Flash Flood in Colorado, August 17, 2003

WESTERN COLORADO & EASTERN UTAH AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
430 AM MDT SUN AUG 17 2003

SHORT TERM DISCUSSION (TODAY THROUGH MONDAY)...
THE UPPER LOW WHICH MOVED INTO THE REGION A FEW DAYS AGO CONTINUED TO
CIRCULATE OVER THE AREA EARLY THIS MORNING. AS A RESULT...A FEW LATE
NIGHT SHOWERS WERE CONTINUING OVER THE HIGHER TERRAIN OF THE NORTH...
WITH A SMALL AREA OF SHOWERS ALSO ONGOING OVER THE WESTERN SAN JUAN
MOUNTAINS.

MODELS INDICATE LOW TO SHIFT EAST OF THE DIVIDE AROUND MIDDAY AS A
SECOND UPPER LOW DROPS SOUTHWARD FROM WESTERN MONTANA. AS THE SYSTEM
APPROACHES FLOW WILL BECOME MORE WESTERLY WITH SOME MID-LEVEL DRYING
WORKING INTO EASTERN UTAH. AIRMASS REMAINS MOIST AND UNSTABLE AHEAD
OF THE APPROACHING SYSTEM SO CWFA WILL SEE ANOTHER ROUND OF
AFTERNOON/EVENING SHOWERS AND THUNDERSTORMS...MORE NUMEROUS ALONG THE
CONTINENTAL DIVIDE AND NORTH. JET NOSING INTO THE NORTH LATE TONIGHT
WILL KEEPS SHOWERS AND THUNDERSTORMS GOING ACROSS THE AREA. UPPER
LEVEL DIVERGENCE ASSOCIATED WITH THE JET...COMBINED WITH FAVORABLE
WIND SHEAR COULD LEAD TO SOME IMPRESSIVE NOCTURNAL STORMS.

LOW CENTER DIPS TO NORTHWEST CO ON MONDAY WITH DRY SLOT WORKING INTO
THE SOUTHWESTERN ZONES. CUT BACK POPS SLIGHTLY TO REFLECT THIS
DEVELOPING SCENARIO. MEANWHILE...SCATTERED SHOWERS AND THUNDERSTORMS
LIKELY TO CONTINUE OVER HIGHER TERRAIN IN THE EASTERN HALF OF THE
CWFA. TEMPERATURES COOL A BIT...AS WEAK COOL FRONT INDICATED TO MOVE
ACROSS THE NORTHERN PORTION OF THE CWFA.   NL

TUESDAY THROUGH THURSDAY...
AT THIS TIME...THE UPPER LOW DISCUSSED ABOVE WILL LIKELY TRACK
SLOWLY ACROSS SOUTHERN WYOMING AND THEN OUT OVER THE NORTHERN PLAINS
BY WEDNESDAY. THEREAFTER...UPPER HIGH BEGINS TO REBUILD OVER THE
DESERT SOUTHWEST FOR THURSDAY.

DRIER AND MORE STABLE AIR MASS MOVES IN TUESDAY IN THE WAKE OF THE
UPPER LOW...SO EXPECT LESS CONVECTIVE ACTIVITY...MAINLY ISOLATED
DIURNAL MOUNTAIN THUNDERSTORMS. UPPER LEVEL RIDGE AXIS APPROACHES
FROM THE WEST WEDNESDAY WITH MID/HIGH LEVEL MOISTURE ADVANCING OVER
THE AREA. WILL MENTION SLIGHT CHANCE OF THUNDERSTORMS IN THE
MOUNTAINS OTHERWISE...WILL KEEP THINGS DRY WITH A WARMING TREND.
SIMILAR CONDITIONS CAN BE EXPECTED FOR THURSDAY.   DJN.83

.FRIDAY-SUNDAY...HIGH CENTER PUSHES FURTHER EAST WHICH APPEARED IN
EARLY RUNS TO ALLOW SOUTH TO SOUTHWEST FLOW TO BRING MOISTURE
ACROSS THE ENTIRE AREA...BUT LATEST MRF SOLN BRINGS DRIER SW
FLOW INTO THE SWRN U.S. WILL NOT MAKE ANY SGFNT CHANGES TO THE
OUT-PERIOD FORECAST UNTIL SOLNS GROW MORE CONSISTENT. CJC

.GJT...NONE.

COZ001>014-017>023-UTZ022>025-027>029-181200-

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
541 AM MDT SUN AUG 17 2003

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

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

SCATTERED THUNDERSTORMS WILL OCCUR OVER MUCH OF WESTERN COLORADO
AND EASTERN UTAH TODAY AND THIS EVENING. LOCALLY HEAVY RAIN IS
EXPECTED WITH A FEW OF THE STRONGER THUNDERSTORMS LATER THIS
AFTERNOON. THE HEAVY RAIN MAY CAUSE SUDDEN WATER RISES IN NORMALLY
DRY CREEKS...SMALL STREAMS AND ARROYOS. STREET FLOODING...ALONG WITH
MUD FLOWS AND ROCK SLIDES...ARE POSSIBLE...ESPECIALLY IN AREAS THAT
HAVE BEEN BURNED BY WILDFIRES. IN ADDITION...GUSTY WINDS TO NEAR 40
MPH...CLOUD TO GROUND LIGHTNING AND HAIL UP TO 1/2 INCH DIAMETER WILL
ACCOMPANY THE STRONGEST STORMS.

.DAYS TWO THROUGH SEVEN...MONDAY THROUGH FRIDAY...

SCATTERED TO ISOLATED THUNDERSTORMS WILL BE POSSIBLE EACH AFTERNOON
AND EVENING...ESPECIALLY OVER THE MOUNTAINS. THE MAIN THREATS FROM
THESE STORMS WILL BE HEAVY RAIN...CLOUD TO GROUND LIGHTNING...WIND
GUSTS TO 40 MPH...AND SMALL HAIL.

.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 RAINFALL.

NL