Flash Flood in Colorado, August 9, 2008

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
320 PM MDT SAT AUG 9 2008

.SHORT TERM...TONIGHT THROUGH MONDAY...

LITTLE CHANGE TODAY AS A VERY MOIST AIRMASS REMAINS OVER EASTERN
UTAH AND WESTERN COLORADO. THE MORNING GJT SOUNDING SHOWED 1.34
INCHES PRECIPITABLE WATER WHICH IS 184 PERCENT OF NORMAL. THE HIGH
MOISTURE CONTENT ALONG WITH WEAK FLOW ALOFT BRINGS HEAVY RAIN
CONCERNS. AFTERNOON HEATING COMBINED WITH WEAKLY DIVERGENT FLOW ALOFT
AND A SHORTWAVE CURRENTLY OVER EASTERN UTAH WILL RESULT IN CONTINUED
STORM DEVELOPMENT THROUGH THE AFTERNOON AND EVENING. A FLASH FLOOD
WATCH REMAINS IN EFFECT FOR THE ENTIRE FORECAST AREA UNTIL 10 PM THIS
EVENING.

THE EASTERN UTAH WAVE IS PROGGED TO MOVE SLOWLY EAST ACROSS THE AREA
OVERNIGHT. THIS SHOULD SUPPORT ISOLATED TO SCATTERED SHOWERS AND
A FEW THUNDERSTORMS BEYOND MIDNIGHT THROUGH DAYBREAK SUNDAY. THIS
WAVE WILL SLIDE EAST OF THE AREA SUNDAY AFTERNOON. TIME HEIGHT
SECTIONS INDICATE A LITTLE DRIER AIR AND WEAK SUBSIDENCE BEHIND THE
WAVE WHICH WILL SLOW DOWN STORM DEVELOPMENT SUNDAY AFTERNOON. FLOW
ALOFT WILL INCREASE SUNDAY REDUCING THE HEAVY RAIN AND FLASH FLOOD
THREAT AS STORM MOTION INCREASES.

THE SUBTROPICAL HIGH CENTER IS PROGGED TO REPOSITION SOUTH OF THE
FORECAST AREA ON MONDAY AS A TROUGH MOVES ACROSS THE NORTHERN
ROCKIES. THIS WILL PRODUCE A WEST FLOW OVER AREA WITH A CONTINUED
DECREASING IN MOISTURE. RESIDUAL LOW LEVEL MOISTURE WILL ALLOW FOR
MORE DIURNALLY DRIVEN STORMS ON MONDAY BUT WITH SIGNIFICANTLY LESS
AREAL COVERAGE.

LITTLE CHANGE TO OVERNIGHT MIN TEMPERATURES TONIGHT WITH CLOUDS AND
HIGH HUMIDITIES LIMITING RADIATIONAL COOLING. DAYTIME HIGH
TEMPERATURES WILL REMAIN ON A WARMING TREND SUNDAY AND MONDAY WITH
INCREASING AMOUNTS OF SUNSHINE AND DRIER AIR RESPONDING BETTER TO
SURFACE HEATING.

.LONG TERM...MONDAY NIGHT THROUGH SATURDAY...
MODELS INDICATE A LULL IN THE MONSOON FLOW WITH FLAT RIDGING
BRINGING DRIER AIR FROM THE WEST. FLOW RETURNS TO SW BY THURSDAY
INCREASING THE MOISTURE FIELD IN THE SW...BUT DOES NOT SEEM TO
WANT TO PUSH THIS MOISTURE INTO OUR NORTHERN FA AT THIS TIME.
CONFIDENCE IS NOT HIGH FOR THIS END OF WEEK SCENARIO.

DID TREND POPS DOWN THU AND FRI A BIT AND INCREASE DIURNAL TEMPS A
LITTLE FOR MID WEEK AS WELL. WILL KEEP MOUNTAIN SHOWERS IN BUT THEY
SHOULD BE ISOLATED IN THE NORTH AND SCATTERED TO THE SOUTH AS
OPPOSED TO THE NUMEROUS SHOWERS WE HAVE BEEN EXPERIENCING.

&&

.AVIATION...
EXPECT SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS THE
REGION THROUGH LATE THIS EVENING. STORMS WILL LIKELY BRING MVFR
CIGS AND VSBY WITH ISOLATED BRIEF IFR CONDITIONS. LOCALIZED MVFR
CEILINGS POSSIBLE IN SOME HIGH MOUNTAIN VALLEYS LATE TONIGHT AND
SUNDAY MORNING IN AREAS THAT RECEIVE SIGNIFICANT RAINFALL LATE TODAY
AND THIS EVENING.

&&

.HYDROLOGY...
THE ATMOSPHERE REMAINS VERY MOIST OVER THE REGION TODAY. DAY TIME
HEATING COMBINED WITH WEAK DYNAMICS ALOFT WILL RESULT IN SCATTERED
TO NUMEROUS THUNDERSTORMS AGAIN LATE THIS AFTERNOON AND THIS EVENING.
SOME STORMS WILL PRODUCE TORRENTIAL DOWNPOURS. SINCE SOILS ACROSS
MUCH OF THE FORECAST AREA REMAIN SATURATED...RUNOFF FROM THESE HEAVY
SHOWERS WILL LIKELY PRODUCE AREAS OF FLASH FLOODING. CONSEQUENTLY...A
FLASH FLOOD WATCH REMAINS IN EFFECT FOR ALL OF EASTERN UTAH AND
WESTERN COLORADO EFFECTIVE UNTIL 10 PM THIS EVENING.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
.CO...FLASH FLOOD WATCH IN EFFECT UNTIL 10 PM MDT FOR ALL
       WESTERN COLORADO ZONES.
.UT...FLASH FLOOD WATCH IN EFFECT UNTIL 10 PM MDT FOR ALL
       EASTERN UTAH ZONES.

SHORT TERM.....TAL
LONG TERM......DC
AVIATION.......TGJT
HYDROLOGY......TAL

HAZARDOUS WEATHER OUTLOOK UPDATE
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
545 AM MDT SAT AUG 9 2008

COZ001>014-017>023-UTZ022>025-027>029-101200-
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-
545 AM MDT SAT AUG 9 2008

...FLASH FLOOD WATCH IN EFFECT FOR ALL OF EASTERN UTAH AND
WESTERN COLORADO FROM NOON UNTIL 10 PM MDT...

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

.DAY ONE...TODAY AND TONIGHT

SCATTERED TO NUMEROUS SHOWERS AND THUNDERSTORMS ARE EXPECTED TO
DEVELOP ACROSS EASTERN UTAH AND WESTERN COLORADO TODAY...LINGERING
THROUGH TONIGHT. HEAVY RAIN IS EXPECTED WITH THE STRONGER STORMS
POSSIBLY RESULTING IN FLOODING. THEREFORE...A FLASH FLOOD WATCH
HAS BEEN ISSUED FOR ALL OF WESTERN COLORADO AND EASTERN UTAH FROM
NOON UNTIL 10 PM THIS EVENING. IN ADDITION TO HEAVY RAIN...TODAYS
THUNDERSTORMS WILL BE CAPABLE OF PRODUCING GUSTY WINDS TO AROUND 40
MPH...SMALL HAIL...AND FREQUENT DANGEROUS LIGHTNING.

PLEASE SEE THE GRAND JUNCTION NATIONAL WEATHER SERVICE WEB SITE AT
WEATHER.GOV/GJT FOR THE LATEST INFORMATION.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THERE IS A CHANCE FOR SHOWERS AND THUNDERSTORMS EACH AFTERNOON AND
EVENING THROUGH THE COMING WEEK.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED LATER THIS AFTERNOON AND INTO THE
EVENING HOURS. SPOTTERS WOULD BE EXPECTED TO REPORT HEAVY RAIN AND
ANY KNOWN FLOODING AS SOON AS SAFELY POSSIBLE.

NL