386
FXUS65 KCYS 151146
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
545 AM MDT FRI MAY 15 2026
KEY MESSAGES
- RED FLAG WARNINGS CONTINUE FOR THE NEBRASKA PANHANDLE THROUGH
7 PM FRIDAY EVENING.
- NEXT CHANCE FOR PRECIPITATION RETURNS DURING THE WEEKEND
ALONGSIDE COOLER CONDITIONS. SEVERE WEATHER WILL BE POSSIBLE
BOTH SATURDAY AND SUNDAY.
- THERE IS A MARGINAL RISK (LEVEL 1 OF 5) FOR SEVERE WEATHER
SATURDAY WITH A SLIGHT RISK (LEVEL 2 OF 5) FOR SEVERE WEATHER
ON SUNDAY.
- A POTENTIAL LATE SEASON SNOWFALL EVENT IS TAKING SHAPE TO
START THE WORK WEEK. COLDER THAN NORMAL TEMPERATURES MAY
LINGER INTO THE MIDDLE OF THE WEEK.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED AT 204 AM MDT FRI MAY 15 2026
ANOTHER WARM AND DRY DAY IS IN STORE FOR SOUTHEAST WYOMING AND
WESTERN NEBRASKA AS AFTERNOON TEMPERATURES WARM INTO THE LOW-70S TO
MID-80S AND HUMIDITY VALUES DROP INTO THE SINGLE DIGITS ONCE AGAIN.
LARGELY ZONAL FLOW ALOFT WILL KEEP PRECIPITATION CHANCES AT BAY,
WHILE WESTERLY 700MB FLOW INCREASES DOWNSLOPE WARMING AND DRYING
ALONG AND EAST OF THE LARAMIE RANGE. A SUBTLE INCREASE IN 700MB
WINDS THROUGH THE AFTERNOON HOURS WILL ENABLE BREEZY CONDITIONS NEAR
THE SURFACE, LEADING TO FAVORABLE CONDITIONS FOR RAPID FIRE STARTS
AND SPREAD. RED FLAG WARNINGS REMAIN IN EFFECT THROUGH 7 PM THIS
EVENING DUE TO THE DRY, CRISPY, AND BREEZY CONDITIONS ANTICIPATED
ACROSS THE REGION. CLEAR SKIES TURN CLOUDY THIS EVENING AS A SUBTLE,
700MB SHORTWAVE PUSHES ACROSS THE REGION. NO PRECIPITATION IS
EXPECTED TODAY.
ACTIVE WEATHER IS PROGGED TO RETURN FOR SATURDAY AND SUNDAY AS THE
NEXT UPPER-LEVEL SYSTEM STARTS TO PUSH TOWARDS THE INTERMOUNTAIN
WEST. SATURDAY AFTERNOON AND EVENING, MUCH OF THE CWA WILL BE PLACED
BROADLY WITHIN THE RIGHT ENTRANCE REGION OF THE UPPER-LEVEL JET,
FAVORING CONTINUED SYNOPTIC ASCENT AND FAVORABLE DYNAMICS ACROSS THE
REGION. MULTIPLE LOBES OF 500MB VORTICITY WILL EJECT OUT AHEAD OF
THE INCOMING TROUGH, FURTHER AIDING IN THE OVERALL SYNOPTIC ASCENT
EXPECTED. FURTHER DOWN AT 700MB, THE ASSOCIATED LOW WILL SLOWLY WRAP
UP THROUGHOUT THE AFTERNOON AND EVENING HOURS, LEADING TO STOUT,
SOUTHERLY TO SOUTHWESTERLY FLOW FOR MOST LOCATIONS EAST OF THE
LARAMIE RANGE. MODEST WARM AIR ADVECTION KICKS UP AFTER NOON, ALLOW
ADDITIONAL UPWARD LIFT TO AID THE SYSTEM AS A WHOLE. THE SURFACE LOW
BEGINS TO DEVELOP SATURDAY AFTERNOON OVER NORTHEAST WYOMING,
INDUCING MOIST, SOUTHEASTERLY FLOW AT THE SURFACE, ESPECIALLY ACROSS
WESTERN NEBRASKA. A MODEST WARM FRONT WILL MOVE NORTHWARD, KEEPING
THE STRONG SOUTHEASTERLY FUNNELING INTO THE SURFACE LOW. WITH THE
WARM FRONT IN AND AROUND THE REGION, AMPLE SURFACE FORCING IS
EXPECTED, ESPECIALLY WITH THE BROADER LIFT TYPICALLY FOUND WITHIN
THE WARM SECTOR OF A MIDLATITUDE CYCLONE. WITH STRONG SOUTHEASTERLY
FLOW, DEWPOINTS WILL SURGE INTO THE MID-40S TO LOW-50S ACROSS
WESTERN NEBRASKA, WITH FAR SOUTHEASTERN WYOMING INCREASING INTO THE
MID-40S. AMPLE CLEARING IS EXPECTED OUT AHEAD OF THE SLOWLY
ADVANCING WARM FRONT, LEADING TO A PROLONGED PERIOD OF
DESTABILIZATION AFTER SUNRISE SATURDAY MORNING. HIRES MODEL GUIDANCE
SUGGESTS 800 TO 1000 J/KG OF MLCAPE WITH FORECAST RAP SOUNDINGS
SUGGESTING AMPLE EFFECTIVE BULK SHEAR, LOW-LEVEL TURNING, AND
MINIMAL CAPING AFTER ABOUT 20Z. HOWEVER, THE LOWER-LEVELS LOOK TO
REMAIN FAIRLY DRY, INCREASING CONCERNS FOR DOWNBURST POTENTIAL.
DCAPE VALUES ARE AROUND 1200 J/KG ACROSS WESTERN NEBRASKA, FURTHER
INCREASING CONCERN FOR A DAMAGING WIND POTENTIAL ON SATURDAY
AFTERNOON. ISOLATED SUPERCELL THUNDERSTORMS LOOK POSSIBLE ON
SATURDAY, BUT MAY GROW UPWARDS INTO A LINE FAIRLY QUICKLY DUE TO
NEARLY PARALLEL BULK SHEAR VECTORS TO THE EXPECTED WARM FRONT. BASED
ON THIS INFORMATION, DISCRETE SUPERCELLS COULD DEVELOP SATURDAY
AFTERNOON, BUT WILL LIKELY GROW UPSCALE INTO A LINE A FEW HOURS
AFTER DEVELOPMENT. FORECAST SOUNDINGS SUGGEST A POTENTIAL FOR LARGE
HAIL, DAMAGING WIND GUSTS, AND AN ISOLATED TORNADO CANNOT BE RULED
OUT DUE TO LOW-LEVEL TURNING IN THE ATMOSPHERE. THE STORM PREDICTION
CENTER HAS HIGHLIGHTED MUCH OF THE AREA IN A MARGINAL RISK (LEVEL 1
OF 5), WITH PORTIONS OF WESTERN NEBRASKA UNDER A SLIGHT RISK (LEVEL
2 OF 5) FOR SEVERE WEATHER SATURDAY AFTERNOON. THE MAIN LIMITING
FACTOR FOR SATURDAY'S SEVERE THREAT WILL BE THE OVERALL WEAKER
FORCING ASSOCIATED WITH A WARM SECTOR AND THE POTENTIAL FOR STRONG
CAPING UNTIL AFTER 18Z OR SO.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED AT 204 AM MDT FRI MAY 15 2026
ACTIVE IN THE LONG RANGE, WITH MODELS COMING INTO BETTER AGREEMENT
WITH A POTENTIAL LATE SEASON SNOW EVENT FOR MOST OF SOUTHEAST
WYOMING AND POSSIBLY THE HIGHER ELEVATIONS OF WESTERN NEBRASKA.
HOWEVER, CONSIDERABLE UNCERTAINTY EXISTS REGARDING A POTENTIAL
SEVERE WEATHER EVENT FOR THE HIGH PLAINS SUNDAY AFTERNOON AND TRAVEL
IMPACTS ON MONDAY.
AT THE END OF THE WEEKEND, MODELS SHOW A DOUBLE-BARREL UPPER LEVEL
LOW PRESSURE SYSTEM OVER MONTANA, IDAHO, AND NORTHERN UTAH. THE
EVOLUTION OF THIS SYSTEM WILL BE KEY IN DETERMINING WHICH END OF THE
SPECTRUM OUR SENSIBLE WEATHER WILL BE. IF THE SOUTHERN UPPER LEVEL
LOW/TROUGH DIGS FURTHER SOUTH AND IS LESS PROGRESSIVE, SOUTHEAST
WYOMING MAY SEE A LATE SEASON SNOW STORM.
IF THE SOUTHERN UPPER LEVEL TROUGH/LOW IS MORE PROGRESSIVE AND
FURTHER NORTH, LESS PRECIPITATION IS EXPECTED, BUT IN THE FORM OF
MAINLY RAIN. FOR 00Z, ALL DETERMINISTIC MODELS SHOW THE LESS
PROGRESSIVE/FURTHER SOUTH SOLUTION OF THE SOUTHERN LOW AS IT DIGS
SOUTH NEAR THE FOUR CORNERS REGION LATE SUNDAY. THE FIRST OF A
SERIES OF COLD FRONTS WILL PUSH ACROSS WYOMING AND EVENTUALLY THE
HIGH PLAINS MIDDAY SUNDAY. WILL HAVE TO MONITOR THIS AREA CLOSELY
FOR SEVERE THUNDERSTORMS OVER THE NEXT FEW DAYS. AT THIS TIME, IT
LOOKS LIKE THE FRONT WILL MOVE THROUGH THE AREA A LITTLE TOO QUICK
FOR MUCH OF A SEVERE THREAT. IN ADDITION, LOW CLOUDS AND A STRONG
CAP INVERSION ARE PRESENT ON BOTH THE GFS AND NAM SOUNDINGS EAST OF
INTERSTATE 25 FOR MOST OF THE DAY. THEREFORE, PRETTY LOW CONFIDENCE
IN THIS EVENT SO FAR (~10%), BUT WILL CONTINUE TO KEEP AN EYE ON IT
AS WE HEAD INTO THE WEEKEND. KEPT SEVERE THUNDERSTORM WORDING FOR
MAINLY JUST THE SOUTHERN NEBRASKA PANHANDLE FOR NOW.
THINGS GET INTERESTING SUNDAY NIGHT AND MONDAY WITH CYCLOGENESIS
OVER THE CENTRAL AND SOUTHERN PLAINS AND AN INTENSE POLAR SURFACE
HIGH BEHIND THE MAIN COLD FRONT. MODELS SHOW A STRONG SURFACE
PRESSURE GRADIENT WITH UPSLOPE NORTH TO NORTHEAST WINDS, PLENTIFUL
MOISTURE, AND DECENT LIFT/DYNAMICS. FORCING WILL BE MAINLY BE FROM
LOW LEVEL UPSLOPE FLOW/CONVERGENCE AND UPPER LEVEL JET DYNAMICS, BUT
THERE IS SOME HINTS OF INSTABILITY AS WELL WITH A PERIOD OF AMPLE
FRONTOGENESIS SUNDAY NIGHT INTO EARLY MONDAY. WILL NEED TO WATCH
THIS EVOLUTION CLOSELY WITH ALL MODELS SHOWING AROUND AN INCH OF
QPF. ENSEMBLE MEANS ARE EVEN HIGHER, CLOSER TO 1.5 INCHES OF
QPF...ESPECIALLY ALONG THE I-80 CORRIDOR AND OVER TOWARDS WESTERN
NEBRASKA. ALL MODELS SHOW 700MB TEMPERATURES PLUMMETING BELOW -5C
AND CLOSE TO -10C BY NOON MONDAY. THIS PLACES THE SNOWLEVEL AROUND
5000 FEET, WITH SOME SNOW FLAKES DOWN TO ELEVATIONS AS LOW AS 4500
FEET. OF COURSE, LOTS OF UNCERTAINTY WITH A SYSTEM LIKE THIS IN THE
MIDDLE OF MAY, SIMILAR TO THE HEAVY SNOW EVENT ON MAY 5TH, WHERE THE
GRASSY AND ELEVATED SURFACES SAW DECENT SNOW ACCUMULATIONS BUT
LITTLE ACCUMULATED ON THE PAVEMENT. FOR THIS FORECAST, WILL TREND
TOWARDS CLIMATOLOGY AND PRIOR MAY LATE-SEASON SNOW EVENTS.
EXPECT MOST OF THE ACCUMULATION BELOW 8000 FEET TO REMAIN ON
GRASSY/ELEVATED SURFACES. HOWEVER, IF MODELS START SHOWING THE
SNOWFALL OCCURRING MORE IN THE NIGHTTIME HOURS, MAY NEED TO
REEVALUATE AND ADJUST.
IN ADDITION, TEMPERATURES WILL BE QUITE COLD WITH HIGHS ON MONDAY
STRUGGLING TO REACH 40 DEGREES. WHEN/IF WIDESPREAD PRECIPITATION IS
FALLING, THESE HIGHS MAY BE OPTIMISTIC. LOW TEMPERATURES MONDAY
NIGHT AND EARLY TUESDAY MORNING MAY BE DOWN RIGHT FRIGID FOR THIS
TIME OF THE YEAR, ESPECIALLY IF WE MAINTAIN A SNOW PACK WITH
CLEARING SKIES OVERNIGHT. AT THIS TIME, THE BASE NBM HAS LOWS IN THE
UPPER TEENS TO UPPER 20S ACROSS MOST OF THE AREA. NBM 10TH
PERCENTILE AND GRAND ENSEMBLE 10TH TO 25TH PERCENTILE ARE WELL INTO
THE TEENS TO LOW 20S ACROSS THE REGION, EVEN WESTERN NEBRASKA. THESE
LOWS MAY SHATTER SOME LONG STANDING LOW TEMPERATURES FOR MID-LATE
MAY (1910S TO 1960S). FOR THE REST OF NEXT WEEK, ALL MODELS AND
ENSEMBLES SHOW A SLOW WARMING TREND AS THE STORM SYSTEM LIFTS
NORTHEAST INTO THE GREAT LAKES REGION. LONG WAVE UPPER LEVEL TROUGH
WILL REMAIN OVER MOST OF THE WESTERN US, BUT WEAKEN OVER TIME AS A
SHORTWAVE RIDGE AXIS MOVES INTO THE WEST COAST. NORTHWEST FLOW WILL
CONTINUE OVER WYOMING, WITH 700MB TEMPERATURES MAYBE CLIMBING ABOVE
0C BY WEDNESDAY NIGHT. CLOUDY AND COOL CONDITIONS ARE EXPECTED WITH
SEVERAL EMBEDDED SHORTWAVE/VORT MAXES MEANDERING ACROSS THE AREA,
RESULTING IN SHOWERS AND POSSIBLY SOME THUNDERSTORMS EACH DAY.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 545 AM MDT FRI MAY 15 2026
DRY WESTERLY FLOW WILL CONTINUE OVER THE NEXT 24 HOURS WITH SOME
MIDLEVEL CLOUDINESS DEVELOPING LATER IN THE DAY. TYPICAL DIURNAL
WINDS ARE EXPECTED WITH GUSTY WEST TO NORTHWEST WINDS BETWEEN 15Z
FRIDAY TO 02Z SATURDAY.
HAZARDS/WEATHER TRENDS: VFR WILL CONTINUE INTO EARLY SATURDAY
MORNING WITH SOME SCT-BKN MIDLEVEL CLOUDINESS AT ALL TERMINALS LATE
IN THE AFTERNOON. WESTERLY WINDS WILL OCCASIONALLY GUST UP TO 35
KNOTS AT KRWL AND KLAR AFTER 15Z, WITH GUSTS UP TO 25 KNOTS
ELSEWHERE.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...RED FLAG WARNING UNTIL 7 PM MDT THIS EVENING FOR NEZ434>437.
SHORT TERM...AM
LONG TERM...TJT
AVIATION...TJT
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page