Flash Flood in Colorado, September 9, 2003

WESTERN COLORADO & EASTERN UTAH AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
349 AM MDT TUE SEP 9 2003

SHORT TERM (TODAY THROUGH WEDNESDAY)...
LONG WAVE TROF OVER THE WESTERN US WILL BRING SOME VAST CHANGES TO
THE WEATHER THROUGH THE NEAR TERM PERIOD. CURRENTLY...WEAK WAVE
MOVING THROUGH THE BASE OF THE TROF BRINGING SCATTERED SHOWERS TO
THE CENTRAL AND SOUTHERN MOUNTAINS OF COLORADO EARLY THIS MORNING.
EXPECT THIS ACTIVITY TO DECREASE AS THIS FEATURE MOVES EAST OF THE
DIVIDE OVER THE NEXT FEW HOURS.

MODELS IN GOOD AGREEMENT WITH TREND TOWARD INCREASING PRECIPITATION
DURING THE DAY. FOCUS WILL INITIALLY BE OVER THE FOUR-CORNERS
REGION AS 110+ KT JET ROUNDS THE BASE OF THE UPPER LEVEL TROF AND
BEGINS TO NOSE INTO THIS AREA. REGION ALREADY MOISTENING AHEAD OF
THIS SYSTEM WITH WEAK TAP INTO SUBTROPICAL MOISTURE. ONCE LEFT EXIT
REGION OF CYCLONICALLY CURVED JET BEGINS TO WORK ON THIS MOISTURE
EXPECT WIDESPREAD SHOWER AND THUNDERSTORM ACTIVITY TO DEVELOP
DURING THE AFTERNOON. APPEARS THESE STORMS NOT LIKELY TO BE AS
ENERGETIC AS EARLIER PREDICTED...THOUGH ISOLATED SEVERE STORMS
CANNOT BE RULED OUT UNDER STRONG UPWARD FORCING ACROSS THE SOUTH.
MAIN CONCERN FOR TODAY GIVEN PATTERN DISCUSSED ABOVE WILL BE HEAVY
RAINS ACROSS THE SOUTHERN PORTION OF THE CWFA. DIFLUENCE ALOFT
COMBINED WITH STRONG SOUTH TO SOUTHWEST FLOW INTO THE SAN JUANS
SUPPORTS REDEVELOPMENT DURING THE AFTERNOON AND EVENING. THOUGH
STORMS WILL BE MOVING RAPIDLY DRIVEN BY 7H WINDS FROM 15 TO 20 KTS...
EXPECT TRAINING ECHOES COULD BECOME AN ISSUE FOR THE FOUR-CORNERS
REGION...ESPECIALLY IN FLOOD PRONE AREAS AND BURN SCARS (MISSIONARY
RIDGE AND MESA VERDE BURN AREAS SPECIFICALLY). TO THE NORTH...FRONT
WHICH MOVED INTO THE NORTHERN PORTION OF THE CWFA RETREATS NORTH AS
FLOW AGAIN BACKS TO THE SOUTHWEST. HOWEVER...SHORTWAVE INDICATED IN
SOUTHWEST FLOW COMBINED WITH DIURNAL WARMING SEEMS SUFFICIENT FOR
SCATTERED SHOWERS AND THUNDERSTORMS ACROSS THE REMAINDER OF THE
CWFA. TEMPERATURES COOL SIGNIFICANTLY UNDER CLOUDS AND SHOWERS AND
MADE ONLY MINOR ADJUSTMENTS TO THE GOING FORECAST.

JET WRAPS AROUND THE BASE OF THE TROF DURING THE NIGHT WITH SURFACE
FRONT NOW INDICATED TO MOVE SOUTHEASTWARD ACROSS MUCH OF THE CWFA
DURING THE NIGHT. 564 THICKNESS LINE MOVES INTO THE CO MOUNTAINS
BY MORNING SO WILL CONTINUE WITH IDEA OF SNOWFALL ACCUMULATIONS
ABOVE 10000 FEET...THOUGH SOME LOWERING BELOW THAT LEVEL LIKELY IN
THE EASTERN UINTAS WHERE 558 LINE ADVANCES. KEPT ACCUMULATIONS LIGHT
FOR NOW GIVEN THE TIME OF YEAR AND RELATIVELY WARM CONDITIONS UP TO
THIS POINT. HOWEVER...URGE DAY SHIFT TO GIVE A CLOSER LOOK AT JET
INTERACTIONS FOR POSSIBILITY OF HIGHER AMOUNTS AND NECESSITY OF
WINTER WEATHER ADVISORY. ELSEWHERE...SCATTERED TO NUMEROUS SHOWERS
WILL CONTINUE WITH SOME ISOLATED THUNDERSTORMS. OVERNIGHT LOWS NOT
GOING TO DROP OFF THE TABLE JUST YET AS COLDER AIR STILL POISED TO
THE WEST AND CLOUDS WILL PROVIDE BLANKETING EFFECT.

TROF AXIS MOVES OVERHEAD ON WEDNESDAY WITH COLD FRONT PUSHING
THROUGH MAJORITY OF THE CWFA BY MIDDAY. 0 DEG C ISOTHERM AT 7H LEVEL
CLIPS NORTHERN ZONES AND EXPECT SNOWFALL TO LOWER TO 9000 FEET OR
LOWER AS A RESULT. MEANWHILE...EXPECT SHOWERS AND THUNDERSTORMS TO
BECOME MORE SCATTERED AS THE DAY PROGRESSES AND DYNAMICS WANE.
DIVIDE STILL UNDER FAVORABLE WESTERLY FLOW...SO WILL CONTINUE WITH
LIKELY POPS IN THE COLORADO MOUNTAINS. TEMPERATURES TAKE ANOTHER
SHARP DOWNTURN AT MIDWEEK WITH TEMPERATURES WELL BELOW NORMAL.  NL

WEDNESDAY NIGHT...LOOK FOR ACTIVITY TO DIMINISH FROM WEST TO EAST
BY WEDNESDAY EVENING AS THE ENTIRE STORM SYSTEM SHIFTS OVER THE
CENTRAL/NORTHERN HIGH PLAINS. LOW CLOUDS AND LINGERING SHOWERS WILL
OCCUR IN THE WESTERN COLORADO HIGH COUNTRY. LOWER VALLEYS COULD
EXPERIENCE AREAS OF DENSE FOG EARLY THURSDAY MORNING...WHERE
CLEARING AND STRONG RADIATIONAL COOLING OCCUR.

THURSDAY...COOL NORTHERLY FLOW WILL DEVELOP BEHIND STORM. DRIER AIR
WILL FILTER IN WITH SOME WARMING ALOFT EXPECTED. TRAPPED LOW LEVEL
MOISTURE LIKELY TO RESULT IN CLOUDS OVER THE MOUNTAINS AND HIGH
VALLEYS OF WESTERN COLORADO DURING THE MORNING. OTHERWISE...SHOULD
BE MUCH QUIETER DAY WITH BELOW NORMAL TEMPERATURES.

FRIDAY AND SATURDAY...LIGHT NORTHWEST DIFFUENT FLOW WILL PERSIST
ACROSS THE AREA...WITH ACTIVE WEATHER REMAINING ACROSS THE U.S./
CANADIAN BORDER. DRY CONDITIONS WILL PREVAIL WITH TEMPERATURES
GRADUALLY APPROACHING NEAR NORMAL LEVELS FOR MID SEPTEMBER.  THE
BACK EDGE OF A TRAILING S/W TROUGH MAY AFFECT THE NORTHERN ZONES
SATURDAY. HAVE INCREASED CLOUDS NORTH AS A RESULT.  DJN.83

SUNDAY THROUGH TUESDAY...
MAIN STORM TRACK FOR PACIFIC DISTURBANCES WILL REMAIN NORTH OF THE
CWA SUNDAY AND MONDAY IN MODERATE WNW FLOW ALOFT. ON TUESDAY IT
APPEARS THE WINDS ALOFT BECOME MORE NORTHWESTERLY ACCORDING TO THE
MRF. THIS BRINGS A SHORTWAVE TROUGH AND COLD FRONT INTO THE NORTHERN
HALF OF THE CWA ON TUESDAY. HAVE INCREASED POPS A NOTCH IN THE
NRN HALF OF THE CWA...DROPPED TEMPS A BIT AND INCREASED RH AND
SFC WINDS FOR TUE.   CJC

.GJT...FLASH FLOOD WATCH FOR SOUTHEAST UTAH AND SOUTHWEST COLORADO
       THROUGH 10:00 PM MDT.

COZ001>014-017>023-UTZ022>025-027>029-101200-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
901 AM MDT TUE SEP 9 2003

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

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

...FLASH FLOOD WATCH IN EFFECT THROUGH 10:00 PM MDT FOR
SOUTHEAST UTAH...SOUTHWEST COLORADO...AND PORTIONS OF WEST CENTRAL
COLORADO...
...WINTER WEATHER EXPECTED ACROSS THE HIGHER PEAKS LATE TONIGHT...

THUNDERSTORMS PRODUCING HEAVY RAIN...SOME RECURRING OVER THE
SAME LOCATION...WILL AFFECT SOUTHEAST UTAH...SOUTHWEST COLORADO...
AND PORTIONS OF WEST CENTRAL COLORADO TODAY. IN ADDITION...SOME
SEVERE THUNDERSTORMS ARE POSSIBLE WITH DAMAGING WINDS THE GREATEST
CONCERN...HOWEVER...LARGE HAIL IS ALSO POSSIBLE WITH THESE STORMS.

ELSEWHERE...SCATTERED TO NUMEROUS THUNDERSTORMS WILL OCCUR DURING THE
AFTERNOON AND EVENING. THUNDERSTORMS TODAY AND TONIGHT WILL BE
CAPABLE OF PRODUCING GUSTY WINDS TO NEAR 40 MPH AND SMALL HAIL UP TO
1/2 INCH IN DIAMETER ALONG WITH LOCALLY HEAVY RAIN.

A STRONG FALL-LIKE STORM SYSTEM WILL MOVE ACROSS THE WESTERN GREAT
BASIN THIS MORNING FOCUSING MUCH OF ITS ENERGY ON THE FOUR CORNERS
REGION BY THIS AFTERNOON AND CONTINUING THROUGH MUCH OF THE
EVENING. COOLER AIR FILTERING IN BEHIND A COLD FRONT SWEEPING ACROSS
THE REGION DURING THE NIGHT WILL RESULT IN SOME SNOW ACCUMULATIONS
OVER THE HIGHER PEAKS OF COLORADO AND UTAH DURING THE NIGHT.

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

SNOWFALL IS EXPECTED TO CONTINUE IN THE HIGH MOUNTAIN AREAS WITH
SOME LOWERING OF SNOW LEVELS ACROSS THE NORTH. SNOW WILL BE
ACCOMPANIED BY THUNDER AT TIMES WHICH WILL LIKELY ENHANCE
ACCUMULATIONS. THE LOWER ELEVATIONS WILL CONTINUE TO SEE THUNDERSTORM
ACTIVITY WITH HEAVY RAIN...SMALL HAIL AND WIND GUSTS TO 30 MPH.

A MOIST AND UNSTABLE AIRMASS WILL REMAIN IN PLACE ACROSS THE REGION
AS THE STORM CENTER MOVES OVERHEAD ON WEDNESDAY.

DRIER CONDITIONS ARE EXPECTED IN THE WAKE OF THE STORM ON THURSDAY
AND FRIDAY...THOUGH ISOLATED THUNDERSTORMS ARE EXPECTED SATURDAY...
SUNDAY AND MONDAY...THOUGH MAINLY OVER HIGHER TERRAIN.

.SPOTTER INFORMATION STATEMENT...

WEATHER SPOTTERS WILL NOT BE NEEDED TODAY OR TONIGHT. HOWEVER...
SPOTTERS ARE ENCOURAGED TO PHONE IN REPORTS OF STRONG WINDS...HAIL
AND HEAVY RAIN AS SOON AS POSSIBLE.

NL/TAL