107
FXUS65 KCYS 160942
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
342 AM MDT SAT MAY 16 2026
KEY MESSAGES
- SEVERE WEATHER WILL BE POSSIBLE BOTH SATURDAY AND SUNDAY. SPC
HAS ISSUED A SLIGHT RISK FOR THE SOUTHERN PANHANDLE ON
SATURDAY 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 SUNDAY/
ISSUED AT 335 AM MDT SAT MAY 16 2026
ACTIVE, WITH MULTIPLE HAZARDS EXPECTED OVER THE NEXT 48 TO 72
HOURS. WILL HANDLE THE WINTRY PORTION OF THIS STORM IN THE LONG
TERM DISCUSSION, AND WILL MAINLY FOCUS ON THUNDERSTORMS AND
SEVERE WEATHER POTENTIAL TODAY AND SUNDAY.
CURRENT KCYS RADAR LOOP SURPRISINGLY SHOWING A FEW ISOLATED
THUNDERSTORM CELLS EARLY THIS MORNING OVER THE SOUTHERN
PANHANDLE OF NEBRASKA NEAR KIMBALL AND SIDNEY. ACTIVITY IS
PRETTY LIMITED, BUT DETECTED CG HAS BEEN PRETTY CONSISTENT OVER
THE LAST FEW HOURS. THIS IS LIKELY DUE TO THE INITIAL MOISTURE
SURGE/WAA ABOVE THE SURFACE ACROSS THE EASTERN PLAINS WITH
SIDNEY'S DEWPOINT INCREASING TO NEAR 40 DEGREES COMPARED TO THE
MID TEENS FRIDAY EVENING. ALSO, A POTENT UPPER LEVEL JET IS ALSO
PRESENT WITH GOOD MID TO UPPER LEVEL LIFT OVER THE AREA AND
NORTHEAST COLORADO. JET DYNAMICS ARE EXPECTED TO PLAY A ROLE IN
CONVECTIVE ACTIVITY TODAY AND SUNDAY ACROSS THE AREA. OTHERWISE,
NOT MUCH GOING ON FOR THE REST OF THE FORECAST AREA WITH MOSTLY
CLOUDY SKIES AND RELATIVELY MILD TEMPERATURES FOR 300 AM.
A MARGINAL TO SLIGHT RISK OF SEVERE THUNDERSTORMS REMAINS OVER
MOST OF SOUTHEAST WYOMING (MARGINAL RISK) AND WESTERN NEBRASKA,
WITH THE SLIGHT RISK MAINLY FOR THE SOUTHERN NEBRASKA PANHANDLE
TODAY WHERE THE BEST MOISTURE AND FORCING EXIST. WILL HAVE TO
KEEP A CLOSE EYE ON THE MOISTURE ADVECTION THIS AFTERNOON AS A
FRONTAL BOUNDARY IS EXPECTED TO DEVELOP ACROSS THE EASTERN
WYOMING HIGH PLAINS AND SLOWLY MOVE EAST. ANY ADDITIONAL LOW
LEVEL FORCING AND CONVERGENCE MAY RESULT IN ADDITIONAL COVERAGE
OF STRONG TO SEVERE THUNDERSTORMS...AND FURTHER WEST THAT
PREVIOUSLY EXPECTED. FOR NOW, EXPECT MOISTURE ADVECTION TO BE
SLOW AND TAKE ITS TIME THROUGH THE DAY. WITH LIMITED MOISTURE,
STRONG TO SEVERE STORMS SHOULD BE PRETTY ISOLATED OR WIDELY
SCATTERED ACROSS THE I-80 CORRIDOR AND NORTHWARD TOWARDS THE
NORTH PLATTE RIVER VALLEY. MAINLY EXPECT STRONG GUSTY WINDS,
ESPECIALLY INITIALLY IN THE EVENT, WITH PLENTY OF DCAPE
(1000-1900 J/KG) OVER THE EASTERN HIGH PLAINS. AS WE HEAD INTO
THIS EVENING, BOUNDARY INTERACTIONS AND ADDITIONAL DEVELOPMENT
MAY RESULT IN A SECONDARY HAIL THREAT. THERE IS AN OUTSIDE
CHANCE OF A TORNADO OR TWO, BUT THIS CHANCE IS MAINLY CONFINED
TO THE SOUTHERN NEBRASKA PANHANDLE LATE THIS AFTERNOON AND THIS
EVENING (2% TO 4%) WITH SOME 0-3 KM HELICITY, ESPECIALLY NEAR
BOUNDARY MERGERS. HOWEVER, LCL'S WILL BE QUITE HIGH DURING THIS
EVENT, SO CONFIDENCE WILL REMAIN LIMITED. OUTSIDE OF THE SLIGHT
RISK AREA, EXPECT MAINLY STRONG GUSTY WINDS FROM THUNDERSTORM
OUTFLOW WITH ALL MODELS SHOWING INVERTED-V SOUNDINGS FOR MUCH OF
THE AFTERNOON, BUT CAN'T RULE OUT AN ISOLATED HAIL THREAT DUE
TO LOWER FREEZING LEVELS. SCATTERED SHOWERS AND ISOLATED
THUNDERSTORMS WILL LINGER THROUGH MOST OF SATURDAY NIGHT WITH
TEMPERATURES IN THE 40S AND 50S.
FOR SUNDAY, CHANCE FOR SEVERE THUNDERSTORMS HAS LOWERED
SIGNIFICANTLY WITH ALL MODELS SHOWING THE INITIAL COLD FRONT
SLIDING THROUGH THE AREA EARLY IN THE DAY, CONSIDERABLY EARLIER
THAN WHAT WAS SHOWN 24 HOURS AGO. LIMITED CAPE BEHIND THE FRONT
WITH THE BEST CHANCE FOR STRONG TO SEVERE THUNDERSTORMS ACROSS
THE SOUTHERN NEBRASKA PANHANDLE AND FAR SOUTHEAST WYOMING WHERE
THE BEST INSTABILITY AND FORCING WILL BE LOCATED. THE SLIGHT
RISK AREA HAS BEEN SHIFTED MUCH FURTHER EAST, INTO CENTRAL AND
EASTERN NEBRASKA. WILL CONTINUE TO MONITOR THIS INTO SUNDAY WITH
SOME HIGH RES GUIDANCE SHOWS SOME PRETTY STRONG THUNDERSTORMS ON
SIMULATED PROG RADAR REFLECTIVELY. WITH ADDITIONAL COOLER AIR
MOVING INTO THE AREA AND GOOD FORCING, ANY THUNDERSTORMS MAY
HAVE SMALL HAIL AND GUSTY WINDS WITH SEVERAL BANDS OF
THUNDERSTORMS EXPECTED. HIGH TEMPERATURES ON SUNDAY WILL BE
AROUND 10 TO 15 DEGREES COOLER COMPARED TO SATURDAY AS AN
EXTENDED RAIN/SNOW EVENT IS EXPECTED TO BEGIN SUNDAY EVENING.
PLEASE SEE LONG TERM DISCUSSION(S) FOR ADDITIONAL DETAILS.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/
ISSUED AT 250 AM MDT SAT MAY 16 2026
PREVIOUS LONG TERM DISCUSSION IS VALID AND ON TRACK, WITH A FEW
UPDATES/MODEL CHANGES COMPARED TO 12 TO 24 HOURS AGO:
1) ISSUED A WINTER STORM WATCH FOR MOST MOUNTAIN ZONES (LARAMIE
RANGE AND SNOWY RANGE), AND INCLUDED NORTHERN CARBON COUNTY AND
THE SNOWY RANGE FOOTHILLS, INCLUDING I-80 BETWEEN LARAMIE AND
RAWLINS. MODELS HAVE BEEN VERY CONSISTENT IN SHOWING STRONG
FRONTOGENESIS AND LIFT IN THESE AREAS. ALTHOUGH FORECAST SNOW
ACCUMULATIONS ARE NOT QUITE AT CRITERIA, DECIDED TO HANDLE THE
WINTER WEATHER PORTION OF THIS STORM TO TAKE SOME PRESSURE OFF
THE DAY SHIFT, WHICH WILL BE DEALING WITH SEVERE WEATHER,
POSSIBLY BOTH TODAY AND SUNDAY. ALTHOUGH THIS STORM IS LATE
SEASON SNOWFALL, THE TIMING OF THE HEAVY SNOW MAY BE PROBLEMATIC
SINCE IT MAINLY STARTS OUT MODERATE TO HEAVY IN THE NIGHTTIME
HOURS, WHERE QUICK ACCUMULATIONS ARE MORE LIKELY.
2) QUITE A BIT OF UNCERTAINTY FOR THE LARAMIE VALLEY SINCE THEY
HOLD ONTO A PREVAILING EASTERLY WIND FOR MUCH OF THE EVENT, AND
THE AXIS OF STRONG LIFT NEAR THE FRONTOGENESIS IS MAINLY JUST
WEST AND NORTH OF THE AREA. ALTHOUGH SNOWFALL AMOUNTS WERE
NUDGED SLIGHTLY HIGHER OVER A GOOD CHUNK OF THE AREA, KEPT
LARAMIE ROUGHLY THE SAME (3 TO 5 INCHES).
3) THERE IS SOME UNCERTAINTY STARTING TO CREEP INTO THE
FORECAST FOR THE EASTERN PLAINS. SEVERAL NAM SOLUTIONS ARE
SHOWING A WARM NOSE ALONG AND EAST OF THE I-25 CORRIDOR THROUGH
MUCH OF THE EVENT. THIS MAY KEEP PRECIP TYPE MAINLY AS RAIN
ALONG AND EAST OF THE I-25 CORRIDOR. WILL MONITOR THIS TO SEE IF
IT BECOMES A ACTUAL TREND. EITHER WAY, PLENTIFUL MOISTURE IS
EXPECTED BUT IMPACTS WILL BE VERY DIFFERENT. AS FOR THE GFS, 00Z
STARTED SHOWING A DRY LAYER ABOVE 700MB CREEPING INTO THE
LARAMIE VALLEY AND ALONG THE I-25 CORRIDOR OUT OF THE SOUTHWEST.
AGAIN, WILL MONITOR THIS OVER THE NEXT 24 HOURS SINCE THIS WILL
RESULT IN SOME AREAS WITH SOMEWHAT LOWER PRECIP AMOUNTS.
PREVIOUS LONG TERM DISCUSSION...
ISSUED AT 315 PM MDT FRI MAY 15 2026
CONFIDENCE IS INCREASING IN YET ANOTHER SIGNIFICANT, LATE SEASON
SNOW EVENT IMPACTING PORTIONS OF THE AREA SUNDAY NIGHT THROUGH
MONDAY NIGHT. THE OVERALL SYNOPTIC SETUP WILL FEATURE A DOUBLE
BARREL UPPER LEVEL LOW DIVING IN ACROSS THE WESTERN CONUS THIS
WEEKEND. THE MAIN TROUGH AXIS WILL BE FAIRLY SLOW MOVING, BUT A
STRONG, SECONDARY VORT-MAX WILL SWING ACROSS THE BASE OF THE TROUGH
SUNDAY NIGHT INTO MONDAY, ENHANCING LOCAL FORCING FOR ASCENT.
SHOWERY TYPE PRECIPITATION SUNDAY AFTERNOON WILL TRANSITION TO A
MORE STRATIFORM PRECIPITATION BY MONDAY MORNING. A REINFORCING COLD
FRONT IS ALSO EXPECTED TO MOVE SOUTHWARD INTO THE AREA SUNDAY
EVENING, LEADING TO A SURGE IN THE NORTHERLY SURFACE WINDS AND
STEADILY DROPPING TEMPERATURES. THE MID-LEVEL CYCLONE WILL DIVE DOWN
INTO THE INTERIOR ROCKIES DURING THIS PERIOD, WHICH WILL CLOSE OFF
BETWEEN ABOUT 700 AND 500-MB. THIS WILL ALLOW MOISTURE AND WIND TO
WRAP IN OVER THE NORTHEAST SIDE OF THE LOW, IN A PSEUDO-TROWAL LIKE
SETUP, JUST ON THE WRONG SIDE OF THE SYSTEM. MODELS ARE RATHER
AGGRESSIVE ON STRONG ISENTROPIC LIFT AND POSITIVE THETA-E ADVECTION
OVER MUCH OF THE AREA SUNDAY EVENING AND CONTINUING THROUGH AT LEAST
MIDDAY MONDAY. IN ADDITION, ENSEMBLES ARE IN FAIRLY GOOD AGREEMENT
SHOWING STRONG FRONTOGENESIS SETTING UP ALONG THE I-80 CORRIDOR WEST
OF LARAMIE. ALL TOGETHER, WE HAVE NUMEROUS LIFTING MECHANISMS AND
AMPLE MOISTURE WITH NEARLY SATURATED VERTICAL PROFILES.
ENSEMBLES ARE PRETTY AGGRESSIVE ON LIQUID PRECIPITATION.
FORTUNATELY, THIS SYSTEM LOOKS TO DELIVER BENEFICIAL MOISTURE TO A
LARGER PORTION OF THE AREA, UNLIKE THE PREVIOUS SNOW EVENT THIS
MONTH WHICH WAS MAINLY CONFINED TO LARAMIE, CHEYENNE, AND AREAS IN
BETWEEN. THE 25TH PERCENTILE LIQUID PRECIPITATION EXCEEDS 0.5" FOR
THE ENTIRE AREA, SUGGESTING A GOOD CHANCE FOR WIDESPREAD MOISTURE.
50TH PERCENTILE AMOUNTS EXCEED 1.0" OVER MUCH OF SOUTHEAST WYOMING
WHERE THE DYNAMICS ARE A BIT STRONGER AND THERE WILL BE MORE OF A
BOOST FROM OROGRAPHIC LIFT. THIS WOULD ORDINARILY BE GREAT NEWS FOR
OUR DROUGHT STRICKEN AREA, BUT UNFORTUNATELY, THIS SYSTEM WILL BE
VERY COLD FOR THIS TIME OF YEAR. LREF MEAN 700-MB TEMPERATURES DROP
TO AROUND -4 TO -7C OVER MUCH OF SOUTHEAST WYOMING, AND -2 TO -5C
OVER WESTERN NEBRASKA. A SHALLOW COLD AIR LAYER IS ALSO EXPECTED TO
UNDERCUT A DEEP WARM NOSE ALOFT, BUT THIS WARM NOSE IS EXPECTED TO
REMAIN LARGELY BELOW FREEZING. THESE TEMPERATURES WILL SUPPORT
ACCUMULATING SNOW DOWN TO ABOUT 5000 FT IN ELEVATION, AND SNOWFLAKES
MIXING IN WITH THE RAIN FOR THE ENTIRE AREA, EVEN IN THE LOWER
ELEVATIONS OF WESTERN NEBRASKA. ACCUMULATIONS AND IMPACTS (DUE TO
SNOW) ARE LESS LIKELY BELOW 5000 FT. RAIN WILL TRANSITION OVER TO
SNOW SUNDAY NIGHT IN SOUTHEAST WYOMING, SO WE MAY BE ABLE TO GET
SOME SNOW STICKING TO THE GROUND BEFORE THE SUN COMES UP. WITH THE
SUN ANGLE JUST A MONTH AWAY FROM THE SUMMER SOLSTICE, IT WILL BE
VERY DIFFICULT TO ACCUMULATE SNOW DURING THE DAY, BUT WE STILL
SHOULD SEE SOME STICKING TO GRASSY/ELEVATED SURFACES. MOST LIKELY
SNOW AMOUNTS ARE CURRENTLY SITTING AROUND 4-7" IN RAWLINS AND
ARLINGTON/ELK MOUNTAIN, 3-6" IN LARAMIE, 2-4" IN CHEYENNE, DOUGLAS,
SARATOGA, AND LUSK, AND A TRACE TO 2" ELSEWHERE. THE MOUNTAINS,
PARTICULARLY THE SNOWY RANGE, LARAMIE RANGE, AND MUDDY GAP AREA CAN
EXPECT HIGHER AMOUNTS IN THE 6 TO 12" RANGE. WHILE THESE ARE THE
MOST LIKELY AMOUNTS, THERE IS SOME CONCERN FOR HIGH END POTENTIAL
WITH THIS EVENT. THE STRONG SIGNAL FOR FRONTOGENESIS IN CARBON
COUNTY IS PARTICULARLY NOTEWORTHY. THERE IS A PLAUSIBLE HIGH END
SCENARIO WHERE 10 TO 16 INCHES FALLS IN CARBON COUNTY, AND 5 TO 10
INCHES FALLS IN OTHER POPULATED AREAS OF SOUTHEAST WYOMING. THE
CURRENT PROBABILITY OF THIS SCENARIO IS AROUND 10 TO 25%.
DECIDUOUS TREES ARE NOW FULLY LEAFED OUT ACROSS THE AREA. WITH
HEAVY, WET SNOW EXPECTED, THE PRIMARY IMPACT OF THIS EVENT IS
EXPECTED TO BE TREE DAMAGE. SNOW WILL HAVE TROUBLE STICKING TO THE
ROADS, BUT THE HIGHER ELEVATIONS OF I-80 IN CARBON AND ALBANY COUNTY
MAY ANTICIPATE SOME ROAD IMPACTS. UNLIKE THE PREVIOUS SNOW EVENT
THIS MONTH, THIS ONE WILL UNFORTUNATELY BE ACCOMPANIED BY
SIGNIFICANT SURFACE WINDS. THE HIGH PLAINS CAN EXPECT A STEADY, COLD
NORTH WIND GUSTING AROUND 25 TO 35 MPH. THE SURFACE HIGH PUSHING UP
AGAINST THE HIGHER TERRAIN AND STALLING WILL LEAD TO AN IMPRESSIVELY
STRONG REVERSE PRESSURE GRADIENT, WHICH IS LIKELY TO LEAD TO STRONG
WINDS IN CARBON AND ALBANY COUNTIES. THERE IS HIGH CONFIDENCE GUSTS
OF 35 TO 45 MPH IN THIS AREA, WITH THE POSSIBILITY OF GUSTS
APPROACHING 55 MPH. BLOWING SNOW IMPACTS WILL BE REDUCED BY THE
EXPECTED WET CONSISTENCY OF THE SNOW, BUT WE WILL NEED TO KEEP AN
EYE ON THIS AS WELL. THERE IS SOME UNCERTAINTY CONCERNING HOW THESE
WINDS WILL AFFECT SNOW ACCUMULATIONS ON LEAFED OUT TREES. ON ONE
HAND, THIS COULD HELP KNOCK SNOW OFF, BUT IT ALSO MIGHT INCREASE THE
STRAIN ON BRANCHES AND LEAD TO MORE DOWNED LIMBS.
THE LAST IMPACT OF THIS EVENT WILL BE THE EXPECTED COLD
TEMPERATURES. 700-MB TEMPERATURES ARE AROUND THE 2.5 PERCENTILE OF
CLIMATOLOGY. WITH PLENTIFUL CLOUD COVER, FORECAST HIGH TEMPERATURES
FOR MONDAY WERE NUDGED DOWN TOWARDS THE NBM 25TH PERCENTILE, BUT
THIS MAY EVEN BE STILL TOO WARM. HIGHS WILL STRUGGLE TO GET ABOVE
THE MID 30S IN SOUTHEAST WYOMING WHERE SNOW IS FALLING, AND EVEN
WESTERN NEBRASKA WILL GET STUCK IN THE LOW 40S. MONDAY NIGHT WILL
BRING THE COLDEST TEMPERATURES OF THE EVENT. EXPECT WIDESPREAD
FREEZING TEMPERATURES, WITH ESSENTIALLY THE ENTIRE AREA EXPECTED TO
FALL BELOW FREEZING. RAWLINS AND LARAMIE ARE FAVORED TO DROP BELOW
25 DEGREES, WITH CHEYENNE EVENT MAINTAINING A PROBABILITY OF AROUND
40%. THE MAIN QUESTION WILL BE CLOUD COVER. IF WE CAN MAINTAIN SOME
LOW CLOUD COVER THROUGH THE NIGHT, WE MAY BE SPARED THE WORST OF THE
IMPACTS OF THE FREEZING TEMPERATURES. HOWEVER, EARLY CLEARING WILL
LIKELY LEAD TO WIDESPREAD 20S AND EVEN SOME POCKETS OF TEENS SHOWING
UP. RECORD LOW MAXIMUM TEMPERATURES ARE LIKELY DURING THE DAY
MONDAY, AND RECORD LOW MINIMUM TEMPERATURES ARE LIKELY BY TUESDAY
MORNING. THOSE WITH SENSITIVE VEGETATION OR OUTDOOR IRRIGATION
SYSTEMS SHOULD TAKE STEPS THIS WEEKEND TO PREPARE FOR THE UPCOMING
COLD TEMPERATURES.
BEHIND THIS STORM SYSTEM, THE WARMUP WILL BE FAIRLY SLOW AS GENERAL
TROUGHING IS EXPECTED TO REMAIN OVER THE AREA THROUGH THE WEEK
AHEAD. EXPECT TEMPERATURES TO REMAIN BELOW SEASONAL AVERAGES THROUGH
AT LEAST WEDNESDAY, AND POSSIBLY THURSDAY. THE STORM TRACK WILL
REMAIN ACTIVE AS WELL WITH A CONTINUED STREAM OF VORT MAXES MOVING
THROUGH THE AREA, WHICH WILL KEEP SLIM CHANCES FOR SHOWERS AND A FEW
THUNDERSTORMS GOING, BUT THE POTENTIAL FOR WIDESPREAD RAINFALL WILL
BE FAIRLY LOW AFTER THE MAIN EVENT CONCLUDES MONDAY AFTERNOON.
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 1122 PM MDT FRI MAY 15 2026
A RELATIVELY CALM NIGHT ALONG WITH VFR CONDITIONS WILL PREVAIL
ACROSS MOST TERMINALS THROUGH THE OVERNIGHT HOURS. THINGS CHANGE
SATURDAY MORNING AS A SYSTEM PUSHES INTO THE CWA, INCREASING THE
THREAT OF THUNDERSTORMS, SOME OF WHICH MAY BE SEVERE. CHANCES OF
THUNDERSTORMS WILL START OFF AROUND KLAR AT ABOUT 18Z, PROGRESSING
EAST AND NORTH THROUGH THE MORNING INTO THE AFTERNOON HOURS. ALL
TERMINALS, EXCEPT KRWL, WILL HAVE THE POSSIBILITY OF THUNDERSTORMS
BY 22Z SATURDAY. IN AND AROUND ANY THUNDERSTORM THAT HITS OR COMES
NEAR A TERMINAL, EXPECT GUSTY AND ERRATIC WINDS ALONG WITH LOWER
CIGS AND REDUCED VIS IN RAIN.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY
AFTERNOON FOR WYZ103-104-110-114-116.
NE...NONE.
SHORT TERM...TJT
LONG TERM...MN/TJT
AVIATION...RZ
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