075
FXUS65 KCYS 160831
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
231 AM MDT WED SEP 16 2026
KEY MESSAGES
- A WET PATTERN IS EXPECTED THROUGH THE END OF THE WEEK, WITH
ALMOST DAILY CHANCES FOR SHOWERS AND THUNDERSTORMS.
- THERE IS A SLIGHT CHANCE OF EXCESSIVE RAINFALL AND FLOODING
ISSUES THURSDAY AS A STRONGER THAN AVERAGE LATE-SEASON
MONSOON WITH TROPICAL MOISTURE MOVES INTO THE REGION.
SHORT TERM /THROUGH THURSDAY NIGHT/
ISSUED AT 230 AM MDT WED SEP 16 2026
FAIRLY ACTIVE THIS WEEK, INCLUDING THE SHORT TERM AND MEDIUM
RANGE FORECAST PERIODS. ALL MODELS CONTINUE TO SHOW SOUTHWEST
FLOW ALOFT THROUGH THE END OF THE WEEK WITH AN ABNORMALLY STRONG
MONSOON PUSH, FOR MID TO LATE SEPTEMBER, AS WE HEAD INTO
THURSDAY AND THURSDAY NIGHT. WILL HAVE TO CLOSELY MONITOR
EXCESSIVE RAINFALL POTENTIAL WITH ALL MODELS SHOWING PWATS NEAR
ALL-TIME MAXES FOR MID TO LATE SEPTEMBER.
FOR TODAY, SURFACE ANALYSIS AND MODEL ANALYSIS SHOWS A WEAK
LOW PRESSURE SYSTEM ACROSS SOUTH CENTRAL WYOMING EARLY THIS
MORNING. THIS FRONTAL SYSTEM IS EXPECTED TO LIFT NORTHEAST, WITH
A NOTABLE WARM FRONT LIFTING ACROSS THE EASTERN PLAINS BY THIS
AFTERNOON. EXPECT WINDS TO SHIFT INTO THE SOUTH AND SOUTHWEST
THROUGH THE AFTERNOON HOURS WITH LOW TO MIDLEVEL WARM AIR
ADVECTION AND GRADUAL MOISTURE ADVECTION. WIDELY SCATTERED RAIN
SHOWERS EARLY THIS MORNING ARE FORECAST TO LIFT NORTHEAST WITH A
BRIEF BREAK IN PRECIPITATION UNTIL AROUND SUNRISE. SURFACE COLD
FRONT BEHIND THE WEAK LOW PRESSURE SYSTEM IS THEN FORECAST TO
DIVE SOUTH ACROSS WYOMING, WITH SHOWERS AND THUNDERSTORMS
REDEVELOPING FROM WEST (WEST OF I-25) TO EAST (HIGH PLAINS) FROM
LATE MORNING THROUGH THIS AFTERNOON. ALTHOUGH LOW TO MIDLEVEL
MOISTURE WILL ONLY START TO INCREASE TODAY, PWAT VALUES WILL
STILL BE ABOVE THE 90TH PERCENTILE FOR MOST OF THE FORECAST
AREA. WILL HAVE TO WATCH FOR HEAVY RAINFALL AS THIS FRONT MOVES
SOUTH...WITH POSSIBLE TRAINING OF THUNDERSTORM ACTIVITY ALONG
AND NEAR THE I-80 CORRIDOR. HOWEVER, FORCING DOESN'T APPEAR TO
BE CONTINUOUS AND THE FRONT MOVES SOUTH RELATIVELY QUICK LATE
THIS AFTERNOON AND THE EVENING HOURS.
AGAIN, WILL HAVE TO MONITOR THURSDAY AND THURSDAY NIGHT FOR
EXCESSIVE RAINFALL AND VERY HEAVY PERSISTENT RAIN AS CURRENT
MODEL ANALYSIS SHOWS A STALLED FRONTAL BOUNDARY NEAR THE I-25
CORRIDOR, PLENTY OF MIDLEVEL FORCING AS A SERIES OF VORT MAXES/SHORT
WAVES LIFT NORTHEAST VERY SLOWLY, AND OF PARTICULAR NOTE...TROPICAL
MOISTURE LIFTING NORTH FROM A TROPICAL DISTURBANCE NEAR BAJA
CALIFORNIA. NAEFS SHOWS PWAT VALUES AT ALL TIME MAXIMUMS ACROSS
MOST OF THE FORECAST AREA FOR MID TO LATE SEPTEMBER AS PWATS
CLIMB TO 1.25 TO 1.50 INCHES...INCLUDING CARBON AND ALBANY
COUNTIES. ALTHOUGH SEVERAL HIGH RES MODELS ARE NOT SHOWING
ANYTHING PARTICULARLY IMPRESSIVE, WOULD LIKE TO NOTE SEVERAL
LOCATIONS ACROSS THE HIGH VALLEYS AND HIGH PLAINS SHOW THE 75TH
TO 90TH PERCENTILE QPF BETWEEN 1.5 TO 2.5 INCHES ON THE HREF
WITH CAPE BETWEEN 600 TO 1200 J/KG OVER A PRETTY LARGE AREA WITH
THE BULLSEYE NEAR CHEYENNE. WPC HAS ADDED A SLIGHT RISK OF
EXCESSIVE RAIN FOR ALL THE HIGH PLAINS THURSDAY. WANT TO GIVE
THIS EVENT ANOTHER MODEL RUN OR TWO BEFORE DECIDING ON A FLOOD
WATCH. ALSO, NOT TERRIBLY IMPRESSED WITH THE LACK OF UPPER LEVEL
FORCING WITH THIS EVENT SINCE WE WOULD LIKE TO SEE MORE JET
DYNAMICS ALOFT, BUT EVERYTHING ELSE LOOKS GOOD, BUT WITH LIMITED
CONFIDENCE ON TIMING.
OTHERWISE, BRIEF WARMING TREND STILL EXPECTED TODAY (WEDNESDAY)
AS THE FRONTAL SYSTEM LIFTS NORTHEAST WITH HIGHS BACK INTO THE
UPPER 70S TO MID 80S. COOL ONCE AGAIN ON THURSDAY. KEPT HIGH
TEMPERATURES IN THE 60S TO MID 70S, BUT MAY NEED TO LOWER THEM
EVEN MORE DEPENDING ON PERSISTENT THE RAINFALL IS THROUGH THE
DAY.
LONG TERM /FRIDAY THROUGH TUESDAY/
ISSUED AT 215 PM MDT TUE SEP 15 2026
ON FRIDAY, MID-LEVEL FLOW SHIFTS TO MORE WSW, WHICH WILL BEGIN TO
SHUT OFF OUR SOURCE FOR MONSOONAL MOISTURE. WITH SOME REMAINING
MOISTURE TRAPPED UNDERNEATH THE RIDGE (I.E. PWAT STILL RANGING FROM
THE 90TH TO 95TH PERCENTILE) COMBINED WITH ANOTHER SUBTLE
SHORTWAVE TROUGH THAT SKIRTS ACROSS WYOMING AND NEBRASKA FRIDAY
EVENING, CANNOT RULE OUT ANOTHER ROUND OF SHOWERS AND STORMS ON
FRIDAY AFTERNOON AND EVENING. ALTHOUGH LREF GUIDANCE HAS MEDIAN
SURFACE DEWPOINTS IN THE MID TO UPPER 50S ACROSS THE PANHANDLE,
DEEP-LAYER SHEAR IS ONLY FORECAST TO BE 20-25 KNOTS, WHICH
SHOULD MINIMIZED THE THREAT OF ANY ORGANIZED SEVERE WEATHER. AT
THIS TIME, HYDROLOGICAL IMPACTS/LOCALIZED FLASH FLOODING WILL BE
THE PRIMARY CONCERN, HENCE WPC PLACING OUR REGION IN ANOTHER
MARGINAL RISK FOR EXCESSIVE RAINFALL ON FRIDAY. COVERAGE IS
EXPECTED TO BE MORE SCATTERED AND LOWER IN COVERAGE RELATIVE TO
THURSDAY, SO WITH LESS CLOUD COVER WE CAN ALSO EXPECT HIGHS
CLOSER TO 80 DEGREES EAST OF THE I-25 CORRIDOR, WITH LOW TO MID
70S TO THE WEST.
ON SATURDAY, ANOTHER WEAK OPEN WAVE WILL TRANSLATE ACROSS SE WYOMING
AND W NEBRASKA. WITH PWAT STILL WITHIN THE 60-70TH PERCENTILE,
PRIMARILY ALONG THE I-80 CORRIDOR, CAN STILL EXPECT A FEW
SHOWERS AND THUNDERSTORMS LATER IN THE DAY, BUT NOTHING APPEARS
TO BE WIDESPREAD AT THIS TIME. LREF GUIDANCE ONLY SHOWS US AT A
20- 40% CHANCE OF RECEIVING MEASURABLE RAINFALL DURING THIS
PERIOD, SO NOT EXACTLY ENTHUSIASTIC THAT WE WILL SEE MUCH OF ANY
PRECIPITATION THAT WE ARE DESPERATELY IN NEED OF. TEMPERATURES
ON SATURDAY WILL BE SLIGHTLY COOLER IN THE 70S ACROSS THE
NEBRASKA PANHANDLE, AND MID TO UPPER 60S FOR SOUTHEASTERN
WYOMING.
A SHORTWAVE RIDGE BEGINS TO BUILD IN TO OUR WEST ON SUNDAY, PLACING
US IN MORE OF A NW FLOW PATTERN. NOT ONLY WILL THIS DECREASE OUR
OVERALL MOISTURE, BUT WITH THE PASSAGE OF A WEAK FRONT SOMETIME
DURING THE DAY, WE CAN EXPECT A SLIGHT COOLING TREND INTO EARLY NEXT
WEEK. AN OPEN WAVE WILL REMAIN SITUATED TO OUR SOUTH AND WEST OVER
CALIFORNIA INTO EARLY NEXT WEEK WHICH WILL EVENTUALLY BECOME CUT OFF
FROM THE POLAR JET TO OUR NORTH, PLACING US IN MORE ZONAL FLOW. THIS
WILL TRANSLATE TO A DRY PATTERN WITH HIGH TEMPERATURES SITTING RIGHT
AROUND CLIMATOLOGY (HIGH TEMPERATURES IN CHEYENNE AVERAGE IN THE LOW
TO MID-70S NEXT WEEK). IT'S TOO FAR OUT TO DISCUSS SPECIFICS AT THIS
RANGE, BUT ENSEMBLE GUIDANCE SUGGESTS ANOTHER LONGWAVE RIDGE
BUILDING ACROSS THE ROCKY MOUNTAIN WEST AND NORTHERN GREAT PLAINS
TOWARDS THE MIDDLE OF NEXT WEEK, WHICH WOULD BRING A WARMING TREND
TO OUR REGION.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1122 PM MDT TUE SEP 15 2026
IN GENERAL, VFR CONDITIONS WILL PREVAIL ACROSS ALL THE
TERMINALS FOR THE DURATION OF THIS TAF PERIOD. EXCEPT KAIA AND
KSNY WHERE LOWER CIGS AND CLOUDS MAY LOWER FLIGHT CATEGORIES
DOWN TO MVFR DURING THE OVERNIGHT HOURS. PRECIPITATION ALONG
WITH CHANCES OF TS MAY IMPACT KRWL AND KLAR AT VARYING TIMES
DURING THIS FORECAST, KEPT VCSH ALONG WITH PROB30 GROUPS IN THE
TAF. GUSTY WINDS, SPEEDS UP TO 25 KNOTS, ARE POSSIBLE AT KCDR,
KSNY, AND KAIA BY 15Z WEDNESDAY. PRECIPITATION CHANCES WILL
SPREAD EAST AND NORTH JUST OUTSIDE OF THIS FORECAST PERIOD.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...TJT
LONG TERM...NB
AVIATION...RZ
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