497
FXUS65 KCYS 172332
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
532 PM MDT THU APR 17 2025
KEY MESSAGES
- AN IMPACTFUL WINTER STORM IS EXPECTED TODAY THROUGH FRIDAY.
WIDESPREAD ACCUMULATING SNOW IS LIKELY. WINTER STORM WARNINGS
AND WINTER WEATHER ADVISORIES ARE IN EFFECT FOR PORTIONS OF
SOUTHEAST WYOMING AND WESTERN NEBRASKA.
- REMAINING UNSETTLED DURING THE WEEKEND THROUGH EARLY NEXT WEEK
WITH CHANCES OF SHOWERS EACH DAY.
SHORT TERM /THROUGH FRIDAY NIGHT/
ISSUED AT 253 PM MDT THU APR 17 2025
BASED ON OBSERVATIONS, THE SURFACE COLD FRONT HAS ALREADY MOVED
THROUGH MOST OF THE CWA. TEMPERATURES BEHIND THE FRONT ARE COLDER
WITH A MORE NORTHERLY COMPONENT TO THE WIND. RADAR SHOWS
PRECIPITATION INCREASING IN COVERAGE BEHIND THE FRONT. THIS TREND
WILL CONTINUE THROUGH THE AFTERNOON HOURS WITH RAIN CONTINUING TO
MAKE THE SWITCH OVER TO SNOW AS THE FRONT ALOFT TRAVERSES THE CWA.
CANNOT RULE OUT A FEW RUMBLES OF THUNDER IN SHOWERS AHEAD OF THE
COLD FRONT ALOFT.
FOR THE MOST PART, THE FORECAST REMAINS ON TRACK. THE POTENT UPPER-
LEVEL TROUGH RESPONSIBLE FOR THE COLD FRONT AND PRECIPITATION WILL
CONTINUE TO PUSH INTO WYOMING TODAY AND BE OUT OF THE CWA BY
SATURDAY. ACCUMULATING SNOW IS STILL EXPECTED THROUGHOUT SOUTHEAST
WYOMING AND MOST OF THE NEBRASKA PANHANDLE, WITH STRONG
FRONTOGENESIS AND UPSLOPE BEING THE MAIN DRIVERS OF SNOWFALL
ACCUMULATION. OF COURSE, GIVEN THE TIME OF YEAR, FACTORS LIKE SUN
ANGLE AND HOW QUICKLY THE GROUND CAN COOL OFF AFTER A FEW DAYS OF
ABOVE AVERAGE TEMPERATURES WILL PLAY A ROLE IN SNOWFALL TOTALS. SNOW
LIKELY WILL NOT START ACCUMULATING UNTIL LATE AFTERNOON OR AFTER
SUNSET.
DIVING DEEPER INTO THIS SYSTEM, A LOT OF THE DYNAMICS FAVOR AREAS OF
HEAVY, BANDED SNOW AND OROGRAPHIC UPSLOPE FLOW. THE GFS SHOWS LARGE
AREAS OF VERY STRONG MID-LEVEL FRONTOGENESIS COLOCATED WITH AREAS OF
QPF AND SATURATED DGZS. THE MAIN AREA OF CONCERN FOR THIS SET-UP
WILL BE WEST OF THE LARAMIE RANGE, WHERE WINTER STORM WARNINGS ARE
IN EFFECT. THIS WILL LIKELY LEAD TO HEAVY SNOW AT TIMES, ESPECIALLY
LATE THURSDAY AFTERNOON THROUGH FRIDAY MORNING. SNOW ACCUMULATIONS
IN MOST OF THE WARNING AREAS WILL BE BETWEEN 6 AND 12 INCHES. EAST
OF THE LARAMIE RANGE, OROGRAPHICS AND UPSLOPE WILL PLAY A LARGER
ROLE IN SNOWFALL ACCUMULATION. NORTH TO NORTHEAST WINDS BEHIND THE
COLD FRONT WILL BE FAVORABLE FOR OROGRAPHIC LIFT IN BOTH THE NORTH
LARAMIE RANGE AND PINE RIDGE. CITIES ALONG THE US-20 CORRIDOR,
ESPECIALLY IN WYOMING CAN EXPECT 5 TO 10 INCHES OF SNOW. THESE
LOCATIONS ARE IN A WINTER STORM WARNING. PINE RIDGE AREAS IN
NEBRASKA COULD SEE UP TO 6 INCHES. THE NORTH LARAMIE RANGE WILL BE
IN A PROLONGED PERIOD OF MOIST UPSLOPE FLOW, SO THIS AREA IS LIKELY
TO SEE THE HIGHEST SNOWFALL TOTALS IN THE CWA FOR THIS EVENT. OTHER
AREAS TO WATCH WILL INCLUDE THE SOUTH LARAMIE RANGE AND FOOTHILLS AS
WELL AS THE CHEYENNE RIDGE. THE CHEYENNE RIDGE ALSO FAVORS UPSLOPE
FLOW IN NORTHERLY FLOW SO AREAS BETWEEN WHEATLAND AND CHEYENNE ARE
CURRENTLY IN A WINTER STORM WARNING FOR 6+ INCHES OF SNOW. ENSEMBLE
MEANS FROM THE GFS AND ECMWF ARE FAIRLY IN LINE WITH THESE TOTALS.
LATER SHIFTS WILL HAVE TO KEEP AN EYE ON LARAMIE, RAWLINS,
WHEATLAND, AND CHEYENNE. HI-RES GUIDANCE FROM THE HRRR HAS INCREASED
SNOWFALL TOTALS ACROSS THE AREA OVERNIGHT. WILL HAVE TO KEEP AN EYE
ON THESE AREAS TO SEE IF WINTER WEATHER ADVISORIES WILL NEED TO BE
UPGRADED. MODELS KEEP CONSISTENTLY SHOWING LARAMIE GETTING WARNING
LEVEL AMOUNTS, HOWEVER, LARAMIE WILL BE DOWNSLOPING THROUGH THE
MAJORITY OF THE EVENT. IF STRONG FRONTOGENESIS CAN OVERCOME
DOWNSLOPING, THEN LARAMIE COULD SEE OVER 6 INCHES OF SNOW. LASTLY,
GUSTY WINDS AT RAWLINS OVERNIGHT COULD CAUSE POOR VISIBILITY WITH
BLOWING SNOW. IT IS POSSIBLE THAT VISIBILITY COULD DROP BELOW A
QUARTER MILE FOR A PROLONGED PERIOD OF TIME, PROMPTING THE NEED FOR
A SHORT FUSE BLIZZARD WARNING. OPTED TO HOLD OFF AT THIS TIME AS
MODELS HAVE TRENDED WINDS DOWNWARD A BIT COMPARED TO PREVIOUS RUNS.
SNOW WILL CONTINUE THROUGH MOST OF THE DAY FRIDAY, BUT WILL
GRADUALLY TAPER OFF THROUGHOUT THE DAY FROM NORTH TO SOUTH. MINIMAL
ACCUMULATIONS ARE EXPECTED AFTER SUNSET ON FRIDAY, HOWEVER THERE
COULD BE A FEW LINGERING SNOW SHOWERS OVERNIGHT. BEHIND THE FRONT,
TEMPERATURES WILL BE MUCH COLDER FOR FRIDAY. HIGH TEMPERATURES WILL
STRUGGLE TO REACH FREEZING FOR MUCH OF SOUTHEAST WYOMING, WITH LOW
40S EXPECTED FOR THE PANHANDLE. COLD TEMPERATURES WILL CONTINUE INTO
FRIDAY NIGHT WITH TEENS AND 20S EXPECTED ACROSS THE AREA.
LONG TERM /SATURDAY THROUGH THURSDAY/
ISSUED AT 350 AM MDT THU APR 17 2025
DETERMINISTIC MODELS AND ENSEMBLES IN REASONABLE AGREEMENT THIS
WEEKEND AND NEXT WEEK...SHOWING AN UNSETTLED WEATHER PATTERN
THROUGH THE EXTENDED. THANKFULLY, IT IS EXPECTED TO BE MORE
SPRING-LIKE WITH MILDER TEMPERATURES BUT WITH A DAILY CHANCE OF
SHOWERS AND SOME THUNDERSTORMS.
FOR THE WEEKEND, ALL MODELS INDICATE THE BEGINNING OF A LONG WAVE
PATTERN SHIFT AS A BROAD UPPER LEVEL TROUGH REPLACES THE GENERAL
MID TO UPPER LEVEL RIDGING THAT HAS PERSISTED ACROSS THE WESTERN
UNITED STATES OVER THE LAST 4 TO 6 WEEKS. STILL REMAINING ON THE
COOL SIDE THIS WEEKEND, ALTHOUGH MODELS SHOW A SLOW WARMING TREND
HEADING INTO SUNDAY. NORTHERLY FLOW ALOFT WILL REMAIN OVER THE
AREA SATURDAY AND SATURDAY NIGHT WITH THE UPPER LEVEL FLOW BACKING
INTO THE WEST ON SUNDAY. REMAINING CHILLY ON SATURDAY WITH HIGHS
STRUGGLING TO REACH 40 DEGREES FOR MOST OF SOUTHEAST WYOMING,
AND 40S TO NEAR 50 BELOW 4500 FEET. OFF/ON RAIN AND SNOW SHOWERS
ARE POSSIBLE SATURDAY, BUT NOT EXPECTING ANY ADDITIONAL SNOW
ACCUMULATION OUTSIDE OF THE MOUNTAINS. SUNDAY LOOKS SOMEWHAT
DRIER WITH MODERATE DOWNSLOPE WESTERLY WIND EXPECTED. IT WILL
ALSO BE MILDER ON SUNDAY WITH TEMPERATURES NEAR NORMAL FOR MID
APRIL (50S TO LOW 60S).
NEXT WEEK LOOKS MOSTLY UNSETTLED AS A LONG WAVE TROUGH SETTLES
OVER THE EASTERN PACIFIC AND WESTERN THIRD OF THE UNITED STATES.
THIS WILL RESULT IN A PROGRESSIVE STORM TRACK ACROSS WYOMING
AND THE ADJACENT HIGH PLAINS OF COLORADO AND WESTERN NEBRASKA.
ALTHOUGH MODELS ARE IN VERY GOOD AGREEMENT WITH THE OVERALL
PATTERN, THERE ARE SIGNIFICANT TIMING AND PLACEMENT DIFFERENCES
BETWEEN INDIVIDUAL MODELS RELATING TO SHORTWAVE DISTURBANCES
AND FRONTAL PLACEMENT. THESE DIFFERENCES DO SHOW UP IN THE
LATEST ENSEMBLE GUIDANCE WITH RELATIVELY HIGH SPREADS IN SURFACE
MOISTURE/PWAT, CLOUD COVER, AND PRECIPITATION CHANCES. THE MORE
POTENT DISTURBANCES ARE FORECAST TO MOVE OVER THE FORECAST AREA
MONDAY NIGHT, WEDNESDAY, AND AGAIN ON THURSDAY AS A TRAIN OF
PACIFIC STORM SYSTEMS MOVE ONSHORE BETWEEN OREGON AND CENTRAL
CALIFORNIA. THE MOST NOTABLE WEATHER EVENT MAY BE TUESDAY NIGHT
AND WEDNESDAY ACROSS SOUTHEAST WYOMING, WITH THE GFS THE MOST
AGGRESSIVE MODEL...SHOWING A STATIONARY FRONT ALONG THE
MOUNTAINS AND I-80 CORRIDOR AS AN UPPER LEVEL DISTURBANCE MOVES
PARALLEL TO THE SURFACE FRONT. GFS SUGGESTS THAT THIS FRONT AND
A MIDLEVEL UPPER LEVEL DISTURBANCE/COLD POOL WILL BE THE FOCUS
FOR NUMEROUS TO WIDESPREAD SHOWERS AND THUNDERSTORMS THROUGH
LATE WEDNESDAY BEFORE THE FRONT DISSIPATES. 00Z GFS SHOWING SOME
PRETTY HIGH QPF TOTALS WITH MOSTLY RAINFALL BELOW 7000 FEET,
BUT SOME SOLID SNOWFALL TOTALS FOR THE MOUNTAINS. HOWEVER, THE
OTHER MODELS ARE NOT AS AGGRESSIVE AND SHOW THE FRONT
DISSIPATING MUCH SOONER COMPARED TO THE GFS. INCREASED POP OVER
THE NBM, BUT DID NOT GO AS HIGH AS 'LIKELY' QUITE YET DUE TO THE
UNCERTAINTY. OTHERWISE, WE ARE EXPECTING A SLOW WARMING TREND
NEXT WEEK WITH NEAR OR SLIGHTLY ABOVE AVERAGE TEMPERATURES IN
THE MID 50S TO MID 60S. WILL NEED TO MONITOR THE POTENTIAL FOR
STRONG THUNDERSTORMS SINCE MODELS AND ENSEMBLE GUIDANCE ARE
SHOWING A GRADUAL INCREASE IN LOW LEVEL DEWPOINTS UNDER EASTERLY
UPSLOPE FLOW DURING THE WEEK.
AVIATION /00Z TAFS THROUGH 00Z SATURDAY/
ISSUED AT 524 PM MDT THU APR 17 2025
A WEATHER DISTURBANCE AND COLD FRONT WILL BRING WIDESPREAD SNOW
TO THE TERMINALS THROUGH TONIGHT.
WYOMING TAFS...CEILINGS WILL RANGE FROM 300 TO 1500 FEET THROUGH
15Z, WITH PERIODS OF LIGHT SNOW AND FOG REDUCING VISIBILITIES
TO 1/4 TO 4 MILES, THEN CEILINGS WILL IMPROVE TO 1500 TO
2500 FEET AFTER 15Z FRIDAY. WINDS WILL GUST TO 25 KNOTS AT
LARAMIE UNTIL 01Z, AND TO 25 KNOTS AT RAWLINS UNTIL 15Z FRIDAY,
AND GUST TO 30 KNOTS AT CHEYENNE.
NEBRASKA TAFS...CEILINGS WILL RANGE FROM 500 TO 2500 FEET UNTIL
15Z FRIDAY, WITH OCCASIONAL LIGHT SNOW AND FOG REDUCING
VISIBILITIES TO 1 TO 4 MILES, THEN CEILINGS WILL IMPROVE TO
2500 TO 3500 FEET AFTER 15Z FRIDAY. WINDS WILL GUST TO 35 KNOTS
UNTIL 06Z, THEN WILL GUST TO 25 KNOTS AT SIDNEY AFTER 12Z
FRIDAY.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER STORM WARNING UNTIL NOON MDT FRIDAY FOR WYZ101>103-105-
109-112-114-116.
WINTER STORM WARNING UNTIL 6 AM MDT FRIDAY FOR WYZ104.
WINTER STORM WARNING UNTIL 6 PM MDT FRIDAY FOR WYZ106.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT FRIDAY FOR WYZ107-108-
113-115.
WINTER STORM WARNING UNTIL 6 PM MDT FRIDAY FOR WYZ110.
WINTER STORM WARNING FROM 9 PM THIS EVENING TO 6 PM MDT FRIDAY
FOR WYZ117.
WINTER WEATHER ADVISORY FROM 9 PM THIS EVENING TO 6 PM MDT
FRIDAY FOR WYZ118-119.
NE...WINTER WEATHER ADVISORY UNTIL NOON MDT FRIDAY FOR NEZ002-095.
SHORT TERM...SF
LONG TERM...TJT
AVIATION...RUBIN
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page