416
FXUS65 KBOU 131745
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
1145 AM MDT SAT SEP 13 2025
KEY MESSAGES
- SCATTERED/NUMEROUS SHOWERS AND THUNDERSTORMS THIS AFTERNOON AND
EVENING, WITH AN ISOLATED THREAT OF SEVERE STORMS ACROSS THE
LOWER ELEVATIONS.
- SCATTERED SHOWERS AND A SLIGHT CHANCE FOR THUNDERSTORMS, MAINLY
NORTH SUNDAY MORNING.
- UNSETTLED, UNCERTAIN PATTERN FOR MOST OF NEXT WEEK.
DISCUSSION /THROUGH FRIDAY/
ISSUED AT 204 PM MDT FRI SEP 12 2025
A SLOW MOVING TROUGH OVER THE WEST IS STILL EXPECTED TO DOMINATE
THE UPPER-LEVEL PATTERN THROUGH THE WEEKEND, KEEPING COOLER
TEMPERATURES IN PLACE, AND WIDESPREAD PRECIPITATION CHANCES INTO
SUNDAY, INCLUDING SOME LIGHT SNOW FOR THE HIGHEST ELEVATIONS.
ANOTHER UPPER-LEVEL LOW IS ON TRACK TO ENTER THE PACIFIC NORTHWEST
EARLY NEXT WEEK, BUT GUIDANCE STILL STRUGGLES TO AGREE ON
SPECIFICS.
THIS MORNING'S UPPER-AIR ANALYSIS SHOWS THAT COLORADO REMAINS
DOWNSTREAM OF AN APPROACHING UPPER-LEVEL LOW CENTERED OVER THE
GREAT BASIN, KEEPING SOUTHWESTERLY FLOW ALOFT OVER THE REGION. A
NEAR 100KT JET STRETCHES DOWNSTREAM OF THE TROUGH AXIS, FROM
SOUTHERN CALIFORNIA INTO WESTERN COLORADO AND WYOMING. WITH AN
UPPER LEVEL HIGH CENTERED OVER THE CENTRAL CONUS, AND THE TROUGH
TO THE WEST, MID-LEVEL MOISTURE FROM BOTH THE GULF AND THE PACIFIC
ARE BEING ADVECTED INTO THE INTERMOUNTAIN WEST, WHICH HAS ALREADY
AIDED IN THE DEVELOPMENT OF SEVERE THUNDERSTORMS ACROSS EASTERN
UTAH AND WESTERN COLORADO THIS MORNING. AS THE DAY PROGRESSES, THE
LOW IS EXPECTED TO SLOWLY SLIDE EASTWARD, INCREASING VERTICAL
ASCENT ACROSS OUR FORECAST AREA. THOUGH THE STRONGEST FORCINGS ARE
EXPECTED TO REMAIN WEST OF OUR FORECAST AREA TODAY, EXPECT
SHOWERS AND A FEW THUNDERSTORMS TO DEVELOP OVER THE HIGHER TERRAIN
THROUGH THE AFTERNOON, AND PUSH EASTWARD THROUGH THE EVENING.
WITH ENSEMBLES SHOWING ELEVATED PWAT VALUES APPROACHING 180% TO
200% OF NORMAL BY THIS AFTERNOON ALONG AND ADJACENT TO THE
CONTINENTAL DIVIDE, THERE IS POTENTIAL FOR A FEW POCKETS OF
HEAVIER RAINFALL, WITH THE HREF LPMM 6-HR PRECIPITATION ZEROING IN
ON AREAS NEAR THE INDIAN PEAKS AND THE HIGHER ELEVATIONS IN
LARIMER COUNTY TO SEE THE HIGHEST ACCUMULATIONS BETWEEN 1 TO 2". A
LITTLE MORE UNCERTAINTY REMAINS FOR THE LOWER ELEVATIONS AS
PATCHY CLOUD COVER THIS MORNING HAS KEPT INSTABILITY LIMITED.
DESPITE TEMPERATURES CLIMBING TO THE MID TO UPPER 80S ACROSS A
LARGE MAJORITY OF THE PLAINS, SPC MESOANALYSIS STILL SHOWS MLCAPE
VALUES REMAIN AT 250 J/KG OR LESS ACROSS THE LOWER ELEVATIONS. THE
LATEST ACARS SOUNDING RESEMBLES AN INVERTED-V PROFILE WITH DCAPE
VALUES APPROACHING 800 J/KG, SO EXPECT TO SEE SOME GUSTY OUTFLOWS
BETWEEN 45 TO 55 MPH WITH ANY SHOWERS OR WEAK STORMS THAT MANAGE
TO MAKE IT OFF THE TERRAIN. SOME OF THE HI-RES MODELS KEEP SHOWERS
IN PLACE THROUGH LATE TONIGHT, MOVING WEST TO EAST ACROSS THE
LOWER ELEVATIONS.
SATURDAY IS STILL ON TRACK TO SEE THE BEST CHANCES FOR MORE
WIDESPREAD PRECIPITATION AS MID-LEVEL MOISTURE CONTINUES TO ADVECT
IN FROM BOTH THE GULF AND THE PACIFIC, AND QG FORCINGS REACH
THEIR HEIGHT AS THE TROUGH DRAWS NEAR. WITH INCREASING
SOUTHWESTERLY FLOW ALOFT, 0-6KM BULK SHEAR VALUES LOOK TO INCREASE
TO BETWEEN 35 TO 45 KTS. MIXED WITH PATCHY ENHANCED INSTABILITY
IN AREAS WHERE LESS CLOUD COVER WILL ALLOW FOR THE BEST SURFACE
HEATING, WILL BE SUFFICE FOR AN ISOLATED THREAT OF MARGINAL TO
SEVERE STORMS ACROSS THE LOWER ELEVATIONS IN THE AFTERNOON, WITH
THE MAIN HAZARDS BEING GUSTY OUTFLOWS TO 50 MPH AND HAIL UP TO
1.5" IN DIAMETER.
SHOWERS ARE EXPECTED TO PERSIST INTO SUNDAY AFTERNOON BEFORE WEAK
RIDGING MOVES IN BEHIND THE EXITING TROUGH BY THE EVENING HOURS.
COOLER TEMPERATURES ARE EXPECTED TO REMAIN THROUGH THE WEEKEND
BEFORE A SLIGHT WARMUP RETURNS WITH THE NEW WORK WEEK ON MONDAY.
WITH ENSEMBLES STILL SHOWING SOME DISCREPANCIES WITH THE NEXT
EXPECTED SHORTWAVE PROGGED TO ENTER THE PACIFIC NORTHWEST EARLY
NEXT WEEK, HAVE LET THE NBM RIDE FROM MONDAY ONWARD. NBM SEEMS
REASONABLE WITH A FEW DAYS OF WARMER AND DRIER CONDITIONS
EXPECTED MONDAY AND TUESDAY, BEFORE ANOTHER POTENTIAL COLD FRONT
ASSOCIATED WITH THE PACIFIC NORTHWEST LOW COOLS THINGS OFF AGAIN
BY MIDWEEK.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1144 AM MDT SAT SEP 13 2025
NORTHEAST WINDS ARE EXPECTED TO PERSIST THROUGH 21Z AHEAD OF THE
SHOWERS AND THUNDERSTORMS. OUTFLOW FROM THE SHOWERS/STORMS SHOULD
BRING A WESTERLY WIND SHIFT AT FIRST. ADDITIONAL WIND SHIFTS WILL
BE POSSIBLE AS SHOWERS AND THUNDERSTORMS DEVELOP. MOST FAVORABLE
TIME FRAME FOR THUNDERSTORMS IS 21-24Z. AIRMASS THEN STABILIZES
AND MOSTLY SHOWERS ARE EXPECTED AFTER 00Z.
THE CHANCES FOR SHOWERS DECREASES OVERNIGHT, BUT THEN INCREASES
INTO SUNDAY MORNING AS WRAP AROUND SHOWERS MOVE SOUTHWARD.
CEILINGS ARE EXPECTED TO FALL LATE TONIGHT/SUNDAY MORNING TO
5000-8000 FEET, AND POSSIBLY LOWER TO 3000 UNDER/NEAR THE SHOWERS.
AS FAR AS WINDS GO, NORMAL SOUTHWEST DRAINAGE WINDS WILL BE
BATTLING THE PREVAILING NORTHWEST FLOW. EXPECT A SHORT PERIOD OF
SOUTHWEST DRAINAGE AROUND 12Z SUNDAY, THEN A QUICKER THAN USUAL
TURN TO THE NORTHWEST BY 13- 14Z SUNDAY. BY 18Z SUNDAY, THE
SHOWERS ARE EXPECTED TO BE WELL NORTHEAST OF THE DENVER AREA WITH
LIGHTER SOUTHEAST WINDS FOR SUNDAY AFTERNOON.
BOU WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...BONNER
AVIATION...MEIER
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