697
FXUS65 KGJT 210609
AFDGJT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
1209 AM MDT WED OCT 21 2026
KEY MESSAGES
- WIDESPREAD RAIN IS EXPECTED TOMORROW THROUGH EARLY FRIDAY.
- STRONG TO SEVERE STORMS WILL BE POSSIBLE NEAR THE FOUR
CORNERS...FAVORING SOUTHEAST UTAH...ON WEDNESDAY AND THURSDAY.
- THE POTENTIAL FOR FLOODING INCREASES THURSDAY AND FRIDAY,
ESPECIALLY FOR PORTIONS OF SOUTHEAST UTAH AND SOUTHWEST
COLORADO.
- RAINFALL AMOUNTS IN THE SOUTHERN MOUNTAINS RANGE FROM 1-3
INCHES WITH HIGHER AMOUNTS OF 2-4" OR MORE POSSIBLE IN THE
SAN JUANS AND SOUTHERN FOOTHILLS.
DISCUSSION
ISSUED AT 1019 PM MDT TUE OCT 20 2026
HAZARDOUS WEATHER POSSIBLE THROUGH FRIDAY:
REMNANT TROPICAL MOISTURE WILL ONCE AGAIN TAKE AIM AT THE
INTERMOUNTAIN WEST AND ROCKIES. THE FIRST WAVE OF THIS DEEPER
MOISTURE ARRIVES TO THE FOUR CORNERS REGION BY SUNRISE AND
TRACK NORTHEASTWARD ACROSS THE REMAINDER OF EASTERN UTAH AND
WESTERN COLORADO THROUGH THE DAY BEFORE BEING SWEPT AWAY ON
FRIDAY. A FULL ARRAY OF HAZARDS ARE POSSIBLE WITH THIS
PROLONGED EVENT INCLUDING RIVER FLOODING, FLASH FLOODING, STRONG
TO SEVERE THUNDERSTORMS, AND SNOW ABOVE 12,000-13,000 FEET. A
FLOOD WATCH HAS BEEN ISSUED FOR PARTS OF SOUTHEAST UTAH AND
SOUTHWEST COLORADO BEGINNING 12 PM TOMORROW AND PERSISTING
THROUGH 12 PM FRIDAY.
TOMORROW THROUGH THURSDAY:
THE 21/00Z KGJT RAOB IS SITTING AT 2/3 OF AN INCH OF PWAT WHICH
IS ALREADY ANOMALOUS AND IN THE 90TH PERCENTILE. IMPRESSIVE FOR
MID OCTOBER BUT JUST THE TIP OF THE ICEBERG. GOES ALL LAYER
PWAT IMAGERY IS SHOWING THE NOSE OF TRUE TROPICAL MOSITURE
MOVING INTO SOUTH-CENTRAL AZ THIS EVENING AND SHOULD ARRIVE TO
THE 4 CORNERS IN THE PRE-SUNRISE HOURS. PWAT IS PROJECTED TO
PUSH ABOVE AN INCH BY SUNSET AT GJT WHICH WOULD BE A NEW DAILY
RECORD AND SOME 300+ PERCENT OF NORMAL. SO THE STAGE WILL ONCE
AGAIN BE SET FOR EXCESSIVE RAINFALL RATES AND IMPRESSIVE TOTAL
PRECIPITATION AMOUNTS THROUGH THE EVENT. THIS MOISTURE WILL ALSO
EFFECTIVELY LIGHTEN AND DESTABILIZE THE ATMOSPHERE AND ALLOW
EVEN MINIMAL LIFT TO PRODUCE ASCENT AND EFFICIENTLY SQUEEZE OUT
THIS ANOMALOUS PWAT. ASCENT OVER THE NEXT FEW DAYS WILL AIDED
BY A STRONG SUBTROP JET ALOFT TOMORROW FOLLOWED BY THE POLAR
JET ON THURSDAY WHICH IS ASSOCIATED WITH THE MAIN UPSTREAM
TROUGH OVER THE WEST. CAPE WILL BE MODEST AT BEST OVER THE 4
CORNERS REGION THE NEXT FEW AFTERNOONS. THE WIND PROFILE WILL
HOWEVER BE IMPRESSIVE...WITH LOW LEVEL EAST/SOUTHEAST FLOW
OVER-TOPPED BY THE STRONG SOUTHWEST FLOW ALOFT. THIS SHEAR WILL
BE FAVORABLE FOR PRODUCING PERIODS OF ORGANIZED CONVECTION EVEN
THOUGH PLENTY OF CLOUD COVER WILL INHIBIT FULL SURFACE HEATING.
STRONG OUTFLOW WINDS WILL REMAIN THE MAIN THREAT BUT SOME
STORMS WILL ALSO BE CAPABLE OF PRODUCING LARGER HAIL. THE
VEERING PROFILE AND LOCAL TERRAIN EFFECTS COULD ALSO LEAD TO
SOME BRIEF SPIN UPS...NOT PROBABLE BUT NOT ZERO EITHER. LASTLY
THE CAPE PROFILE WILL BE LONG AND SKINNY...AN INDICATION OF DEEP
WARM CLOUD PROCESSES WHICH FAVOR HIGH PRECIPITATION RATES AS
WELL AS HIGH SNOW LEVELS. IT SHOULD BE NO SURPRISE THAT THE
FERTILE CRESCENT OF THE SAN JUANS WILL ALSO BE EFFECTIVE AT
PRODUCING THE ASCENT IN THIS SOUTHERLY FLOW PATTERN. WITH THE
FIRE HOSE POINTED DIRECTLY AT THEM PRECIPITATION AMOUNTS IN THE
2-4 INCH RANGE ARE STILL FORECAST WITH HIGHER AMOUNTS POSSIBLE
DUE TO CONVECTION. RAIN OR A NIGHTTIME MIX AT PASS LEVEL COULD
TRANSLATE TO 6 TO 12 INCHES OR MORE OF SNOW OVER THE HIGHEST
PEAKS.
FRIDAY:
UNLIKE THE LAST EVENT THE UPSTREAM SYSTEM WILL BE LIFTING
NORTHWARD THROUGH THE GREAT BASIN INSTEAD OF SENDING THE MAIN
CIRCULATION OVERHEAD. DRIER AIR WILL BE PULLED IN AS THIS SYSTEM
LIFTS INTO THE NORTHERN ROCKIES THROUGH THE DAY ON FRIDAY. A
DECREASE IN PRECIPITATION COVERAGE AND INTENSITY IS EXPECTED
THROUGH THE DAY AS PWAT IS FORECAST TO CRASH BELOW A HALF OF AN
INCH BY MIDDAY. EVEN AFTER IT STOPS RAINING, THE RISK FOR
FLOODING WILL REMAIN ELEVATED ON FRIDAY AS WATER CONTINUES TO
WORK THROUGH THE SYSTEM. SOME MAIN STEM RIVERS ARE FORECAST TO
CREST ON FRIDAY MORNING. WE'LL HAVE A BETTER IDEA OF HOW LONG
FLOODING MAY CONTINUE TO CAUSE ISSUES AFTER WE GET A BETTER
SENSE OF HOW MUCH RAINFALL IS RECEIVED ON THURSDAY.
LOOKING AHEAD:
CHANCES FOR LIGHT PRECIPITATION (VALLEY RAIN, MOUNTAIN SNOW
ABOVE 10,000 FEET) CONTINUE THROUGH THE WEEKEND AS A LOW
PRESSURE SYSTEM, CURRENTLY SPINNING OFF THE CALIFORNIA COAST,
TRAVERSES THE INTERMOUNTAIN WEST. PLENTY OF UNCERTAINTY REMAINS
IN HOW THIS LOW WILL EVOLVE AS IT MOVES INLAND, BUT ENSEMBLE
GUIDANCE TENDS TO SHOW A WEAKENING SYSTEM BY THE TIME IT REACHES
OUR FORECAST AREA. REGARDLESS, THIS SYSTEM WILL PROVIDE ENOUGH
FORCING FOR SCATTERED TO WIDESPREAD PRECIPITATION AS IT MOVES
THROUGH, ALONGSIDE A BRIEF REDUCTION IN TEMPERATURES.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1126 PM MDT TUE OCT 20 2026
VFR CONDITIONS AND LIGHT WINDS ARE EXPECTED TO PERSIST THROUGH
THE OVERNIGHT HOURS. AROUND 12Z PRECIPITATION FROM THE INCOMING
WEATHER SYSTEM WILL BEGIN MOVING INTO THE FOUR CORNERS AREA,
GRADUALLY SPREADING ACROSS EASTERN UTAH AND WESTERN COLORADO
THROUGH THE MORNING AND AFTERNOON. BY THE AFTERNOON IMPACTS FROM
SHOWERS ARE POSSIBLE AT ALL TAF SITES. IMPACTS INCLUDE PERIODS
OF LOWER CEILINGS AND VISIBILITY, POTENTIALLY LEADING TO MVFR
CONDITIONS OR DROPS BELOW ILS BREAKPOINTS. RAIN SHOWERS WILL
CONTINUE THROUGH THE TAF PERIOD.
HYDROLOGY
ISSUED AT 1019 PM MDT TUE OCT 20 2026
HYDROLOGIC CONCERNS RAMP UP TOMORROW (WEDNESDAY), DUE TO THE
POTENTIAL FOR THUNDERSTORM DEVELOPMENT. ATMOSPHERIC MOISTURE
INCREASES UNDER STRONG SOUTH-SOUTHWESTERLY FLOW, LOFTING AN
ABUNDANCE OF WARM TROPICAL MOISTURE ACROSS THE FORECAST AREA.
WHILE BANDS OF SHOWERS EXPAND AS EARLY AS WEDNESDAY MORNING,
THUNDERSTORMS ARE EXPECTED TO MOVE INTO EAST/SOUTHEAST UTAH
TOMORROW AFTERNOON. SOUTHEAST UTAH AND LOWER VALLEYS ALONG THE
CO/NM BORDER SHOW THE HIGHEST POCKETS OF INSTABILITY, WHICH
FOCUSES THE BETTER CONFIDENCE FOR FLASH FLOODING ACROSS DESERT
FLOORS AND DRY WASHES. COVERAGE OF RAINFALL RATES EXCEEDING 0.5
INCHES IN AN HOUR REMAINS LOW EVEN 24 HOURS OUT. HOWEVER,
WHATEVER EMBEDDED THUNDERSTORMS THAT DEVELOP TOMORROW WILL ONLY
HELP SATURATE SOILS LEADING INTO THE MAIN SURGE OF MOISTURE
EXPECTED WEDNESDAY NIGHT THROUGH THURSDAY.
THE BULK OF PRECIPITATION REMAINS ON TRACK FOR THURSDAY, WITH
GENERALLY 1 TO 3 INCHES OF RAIN FALLING ACROSS THE SOUTHERN HALF
THE CWA WITHIN A 24 TO 36 HOUR WINDOW. BULLSEYE QPFS ARE
HIGHEST OVER THE SAN JUAN'S, WHERE LOCALLY HIGHER AMOUNTS OF 4
TO 5 INCHES ARE POSSIBLE. THIS SYSTEM CONTINUES TO TRACK
ANOMALOUSLY WARM, AS THE MAIN MOISTURE PLUME REMAINS WELL AHEAD
OF A COLD, CLOSED LOW DEEPENING ALONG THE PACIFIC COAST. THUS,
RAIN ON SNOW IS A VIABLE CONCERN. SNOW LEVELS ARE FORECAST ABOVE
12-13 KFT THROUGHOUT THE DAY THURSDAY, WHICH WILL LIKELY RESULT
IN MELTING MUCH OF THE EXISTING EARLY-SEASON SNOW PACK. THE
COMBINED RUNOFF FROM RAIN AND RAIN-ON-SNOW WILL RESULT IN A
RAPID RISE IN MANY OF OUR CREEKS, STREAMS AND RIVERS. MODELED
RESPONSES ALSO NUDGED UPWARD ACROSS MANY RIVER FORECAST POINTS
ACROSS SOUTHWEST COLORADO. WE HAVE THE HIGHEST CONFIDENCE IN
MINOR FLOODING AND IMPACTS ALONG THE SAN JUAN RIVER, PIEDRA,
ANIMAS, LA PLATA RIVERS AND ABOVE VALLECITO RESERVOIR. HOWEVER,
OTHER CREEKS AND TRIBUTARIES WITHIN THE FOUR CORNERS REGION
REMAIN SUSCEPTIBLE. ALL RIVER RESPONSES ARE HEAVILY DEPENDENT ON
WHERE THE HEAVIEST PRECIPITATION FALLS, SO PLEASE CONTINUE TO
MONITOR THE FORECAST AS THE WEEK UNFOLDS.
GJT WATCHES/WARNINGS/ADVISORIES
CO...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY MORNING
FOR COZ019-021>023.
UT...FLOOD WATCH FROM WEDNESDAY AFTERNOON THROUGH FRIDAY MORNING
FOR UTZ022-027>029.
DISCUSSION...TGJT
AVIATION...TGJT
HYDROLOGY...ERW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page