265
FXUS65 KBOU 260009
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
609 PM MDT FRI SEP 25 2026
KEY MESSAGES
- ANOTHER ROUND OF SHOWERS AND ISOLATED STORMS FRIDAY AFTERNOON
AND EVENING.
- DRIER AND WARMER THIS WEEKEND BEFORE AN UPPER LEVEL TROUGH
BRINGS COOLER TEMPERATURES AND POTENTIALLY OUR NEXT CHANCES FOR
SHOWERS/STORMS EARLY NEXT WEEK.
- LOW CHANCES (30%-40%) FOR MOUNTAIN SNOW ABOVE 11,000FT LATE
MONDAY INTO TUESDAY.
DISCUSSION /THROUGH FRIDAY/
ISSUED AT 304 PM MDT FRI SEP 25 2026
A SHORTWAVE TROUGH MOVING THROUGH COLORADO THIS AFTERNOON IS
PROMOTING ANOTHER ROUND OF SHOWERS AND STORMS WITH LOCALIZED HEAVY
RAIN POSSIBLE. CURRENT SOUNDINGS SHOW A VERY MOIST PROFILE, LONG-
SKINNY CAPE, AND PRECIPITABLE WATER (PW) VALUES 0.7-1.0". WITH THE
THE COOL TEMPERATURES AND CLOUD COVER TODAY, INSTABILITY WILL BE THE
MAIN LIMITING FACTOR. CURRENT VISIBLE SATELLITE DOES SHOW SOME
CLEARING OVER THE DENVER METRO AND EAST COLORADO PLAINS, ALLOWING
FOR SOME SURFACE HEATING TO OCCUR. ADDITIONALLY, NUMEROUS
THUNDERSTORMS HAVE ALREADY DEVELOPED OVER THE FOOTHILLS. ALTHOUGH
STORM MOTIONS (15-20 MPH) AND DEEP WARM CLOUD LAYERS (4,000-5,000
FT) ARE NOT EXCEEDINGLY FAVORABLE FOR FLASH FLOODING, LOCALIZED
FLOODING CANNOT BE RULED OUT, PARTICULARLY IF THE HEAVIEST SHOWERS
TRACK OVER THE DENVER METRO OR PALMER DIVIDE. CLEARING BEHIND THE
SHORTWAVE LATE TONIGHT MAY LEAD TO SOME PATCHY FOG OVER THE EAST
COLORADO PLAINS FOR A FEW HOURS AROUND, CLEARING SOON AFTER SUNRISE.
FOR THE MOUNTAINS, ZONAL FLOW ALOFT AND WEAK DOWNSLOPING WILL BRING
BREEZY CONDITIONS DURING THE EARLY MORNING, WITH GUSTS UP TO 40 MPH
POSSIBLE ABOVE THE TREELINE, AND GUSTS UP TO 25 MPH FOR THE
FOOTHILLS.
WE EXPECT QUIET WEATHER TO PREVAIL FOR SATURDAY AND SUNDAY DUE TO AN
UPPER LEVEL RIDGE BUILDING OVER COLORADO AND CONSIDERABLE
SUBSIDENCE. AS SUCH, SKIES WILL REMAIN MOSTLY SUNNY AND THE CHANCES
FOR SHOWERS OVER OUR CWA ARE NEAR-ZERO SATURDAY AFTERNOON. THE UPPER
LEVEL RIDGE WILL CONTINUE TO TRACK EAST ON SUNDAY AND FLOW ALOFT
WILL BECOME SOUTHWESTERLY, BRINGING A SLIGHT INCREASE IN MID LEVEL
MOISTURE. RAIN CHANCES WILL GENERALLY REMAIN VERY LOW (<25% CHANCE)
SUNDAY AFTERNOON, ALTHOUGH A FEW SPRINKLES MAY BE POSSIBLE OVER THE
MOUNTAINS. TEMPERATURES WILL RUN WARMER THAN SEASONABLE BOTH DAYS,
WITH HIGHS IN THE LOW TO MID 80S AT LOW ELEVATIONS AND 60S-70S FOR
THE MOUNTAINS.
THE PATTERN BECOMES MUCH MORE COMPLEX STARTING MONDAY. DETERMINISTIC
GLOBAL MODEL RUNS AND LONG-RANGE ENSEMBLE MEMBERS STILL SHOW
CONSIDERABLE SPREAD REGARDING THE EVOLUTION OF AN UPPER LEVEL TROUGH
AND THE REMNANTS OF WHAT IS CURRENTLY HURRICANE POLO. ONE OF THE
REASONS FOR THIS LEVEL OF UNCERTAINTY IS THE DISAGREEMENT REGARDING
THE SPEED OF UPPER LEVEL TROUGH AND THE POST-TROPICAL CYCLONE
(POLO) AS IT APPROACHES THE NEW MEXICO/TEXAS-MEXICO BORDER.
BROADLY SPEAKING, THERE ARE TWO POSSIBLE SCENARIOS HERE. ONCE
SCENARIO FAVORS A SLOWER TRACK OF THE UPPER-LEVEL TROUGH, ALLOWING
IT TO ENCOUNTER AND PHASE WITH THE POST-TROPICAL CYCLONE JUST
SOUTH OF THE FOUR CORNERS. IF THIS OCCURS, A MORE MEANINGFUL
PORTION OF THE POST- TROPICAL CYCLONE'S MOISTURE WOULD BE LOFTED
NORTHWARDS INTO OUR AREA AND LEAD TO WIDESPREAD RAINFALL COVERAGE
FOR TUESDAY-WEDNESDAY. ANOTHER SCENARIO, AND WHAT LOOKS MOST
LIKELY AT THIS POINT, IS AN EARLIER ARRIVAL OF THE UPPER LEVEL
TROUGH AND PHASING WITH THE POST- TROPICAL CYCLONE OCCURRING
FARTHER EAST CLOSER TO THE TEXAS PANHANDLE, WHICH WOULD GREATLY
DECREASE RAINFALL CHANCES FOR OUR AREA AS THE BULK OF THE MOISTURE
IS PUSHED OVER THE CENTRAL GREAT PLAINS. REGARDLESS, ENSEMBLE
SOLUTIONS DO HINT AT ANOMALOUS MOISTURE (>90TH PERCENTILE OF
CLIMATOLOGY) IN ASSOCIATION WITH THIS EVENT TUESDAY THROUGH
WEDNESDAY. AS THE PREVIOUS AFD STATED, THIS SYSTEM IS A
POTENTIALLY HIGH IMPACT, LOW CONFIDENCE EVENT, WHERE A WESTWARD
SHIFT IN THE MEETING POINT OF THE TROUGH AND POST-TROPICAL CYCLONE
WOULD IMPLY HEAVY RAINFALL CONCERNS. AT THIS POINT, IT LOOKS LIKE
MOUNTAIN SNOW CHANCES ARE DECREASING (30%-40% CHANCE) WITH THIS
SYSTEM. A POST-TROPICAL CYCLONE WOULD IMPLY A MOIST AND WARM
AIRMASS, WHILE A FARTHER TRACK AND DIRECT HIT FROM THE TROUGH
ALONE WOULD IMPLY A COLDER BUT DRIER AIRMASS.
LOOKING AHEAD, ENSEMBLES ARE TRENDING TOWARDS A RETURN TO ZONAL
FLOW, NEAR-AVERAGE TEMPERATURES, AND DRIER AIR FOR THURSDAY AND
FRIDAY. THE NEXT WEATHER SYSTEM MAY ARRIVE LATE SATURDAY INTO SUNDAY
OF NEXT WEEK, WITH SOME GFS ENSEMBLE MEMBERS HINTING AT A COUPLE
INCHES OF ACCUMULATING MOUNTAIN SNOW. HOWEVER, GREAT UNCERTAINTY
REMAINS GIVEN THAT SOME ENSEMBLE MEMBERS SHOW NO PRECIPITATION, AND
THE ECMWF HINTS AT RIDGING OVER OUR REGION. THIS WILL BE ANOTHER
SYSTEM TO WATCH AS THE DETAILS BECOME MORE CLEAR.
AVIATION /00Z TAFS THROUGH 00Z SUNDAY/
ISSUED AT 607 PM MDT FRI SEP 25 2026
MOST OF OUR STRONGEST THUNDERSTORMS HAVE MOVED EAST OVER THE
PLAINS, OUT OF THE VICINITY OF THE TAF SITES; HOWEVER, SOME STORMS
HAVE STALLED OVER THE AIRFIELD AT DEN, BRIEFLY REDUCING
VISIBILITY TO AS LOW AS 2SM. WE EXPECT THESE SHOWERS TO LINGER
OVER THE AIRPORT FOR AT LEAST THE NEXT HALF HOUR BEFORE CONTINUING
EASTWARD. AS SUCH, WE'VE EXTENDED THE TEMPO GROUP OUT ANOTHER
HOUR FOR KDEN, WITH VISIBILITY REDUCTIONS FROM HEAVY RAIN BEING
THE MAIN CONCERN.
ONCE SHOWERS FULLY MOVE OUT OF THE AREA, WINDS SHOULD TURN TO THE
SOUTH/SOUTHWEST AND SETTLE ON DRAINAGE OVERNIGHT. CLOUD BASES SHOULD
START TO LIFT, AS WELL, WITH CLEAR SKIES EXPECTED OVERNIGHT AND INTO
TOMORROW. WINDS SHOULD BECOME LIGHT AND VARIABLE AFTER SUNRISE, THEN
BECOME EAST/SOUTHEASTERLY IN THE AFTERNOON AND EVENING.
BOU WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...AA
AVIATION...AGS
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