487
FXUS65 KBOU 152103
AFDBOU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE DENVER/BOULDER CO
303 PM MDT TUE SEP 15 2026
KEY MESSAGES
- COOLER WEATHER TODAY. LIMITED SHOWER AND STORM CHANCES, MOSTLY
OVER THE HIGHER TERRAIN.
- TEMPERATURES BOUNCE BACK TOMORROW, BUT THEN AVERAGE NEAR OR
EVEN SLIGHTLY BELOW SEASONAL NORMALS THROUGH NEXT WEEKEND.
- UNSETTLED PATTERN REST OF THIS WEEK. THURSDAY LOOKS LIKE THE
HIGHEST OPPORTUNITY OF MEASURABLE RAIN AND A LOCALLY HEAVY
RAINFALL THREAT.
DISCUSSION /THROUGH TUESDAY/
ISSUED AT 256 PM MDT TUE SEP 15 2026
TEMPERATURES ACROSS OUR ENTIRE CWA ARE CURRENTLY IN THE 60S AND 70S,
WITH EVEN COOLER READINGS AT MOUNTAIN PEAKS AND RIDGES, A REMINDER
THAT FALL IS JUST AROUND THE CORNER. HOWEVER, THE MONSOON IS NOT
OVER JUST YET, WITH DAILY CHANCES FOR SHOWERS AND STORMS PERSISTING
THROUGH AT LEAST SATURDAY. RAIN CHANCES TODAY REMAIN VERY LOW (<20%)
FOR THE DENVER METRO AND EAST CO PLAINS GIVEN THE COOLER
TEMPERATURES AND LIMITED INSTABILITY AS WE SIT IN A POST-FRONTAL
AIRMASS. THE HIGH TERRAIN WILL HAVE A BETTER CHANCE FOR SHOWERS AND
STORMS LATE THIS AFTERNOON AND EVENING, ALTHOUGH COVERAGE WILL BE
SCATTERED TO ISOLATED IN NATURE.
AT THE UPPER LEVELS, A CLOSED LOW PRESSURE SYSTEM OVER NORTHERN
CALIFORNIA AND SLIGHT RIDGING TO OUR NORTHWEST WILL TURN FLOW ALOFT
SOUTH-SOUTHWESTERLY BY TOMORROW AFTERNOON, WHICH WILL INCREASE
MONSOONAL MOISTURE ADVECTION. WE EXPECT SHOWER COVERAGE TO INCREASE
TOMORROW AFTERNOON AND EVENING, WITH WIDESPREAD SHOWER DEVELOPMENT
OVER THE MOUNTAINS AS PRECIPITABLE WATER (PW) RISES TO VALUES THAT
ARE GREATER THAN THE 90TH PERCENTILE OF CLIMATOLOGY. TEMPERATURES
OVER THE DENVER METRO WILL STILL HAVE A CHANCE TO CLIMB INTO THE
80S BEFORE CLOUD COVER INCREASES LATE IN THE AFTERNOON.
BY THURSDAY MORNING, A DISTURBANCE TRACKS THROUGH ARIZONA AND ONTO
SOUTHERN COLORADO. AS THE PREVIOUS AFD STATED, THE ARRIVAL OF THIS
DISTURBANCE WILL BE KEY IN THE COVERAGE AND INTENSITY OF RAINFALL ON
THURSDAY. AN ARRIVAL BY EARLY AFTERNOON WOULD COINCIDE WITH PEAK
INSTABILITY AND MOISTURE, WHICH WOULD IMPLY A BETTER CHANCE FOR
WIDESPREAD SHOWERS AND STORMS OVER BOTH MOUNTAINS AND EAST CO
PLAINS, INCLUDING THE DENVER METRO. WITH THIS SCENARIO, THE THREAT
FOR LOCALIZED HEAVY RAINFALL AND FLASH FLOODING WOULD ALSO BE
HIGHER. LOOKING AT FLASH FLOODING PARAMETERS, MOISTURE ALONE LOOKS
QUITE IMPRESSIVE, WITH PW VALUES AS HIGH AS 5 STANDARD DEVIATIONS
ABOVE NORMAL FOR THE TIME OF YEAR. HIGH-RES MODEL GUIDANCE ALSO
SHOWS WARM CLOUD LAYER DEPTHS AS DEEP AS 4,000-7,000 FT, AND STORM
MOTIONS AROUND 20KT. WITH THESE INGREDIENTS IN MIND, AT LEAST SOME
LOCALIZED FLASH FLOODING SEEMS POSSIBLE, ALTHOUGH THE SPATIAL
FOOTPRINT OF THE HEAVIEST PRECIPITATION REMAINS UNCLEAR.
FOR FRIDAY, MOISTURE REMAINS ABOUT 100-150% OF NORMAL, AND A WEAK
UPPER LEVEL TROUGH BEGINS TO TRACK EASTWARDS PROVIDING YET ANOTHER
PUSH FOR SHOWERS AND STORMS. DEPENDING ON THE EVOLUTION OF THIS
TROUGH AND ANOTHER SHORTWAVE TO THE SOUTH OVER THE FOUR CORNERS,
SATURDAY COULD ALSO BE AN ACTIVE DAY, PARTICULARLY FOR THE HIGH
TERRAIN AS MOISTURE REMAINS WELL ABOVE NORMAL THROUGH SATURDAY
EVENING. TEMPERATURES WILL REMAIN SLIGHTLY BELOW NORMAL THURSDAY
THROUGH TUESDAY, WITH AFTERNOON HIGHS IN THE MID 70S FOR LOW
ELEVATIONS, AND 50S-60S FOR THE MOUNTAINS. LONG-RANGE MODEL
ENSEMBLES SHOW A SERIES OF UPPER LEVEL TROUGHS AND DISTURBANCES
TRACKING THROUGH THE WESTERN UNITED STATES, WHICH INTRODUCES QUITE
A BIT OF UNCERTAINTY NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1157 AM MDT TUE SEP 15 2026
LOW CLOUDS HAVE DISSIPATED RECENTLY DISSIPATED AND VFR CONDITIONS
ARE EXPECTED TO PREVAIL FOR THE REST OF THE TAF PERIOD (THRU
WED). ACARS AND FORECAST SOUNDINGS SHOW A STRONGLY CAPPED
AIRMASS. THE CHANCE A SHOWER SURVIVES OFF THE HIGHER TERRAIN AND
REACHES DEN AND APA IS VERY LOW, THEREFORE REMOVED THE PROB30 FOR
SHOWERS. KEPT THE PROB30 FOR SHOWERS AT BJC SINCE IT IS CLOSER TO
THE FOOTHILLS AND MOUNTAINS. SOUTHEASTERLY WINDS WILL PREVAIL THIS
AFTERNOON AND A DENVER CYCLONE IS EXPECTED TO FORM. MODELS SHOW
THE CYCLONE TRACKING NORTH OF DEN AND APA, WHICH WOULD CAUSE
SOUTHEAST WINDS TO SHIFT TO THE SOUTHWEST THIS EVENING. CROSS
SECTIONS SHOW A GOOD AMOUNT OF MID AND HIGH CLOUD COVER FOR
TONIGHT AND WEDNESDAY WITH CEILINGS EXPECTED TO STAY ABOVE 6000
FEET. MODELS DO NOT SHOW THIS, BUT IF THE DENVER CYCLONE TRACKS
FARTHER SOUTH THAN EXPECTED, NORTHERLY WINDS COULD PULL IN ENOUGH
LOW-LEVEL MOISTURE FOR LOW CLOUDS TOWARDS 12Z WEDNESDAY. A STORM
SYSTEM MOVING OUT OF THE DESERT SOUTHWEST WILL BRING SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS TO THE CENTRAL ROCKIES
WEDNESDAY AFTERNOON, BUT THE BEST CHANCE FOR SHOWERS AND
THUNDERSTORMS IN THE DENVER AREA IS EXPECTED TO BE AFTER 00Z
THURSDAY.
BOU WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...AA
AVIATION...BM
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