911
FXUS65 KCYS 180020
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
620 PM MDT SUN MAY 17 2026
KEY MESSAGES
- MARGINAL RISK OF STRONG TO SEVERE STORMS THIS AFTERNOON,
MOSTLY LIMITED TO THE NEBRASKA PANHANDLE INCLUDING BOTH GUSTY
WINDS AND HAIL.
- ACCUMULATING SNOW EXPECTED SUNDAY NIGHT THROUGH MONDAY WITH
WINTER STORM WARNINGS FOR MANY OF OUR HIGH ELEVATION AND
MOUNTAIN ZONES AND WINTER WEATHER ADVISORIES FOR ATTENDANT
NEARBY ZONES.
- 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 230 PM MDT SUN MAY 17 2026
NOTABLE INSTABILITY HAS STRUGGLED TO RETURN TO THE REGION THIS
AFTERNOON, LIKELY THANKS TO THE PROGRESS OF THE BOUNDARY AND
CLOUDS ALLOWING SOME LIMITING OF HEATING DURING THE MORNING
HOURS. BUT MESOANALYSIS DOES SHOW SOME POCKETS OF WEAK
INSTABILITY, AND A FEW STORMS ARE FORMING JUST OVER THE BORDER
IN COLORADO IN A SIMILARLY UNIMPRESSIVE ENVIRONMENT. WITH SOME
STOUT SHEAR IN THE SOUTHERN NEBRASKA PANHANDLE WE COULD SEE A
STORM OR POSSIBLY TWO STRENGTHEN AND PRODUCE SOME BREEZY WINDS
OR SMALL HAIL THANKS TO LOW FREEZING LEVELS, BUT AT THIS POINT
SPC HAS TAKEN MOST OF OUR AREA OUT OF THE MARGINAL RISK WITH
ONLY THE SOUTHEASTERN NEBRASKA PANHANDLE REMAINING IN, SO OUR
CHANCES FOR STRONGER TO SEVERE WEATHER ARE DWINDLING TODAY.
MOVING INTO THIS EVENING, WE'LL SHIFT GEARS AWAY FROM SEVERE
WEATHER AND RETURN TO WINTER, WITH WINTER STORM
WARNINGS/ADVISORIES OUT FOR A MAJORITY OF THE WESTERN PORTION OF
OUR CWA. AT THE UPPER LEVELS, A LOW PRESSURE SYSTEM WILL SWING
INTO THE FOUR CORNERS AND THEN AROUND AND UP INTO THE NORTHERN
PLAINS, WHILE AT THE SURFACE WE'LL SEE SOME IMPRESSIVE
CYCLOGENESIS ACROSS COLORADO. SIMILAR TO PREVIOUS THINKING, WE
SHOULD SEE THE MOST FAVORABLE FORCING LOCATED ACROSS SOUTH-
CENTRAL WYOMING INCLUDING PORTIONS OF CARBON AND PERHAPS EVEN
LARAMIE COUNTIES. MODELS REMAIN IN SOLID AGREEMENT ON STRONG
SNOWFALL ACROSS THIS AREA, AND THIS UPDATE DOESN'T FEATURE MANY
SIGNIFICANT CHANGES. OF NOTE THOUGH, HAVE SEEN SOME CONSISTENT
FORCING NEAR THE SIERRA-MADRE RANGE THAT UPGRADING TO A WARNING
SEEMED WORTHWHILE, AND WHILE THE WHOLE RANGE MAY LAND JUST SHY
OF A FOOT OF NEW SNOWFALL, EXPECTING ENOUGH LOCATIONS AROUND
12-16 INCHES THAT A WARNING FELT JUSTIFIED. A WINTER WEATHER
ADVISORY WAS ALSO ISSUED FOR THE LARAMIE VALLEY, AND WHILE
EASTERLY FLOW MAY HELP TO PRECLUDE STRONGER ACCUMULATIONS,
NORTHERN PORTIONS OF THIS ZONE AS WELL AS ALONG THE INTERSTATE
SHOULD SEE ENOUGH ACCUMULATION OR AT LEAST REDUCED VISIBILITY
FROM HEAVY, WET, AND BLOWING SNOW. SPEAKING OF REDUCED
VISIBILITY, 850 MB PRESSURE GRADIENTS SHOW SOME VERY STOUT
GRADIENTS FROM CRAIG TO CASPER, AND STRONG WINDS WILL ACCOMPANY
THIS SNOWFALL WITH GUSTS OF 30-50 MPH POSSIBLE. FOR NOW, STILL
HOLDING OFF ON UPGRADING EVEN FURTHER TO BLIZZARD WARNINGS AS
CONFIDENCE IS JUST NOT HIGH ENOUGH THAT WE WILL SEE WIDESPREAD
REDUCTIONS IN VISIBILITY. BUT THE HREF DOES PAINT SOME SWATHS OF
AROUND 40-60% PROBABILITY ACROSS CARBON COUNTY FOR BLIZZARD
CONDITIONS, AND THIS WILL NEED TO BE MONITORED CLOSELY MOVING
INTO TONIGHT IN CASE CONFIDENCE GROWS FURTHER.
WITH STOUT COLD AIR OVERSPREADING THE REGION AND LOCATIONS WEST
OF THE LARAMIE RANGE EXPECTED TO SEE SNOW ON THE GROUND,
TEMPERATURES WILL PLUMMET ON MONDAY. WIDESPREAD HIGHS ARE ONLY
EXPECTED TO MAX AT THE LOW 30'S TO 40'S, AND BY THE EVENING
THESE WILL BOTTOM OUT AS WE MOVE OVERNIGHT INTO TUESDAY MORNING.
SKIES SHOULD ALSO BEGIN CLEARING OVERNIGHT WHICH WILL AID IN
RADIATIONAL COOLING, AND MANY LOCATIONS ACROSS THE CWA MAY TIE
OR SET NEW ALL TIME LOW TEMPERATURE RECORDS. OUTSIDE OF THE
MOUNTAIN ZONES, EVERY ZONE IN OUR AREA IS NOW UNDER A FREEZE
WATCH FOR THIS TIMEFRAME, THOUGH THE NEBRASKA PANHANDLE MAY
STRUGGLE IN SOME LOCATIONS TO REACH 28 DEGREES, THE NEEDED LOW
FOR FREEZE PRODUCTS. NONETHELESS, UNSEASONABLE COLD WILL BE HERE
AND LOWS ACROSS THE ENTIRE REGION ARE EXPECTED TO REACH AT OR
BELOW FREEZING (INCLUDING TEENS IN CARBON COUNTY), WHICH WILL
IMPACT PLANTS AND CROPS AS WELL AS OUTDOOR EQUIPMENT. TAKE THE
APPROPRIATE PRECAUTIONS NOW FOR THIS LATE SEASON FREEZE.
LONG TERM /TUESDAY THROUGH SUNDAY/
ISSUED AT 230 PM MDT SUN MAY 17 2026
CERTAINLY LESS ACTIVE THAN THE SHORT TERM, BUT THE LONG TERM PERIOD
WILL STILL HAVE SOME IMPACTS, WITH THE MAIN STORY BEING THE RECORD-
BREAKING COLD IN THE WAKE OF A VIGOROUS WINTER STORM. TUESDAY
MORNING WILL START OUT IN THE 20S IN A COLD ADVECTION REGIME, HENCE
THE ISSUANCE OF FREEZE WATCHES/WARNINGS TO ACCOUNT FOR AGRICULTURAL
IMPACTS AND RECENTLY PLANTED VEGETATION GIVEN THE RECENT MILD
PATTERN. IN FACT, LREF 10TH PERCENTILE TEMPERATURES SHOW RAWLINS
GETTING WELL INTO THE TEENS FOR A LOW TUESDAY MORNING, WHICH SEEMS
REASONABLE GIVEN AMPLE SNOW COVER AND COLD ADVECTION. TUESDAY WILL
ALSO FEATURE HIGH TEMPERATURES 15-20 DEGREES BELOW CLIMATOLOGY,
RESULTING IN HIGHS IN THE 40S FOR OUR WYOMING COUNTIES AND 50S FOR
OUR NEBRASKA COUNTIES. WE WILL LIKELY DIP BELOW FREEZING AGAIN ON
TUESDAY NIGHT ESPECIALLY IN REGIONS THAT DON'T MELT AWAY ALL OF
THEIR SNOW (I.E. AREAS WEST OF THE I-25 CORRIDOR). ON WEDNESDAY,
TEMPERATURES WILL GRADUALLY MODERATE INTO THE UPPER 50S TO NEAR 60
EAST OF THE LARAMIE RANGE AND UPPER 40S TO LOWER 50S WEST GIVEN WEAK
ISENTROPIC ASCENT/WARM ADVECTION AS THE LONGWAVE TROUGH RESPONSIBLE
FOR OUR ANOMALOUSLY COOL WEATHER DAMPENS. THERE MAY BE ENOUGH
LINGERING MOISTURE FOR A FEW SHOWERS AND THUNDERSTORMS PRIMARILY
OVER THE HIGHER TERRAIN, HOWEVER PROBABILITIES OF SEEING QPF > 0.05"
ARE RUNNING AT ABOUT 25%, SO ANY MOISTURE IS UNLIKELY TO BE
BENEFICIAL. GIVEN DRY BOUNDARY LAYERS AS SHOWN ON MODEL FORECAST
SOUNDINGS SHOW A VERY DRY BOUNDARY LAYER WITH SURFACE DEWPOINT
DEPRESSIONS EXCEEDING 40 DEGREES, SHOWERS AND THUNDERSTORMS WILL
LIKELY PRODUCE FAR MORE WIND THAN RAIN.
TEMPERATURES GRADUALLY WARM ON THURSDAY AND FRIDAY AS A SERIES OF
SHORTWAVE TROUGHS EMBEDDED IN QUASI-ZONAL FLOW TRAVERSE ACROSS
EASTERN WYOMING AND WESTERN NEBRASKA, LEAVING IN LOW (30%) CHANCES
FOR HIGH-BASED SHOWERS AND THUNDERSTORMS. HIGHS WILL GRADUALLY
INCREASE TO CLIMATOLOGICAL VALUES (MID-UPPER 60S FOR CHEYENNE TO
NEAR 70 FOR THE NEBRASKA PANHANDLE). HEADING INTO THE WEEKEND, WE
WILL BEGIN TO DRY OUT AND ENCOUNTER A FASTER WARMING TREND TO ABOVE-
AVERAGE TEMPERATURES AS WEAK MID-LEVEL RIDGING ESTABLISHES ITSELF
OVER THE ROCKY MOUNTAIN WEST, WITH NO WIDESPREAD OR BENEFICIAL
PRECIPITATION CHANCES IN SIGHT.
AVIATION /00Z TAFS THROUGH 00Z TUESDAY/
ISSUED AT 557 PM MDT SUN MAY 17 2026
WIDESPREAD RAIN AND SNOW SHOWERS, WITH ISOLATED THUNDERSTORMS,
ARE MOVING THROUGH THE WYOMING TERMINALS. VISIBILITIES OF 2 TO 5
STATUE MILES HAVE BEEN OBSERVED IN THE HEAVIEST ACTIVITY OVER
KLAR AND KCYS. CONDITIONS WILL CONTINUE TO DETERIORATE AT
WYOMING TERMINALS OVERNIGHT WITH IFR AND LIFR CONDITIONS WITH
INCREASING RAIN AND SNOW SHOWER ACTIVITY. PARTICULARLY OF
CONCERN WITH THIS SYSTEM IS GUIDANCE IS TRENDING TOWARDS HIGHER
SNOW AND WIND POTENTIAL. HEAVY SNOW AND WIND GUSTS TO 50 KTS MAY
OCCUR IN THE MOUNTAIN BASINS TO IMPACT KRWL REDUCING HORIZONTAL
VISIBILITIES DOWN TO 1/4 SM OR LESS AND VERTICAL VISIBILITIES
TO THE SURFACE. AT KLAR AND KCYS, WHILE NOT AS SEVERE IN
CONDITIONS AS KRWL, WILL MOST LIKELY BE IN LIFR CONDITIONS WITH
HEAVY SNOW AND CEILINGS BELOW 500 FEET. SHOWER ACTIVITY AT THE
NEBRASKA PANHANDLES WILL CONTINUE TO INCREASE THROUGH THE
FORECAST PERIOD TO INDUCE MVFR CONDITIONS AT TIMES, PARTICULARLY
AT KBFF. IT IS UNCERTAIN AT THIS TIME IF THE RAIN WILL
TRANSITION TO SNOW AT THESE TERMINALS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...FREEZE WATCH FROM LATE MONDAY NIGHT THROUGH TUESDAY MORNING
FOR WYZ101-102-106>108-113-115>119.
WINTER WEATHER ADVISORY FROM MIDNIGHT TONIGHT TO 6 PM MDT
MONDAY FOR WYZ101-105-106-111-115-117.
FREEZE WARNING FROM 5 AM TO 10 AM MDT MONDAY FOR WYZ102.
WINTER STORM WARNING UNTIL 6 PM MDT MONDAY FOR WYZ103-104-110-
112-114-116.
FREEZE WATCH FROM MONDAY EVENING THROUGH TUESDAY MORNING FOR
WYZ104-105-109>111.
WINTER STORM WARNING FROM MIDNIGHT TONIGHT TO 6 PM MDT MONDAY
FOR WYZ109.
NE...FREEZE WATCH FROM LATE MONDAY NIGHT THROUGH TUESDAY MORNING
FOR NEZ002-003-019>021-054-055-095-096.
SHORT TERM...CG
LONG TERM...NB
AVIATION...RV
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