264
FXUS65 KCYS 171735
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1135 AM MDT SUN MAY 17 2026
KEY MESSAGES
- SEVERE WEATHER WILL BE POSSIBLE SUNDAY AFTERNOON WITH A
MARGINAL RISK OF STRONG TO SEVERE THUNDERSTORMS ALONG THE
INTERSTATE 80 CORRIDOR.
- ANOTHER ROUND OF ACCUMULATING LATE SEASON SNOW IS
INCREASINGLY LIKELY ON MONDAY, MAINLY ABOVE 5000 FEET IN
ELEVATION.
- NEAR RECORD COLD MONDAY AND MONDAY NIGHT WILL LEAD TO
WIDESPREAD FREEZING TEMPERATURES, WHICH MAY DAMAGE SENSITIVE
VEGETATION AND OUTDOOR IRRIGATION SYSTEMS.
- SLOW WARMING TREND BY THE MID TO LATE WEEK WITH TEMPERATURES
NEAR NORMAL BY THURSDAY AND FRIDAY. CHANCE OF SHOWERS AND A
SLIGHT CHANCE OF THUNDERSTORMS EACH DAY THROUGH FRIDAY
EVENING.
SHORT TERM /THROUGH MONDAY NIGHT/
ISSUED AT 335 AM MDT SUN MAY 17 2026
POTENT STORM SYSTEM APPEARS ON TRACK OVER THE NEXT 48 HOURS, SO
MAINLY MADE SOME TWEAKS TO THE CURRENT FORECAST AND UPGRADED
MOST OF THE WINTER STORM WATCHES. ALSO, ISSUED WINTER WEATHER
ADVISORIES FOR THE NEARBY VALLEYS AND HIGH PLAINS NEAR THE
MOUNTAINS.
TODAY'S STRONG/SEVERE THUNDERSTORM RISK...
FOR THIS MORNING AND TODAY, CURRENT KCYS RADAR LOOP SHOWS SCATTERED
SHOWERS DEVELOPING ACROSS THE MOUNTAINS AND LIFTING NORTHEAST
ACROSS THE AREA. A MIDLEVEL SHORTWAVE/VORT MAX OUT AHEAD OF THE
MAIN STORM SYSTEM IS FORECAST TO LIFT NORTHEAST ACROSS WYOMING
EARLY THIS MORNING. THIS FEATURE MAY BRING INCREASING RAINFALL
RATES FOR A TIME AROUND SUNRISE. CAN'T RULE OUT SOME THUNDER AS
WELL. ALL HIGH RES MODELS SHOW QUIET CONDITIONS FOR A TIME LATER
THIS MORNING AND EARLY THIS AFTERNOON BEFORE A MORE POTENT
SHORTWAVE MOVES EASTWARD ACROSS THE AREA AHEAD OF THE DEVELOPING
STORM SYSTEM TO OUR WEST AS IT DIGS SOUTH INTO NORTHEAST NEVADA
AND UTAH. THIS SHORTWAVE WILL BRING OUR NEXT THREAT OF STRONG
TO POSSIBLY SEVERE THUNDERSTORMS, MAINLY ALONG INTERSTATE 80 AND
SOUTH OF THE NORTH PLATTE RIVER VALLEY THIS AFTERNOON AND THIS
EVENING. SPC CONTINUES WITH THE MARGINAL RISK FOR SEVERE STORMS
AS THE EVENT DOESN'T LOOK NEARLY AS GOOD AS IT DID A FEW DAYS
AGO. THIS IS MAINLY BECAUSE OF A POTENTIAL STRATUS DECK FORMING
THIS MORNING AND REMAINING OVER THE EASTERN PLAINS FOR MUCH OF
THE DAY. WITH A REINFORCING SHOT OF COOLER AIR TODAY/SECONDARY
COLD FRONT, IT MAY BE DIFFICULT TO GET MUCH INSTABILITY GOING
BEFORE THE FORCING FROM THE SHORTWAVE MOVES OVER THE AREA, WITH
HIGH RES MODEL GUIDANCE SHOWING SEVERAL BANDS OF FAST MOVING
SHOWERS AND EMBEDDED THUNDERSTORMS LIFTING NORTHEAST ACROSS THE
AREA. WITH LOWER FREEZING LEVELS TODAY AND PLENTIFUL FORCING,
CAN'T RULE OUT SOME MARGINAL HAIL AND STRONG GUSTY
WINDS...MAINLY NEAR THE COLORADO BORDER.
MUCH NEEDED WIDESPREAD PRECIPITATION AND SOUTHEAST WYOMING
HEAVY SNOWFALL...
THE MAIN EVENT STARTS THIS EVENING AND OVERNIGHT. THIS IS GOING
TO BE A COMPLEX LATE SEASON WINTER STORM WITH THE POSSIBILITY OF
SEVERAL ADDITIONAL WINTER WEATHER HEADLINES ADDED/EXPANDED BY
MONDAY. THERE IS ALSO SOME POTENTIAL OF A BUST (MAINLY OVER
CARBON AND ALBANY COUNTIES) DUE TO THE NATURE OF THE COLD FRONT,
SURFACE LOW, AND HOW THEY INTERACT WITH THE HIGHER TERRAIN.
ALL MODELS CONTINUE TO SHOW THE WESTERN DOUBLE-BARREL LOW
PRESSURE CENTER, CURRENTLY OVER OREGON, DIGGING SOUTHEAST INTO
UTAH AND WESTERN COLORADO TODAY AND TONIGHT. THIS UPPER LEVEL
LOW IS FORECAST TO BECOME DOMINANT BY TONIGHT AS A STRONG COLD
FRONT SLIDES SOUTH AND THEN STALLS NEAR THE COLORADO/WYOMING
BORDER WITH SURFACE CYCLOGENESIS TAKING PLACE OVER NORTHWEST
COLORADO. WITH THESE SYSTEMS, THE STRONGEST LIFT IS USUALLY TO
THE NORTH AND NORTHWEST OF THE SURFACE LOW, WHICH PLACES THIS
AREA OVER CENTRAL WYOMING AND SOUTH CENTRAL WYOMING...INCLUDING
CARBON, ALBANY, AND POSSIBLY PLATTE AND LARAMIE COUNTIES. WITH
STRONG FRONTOGENESIS FOR MORE THAN 6 TO 12 HOURS AND VERY GOOD
CONVERGENCE, DECIDED TO UPGRADE THE WINTER STORM WATCH TO A
WARNING FOR MOST OF THE MOUNTAIN ZONES AND INCLUDED THE LOWER
ELEVATIONS OF NORTHERN AND CENTRAL CARBON COUNTY AND THE
ARLINGTON/ELK MOUNTAIN AREA. ADJACENT ZONES NORTH OF INTERSTATE
80 WILL SEE SNOW, BUT A LATER TRANSITION FROM RAIN TO SNOW, SO
ISSUED WINTER WEATHER ADVISORIES FOR THE SHIRLEY BASIN, CENTRAL
LARAMIE RANGE, SOUTHERN LARAMIE RANGE FOOTHILLS, AND CONVERSE
COUNTY FOR 2 TO 5 INCHES OF SNOW BUT LITTLE ROAD IMPACTS. AREAS
SOUTH OF I-80 AND THE REST OF THE I-25 CORRIDOR FROM WHEATLAND
TO CHEYENNE REMAIN IN THE AREA OF LOWEST CONFIDENCE WITH SNOW
AMOUNTS AND CHANGE OVER TIMES, SO KEPT SOME ACCUMULATION BUT
DIDN'T ISSUE ANY HEADLINES FOR THESE AREAS QUITE YET. THE
LARAMIE VALLEY WILL BE FIGHTING EASTERLY DOWNSLOPE WINDS OFF THE
LARAMIE RANGE DURING MOST OF THIS EVENT, SO KEPT THEM OUT OF
ANY HEADLINE FOR NOW. FURTHER WEST, EXPECT THERE TO BE A VERY
SHARP GRADIENT WITH SNOWFALL RATES SOUTH OF INTERSTATE 80 ACROSS
SOUTH CENTRAL WYOMING. FURTHER EAST, EXPECT A LATER TRANSITION
TIME TO SNOWFALL...WHICH MAY BUMP INTO THE EARLY DAYTIME HOURS
WHERE SNOW MAY STRUGGLE TO ACCUMULATE. FOR THIS TIME OF THE
YEAR, TYPICALLY NEED 1+ INCH/HR SNOWFALL RATES TO OVERCOME THE
WARM PAVEMENT DURING THE DAYTIME. AS OF RIGHT NOW, ONLY SEEING
THIS CRITERIA BEING MET OVER CARBON AND PORTIONS OF ALBANY
COUNTY, HENCE THE WINTER STORM WARNING. THESE CONDITIONS ARE
POSSIBLY FURTHER EAST TOWARDS I-25, BUT NOT NEARLY AS CONFIDENT
AT THIS TIME. ALSO, THE 00Z ECMWF HAVE BACKED OFF ON QPF AMOUNTS
A LITTLE BIT ALONG THE I-25 CORRIDOR AND FURTHER EAST, WHICH IS
ALSO INFLUENCING THIS DECISION. AREAS WELL EAST OF I-25
INCLUDING WESTERN NEBRASKA WILL STILL SEE GOOD PRECIP AMOUNTS
MAINLY IN THE FORM OF RAIN. RAIN SHOULD MIX WITH AND CHANGE OVER
TO SNOW AT TIMES ON MONDAY, BUT ANY SNOWFALL SHOULD MAINLY FALL
DURING THE DAYTIME HOURS. LITTLE IF ANY SNOW IS EXPECTED TO
ACCUMULATE DUE TO THE HIGH MID-MAY SUN ANGLE.
IN ADDITION TO THIS, MODELS HAVE INCREASED EAST TO NORTHEAST
WINDS WITH THE REVERSE PRESSURE GRADIENT ACROSS CARBON AND
WESTERN ALBANY COUNTIES. THIS MAKES SENSE SINCE MODELS HAVE
TRENDED MORE AGGRESSIVE WITH CYCLOGENESIS TO THE SOUTH ACROSS
COLORADO. INCREASED WINDS ALONG INTERSTATE 80 WITH FORECAST
GUSTS UP TO 50 MPH. THIS WILL PRESENT ANOTHER PROBLEM...POSSIBLE
BLIZZARD CONDITIONS. ALTHOUGH LOW CONFIDENCE, SUSTAINED WINDS
OVER 40 MPH WITH GUSTS OVER 50 MPH SHOULD BE ENOUGH TO LOFT THE
WET SNOW FLAKES...AND WITH FALLING SNOW NEAR 1 INCH/HOUR, CAN'T
RULE OUT PERIODS OF VERY LOW VIS AROUND ONE QUARTER MILE.
VERY COLD INTO TUESDAY...
THANKFULLY, THIS STORM SYSTEM WON'T STICK AROUND FOR TOO LONG AS
IT WILL ALREADY BE IN ITS WEAKENING PHASE BY MONDAY AFTERNOON,
AS THE REMNANT OPEN WAVE TROUGH QUICKLY EJECTS EAST OVER THE
AREA. SNOW OR RAIN/SNOW MIX WILL GRADUALLY COME TO AN END MID TO
LATE MONDAY AFTERNOON. WITH THAT SAID, IMPACTS WILL NOT
COMPLETE GO AWAY WITH A REMAINING SNOWPACK LIKELY AND POSSIBLY
SOME CLEARING SKIES. EXPECT RECORD LOW TEMPERATURES OR NEAR-
RECORD LOW TEMPERATURES MONDAY NIGHT AND EARLY TUESDAY MORNING
WITH TEMPS POSSIBLY LOWERING INTO THE TEENS TO LOW 20S. EXPECT
FAR EASTERN WYOMING AND WESTERN NEBRASKA TO BE SLIGHTLY WARMER
WITH THE LACK OF A SNOW PACK, BUT STILL COULD SEE RECORD LOWS IN
THE MID TO UPPER 20S. THIS CLASSIFIES AS A VERY LATE HARD
FREEZE FOR THE REGION AND WE'LL LIKELY NEED FREEZE WATCHES OR
WARNINGS SHORTLY. FOR NOW, WILL SEE HOW THE EVENT PLAYS OUT
BEFORE COMMITTING. PLUS IT'S STILL 4 TO NEARLY 5 PERIODS OUT, SO
WE HAVE SOME TIME TO MAKE ADDITIONAL ADJUSTMENTS.
LONG TERM /TUESDAY THROUGH SATURDAY/
ISSUED AT 216 PM MDT SAT MAY 16 2026
THE LONG TERM PERIOD WILL BEGIN UNDER AN ANOMALOUSLY COLD AIR MASS
IN THE WAKE OF A POWERFUL WINTER STORM, WITH RECORD LOW TEMPERATURES
ACROSS EASTERN WYOMING AND THE NEBRASKA PANHANDLE ON TUESDAY MORNING
(RECORD LOW FOR CHEYENNE ON TUESDAY IS 27 DEGREES SET BACK IN 1966).
UNSURPRISINGLY, HIGH TEMPERATURES ON TUESDAY WILL REMAIN 15-20
DEGREES BELOW CLIMATOLOGY MAINLY IN THE 40S WEST OF THE LARAMIE
RANGE, AND 50S EAST, AS WE REMAIN UNDER THE INFLUENCE OF A BROAD,
POSITIVELY-TILTED TROUGH CENTERED OVER THE ROCKY MOUNTAIN WEST.
AREAS WITH THE MOST SNOW COVER WILL BE THE COLDEST SPOTS, AS
SNOWFALL HAS A HIGH ALBEDO AND IS HIGHLY EFFECTIVE AT RADIATING BACK
INTO SPACE. FURTHER, MELTING AND SUBLIMATION OF SNOW ARE COOLING
PROCESSES, SO THIS WILL FURTHER LIMIT WARMING EVEN GIVEN THE HIGH
MAY SUN ANGLE. TUESDAY NIGHT WILL AGAIN FEATURE RECORD LOW TO NEAR
RECORD LOW TEMPERATURES AS WE REMAIN UNDER WEAK ISENTROPIC DESCENT
AND COLD AIR ADVECTION WITH PARTLY CLEAR SKIES WHICH SHOULD ALLOW
FOR ANOTHER NIGHT OF EFFECTIVE RADIATIVE COOLING.
THE GRADUAL WARM UP CONTINUES AS WE HEAD INTO WEDNESDAY AND ARE
SITUATED IN A ZONAL FLOW REGIME AS WELL AS IN THE LEFT-ENTRANCE
REGION OF A DEPARTING 90-100 KNOT 250 MB JET, WHICH ISN'T EXACTLY A
FAVORABLE RELATIVE LOCATION FOR WIDESPREAD ASCENT AND PRECIPITATION.
HOWEVER, GIVEN THAT NUMEROUS VORTICITY MAXIMA WILL BE PROPAGATING
ALONG THE BASE OF THE TROUGH COMBINED WITH DIFFERENTIAL HEATING OF
THE SLOPED TERRAIN, CHANCES FOR A FEW HIGH-BASED SHOWERS AND
THUNDERSTORMS ARE IN THE FORECAST. THESE ARE LIKELY TO PRODUCE MORE
WIND THAN BENEFICIAL RAIN (IT IS WYOMING, OF COURSE) AS FORECAST
SOUNDINGS ARE SHOWING INVERTED-V PROFILES AND MUCAPE AROUND 100
J/KG.
THURSDAY WE SEE ANOTHER SHORTWAVE TROUGH PROPAGATE WITHIN THE
LONGWAVE PATTERN, SO CHANCES FOR HIGH-BASED SHOWERS AND
THUNDERSTORMS WILL REMAIN IN THE FORECAST AS HIGH TEMPERATURES CREEP
BACK UP TOWARDS CLIMATOLOGY IN THE LOW TO MID 60S. FLOW TURNS MORE
NORTHWESTERLY INTO FRIDAY, HOWEVER WITH THE ABSENCE OF ANY LARGE-
SCALE FORCING FOR ASCENT, CONDITIONS WILL REMAIN MOSTLY DRY WITH
HIGH TEMPERATURES AROUND SEASONAL VALUES.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1134 AM MDT SUN MAY 17 2026
AN ACTIVE 24 HOURS AHEAD WITH MULTIPLE ROUNDS OF SHOWERS AND
THUNDERSTORMS AHEAD OF A POTENT WINTER STORM THAT WILL IMPACT
SOUTHEASTERN WYOMING AND WESTERN NEBRASKA OVERNIGHT. MVFR WILL BE IN
PLACE IN THE VICINITY OF ANY SHOWERS AND THUNDERSTORMS THIS
AFTERNOON INTO THIS EVENING WITH CIGS AT OR BELOW 2K FT, IN ADDITION
TO ERRATIC AND GUSTY WINDS AS HIGH AS 50-60 KNOTS. INTO THE
OVERNIGHT HOURS WE BEGIN TO TRANSITION TO SNOW AT THE WYOMING
TERMINALS, CAN EXPECT MORE WIDESPREAD IFR TO LIFR CONDITIONS WITH
VISIBILITIES AS LOW AS 1/4 SM AND CIGS BELOW 1 KFT ESPECIALLY IN
AREAS OF HEAVY, BLOWING SNOW. EXPECT WIND GUSTS TO PICK UP TO 30-35
KNOTS INTO THE EARLY MORNING HOURS FOR ALL TERMINALS, WITH
PREVAILING WINDS OUT OF THE NE RANGING FROM 25-30 KNOTS AT THE
WYOMING TERMINALS AND 20-25 KNOTS FOR THE NEBRASKA TERMINALS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM MDT
MONDAY FOR WYZ101-105-106-117.
WINTER STORM WARNING FROM 6 PM THIS EVENING TO 6 PM MDT MONDAY
FOR WYZ103-104-110-114-116.
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 PM MDT MONDAY
FOR WYZ109.
WINTER WEATHER ADVISORY FROM 10 PM THIS EVENING TO 6 PM MDT
MONDAY FOR WYZ112.
NE...NONE.
SHORT TERM...TJT
LONG TERM...NB
AVIATION...NB
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page