345
FXUS65 KGJT 121130
AFDGJT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND JUNCTION CO
530 AM MDT FRI SEP 12 2025
KEY MESSAGES
- WIDESPREAD TO NUMEROUS SHOWERS AND STORMS ARE EXPECTED TODAY
THROUGH FRIDAY. SOME STORMS COULD BE STRONG TO SEVERE THIS
AFTERNOON AS WELL AS FRIDAY AFTERNOON. LARGE HAIL, DAMAGING
WINDS, AND FLASH FLOODING WILL BE THE PRIMARY THREATS OF THE
STRONGEST STORMS.
- THERE WILL BE AN ELEVATED THREAT OF FLASH FLOODING BOTH TODAY
AND FRIDAY, ESPECIALLY IF MULTIPLE ROUNDS OF STORMS TRACK OVER
THE SAME AREAS. FRESH BURN SCARS WILL BE ESPECIALLY CONDUCIVE
TO FLASH FLOODING AND DEBRIS FLOWS.
- TEMPERATURES WILL TREND COOLER TODAY AND BEYOND WITH FALL-
LIKE CONDITIONS EXPECTED AND DRIER CONDITIONS RETURNING SUNDAY.
SHORT TERM /THROUGH SATURDAY/
ISSUED AT 352 AM MDT FRI SEP 12 2025
WIDELY SCATTERED CONVECTION CONTINUES EARLY THIS MORNING WITH
SOME ISOLATED THUNDERSTORMS STILL DEVELOPING IN THE FAST ROBUST
SOUTHWEST FLOW ALOFT. THE LOW PRESSURE TROUGH TO OUR WEST LOOKS
TO SHIFT FURTHER SOUTHEAST AND BECOME POSITIVELY TILTED WITH THE
BASE SETTLING OVER SOUTHERN NEVADA. THIS WILL ALLOW THE 90+ KT
JET STREAK TO TILT MORE UPRIGHT OVER EASTERN UTAH, KEEPING US IN
A FAVORABLE REGION OF DYNAMIC LIFT...SIMILAR TO YESTERDAY. A KEY
DIFFERENCE TO YESTERDAY IS THAT THE MONSOONAL MOISTURE PLUME
WILL ADVECT MORE MOISTURE INTO WESTERN COLORADO STARTING THIS
MORNING AND KEEP IT OVER US THROUGH THE EVENING. THE HI-RES CAMS
ARE ALL INDICATING WIDESPREAD SHOWERS TO DEVELOP ACROSS
SOUTHWEST COLORADO AND MOVE NORTHWARD THROUGH THE MORNING HOURS,
WHICH COULD LEAVE THIS REGION UNDER SUFFICIENT CLOUD COVER,
RESULTING IN MORE STRATIFORM RAINS WITH EMBEDDED THUNDERSTORM
ACTIVITY. MIXING RATIOS ARE FORECAST TO RISE ABOVE 8 G/KG, WHICH
IS PLENTY SUFFICIENT FOR THESE SHOWERS AND STORMS TO BE
EFFICIENT RAIN PRODUCERS.
SOME CLEARING IS EVIDENT ACROSS EASTERN UTAH AND DEPENDING ON
HOW EXPANSIVE THE SHOWERS AND CLOUD COVER ARE THIS MORNING, THE
EDGE OF THAT MOISTURE/CLOUD SHIELD ALONG THE WESTERN COLORADO
BORDER COULD SPARK SOME STRONGER CONVECTION IF THE INSTABILITY
IS REALIZED. AGAIN, LITTLE TO NO CIN EXISTS ACROSS THE AREA SO
ANY LITTLE BIT OF SUN WILL WASTE NO TIME GENERATING NEW
CONVECTION. CAPE IS SIMILAR TO YESTERDAY, WITH AROUND 400 TO 800
J/KG...POSSIBLY UPWARDS OF 1000 J/KG IF WE GET MORE SURFACE
HEATING. SHEAR IS ALSO SIMILAR WITH 40 TO 50 KTS SO STORMS WILL
BE FAST MOVING. POTENTIAL EXISTS FOR A FEW STORMS TO BE STRONG
TO SEVERE WITH LARGE HAIL, DAMAGING WINDS AND HEAVY RAIN LEADING
TO FLASH FLOODING POTENTIAL, ESPECIALLY OVER RECENT BURN SCARS,
ALREADY SATURATED AREAS AND AREAS OF STEEP TERRAIN. THE CAVEAT
WILL BE THE AMOUNT OF CLOUD COVER WITH THE MOISTURE ADVECTION
AND DEVELOPMENT OF SHOWERS IN THE MORNING WHETHER MORE ROBUST
STRONGER CONVECTION IS SEEN OR MORE STRATIFORM ENVIRONMENT PLAYS
OUT. HI RES CAMS, ESPECIALLY THE HRRR WHICH HAS HAD A PRETTY
GOOD TRACK RECORD, SHOW MORE ROBUST CONVECTION DEVELOPING BY MID
AFTERNOON INTO THE EVENING. THE FLOOD WATCH REMAINS IN EFFECT
THROUGH MIDNIGHT TONIGHT.
ON SATURDAY, THE LOW PRESSURE SYSTEM LIFTS OUT OF THE GREAT
BASIN AND TRACKS ACROSS IDAHO AND WYOMING WITH THE BASE OF THE
TROUGH BECOMING NEGATIVELY TILTED AND SWINGING THROUGH EASTERN
UTAH AND WESTERN COLORADO. MOISTURE WILL BE LESS AS THE PLUME
IS PUSHED EASTWARD BUT ENOUGH MOISTURE WILL REMAIN IN PLACE FOR
SCATTERED TO WIDESPREAD SHOWERS AND STORMS AS LAPSE RATES
STEEPEN. TEMPERATURES TODAY AND SATURDAY WILL BE MUCH COOLER
WITH HIGHS 5 TO 10 DEGREES BELOW NORMAL TODAY AND AROUND 10
DEGREES BELOW NORMAL FOR SATURDAY.
LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/
ISSUED AT 139 PM MDT THU SEP 11 2025
A RIDGE BUILDS OVER THE REGION ON SUNDAY AND A CAP IN PLACE
SHOULD HOLD CONVECTION TO A MINIMUM. ATTENTION THEN TURNS TO THE
STORM OVER THE PACNW, WHICH HAS NOT BEEN HANDLED WELL BY THE
MODELS. THAT SYSTEM MAY BE ABLE TO TAP INTO THE MOISTURE TO OUR
SOUTH. IF THAT HAPPENS THEN THE CHANCES FOR SHOWERS INCREASES ON
TUESDAY AND WEDNESDAY, AND BY THURSDAY THE TROUGH CROSSES THE
DIVIDE BRINGING DRY AIR IN FROM THE WEST.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 530 AM MDT FRI SEP 12 2025
ISOLATED TO WIDELY SCATTERED SHOWERS WILL CONTINUE THROUGH THE
MORNING WITH THUNDERSTORMS DEVELOPING ACROSS THE SOUTH AND
COVERAGE INCREASING THROUGH THE MORNING AS MORE MOISTURE MOVES
UP FROM THE SOUTH. THIS WILL RESULT IN AREAS OF STRATIFORM
RAINFALL WITH EMBEDDED THUNDERSTORM ACTIVITY. MORE WIDESPREAD TO
NUMEROUS THUNDERSTORMS ARE EXPECTED THIS AFTERNOON AND EVENING,
ESPECIALLY WHERE PERIODS OF SUN BREAK OUT TO ALLOW FOR SURFACE
HEATING. EXPECT GUSTY OUTFLOW WINDS AND BRIEF HEAVY RAIN WITH
ANY CONVECTION, WITH CIGS AND VSBY REDUCTIONS TO MVFR AND BELOW
ILS BREAKPOINTS AT TIMES. MOST ACTIVITY WILL REDUCE AFTER 06Z
WITH ISOLATED CONVECTION LINGERING OVERNIGHT.
HYDROLOGY
ISSUED AT 352 AM MDT FRI SEP 12 2025
SCATTERED TO WIDESPREAD STORMS ARE EXPECTED THROUGH LATE THIS
EVENING. HEAVY RAINFALL IS POSSIBLE WITH THE STRONGER STORMS.
STORM MOTION WILL INHIBIT RESIDENCE TIME, BUT ANY CELL TRAINING
COULD LEAD TO EXCESSIVE RAIN. RECENT BURN SCARS ARE THE MOST
SUSCEPTIBLE RIGHT NOW. IF THE MOUNTAINS CAN RECEIVE MULTIPLE
ROUNDS OF MODERATE RAIN THEN THERE COULD BE ROCK AND DEBRIS
SLIDES. THE SOUTHERN AND CENTRAL MOUNTAINS HAVE THE HIGHEST
FORECAST RAINFALL AMOUNTS.
GJT WATCHES/WARNINGS/ADVISORIES
CO...FLOOD WATCH THROUGH THIS EVENING FOR COZ003-006>014-017>023.
UT...FLOOD WATCH THROUGH THIS EVENING FOR UTZ027-028.
SHORT TERM...MDA
LONG TERM...KJS
AVIATION...TGJT
HYDROLOGY...TGJT
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