTINUE TO MOVE OVER COLORADO TODAY...ESPECIALLY
DURING THE AFTERNOON HOURS...AND CAUSE SHOWERS AND THUNDERSTORMS TO
FORM ACROSS EASTERN UTAH AND WESTERN COLORADO.  SOME OF THE STORMS
WILL HAVE BRIEF HEAVY RAIN ASSOCIATED WITH THEM.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY...

THERE IS A CHANCE FOR SHOWERS AND THUNDERSTORMS WEDNESDAY EVENING...
MAINLY OVER THE MOUNTAINS. GUSTY WINDS AND BRIEF HEAVY RAIN WILL
ACCOMPANY THE STORMS. ANOTHER CHANCE FOR SHOWERS AND THUNDERSTORMS
ARRIVES FRIDAY AFTERNOON AND EACH AFTERNOON THEREAFTER THROUGH
SUNDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT ANTICIPATED TODAY OR TONIGHT.