Heavy Rain in Colorado, September 6, 2003

WESTERN COLORADO & EASTERN UTAH AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
427 AM MDT SAT SEP 6 2003

SHORT TERM (TODAY THROUGH SUNDAY)...
SYNOPTIC PATTERN FEATURES RIDGE OF HIGH PRESSURE EAST OF THE DIVIDE
WITH UPPER LOW ACROSS THE GREAT BASIN AND WESTERN SLOPE. SATELLITE
IMAGERY SHOWED SHORTWAVE EXITING THE MOUNTAIN AREAS OF THE CWFA
EARLY THIS MORNING WITH ADVANCED ELEMENTS OF NEXT WAVE ALREADY
MOVING INTO EASTERN UTAH. COMBINATION OF DAYTIME HEATING COMBINED
WITH UPWARD FORCING ASSOCIATED WITH NEXT SHORTWAVE WILL KEEP WEATHER
UNSETTLED ACROSS THE REGION TODAY. THEREFORE...CONTINUED FORECAST
CALLING FOR NUMEROUS SHOWERS AND THUNDERSTORMS ACROSS THE MOUNTAINS
THIS AFTERNOON WITH SCATTERED SHOWERS AND THUNDERSTORMS ELSEWHERE.
DESPITE PW VALUES NEAR AN INCH IN THE 00Z SAT GJT SOUNDING...WILL NOT
ISSUE FFA AS SHEAR...K-INDICES...POSITIONING OF THETA-E RIDGE NOT
FAVORABLE FOR WIDESPREAD FLOODING EVENT. THAT SAID...LOCALIZED HEAVY
RAIN IS LIKELY.

SHOWERS AND THUNDERSTORMS WILL CONTINUE INTO THE EVENING HOURS AS
THE COMING WAVE MOVES OVERHEAD. INCREASED POPS ACROSS THE HIGHER
ELEVATIONS OF THE SAN JUAN MOUNTAINS IN RESPONSE TO INFLUENCE OF
LEFT EXIT REGION OF 60-70KT JET MOVING ACROSS NORTHERN AZ. SHOWERS
AND THUNDERSTORMS DIMINISH LATE TONIGHT DUE TO DIURNAL COOLING AND
DOWNWARD FORCING ON THE BACKSIDE OF THE EJECTING WAVE.

NORTHWEST FLOW IN STORE SUNDAY AS WEAK UPPER LEVEL RIDGE BEGINS TO
BUILD OVER THE GREAT BASIN. DRIER AIR INDICATED TO FILTER IN...SO
SAW NO REASON TO CHANGE GOING FORECAST CALLING FOR SCATTERED
MOUNTAIN SHOWERS AND THUNDERSTORMS ACROSS THE DIVIDE.

COOLER TEMPERATURES TO CONTINUE TODAY UNDER CLOUDS...SHOWERS AND
THUNDERSTORMS...THEN WARMING INTO SUNDAY WITH INCREASED SUNSHINE.
NL

MONDAY THROUGH WEDNESDAY...UPPER LEVEL WAVE OVER ERN COLORADO
FINALLY WEAKENS AND SHIFTS EAST MONDAY AS LONG-WAVE TROUGH ENTERS
THE PACIFIC NORTHWEST. A SOUTHWEST FLOW WILL DEVELOP ACROSS THE
AREA WITH A DRIER AIR MASS IN PLACE. OUTSIDE OF ISOLD DIURNAL
CONVECTION IN THE MOUNTAINS...SEE NO SIGNF POTENTIAL FOR SHOWERS AND
THUNDERSTORMS MONDAY AND TUESDAY. SECONDARY PACIFIC ENERGY
RE-INFORCES LONG-WAVE PATTERN ACROSS THE WESTERN CONUS TUESDAY AND
WEDNESDAY...WITH BROAD LONG-WAVE TROUGH FORECAST TO PUSH ACROSS THE
FORECAST AREA WEDNESDAY. BLEND OF ECMWF AND GFS MODELS SUGGEST THE
CHANCE OF PRECIPITATION WEDNESDAY. TEMPERATURES WILL COOL WITH
TROUGH PASSAGE MID WEEK...BUT TROUGH IS NOT AS DEEP AND COLD AS
EARLIER FORECASTS POINTED OUT.  DJN.83

THURSDAY THROUGH SATURDAY...THE LONGWAVE TROUGH IS PROGGED TO MOVE
EAST OF THE AREA EARLY THURSDAY WITH DRIER AIR AND WNW FLOW ALOFT
THROUGH SATURDAY. THU MIGHT ACTUALLY BE THE COOLEST DAY OF THE
WEEK WITH SLOW WARMING EACH DAY AFTER. WILL ELIMINATE THE VALLEY
POPS AND CUT BACK MOUNTAIN POPS EVEN MORE.  CJC

.GJT...NONE.

COZ001>014-017>023-UTZ022>025-027>029-071200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
530 AM MDT SAT SEP 6 2003

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

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

SCATTERED TO NUMEROUS THUNDERSTORMS WILL OCCUR OVER MUCH OF
EASTERN UTAH AND WESTERN COLORADO THIS AFTERNOON AND TONIGHT.
THUNDERSTORMS TODAY AND TONIGHT WILL BE CAPABLE OF PRODUCING LOCALLY
HEAVY RAINFALL...GUSTY WINDS TO NEAR 40 MPH AND SMALL HAIL UP TO 1/2
INCH IN DIAMETER.

THE LOCALLY HEAVY RAINFALL OVER PORTIONS OF SOUTHWEST COLORADO MAY
CAUSE SUDDEN RISES OF NORMALLY DRY CREEKS...SMALL STREAMS AND
ARROYOS. MINOR STREET FLOODING...ALONG WITH MUD FLOWS AND ROCK
SLIDES ARE POSSIBLE...ESPECIALLY OVER THE SAN JUAN MOUNTAINS NEAR
TELLURIDE AND OVER THE MISSIONARY RIDGE BURN SITE NORTHEAST OF
DURANGO.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY...

DRIER CONDITIONS TO SPREAD OVER THE AREA FROM WEST TO EAST ON
SUNDAY. THE DRIER CONDITIONS ARE EXPECTED TO PERSIST THROUGH
TUESDAY...WITH ANOTHER ROUND OF LATE DAY THUNDERSTORMS MOVING BACK
INTO THE REGION WEDNESDAY AND CONTINUING ON THURSDAY.

.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