314
FXUS65 KCYS 181145
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
545 AM MDT FRI APR 18 2025
KEY MESSAGES
- WINTER STORM WARNINGS AND WINTER WEATHER ADVISORIES REMAIN IN
EFFECT THROUGH THIS AFTERNOON AND EVENING. CONTINUED SNOWFALL
EXPECTED THROUGH THE DAY.
- MUCH COLDER SATURDAY MORNING, WITH LOWS STRUGGLING TO REACH
THE 20S.
- WARMER AND SLIGHTLY DRIER SUNDAY THROUGH TUESDAY. WINDY
CONDITIONS POSSIBLE SUNDAY NIGHT AND MONDAY.
- ANOTHER PERIOD OF UNSETTLED WEATHER EXPECTED MID TO LATE WEEK
WITH NUMEROUS SHOWERS AND WIDELY SCATTERED THUNDERSTORMS.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED AT 306 AM MDT FRI APR 18 2025
ACTIVE NIGHT TONIGHT AS SNOW SHOWERS CONTINUE TO MOVE AND SPREAD TO
THE NORTHEAST, WITH A HEAVY BAND JUST EAST OF LARAMIE AS OF 08Z.
RATES WITH THIS BAND WERE PRETTY GOOD, AS WEBCAMS SOME SIGNIFICANT
DETERIORATION OF ROAD CONDITIONS IN AND AROUND LARAMIE AFTER THE
BAND PUSHED THROUGH. THIS BAND WILL SLOWLY MOVE EAST-NORTHEAST AND
LIKELY IMPACT CHEYENNE IN THE NEXT FEW HOURS. WEBCAMS ALONG I-80
SHOW FAIRLY HEAVY SNOW EAST OF CHEYENNE SLOWLY MOVING TOWARDS THE
CAPITAL CITY. CONTINUED UPSLOPE DEVELOPMENT IS PRESENT ACROSS THE
NORTHERN COLORADO MOUNTAIN RANGES AS HEAVY SNOW BANDS DEVELOP AND
MOVE NORTHERLY, PUSHED ALONG BY SYNOPTIC WINDS, INTO THE CWA. MUCH
COLDER TEMPERATURES ARE ONGOING TONIGHT COMPARED TO PREVIOUS NIGHTS,
WITH TEMPERATURES CURRENTLY IN THE 20S AND 30S ACROSS THE REGION.
THE PANHANDLE IS THE WARMEST AT THIS TIME WITH A FEW SITES
APPROACHING THE MID-30S. DESPITE THIS, STOUT NORTHERLY WINDS ARE
MAKING MOST LOCATIONS FEEL LIKE THEY ARE IN THE TEENS TO 20S.
UPPER-LEVEL TROUGHING REMAINS OVERHEAD THIS MORNING AS THE ONGOING
WEATHER SYSTEM SLOWLY CONTINUES ITS EASTWARD CRAWL. THE STRONG,
UPPER-LEVEL JET HAS BEEN PUSHED JUST EAST OF THE CWA OVERNIGHT
TONIGHT, BUT WITH THE SLOW PROGRESSION OF THIS SYSTEM THE REGION IS
EXPECTED TO REMAIN BROADLY IN THE LEFT EXIT REGION OF THE UPPER-
LEVEL JET. AS A RESULT, CONTINUED SYNOPTIC LIFT WILL BE PRESENT,
LEADING TO CONTINUED PRECIPITATION CHANCES THIS MORNING INTO THE
AFTERNOON HOURS. MULTIPLE 500MB VORTICITY MAXIMA CONTINUE TO EJECT
OVERHEAD, WITH THE MAIN LOBE STILL OFF TO THE WEST OF THE CWA. AS
THESE INITIAL MAXIMA TRAVERSE OVERHEAD, CONTINUED SYNOPTIC LIFT AND
PRECIPITATION SUPPORT THROUGH THE EARLY MORNING HOURS. WITH THE
SUPPORT OF THESE MAXIMA, ANOTHER DECENT SURGE OF PRECIPITATION IS
EXPECTED THIS MORNING INTO THE LATE AFTERNOON HOURS. CURRENT GOES-19
LOW-, MID-, AND UPPER-LEVEL WATER VAPOR IMAGERY SHOW AN ADDITION
PUSH OF MOISTURE CURRENTLY FUELING THE DEVELOPMENT OF THE HEAVIER
SNOW SHOWERS ACROSS NORTHERN COLORADO. BEHIND THIS PUSH IS A STEAMER
OF ADDITIONAL MOISTURE FROM SOUTHERN CALIFORNIA NORTHEASTERLY
THROUGH NORTHERN ARIZONA, UTAH, WESTERN COLORADO, AND CENTRAL
WYOMING. THIS WILL ACT TO PROVIDE CONTINUED MOISTURE FOR THE SECOND
PUSH OF PRECIPITATION LATER THIS MORNING, LIKELY WHEN THE BEST
ACCUMULATIONS ARE GOING TO OCCUR IN LOCATIONS THAT HAVE NOT SEEN
MUCH SNOW UP TO THIS POINT. A FRONTOGENESIS BAND IS PROGGED TO SETUP
ACROSS THE CARBON/ALBANY COUNTY LINE IN BOTH THE GFS AND NAM,
SUGGESTING CONTINUED SUPPORT FOR BANDED PRECIPITATION ACROSS THIS
AREA, LIKELY ENHANCED BY ONGOING UPSLOPE DEVELOPMENT ALONG THE
MOUNTAINS OF NORTHERN COLORADO. THIS SECONDARY SURGE OF
PRECIPITATION SHOULD COME TO AN END BY FRIDAY AFTERNOON, WITH
PRECIPITATION CHANCES QUICKLY FALLING OFF AFTER THIS TIME. DID
DECREASE EXPECTED ACCUMULATIONS ACROSS THE REGION DUE TO FORECAST
SNOW RATIOS BEING MUCH HIGHER THAN ONGOING RATIOS. AS A RESULT,
SEVERAL LOCATIONS HAD THEIR SNOWFALL FORECAST DROP BY AN INCH OR TWO.
OVERNIGHT LOWS TONIGHT INTO SATURDAY MORNING WILL BOTTOM OUT IN THE
TEENS AND 20S DUE TO CONTINUE COLD AIR INTRUSION INTO THE REGION
FRIDAY. WITH A SNOWPACK EXPECTED IN MANY OF THESE LOCATIONS, BLENDED
CURRENT FORECAST LOWS WITH THE NBM10TH PERCENTILE, TO TRY TO ACCOUNT
FOR SOME OF THE SNOWPACK ACROSS THE REGION FRIDAY NIGHT. SATURDAY
WILL BE ON THE COOLER SIDE AS THE UPPER-LEVEL TROUGH CONTINUES TO
INFLUENCE THE REGION. WITH SOME QUESTIONS ABOUT HOW LONG THE
SNOWPACK WILL LAST WITH APRIL SUN ANGLES, HIGH TEMPERATURE FORECASTS
ON SATURDAY HAVE SOME UNCERTAINTY. DID DECREASE HIGHS A BIT ACROSS
AREAS FAVORED FOR A HIGHER SNOWPACK, BUT THE APRIL SUN ANGLES WILL
BE HARSH ON THE LINGERING SNOWPACK. LITTLE TO NO PRECIPITATION IS
EXPECTED ON SATURDAY AS THE UPPER-LEVEL TROUGH FINALLY PUSHES EAST
OF THE REGION AND A WEAK RIDGE ATTEMPTS TO DEVELOP IN THE UPPER-
LEVELS.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED AT 306 AM MDT FRI APR 18 2025
MOST OF THE LONG RANGE FORECAST LOOKS ON TRACK, BUT SOME RUN TO RUN
INCONSISTENCIES HAVE APPEARED IN RESPONSE TO THE SLOWER MOVEMENT
SPEED OF THE DEPARTING UPPER LEVEL TROUGH AXIS FROM FRIDAY AND
SATURDAY. IN ADDITION THE NEXT PACIFIC DISTURBANCE FOR LATE MONDAY,
AND THE ASSOCIATED JET MAX, ARE POSITIONED A BIT FURTHER SOUTH
COMPARED TO PREVIOUS RUNS, WHICH WOULD LEAD TO INCREASING WINDS
ALONG WITH SOME ADDITIONAL DRYING OF THE BOUNDARY LAYER DUE TO
WESTERLY DOWNSLOPE WINDS. ENSEMBLES ARE STARTING TO CATCH ONTO THIS
TREND, WITH ENS AND GEFS GUIDANCE SHOWING INCREASING WINDS ON MONDAY
AND MONDAY NIGHT AND LOWER DEWPOINTS ACROSS THE AREA. THIS MAY LIMIT
ANY DEVELOPING CONVECTION TO ISOLATED OR WIDELY SCATTERED AT BEST,
BUT STILL EXPECT SOME ACTIVITY CLOSE TO THE LEFT-ENTRANCE REGION OF
THE UPPER LEVEL JET MAX. WITH 700MB WINDS AROUND 40 KNOTS, ALONG
WITH HIGHER WINDS ABOVE 700MB, INCREASED WINDS SPEEDS ACROSS THE
AREA. DO NOT EXPECT HIGH WIND CRITERIA AT THIS TIME, BUT WILL HAVE
TO WATCH THE WIND PRONE AREAS ALONG WITH THE SUB-WIND PRONE AREAS TO
SEE IF MODELS CONTINUE TO TREND HIGHER ON WIND SPEEDS AND GUSTS.
KEPT TEMPERATURES NEAR OR SLIGHTLY BELOW AVERAGE ON SUNDAY SINCE
MODELS HAVE TRENDED LESS PROGRESSIVE WITH THE DEPARTURE OF THE
EXITING UPPER LEVEL TROUGH.
OTHERWISE, NEXT WEEK STILL LOOKS MOSTLY UNSETTLED AS A LONG WAVE
TROUGH SETTLES OVER THE EASTERN PACIFIC AND WESTERN THIRD OF THE
UNITED STATES. THE ECMWF AND CANADIAN HAVE TRENDED TOWARDS THE GFS
SOLUTION, SHOWING A QUASI-STATIONARY FRONT ALONG OR NEAR THE LARAMIE
RANGE IN ADDITION TO SEVERAL PACIFIC SHORTWAVES LIFTING NORTHEAST
ACROSS THE AREA EVERY 24 TO 36 HOURS. TUESDAY IS THE ONLY
QUESTIONABLE DAY WITH MOST MODELS SHOWING A LINGERING DRY BOUNDARY
LAYER FROM MONDAY. HOWEVER, LOW LEVEL MOISTURE ADVECTION IS EXPECTED
BY LATER IN THE DAY WHICH MAY AID IN THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS. WEDNESDAY THROUGH THE END OF THE WEEK LOOK UNSETTLED
AND CLOUDY WITH ANY MORNING SUNSHINE GIVING AWAY TO WIDESPREAD
SHOWERS AND THUNDERSTORMS EACH AFTERNOON. MODELS ALSO STARTING TO
SHOW INCREASING NORTHWARD MOISTURE ADVECTION OUT OF THE GULF WITH
NAEFS ALREADY ABOVE THE 90TH TO 95TH PERCENTILE FOR PWAT BY THURSDAY
(AROUND THE 850MB LEVEL). THE NBM HAS STRUGGLED TO CATCH UP WITH
THIS TYPICAL SPRING PATTERN, BUT HAD SUDDENLY BUMPED POP UP TOWARDS
80 PERCENT. PREFER A MORE BALANCED APPROACH AND SLIGHT UPWARD TREND,
SO INCREASING POP A LITTLE OVER THE PREVIOUS FORECAST PACKAGE WITH
VALUES GENERALLY BETWEEN 40 TO 60 PERCENT. ALSO, WILL HAVE TO WATCH
FOR FOG POTENTIAL EACH DAY WITH AMPLE MOISTURE AND COOL TEMPERATURES
EACH NIGHT. ALL MODELS NOW SHOW SOME RESPECTABLE QPF TOTALS.
PRECIPITATION LOOKS TO BE ALL RAIN BELOW 7500 FEET WITH SOME
MOUNTAIN SNOW POSSIBLE. THANKFULLY, TEMPERATURES (BOTH MAX AND MIN)
SHOULD BE SLIGHTLY ABOVE AVERAGE FOR THIS TIME OF THE YEAR AND
GENERALLY IN THE UPPER 50S AND 60S. UPSLOPE EASTERLY WINDS AND
PERSISTENT CLOUD COVER MAY RESULT IN COOLER TEMPERATURES FOR A FEW
AREAS, BUT SHOULD STILL REMAIN NEAR AVERAGE FOR LATE APRIL.
AVIATION /12Z TAFS THROUGH 12Z SATURDAY/
ISSUED AT 545 AM MDT FRI APR 18 2025
SLOW MOVING UPPER LEVEL TROUGH WILL REMAIN OVER WYOMING AND UTAH
OVER TODAY. LIGHT TO OCCASIONAL MODERATE SNOW WILL CONTINUE THIS
MORNING, EVENTUALLY TAPERING OFF TO FLURRIES BY MIDAFTERNOON. LOW
CIGS AND SOME PATCHY FOG ARE POSSIBLE TONIGHT, MAINLY ALONG THE
INTERSTATE 80 TERMINALS.
HAZARDS/WEATHER TRENDS: IFR TO LIFR CONDITIONS IN SNOW AND LOW CIGS
WILL PREVAIL OVER THE SOUTHEAST WYOMING TERMINALS, WITH OCCASIONAL
MVFR CIGS/VIS. CONDITIONS ARE EXPECTED TO IMPROVE AFTER 20Z. WITH
ANY CLEARING SKIES TONIGHT, LOW CIGS AND FOG ARE POSSIBLE, BUT NOT
CONFIDENT ENOUGH TO ADD TO THE SOUTHEAST WYOMING TAFS JUST YET.
FOR WESTERN NEBRASKA, FORECAST IS LESS CERTAIN DUE TO THE LACK OF
STEADY SNOWFALL OBSERVED. KEPT VFR OR NEAR VFR CONDITIONS FOR KCDR
AND KBFF WITH LOCALIZED DOWNSLOPE WINDS OBSERVED. HOWEVER, CAN'T
RULE OUT A FEW BANDS OF SNOW REDUCING VIS TO 2SM AT TIMES. HIGHER
CONFIDENCE THAT KSNY AND KAIA WILL SEE PROLONGED IFR CONDITIONS IN
SNOW TODAY, WITH CONDITIONS IMPROVING AFTER 20Z. HIGH RES GUIDANCE
IS SHOWING SOME LOCALLY HEAVY RAIN/SNOW SHOWERS DEVELOPING OVER
WESTERN NEBRASKA THIS AFTERNOON, SO ADDED PROB30 GROUPS FOR IFR
CONDITIONS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER STORM WARNING UNTIL NOON MDT TODAY FOR WYZ101>103-105-
109-112-114-116.
WINTER STORM WARNING UNTIL 6 AM MDT EARLY THIS MORNING FOR
WYZ104.
WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ106-
110-117.
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ107-
108-113-115-118-119.
NE...WINTER WEATHER ADVISORY UNTIL NOON MDT TODAY FOR NEZ002-095.
SHORT TERM...AM
LONG TERM...TJT
AVIATION...TJT
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