741
FXUS65 KCYS 181151
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
550 AM MDT MON MAY 18 2026
UPDATE
ISSUED AT 449 AM MDT MON MAY 18 2026
MONITORING BLIZZARD CONDITIONS OVER THE NORTHERN SNOWY RANGE
FOOTHILLS AT THIS HOUR. CURRENT OBSERVATIONS ALONG THE
INTERSTATE 80 CORRIDOR FROM WALCOTT JUNCTION TO ARLINGTON SHOW
VISIBILITY AS LOW AS 1/8TH OF A MILE WITH WINDS GUSTING 50 TO 65
MPH. GOING TO GIVE THIS ANOTHER HOUR OR SO, AND THEN MAY NEED TO
UPGRADE TO A BLIZZARD WARNING IF THIS CONTINUES. ALSO
MONITORING CENTRAL CARBON COUNTY WITH SIMILAR CONDITIONS JUST
STARTING IN AND AROUND RAWLINS.
KEY MESSAGES
- ACCUMULATING SNOW THROUGH MONDAY AFTERNOON WITH WINTER STORM
WARNINGS FOR MANY OF OUR HIGH ELEVATION AND MOUNTAIN ZONES AND
WINTER WEATHER ADVISORIES FOR 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 TUESDAY/
ISSUED AT 255 AM MDT MON MAY 18 2026
LATE SEASON WINTER STORM ONGOING ACROSS SOUTHEAST WYOMING WITH
EVERYWHERE ABOVE 6500 FEET CHANGING TO SNOW WITHIN THE LAST 3
HOURS. RAIN/SNOW LINE IS ROUGHLY 10 MILES WEST OF CHEYENNE AT
THIS HOUR BASED ON AREA WEBCAMS WHICH SHOW SNOWFALL AT THE
WARREN EXCHANGE ALONG I-80. MOST OF INTERSTATE 80 WEST OF THERE
SHOWS VERY DIFFICULT TRAVEL CONDITIONS WITH SOME OF THE WORST
CONDITIONS ON THE I-80 SUMMIT, WHICH IS CURRENTLY EXPERIENCING
VISIBILITY BELOW ONE HALF MILE IN HEAVY SNOW. SNOW IS STARTING
TO ACCUMULATE ON THE ROADS ABOVE 7000 FEET AND EXPECT THIS TO
CONTINUE THROUGH MUCH MONDAY MORNING. STORM SYSTEM IS JUST
STARTING TO INTENSIFY AT THIS HOUR...AS SEEN BY THE CURRENT IR
SATELLITE LOOP WITH COOLING CLOUD TOPS OVER MOST OF WYOMING AND
THE DISTINCT "COMMA CLOUD" BEGINNING TO TAKE SHAPE. NO CHANGES
YET TO WINTER WEATHER HEADLINES, BUT WILL NEED TO KEEP A CLOSE
EYE ON THE I-25 CORRIDOR, THE PINE RIDGE, AND THE HIGHER HILLS
AROUND SCOTTSBLUFF AND BANNER COUNTY FOR POTENTIAL EXTENSIONS
THIS MORNING. THANKFULLY, EVEN IF SNOWFALL RATES BECOME AN
ISSUE, SNOW WILL STRUGGLE TO STICK ON THE PAVEMENT SHORTLY AFTER
SUNRISE.
SNOW WILL BE ONGOING AS WE HEAD INTO THIS AFTERNOON, ALTHOUGH
WITH THE HIGH MAY SUN ANGLE IMPACTS SHOULD BE LIMITED WITH
MELTING ON AREA ROADWAYS. SNOWFALL RATES WILL BEGIN TO EASE DOWN
DURING THE MIDDLE OF THE AFTERNOON AS THE BEST DYNAMIC FORCING
SHIFTS EAST INTO THE HIGH PLAINS. SOME RAIN/SNOW MIX EXPECTED
DOWN TO 4500 TO 5000 FEET, BUT LITTLE IN THE WAY OF ACCUMULATIONS
SINCE THIS WILL OCCUR DURING THE DAYTIME HOURS. REMNANT SNOW (OR
RAIN/SNOW MIX BELOW 5000 FEET) WILL TAPER OFF AND FINALLY END
BY MIDNIGHT TONIGHT AS THE STORM SYSTEM TRANSITIONS TO AN OPEN
WAVE TROUGH AND RAPIDLY EJECTS NORTHEAST. ONCE ALL IS SAID AND
DONE, THIS SYSTEM SHOULD PROVIDE MUCH NEEDED MOISTURE TO THE
AREA WITH AROUND A HALF INCH OF PRECIP FOR THE EASTERN PLAINS,
AND CLOSE TO 1.00 INCH TO AS HIGH AS 1.50 INCHES FOR SOUTHEAST
WYOMING.
MAIN FORECAST CONCERN AFTER TODAY WILL BE HOW QUICKLY WE CLEAR
OUT AT NIGHT. THERE IS INCREASING CONFIDENCE THAT A GOOD PART OF
THE EASTERN PLAINS WITH CLEAR OUT BY DAYBREAK TUESDAY WITH
PORTIONS OF CARBON COUNTY BELOW 50% CLOUD COVER AS WELL. A HARD
FREEZE IS EXPECTED LATE TONIGHT THROUGH MOST OF TUESDAY MORNING,
WITH FREEZING TEMPERATURES LIKELY LASTING UNTIL SHORTLY BEFORE
NOON IN PORTIONS OF THE FORECAST AREA. THIS IS DUE TO A RECORD
BREAKING UNSEASONABLY COLD AIRMASS BEHIND THE MAIN STORM SYSTEM,
WHICH IS FORECAST TO SETTLE OVER THE AREA TODAY. CURRENT 10TH TO
25TH PERCENTILE LOW TEMPERATURES TONIGHT ARE BETWEEN 14 TO 20
DEGREES OVER MOST OF THE HIGH VALLEYS IN SOUTHEAST WYOMING, WITH
17 TO 27 DEGREES ACROSS THE EASTERN PLAINS. UPGRADED THE FREEZE
WATCH TO A FREEZE WARNING FOR EAST CENTRAL WYOMING AND FAR
NORTHWESTERN NEBRASKA SINCE THESE ARE THE MOST LIKELY ZONES TO
SEE CLEARING SKIES EARLIER IN THE NIGHT. KEPT THE WATCH GOING
FOR THE REMAINDER OF THE AREA, BUT MAINLY TO SEE HOW THIS
CURRENT STORM SYSTEM AND POTENTIAL SNOWFALL PANS OUT FIRST.
CONDITIONS WILL IMPROVE A LITTLE ON TUESDAY WITH 700MB
TEMPERATURES BETWEEN -2C TO -5C UNDER NORTHWEST FLOW. HIGH
TEMPERATURES WILL BE WARMEST WHERE THERE IS NO
SNOW PACK...MAINLY OVER FAR EASTERN WYOMING AND WESTERN
NEBRASKA WITH HIGHS IN THE 50S TO LOW 60S. FURTHER WEST, EXPECT
HIGHS TO GENERALLY BE IN THE 40S AND EVEN UPPER 30S IN AREAS
WITH THE DEEPEST SNOW PACK.
LONG TERM /TUESDAY NIGHT 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. 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 /12Z TAFS THROUGH 12Z TUESDAY/
ISSUED AT 550 AM MDT MON MAY 18 2026
POTENT LATE SPRING STORM SYSTEM WILL BRING WIDESPREAD SNOW ABOVE
5000 FEET, AND RAIN/SNOW MIX BELOW 5000 FEET THROUGH MUCH OF THE DAY
TODAY. STORM SYSTEM IS FORECAST TO WEAKEN AND QUICKLY EJECT EASTWARD
BY TONIGHT.
HAZARDS/WEATHER TRENDS: ALL SOUTHEAST WYOMING ARE IFR OR LIFR OR
WILL BE SHORTLY. EXPECT THESE CONDITIONS THROUGH MOST OF TODAY, WITH
CONDITIONS SLOWLY IMPROVING TO MVFR OR VFR BETWEEN 22Z TODAY AND 03Z
TUESDAY. FOR WESTERN NEBRASKA, MVFR CIGS HAVE DEVELOPED WITH PERIODS
OF RAIN. THESE CIGS WILL CONTINUE TO LOWER THIS MORNING WITH
WIDESPREAD IFR CONDITIONS EXPECTED BY 14Z TO 20Z. SHOWERS WILL ALSO
BECOME HEAVIER AND MIX WITH SNOW AT TIMES LATER THIS AFTERNOON.
CYS WATCHES/WARNINGS/ADVISORIES
WY...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
WYZ106-113-115>119.
FREEZE WARNING FROM 8 PM THIS EVENING TO 10 AM MDT TUESDAY FOR
WYZ101-102-107-108.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ101-
105-106-111-115-117.
FREEZE WARNING UNTIL 10 AM MDT THIS MORNING FOR WYZ102.
WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ103-
104-109-110-112-114-116.
FREEZE WATCH FROM THIS EVENING THROUGH TUESDAY MORNING FOR
WYZ104-105-109>111.
NE...FREEZE WATCH FROM LATE TONIGHT THROUGH TUESDAY MORNING FOR
NEZ002-003-020-021-054-055.
FREEZE WARNING FROM 8 PM THIS EVENING TO 10 AM MDT TUESDAY FOR
NEZ019-095-096.
UPDATE...TJT
SHORT TERM...TJT
LONG TERM...NB
AVIATION...TJT
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