700
FXUS65 KCYS 152333
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
533 PM MDT MON SEP 15 2025
KEY MESSAGES
- ISOLATED SHOWERS AND THUNDERSTORMS THROUGH MONDAY EVENING WILL
HAVE THE POTENTIAL TO PRODUCE LOCALLY STRONG WIND GUSTS.
- ANOTHER COLD FRONT AND POTENT PACIFIC SYSTEM WILL PUSH ACROSS
WYOMING TUESDAY AND WEDNESDAY, RESULTING IN COOLER
TEMPERATURES, THUNDERSTORMS, AND MORE WIDESPREAD RAINFALL
THROUGH THE END OF THE WEEK.
- SLIGHT WARMING TREND POSSIBLE FOR NEXT WEEKEND.
SHORT TERM /THROUGH TUESDAY NIGHT/
ISSUED AT 245 PM MDT MON SEP 15 2025
TODAY IS A BRIEF INTERLUDE BETWEEN UPPER LEVEL STORM SYSTEMS, BUT
THE NEXT SYSTEM IS ALREADY MOVING INTO NORTHWEST WYOMING. THE
TRANSIENT RIDGE IN BETWEEN STORM SYSTEM HAS HELPED BOOST
TEMPERATURES ABOVE NORMAL THIS AFTERNOON, WITH WIDESPREAD UPPER 70S
TO 80S ACROSS THE AREA. THE LOWER ATMOSPHERE IS FAIRLY DRY WITH
DEWPOINTS SITTING IN THE 30S TO MID 40S FOR MOST AREAS. GOES WATER
VAPOR CHANNEL IMAGERY SHOWS A COMPACT UPPER LEVEL CIRCULATION NOW
MOVING INTO NORTHWEST WYOMING WHICH HAS ALREADY BEGUN TO IMPROVE MID
TO UPPER LEVEL MOISTURE ON TOP OF THE DRY BOUNDARY LAYER. CURRENT
MESOANALYSIS SHOWS FAIRLY LIMITED INSTABILITY OVER THE AREA, AS
MLCAPE SITS AROUND 250 J/KG. SHEAR IS ALSO WEAK CURRENTLY, BUT
STRONGER WINDS ALOFT ARE NOW POSITIONED OVER CENTRAL WYOMING AND ARE
EXPECTED TO SHIFT EASTWARD OVER THE NEXT SEVERAL HOURS. THE BEST
ENVIRONMENT FOR THUNDERSTORMS IS EXPECTED TO END UP ROUGHLY ALONG
AND NORTH OF A CHADRON TO RAWLINS LINE, WHICH COINCIDES WITH THE
MARGINAL RISK FROM SPC FOR TODAY. THE MAIN HAZARD IS STRONG GUSTY
WINDS DUE TO DRY MICROBURSTS IN THE INVERTED-V SOUNDINGS PRESENT
TODAY, BUT ISOLATED HAIL CANNOT BE RULED OUT. A SECONDARY AREA OF
FOCUS IS LOCATED IN A REGION OF LOW-LEVEL CONVERGENCE IN FAR EASTERN
WYOMING AND INTO WESTERN NEBRASKA. THIS AREA HAS PRODUCED MOST OF
THE RADAR ECHOES OBSERVED SO FAR. THIS SHOULD BE MORE ISOLATED THAN
THE EXPECTED STORMS MOVING INTO OUR NORTHERN AND WESTERN ZONES, BUT
AN ISOLATED SEVERE WIND GUST CANNOT BE RULED OUT.
WHILE TODAY'S UPPER LEVEL LOW HAS BEEN MOVING VERY QUICKLY SO FAR,
IT IS EXPECTED TO SLOW DOWN DRAMATICALLY TONIGHT AND MEANDER OVER
THE AREA FOR THE NEXT SEVERAL DAYS. OVERNIGHT, FAIRLY PERSISTENT
MOIST ISENTROPIC LIFT WILL BE PRESENT OVER MUCH OF THE AREA,
KEEPING WIDELY SCATTERED SHOWERS ON THE RADAR FOR MOST OF THE
NIGHT INTO TUESDAY MORNING. A LITTLE BIT OF ELEVATED INSTABILITY
WILL BE LINGERING, SO WE MAY SEE A FEW RUMBLES OF THUNDER
THROUGHOUT THE NIGHT. EXPECT A DISORGANIZED SURFACE PRESSURE
FIELD TO RESULT IN VARIABLE WINDS FOR MUCH OF THE HIGH PLAINS,
BUT A SURFACE COLD FRONT WILL SLOWLY MOVE SOUTHWARD TUESDAY
MORNING. WHILE IT WON'T BE RACING, THE PRESSURE GRADIENT ALONG
THIS BOUNDARY LOOKS TO BE FAIRLY STRONG, SO WE MAY SEE A PERIOD
OF GUSTY NORTH WINDS AS IT MOVES THROUGH. THIS WILL BRING COOLER
TEMPERATURES AND HIGHER LOW-LEVEL MOISTURE IN FOR TUESDAY.
TUESDAY WILL BE A DYNAMIC DAY ACROSS THE AREA. HIGHER SURFACE
MOISTURE WILL LEAD TO MORE IMPRESSIVE INSTABILITY. WITH THE UPPER
LEVEL LOW LIKELY SITTING OVER NORTHERN WYOMING, WE WILL STILL HAVE
DECENT SOUTHWEST FLOW ALOFT OVER THE AREA, SUPPORTING ABOUT 30 TO 40
KNOTS OF VERTICAL WIND SHEAR IN THE 0 TO 6 KM LAYER (BUT WIND
PROFILES ARE QUITE DISORGANIZED WITH NORTHERLY WINDS AT THE SURFACE
UNDER SSE WINDS IN THE LOWER FREE TROPOSPHERE AND SOUTHWEST
WINDS HIGHER UP). FORCING VIA ISENTROPIC LIFT IS EXPECTED TO
CONTINUE INTO THE DAYTIME HOURS ON TUESDAY, WHICH SHOULD LEAD TO
AN EARLY START TO THE DAY'S SHOWER AND THUNDERSTORM ACTIVITY.
STRONG THUNDERSTORMS COULD BE POSSIBLE AS EARLY AS 10-11AM. THIS
FIRST ROUND IS EXPECTED TO DEVELOP ALONG THE STALLED FRONTAL
BOUNDARY, WHICH SHOULD BE LOCATED ROUGHLY FROM KIMBALL TO
ALLIANCE. THE INITIAL ROUND SHOULD DEPART BY AROUND 3PM OR SO AS
THE FRONTAL FORCING SKIRTS OFF TO THE EAST. THEN, ATTENTION
SHIFTS WEST TO A DEVELOPING SECOND ROUND OVER WYOMING. THIS
ROUND WILL BE FORCED BY ANOTHER AREA OF FAIRLY STRONG ISENTROPIC
LIFT / OVERRUNNING OVER THE STALLED FRONTAL BOUNDARY ALONG WITH
VORTICITY ADVECTION ALOFT AS THE SLOW MOVING UPPER LEVEL LOW
DRIFTS EAST. THE CIRCULATION CENTER IS EXPECTED TO MOVE MORE OR
LESS DIRECTLY OVER THE AREA TUESDAY NIGHT INTO EARLY WEDNESDAY,
WHICH RESULTS IN A FAIRLY LOW CONFIDENCE PRECIPITATION FORECAST.
WITH STRONG FORCING AND SUFFICIENT INSTABILITY AND VERTICAL
WIND SHEAR, EXPECT THE SECOND ROUND TO BE CHARACTERIZED BY
WIDESPREAD SHOWERS WITH SCATTERED EMBEDDED THUNDERSTORMS AND THE
POTENTIAL FOR A FEW ISOLATED STRONG STORMS. THE EXPECTED HIGH
COVERAGE OF STORMS WILL LIKELY LIMIT THE SEVERE WEATHER
POTENTIAL, BUT WE CAN'T RULE OUT SOME LOCALLY HEAVY RAINFALL,
HAIL, AND STRONG WIND GUSTS. DISORGANIZED SHOWERS WITH SOME
EMBEDDED THUNDER WILL CONTINUE THROUGH THE OVERNIGHT HOURS AS
THE UPPER LEVEL LOW MOVES ACROSS THE AREA. BY DAYBREAK
WEDNESDAY, EXPECT THE UPPER LEVEL LOW TO HAVE SET UP SOMEWHERE
IN WESTERN NEBRASKA WITH MOISTURE WRAPPING AROUND THE BACKSIDE
INTO OUR AREA. MODELS ARE COMING INTO A LITTLE BETTER AGREEMENT
SHOWING A MODEST TROWAL DEVELOPING BY WEDNESDAY AM,
TRANSITIONING PRECIPITATION TO STRATIFORM RAINFALL.
LONG TERM /WEDNESDAY THROUGH MONDAY/
ISSUED AT 245 PM MDT MON SEP 15 2025
THE PERSISTENT MID AND UPPER-LEVEL LOW PRESSURE SYSTEM WILL
REMAIN IN PLACE CENTERED OVER FAR EASTERN WYOMING ON WEDNESDAY.
WITH THIS SYSTEM PRESENT, THERE IS HIGH CONFIDENCE (90% OR
HIGHER) OF BELOW- AVERAGE TEMPERATURES CONTINUING ON WEDNESDAY
THROUGH THURSDAY. COLD AIR ALOFT COMBINED WITH DAYTIME HEATING
WILL RESULT IN LOW-END INSTABILITY WITH SHOWERY WEATHER
CONTINUING ON WEDNESDAY AND THURSDAY AS WELL. HOWEVER, POOR WIND
SHEAR PROFILES AND A LACK OF DEEP SURFACE MOISTURE WILL LIMIT
ANY THUNDERSTORM ACTIVITY TO THE WEAK END OF THE SPECTRUM AND NO
SEVERE WEATHER IS EXPECTED WITH ANY AFTERNOON ACTIVITY ON
EITHER DAY.
ENSEMBLE FORECAST GUIDANCE IS IN GENERALLY GOOD AGREEMENT MOVING
THIS SYSTEM TO THE EAST BY FRIDAY, WITH A SURGE OF DRY NORTHWEST
FLOW COMING IN ALOFT. THERE IS QUITE A BIT OF DISPERSION WITH REGARD
TO A POSSIBLE SHORTWAVE TROUGH SPIRALING AROUND THE DEPARTING UPPER-
LEVEL LOW ON FRIDAY AFTERNOON, WITH SOME ENSEMBLE MEMBERS TRACKING A
WEAK SYSTEM THROUGH THE BLACK HILLS. THIS WOULD POSITION SOUTHEAST
WYOMING AND WESTERN NEBRASKA IN A FAVORABLE LOCATION FOR BROAD-SCALE
SYNOPTIC WIND, POSSIBLY ON THE ORDER OF 30-40 MPH ON FRIDAY
AFTERNOON. WHILE THE CURRENT FORECAST DOES NOT REFLECT THIS HIGHER-
END WIND OPPORTUNITY, IF FAVORABLE GRADIENT FLOW BECOMES MORE
EVIDENT IN ENSEMBLE GUIDANCE THE WIND FORECAST FOR FRIDAY MAY NEED
TO BE INCREASED.
A WARMING TREND IS EXPECTED WITH REGARD TO AFTERNOON HIGH
TEMPERATURES FROM FRIDAY THROUGH THE WEEKEND AS THE GENERAL FLOW
PATTERN SHIFTS TO WEST-SOOUTHWESTERLY. EXPECT A MAINLY DRY DAY ON
SATURDAY WITH ABOVE-NORMAL TEMPERATURES. ENSEMBLE GUIDANCE AND
CLUSTERING BEGINS TO DIVERGE SIGNIFICANTLY BY THE END OF THE WEEKEND
WITH NEARLY EQUAL CHANCES OF WEAK RIDGING AND MODERATE TROUGHING AS
A NEW SYSTEM APPROACHES THE PACIFIC NORTHWEST. SHOWERY WEATHER WOULD
LIKELY RETURN TO THE ROCKIES AND HIGH PLAINS IF THE PACIFIC SYSTEM
TAKES A MORE SOUTHERN TRACK, ALTHOUGH THIS OUTCOME IS ONLY SHOWN BY
AROUND 30-40% OF ENSEMBLE MEMBERS. OVERALL, TEMPERATURES DO STILL
LOOK TO FAVOR ABOVE-AVERAGE TRENDS IN GUIDANCE THROUGH THE END OF
THE WEEKEND INTO EARLY NEXT WEEK.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1130 AM MDT MON SEP 15 2025
THE NEXT STORM SYSTEM IS RAPIDLY MOVING INTO THE AREA THIS
AFTERNOON AND EVENING WITH GUSTY WEST TO SOUTHWEST WINDS
PRECEDING IT. CONSISTENT GUSTS UP TO AROUND 35 MPH ARE EXPECTED
AT WYOMING TERMINALS, AND TO AROUND 25 MPH AT NEBRASKA
TERMINALS.
ISOLATED TO WIDELY SCATTERED SHOWERS AND THUNDERSTORMS WILL
DEVELOP OVER THE NEXT FEW HOURS AND MOVE EASTWARD ACROSS THE
AREA THROUGH THE LATE EVENING HOURS. WITH FAIRLY DRY CONDITIONS
IN THE LOWER ATMOSPHERE, THE PRIMARY HAZARD WITH THIS ACTIVITY
WILL BE GUSTY WINDS IN ADDITION TO LIGHTNING. ISOLATED WIND
GUSTS OF 40 TO 50 KNOTS COULD OCCUR WITH THIS ACTIVITY. THIS IS
MOST LIKELY AROUND KRWL, KCDR, KBFF, AND KAIA, BUT CAN'T BE
RULED OUT ELSEWHERE. LOOK FOR VARIABLE WINDS AND A FEW LINGERING
SHOWERS OVERNIGHT, BEFORE WINDS GAIN A NORTHERLY COMPONENT
TUESDAY MORNING AND CONVECTION GETS AN EARLY START IN THE LATE
MORNING HOURS.
AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/
ISSUED AT 526 PM MDT MON SEP 15 2025
NORTHWEST FLOW ALOFT WILL PREVAIL, WHILE A COLD FRONT MOVES
ACROSS THE TERMINALS TONIGHT.
WYOMING TAFS...SCATTERED TO BROKEN CLOUDS FROM 8000 TO
10000 FEET WILL PREVAIL. SHOWERS WILL BE IN THE VICINITY UNTIL
01Z TO 03Z, AND AGAIN AFTER 12Z TO 16Z TUESDAY. WINDS WILL GUST
TO 25 KNOTS UNTIL 03Z, AND TO 25 KNOTS AT LARAMIE AND CHEYENNE
AFTER 14Z TO 16Z TUESDAY.
NEBRASKA TAFS...SCATTERED TO BROKEN CLOUDS FROM 8000 TO
12000 FEET WILL PREVAIL. THUNDERSTORMS WILL BE IN THE VICINITY
AT SCOTTSBLUFF UNTIL 02Z, WITH SHOWERS IN THE VICINITY AT
CHADRON AND ALLIANCE UNTIL 05Z, AND SHOWERS IN THE VICINITY AT
ALL TERMINALS AFTER 15Z TUESDAY. WINDS WILL REMAIN 13 KNOTS OR
LESS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MN
LONG TERM...MAC
AVIATION...RUBIN
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