431
FXUS65 KCYS 162019
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
219 PM MDT SAT MAY 16 2026
KEY MESSAGES
- SEVERE WEATHER WILL BE POSSIBLE BOTH SATURDAY AND SUNDAY. A
SLIGHT RISK IS IN EFFECT THIS AFTERNOON FOR THE NEBRASKA
PANHANDLE, WITH A MARGINAL RISK FOR SUNDAY.
- 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 AVERAGE BY THURSDAY.
SHORT TERM /THROUGH MONDAY NIGHT/
ISSUED AT 216 PM MDT SAT MAY 16 2026
RADAR ECHOES ARE SEEN ACROSS THE AREA THIS AFTERNOON WITH
STRONGER STORM ACTIVITY CURRENTLY JUST SOUTH AND EAST OF THE
CWA. CURRENT MESOANALYSIS SHOWS SOME WEAK TO MODEST MUCAPE
ACROSS THE REGION, RANGING FROM 250-600 J/KG, STRONGEST IN THE
SOUTHERN NEBRASKA PANHANDLE. BULK SHEAR IS LOOKING A BIT MORE
FAVORABLE WITH AROUND 35-40 KNOTS FOR OUR EASTERN ZONES, AND 100
M2/S2 OF HELICITY WITH A BULLSEYE OF 200 JUST SOUTH OF SIDNEY.
HIGH RESOLUTION GUIDANCE HAS BEEN IN PRETTY SOLID AGREEMENT ON
THE OVERALL SETUP TODAY WITH THE ONGOING PRECIPITATION AND
EXPECTATION THAT STORMS WILL BEGIN TO CONSOLIDATE IN EXTREME
EASTERN WYOMING/NORTHERN COLORADO, AND FORM INTO A STRONG LINE
AS THEY REACH THE EASTERN PERIPHERY OF OUR CWA IN THE NEBRASKA
PANHANDLE. CURRENT TIMING FOR THIS WOULD BE BETWEEN 22-02Z, WITH
THE BULK OF THE ACTIVITY EXITING THE CWA AFTER THAT TIME. THIS
LOOKS TO FAVOR THE STRONGEST ACTIVITY FROM ABOUT SCOTTSBLUFF
SOUTHEASTWARDS DURING THAT TIMEFRAME, WITH LARGE HAIL INITIALLY
FOLLOWED BY STRONG WINDS QUICKLY THEREAFTER AS THE PRIMARY
HAZARDS, ALONG WITH A LOW-END TORNADO RISK MOST LIKELY ALONG
THE I-80 CORRIDOR IN THE PANHANDLE. THAT BEING SAID, MODELS WERE
KEEPING ACTIVITY FAIRLY QUIET UNTIL THAT TIME FOR OUR NEBRASKA
PANHANDLE ZONES, BUT SOME DECENT THUNDERSTORMS HAVE FORMED JUST
SOUTH AND EAST OF SIDNEY, WHICH COULD HELP TO LIMIT SEVERE
POTENTIAL FOR THIS AREA. STILL, WOULD EXPECT THAT THE ATMOSPHERE
WOULD BE ABLE TO RECOVER AND PRODUCE ANOTHER ROUND OF STRONGER
STORMS INTO THE LATER AFTERNOON AND EVENING EVEN AT SIDNEY.
ELSEWHERE ACROSS THE CWA, EXPECTATION OF STRONG TO SEVERE WIND
GUSTS POSSIBLE WITH INVERTED V SOUNDINGS PRESENT PROMOTING SOME
DOWNDRAFT ACTIVITY THIS AFTERNOON AND EVENING.
OVERNIGHT SCATTERED SHOWERS AND WEAK THUNDERSTORMS SHOULD
PERSIST WITH ANOTHER ROUND OF STRONG TO SEVERE THUNDERSTORMS
POSSIBLE ON SUNDAY. THIS TIME THE FRONT IS EXPECTED TO BE
THROUGH THE REGION, LIMITING OVERALL SEVERE POTENTIAL AS
TEMPERATURES WILL BE AROUND TEN DEGREES COOLER TOMORROW WITH
MUCH MORE LIMITED INSTABILITY. STILL, SOME LINGERING SEVERE
PARAMETERS SHOULD BE PRESENT ONCE AGAIN ACROSS OUR SOUTHEASTERN
ZONES, SO A FEW STRONG TO NEAR SEVERE STORMS MAY BE POSSIBLE
DURING THE DAY WITH MULTIPLE ROUNDS OF ACTIVITY, WITH SMALL HAIL
AND GUSTY WINDS POSSIBLE.
NOW BEHIND THE COLD FRONT SUNDAY EVENING, LOOK FOR TEMPERATURES
TO PLUMMET AS A SURGE OF COLD CANADIAN AIR DESCENDS AS THE
STOUT UPPER LOW DIVES ACROSS THE FOUR CORNERS AND THEN SWINGS UP
INTO NEBRASKA BY TUESDAY MORNING. THIS WILL PROMOTE SOME
AGGRESSIVE FORCING AND WITH MODEST MOISTURE PRESENT, WE'LL SEE
RAIN CONTINUING ACROSS THE AREA WITH ELEVATIONS GENERALLY ABOVE
5000 FEET TRANSITIONING TO SNOWFALL SUNDAY EVENING AND
CONTINUING INTO MONDAY. FOR THIS UPDATE, HAVE ADDED THE RAWLINS
AREA INTO THE WINTER STORM WATCH AS WE'RE LOOKING AT THE
POTENTIAL FOR 6+ INCHES OF FRESH, HEAVY WET SNOW. THE ONE CAVEAT
TO LOCATIONS OUTSIDE OF THE MOUNTAINS WILL BE THE FACT THAT
TEMPERATURES HAVE BEEN WARM, AND WITH HOW LATE SEASON THIS
SYSTEM IS, SNOW RATIOS OF AROUND 7-10:1 ARE EXPECTED, KEEPING US
FROM SEEING NOTABLY HEAVIER SNOWFALL. THAT BEING SAID, WITH
HEAVY WET SNOW WE DO HAVE TO WORRY ABOUT TREES AND POWER LINES
SUFFERING FROM THE WEIGHT OF THIS ACTIVITY AND CAUSING LOCAL
DAMAGE AND POWER OUTAGES. AND IF SNOW FALLS QUICKLY, IT CAN
ACCUMULATE ON ROADS ENOUGH TO SHUT DOWN TRAVEL BEFORE MELTING
OFF. HIGH RESOLUTION GUIDANCE HAS DIALED BACK ACCUMULATIONS
FURTHER EAST INTO CHEYENNE PROPER THOUGH, SO FOR THIS UPDATE DID
REDUCE US BACK TO AROUND AN INCH. AND ONCE AGAIN WITH HOW WARM
TEMPERATURES HAVE BEEN, IT'S GOING TO BE TOUGH TO MAKE
ACCUMULATIONS STICK EVEN ON ELEVATED SURFACES OR GRASSES EAST OF
THE MOUNTAINS, BUT WE WILL DEFINITELY FEEL THE COLD AT THE BARE
MINIMUM. TEMPERATURES WILL STRUGGLE TO ECLIPSE THE MID 30'S TO
MID 40'S ON MONDAY, AND LOWS WILL BOTTOM OUT OVERNIGHT INTO
TUESDAY MORNING BELOW FREEZING ACROSS OUR ENTIRE CWA, NEARING
RECORD COLD. ANY SENSITIVE PLANTS AND CROPS WILL SURELY BE
IMPACTED BY THIS SYSTEM, AND THE APPROPRIATE PRECAUTIONS SHOULD
BE TAKEN ACCORDINGLY.
LONG TERM /TUESDAY THROUGH FRIDAY/
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 SUNDAY/
ISSUED AT 1140 AM MDT SAT MAY 16 2026
A COMPLICATED FORECAST FOR THE FIRST 12 HOURS OF THE TAF PERIOD, AS
NUMEROUS ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TO MOVE
THROUGH EASTERN WYOMING AND THE NEBRASKA PANHANDLE. CAN EXPECT VFR
AT ALL TERMINALS WITH THE EXCEPTION OF BRIEF MVFR CONDITIONS IN THE
VICINITY OF ANY SHOWERS AND THUNDERSTORMS IN ADDITION TO ERRATIC,
GUSTY WINDS AS HIGH AS 50-60 KNOTS. THE HIGHEST CONFIDENCE IN
WIDESPREAD SHOWER AND THUNDERSTORM COVERAGE IS ACROSS WESTERN
NEBRASKA FROM 22Z-02Z, WITH ADDITIONAL ROUNDS OF SCATTERED SHOWERS
AND THUNDERSTORMS OCCURRING THROUGH THE OVERNIGHT HOURS. TERMINALS
WITH THE HIGHEST CONFIDENCE OF BEING IMPACTED (>70% CHANCE) ARE KSNY
AND KAIA ESPECIALLY DURING THIS TIME FRAME. LOWERING CIGS AND A
NEARLY SATURATED BOUNDARY LAYER INTRODUCES THE POTENTIAL FOR FOG AT
KSNY, KAIA, AND KCDR ESPECIALLY IF WINDS REMAIN LIGHT.
KCYS WILL LIKELY BE IMPACTED BY THESE INITIAL SHOWERS AND
THUNDERSTORMS AROUND 21Z, ALTHOUGH CONFIDENCE IS LOW (20%) THAT
MATURE CONVECTION WILL IMPACT THE TERMINAL AT THIS TIME, SO
AMENDMENTS MAY BE NECESSARY IN FUTURE UPDATES.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY
AFTERNOON FOR WYZ103-104-110-114-116.
WINTER STORM WATCH FROM LATE SUNDAY NIGHT THROUGH MONDAY
AFTERNOON FOR WYZ109.
NE...NONE.
SHORT TERM...CG
LONG TERM...NB
AVIATION...NB
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