Heavy Rain in Colorado, September 17, 2007

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
426 AM MDT MON SEP 17 2007

.SHORT TERM (TODAY THROUGH TUESDAY NIGHT)...
WIDESPREAD SHOWERS WITH SCATTERED THUNDERSTORMS EMBEDDED WITHIN THE
PRECIPITATION SHIELD CONTINUED INTO THE EARLY MORNING HOURS. SOME
STORMS WERE PUTTING DOWN HEAVY RAIN...THOUGH RAPID STORM MOVEMENT HAD
PRECLUDED FLOODING. STORMS AND RAIN WERE THE RESULT OF A VIGOROUS LOW
PRESSURE SYSTEM OVER THE GREAT BASIN. STRONGEST CONVECTION WAS
BENEATH THE RIGHT ENTRANCE REGION OF JET STREAK NOW EJECTING TO THE
NORTH.

MODELS SHOWED AGEOSTROPHIC LIFT ASSOCIATED WITH JET STREAK OVER
WESTERN COLORADO TO SLIDE TO THE NORTHEAST THIS MORNING. HOWEVER...A
SHORTWAVE AHEAD OF THE MAIN TROF AXIS PROGGED TO CONTINUE TO PROVIDE
LARGE SCALE LIFT FOR CONTINUED CONVECTION THROUGHOUT THE MORNING.
THIS SHORTWAVE COMBINED WITH THE NEXT JET STREAK ROUNDING THE BASE OF
THE WESTERN LOW PRESSURE SYSTEM ALONG WITH DAYTIME WARMING  POINTS TO
CONTINUED WIDESPREAD MOIST CONVECTION THIS AFTERNOON AS WELL. HOWEVER
...DRIER AIR FILTERING IN BEHIND THE SHORTWAVE WHICH WILL LIMIT
THUNDERSTORMS OVER EASTERN UTAH AND EXTREME WESTERN COLORADO LATER
TODAY. LESS CAPE AND SHEAR AVAILABLE FOR ORGANIZED CONVECTION...
HOWEVER SUSPECT A FEW ORGANIZED CELLS WILL FORM WITH THE POTENTIAL
FOR ISOLATED SEVERE WIND GUSTS OR HAIL TO THREE-QUARTER INCH.
MEANWHILE...DEEP SUBTROPICAL MOISTURE TAP IN PLACE SO EXPECT SOME
ISOLATED POCKETS OF HEAVY RAIN. HOWEVER...FLOW WILL REMAIN STRONG
AND THEREFORE STORMS WILL BE FAST MOVING LIMITING THE POTENTIAL FOR
FLOODING. HOWEVER...GIVEN THE SYNOPTIC FORCING...TRAINING CELLS ARE
POSSIBLE WHICH COULD BRING SOME LOCALIZED FLOODING.

DRY SLOT MENTIONED ABOVE WILL SLIDE EASTWARD ACROSS THE REGION THIS
EVENING AS THE MAIN TROF AXIS MOVES INTO WESTERN UTAH THIS EVENING
AND CONTINUES OVER WESTERN COLORADO LATER TONIGHT. DESPITE SOME
DRYING...EXPECT LARGE SCALE LIFT AND RESIDUAL LOW-LEVEL MOISTURE
SUFFICIENT TO CONTINUE MENTION OF NUMEROUS SHOWERS AND THUNDERSTORMS
THIS EVENING...BECOMING MORE SCATTERED OVERNIGHT.

WITH TROF AXIS EAST OF THE DIVIDE BY MIDDAY DAY TUESDAY AND DRIER
AIR OVER THE SOUTHERN HALF OF THE CWFA...EXPECT DRY CONDITIONS TO
RETURN EXCEPT FOR A SLIGHT CHANCE OF MORNING SHOWERS OVER THE
NORTHERN MOUNTAINS.

HIGHS TODAY WILL BE MUCH COOLER THAN YESTERDAY IN RESPONSE TO CLOUDS
AND CONTINUING SHOWERS AND SLIGHTLY WARMER IN RESPONSE TO DRYING
CONDITIONS ON TUESDAY. LOWS WILL BE MILD TONIGHT AS CLOUDS AND
MOISTURE LINGER...THEN COOLER TUESDAY NIGHT WITH DRYING AND
CLEARING.

.LONG TERM...(WEDNESDAY THROUGH SUNDAY)...
UPPER LOW FORMING ALONG THE WEST COAST IS THE BIG VARIABLE IN THIS
FORECAST. MODEL DIFFERENCES CONTINUE WITH THE EC/S MORE NORTH AND
PROGRESSIVE TRACK FOLLOWED FOR THIS FORECAST.

WEDNESDAY...SOUTHWEST FLOW PULLS MOISTURE INTO THE GREAT
BASIN BUT STILL LOOKS DRY THIS FAR EAST.

THURSDAY-FRIDAY...A STRENGTHENING SOUTH FLOW ALOFT STILL LOOKS TO
PULL MOISTURE AT LEAST INTO THE SOUTHERN ZONES. THIS IS THE SECOND
RUN OF THE GFS THAT PRODUCES SOME LIGHT QPF IN THE SAN JUANS ON
THURSDAY BUT NOT ON FRIDAY.

FOR THE WEEKEND...FORECAST IS COOLER AND WETTER THAN MEX GUIDANCE AS
UPPER LOW IS EXPECTED TO APPROACH. FORECAST CONFIDENCE FOR DETAILS IS
LOW.

&&

.AVIATION...
MOUNTAIN OBSCURATION AND AREAS OF MVFR CIGS/VSBYS IN SHOWERS AND
THUNDERSTORMS WILL BE FAIRLY WIDESPREAD ACROSS THE AREA DURING THE
NEXT 12 HOURS. THEN RETURN TO VFR CONDITIONS BY TUESDAY FOR MOST OF
OUR AREA LATER TONIGHT AND TUESDAY AS THE AIRMASS DRIES FROM THE
WEST AND CLOUDS DECREASE.

&&

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

SHORT TERM...NL
LONG TERM....JOE
AVIATION.....NL

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
732 PM MDT SUN SEP 16 2007

COZ001>014-017>023-UTZ022>025-027>029-171200-
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-
732 PM MDT SUN SEP 16 2007

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

.DAY ONE...REST OF TONIGHT

SCATTERED THUNDERSTORMS WILL OCCUR THROUGH THIS EVENING BECOMING
ISOLATED LATE TONIGHT. SOME STORMS WILL PRODUCE BRIEF BUT LOCALLY
HEAVY RAINFALL ALONG WITH DEADLY CLOUD-TO-GROUND LIGHTNING. ERRATIC
WIND GUSTS WILL ALSO ACCOMPANY THESE STORMS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH SATURDAY

WIDESPREAD SHOWERS AND THUNDERSTORMS WILL CONTINUE MONDAY THROUGH
MONDAY NIGHT. AFTER A BRIEF DRY PERIOD AT MIDWEEK...THERE WILL BE A
SLIGHT CHANCE OF THUNDERSTORMS THURSDAY NIGHT THROUGH SATURDAY.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION IS NOT NEEDED FOR THE REST OF TONIGHT. BUT PLEASE
RELAY ANY RAINFALL REPORTS TO THE NATIONAL WEATHER SERVICE IN GRAND
JUNCTION.

JOE