Flash Flooding in Colorado, September 8, 2002

NORTHEAST AND NORTH CENTRAL COLORADO AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER COLORADO
220 PM MDT SUN SEP 8 2002

SHORT TERM DISCUSSION: TROPICAL CONNECTION STILL IN PLACE ACRS THE
DESERT SW AND ROCKY MTN STATES. ETA AND AVN HAVE BOTH TRENDED
TOWARDS A SLOWER AND SOMEWHAT DRIER SOLUTION TODAY. FURTHERMORE SFC
COLD FRONT LYING ACRS NERN WY AND SD NOW PROGD TO SLIDE THRU NERN CO
MON MORNING AS OPPOSED TO OVERNIGHT TONIGHT AS EARLIER PROGD. LOW
CIGS AND LIGHT PCPN NOW OBSERVED BEHIND THE FRONTAL BNDRY IN NERN
WY/SERN MT. QUITE A BIT OF WEATHER TO SORT OUT THRU MID-WEEK...NOT
THE LEAST THE STRENGTH AND TIMING OF THE WESTERN TROUGH...MOVEMENT
OF TROPICAL MOISTURE PLUME...STRENGTH OF POST FRONTAL UPSLOPE FLOW
AND THE POSSIBLE INFLUX OF GULF MOISTURE ASSOCIATED WITH TROPICAL
DEPRESSION FAY. MODELS OFTEN SEEM TO HAVE A TOUGH TIME WITH TROPICAL
SYSTEMS...SO WITH CONFIDENCE LOW TO MODERATE IN THE MODELS...WILL
AVOID MAKING BIG CHANGES TO ONGOING FCST PACKAGE. HWVR...WILL DELAY
PCPN AND COOL DOWN. THIS INCLUDES TRENDING POPS UPWARD AFTER 1ST
PERIOD WITH MOISTURE INCREASING AT ALL LEVELS WITH SUBTROPICAL JET
MOVG CLOSER TO FCST AREA AND WITH POST FRONTAL UPSLOPE FLOW
DEEPENING LATE MON. LOOKS AS THOUGH TEMPS MON MAY NOT BE AS COOL AS
EARLIER FCSTD AS LOW CLOUD CVR MAY NOT BE AS WIDESPREAD. THIS MAY
ALLOW JUST ENOUGH HEATING IN THE MORNING TO DESTABLIZE THE AMS FOR
AFTERNOON T-STORMS. FURTHERMORE WAVES EMBEDDED WITHIN MOIST
SOUTHWESTERLY FLOW WILL ALSO PROVIDE ADDITIONAL LIFT FOR T-STORM
DVLPMNT MON AFTN AND EVE. MODEL PCPN PROBABILITIES FOR THE
FRNT RNG AND NERN CO PLAINS AT THEIR HIGHEST MON NIGHT THRU TUE
NIGHT. MOS POP GUIDANCE GIVING 70-90 PCT POPS...BUT BECAUSE
CONFIDENCE NOT TERRIBLY HIGH IN MODELS WILL KP SCTD POPS/PCPN
COVERAGE ON THE PLAINS THRU TUE NIGHT. WHEREAS WILL KEEP SCTD
COVERAGE IN THE HIGH COUNTRY...BUT WILL GO WITH LIKELY POPS TUE IN
THE FRONT RANGE FTHL ZONES. FURTHERMORE WITH COOLING ALOFT AND WEAK
MID-LVL DIV-Q OVR THE AREA MON NIGHT/TUE MORNING...MTN AREAS
GENERALLY ABOVE 10K FT COULD SEE MEASURABLE SNOWFALL. SNOW ACCUM
GRIDS GIVE SVRL INCHES OVRNGT BULLEYED ON SUMMIT CTY WITH H7 TEMP
LOWERING TO NR 0C BY TUE MORNING. TUE NOW LOOKS TO BE COOLEST DAY OF
WEEK UNDER HVY CLOUD CVR. AVN/MRF MOS GUIDANCE GIVING A MAX TEMP ON
THE PLAINS TUE IN THE UPR 50S/LWR 60S. THAT DOESN/T SEEM TOO OUT OF
LINE...ASSUMING MODELS ANYWHERE NEAR BEING CORRECT.

WED AND THU...STILL LOOKS MOIST AND UNSETTLED WITH INFLUX OF
SUBTROPICAL MOISTURE FM OLD T.D. FAY AND GULF OF MEX. MOISTURE APRS
TO GET TRAPPED UNDER MID-LVL RIDGE SITTING OVR SRN AND CNTRL HIGH
PLAINS...AND WITH MID-LVL SHRTWAVES LIFTING OUT THE DESERT SW...WILL
NEED TO KP AT LEAST A CHANCE OF SHWRS/T-STORMS IN THE FCST THRU THU
UNTIL PASSAGE OF WESTERN UPR LVL TROUGH FRI. OF COURSE THIS MAY ALL
CHANGE WITH NEXT FCST PACKAGE SHOULD LARGE SCALE PATTERN BECOME
CONSTIPATED.  BAKER

APPRECIATE THE COORDINATION CALL FM WFO KLBF.

.DEN...NONE.