084
FXUS65 KCYS 271730
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
1130 AM MDT MON APR 27 2026
KEY MESSAGES
- A MESSY PATTERN IS ANTICIPATED TODAY THROUGH MUCH OF THE
UPCOMING WEEK, ALLOWING FOR ONGOING PRECIPITATION CHANCES
ACROSS THE ENTIRE CWA. THE BEST CHANCE FOR PRECIPITATION WILL
BE MONDAY NIGHT, WITH WIDESPREAD RAIN AND SNOW SHOWERS.
- A WINTER WEATHER ADVISORY HAS BEEN ISSUED FOR THE SIERRA MADRE
AND SNOWY RANGES FROM 6PM SATURDAY THROUGH 6AM MONDAY.
- THE MESSY, UPPER-LEVEL PATTERN CONTINUES MID-WEEK THROUGH AT
LEAST FRIDAY BEFORE WEAK RIDING RETURNS FOR THE WEEKEND.
SHORT TERM /THROUGH WEDNESDAY/
ISSUED AT 340 AM MDT MON APR 27 2026
THE EARLY MORNING AREAS OF FOG SHOULD BE CLEARING UP FROM WEST TO
EAST THIS EARLY MORNING, BUT A FEW AREAS COULD BE STUBBORN IN VALLEY
AREAS THROUGH DAYBREAK. A WEAK BACKDOOR COLD FRONT IS MOVING IN
WHICH IS DRY OUT THE AREA SLIGHTLY AND SHIFTING WINDS OUT OF THE
NORTHWEST. SOME SNOW SHOWERS ARE OCCURRING THIS MORNING IN THE
NORTHERN CWA WITH RAIN/SNOW MIX EXTENDING ELSEWHERE. MOST PLACES
WILL ONLY SEE A DUSTING FROM THIS ACTIVITY, THOUGH AMOUNTS UP TO
ABOUT HALF AN INCH MAY BE POSSIBLE IN CONVERSE AND NIOBRARA
COUNTIES. THE SIERRA MADRE AND SNOWY RANGES WILL BE THE EXCEPTION
WHERE ANOTHER 1 OR 2" MAY BE POSSIBLE BEFORE NOON. THIS SHOWER
ACTIVITY WILL START TO DIMINISH AS WE GO INTO THE AFTERNOON HOURS
AND THE SHORTWAVE DISTURBANCE DEPARTS TO THE EAST. BREAKS IN CLOUD
COVERAGE MAY ALLOW JUST ENOUGH INSTABILITY IN THE AFTERNOON TO
PRODUCE SCATTERED SHOWER AND STORM ACTIVITY WEST OF THE LARAMIE
RANGE. HI-RES GUIDANCE SUGGESTS THAT CAPE VALUES WILL NOT BE QUITE
AS HIGH AS THEY WERE YESTERDAY. STILL, A FEW OF THE STRONGER
UPDRAFTS COULD PRODUCE GUSTY DOWNDRAFTS AND LIGHTNING. HIGHS TODAY
WILL BE COOL, REACHING THE 40S IN OUR NORTHERN COUNTIES AND THE
INTERIOR MOUNTAIN BASINS. LOW 50S FOR THE CHEYENNE RIDGE AND NORTH
PLATTE RIVER VALLEY.
THIS EVENING AND OVERNIGHT, YET ANOTHER SHORTWAVE MOVES IN GIVING US
A ROUND OF RAIN AND SNOW. THIS ACTIVITY WILL BEGIN IN THE
SOUTHWESTERN COUNTIES AROUND 5 OR 6 PM AND SPREAD NORTHEAST THROUGH
THE NIGHT. RAIN AMOUNTS SHOULD BE BELOW HALF AN INCH AT MOST
LOCATIONS. THE SNOWY AND SIERRA MADRE MOUNTAINS MAY PICK UP AMOUNTS
BETWEEN 5-10 INCHES, WITH HIGHER AMOUNTS. THEREFORE, A SECOND WINTER
WEATHER ADVISORY IS IN EFFECT FOR THIS PERIOD OF SNOWFALL. SOME HIGH
RESOLUTION MODELS ARE DEPICTING A SWATH OF HIGHER AMOUNTS FOR THE
CENTRAL AND NORTHERN LARAMIE RANGE, EXTENDING INTO CONVERSE AND
NIOBRARA COUNTIES. THE CONFIDENCE IS LOW IN THIS SOLUTION AT THIS
TIME, BUT WE MAY NEED TO REVISIT SNOWFALL AMOUNTS IN THESE AREAS IF
CONFIDENCE INCREASES LATER TODAY. THIS DISTURBANCE MOVES EAST
THROUGHOUT THE DAY AND BY THE AFTERNOON ONLY A FEW LINGERING SHOWERS
SHOULD BE AROUND. CONDITIONS DRY OVERNIGHT WITH THE DOWNSLOPING
WINDS. A SUBTLE UPPER-LEVEL RIDGE BEGINS TO NOSE ITS WAY INTO THE
AREA GOING INTO THE DAY WEDNESDAY, KEEP THINGS DRY AND COOL TO START
THE MORNING.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/
ISSUED AT 340 AM MDT MON APR 27 2026
LARGELY ZONAL UPPER-LEVEL FLOW IS ANTICIPATED TO RETURN WEDNESDAY
THROUGH THURSDAY AS THE BROAD UPPER-LEVEL LOW OVER SOUTHERN CANADA
MOVES TO THE EAST AS A SHORTWAVE DEVELOPS ACROSS IDAHO. AHEAD OF THE
INCOMING SHORTWAVE TROUGH, WESTERLY FLOW WILL DOMINATE ALOFT WITH A
STRONG SUBTROPICAL JET JUST SOUTH OF THE WYOMING/COLORADO BORDER.
THE SHORTWAVE TROUGH REMAINS FAIRLY BROAD BEFORE SLOWLY BECOMING
MORE DEFINED THROUGHOUT WEDNESDAY EVENING INTO THE OVERNIGHT HOURS.
WEAK 500MB VORTICITY WILL EJECT OUT AHEAD OF THE APPROACHING
SHORTWAVE LEADING TO MODEST SYNOPTIC SUPPORT FOR ASCENT ACROSS THE
REGION, THOUGH WEAK 500MB FLOW IS EXPECTED. WESTERLY FLOW AT 700MB
WILL SLOWLY TURN NORTHWESTERLY THROUGH THE AFTERNOON HOURS BEFORE
BECOMING FAIRLY LIGHT AND VARIABLE AS HEIGHT GRADIENTS REMAIN WEAK.
WEAK WARM AIR ADVECTION (WAA) IS ANTICIPATED FOR WEDNESDAY AFTERNOON
AS 700MB TEMPERATURES WARM FROM ABOUT -3C TO AROUND 0C. THIS WEAK,
WAA AT 700MB WILL SUPPORT SOME ASCENT ACROSS THE REGION WITH ISOLATED
TO SCATTERED SHOWERS TO DEVELOP WEDNESDAY AFTERNOON. PRIMARILY RAIN
IS EXPECTED EAST OF THE LARAMIE RANGE WHERE THE BEST 700MB WAA IS
OCCURRING AND SURFACE TEMPERATURES WARM INTO THE MID-50S TO MID-60S,
WHILE SNOW IS EXPECTED WEST OF THE LARAMIE RANGE DURING THE MORNING
HOURS BEFORE TRANSITIONING TO RAIN/SNOW MIX WHERE WEAKER 700MB WAA
IS ANTICIPATED AND SURFACE TEMPERATURES STRUGGLE TO REACH THE 50F
MARK. SIGNIFICANT PRECIPITATION ACCUMULATION IS NOT EXPECTED WITH
THIS SYSTEM DUE TO THE AVERAGE PRECIPITABLE WATER VALUES FOR THIS
TIME OF YEAR AND OVERALL WEAK FORCING ACROSS THE AREA. HOWEVER,
ANOTHER TRACE TO 0.1 INCHES OF PRECIPITATION WILL BE POSSIBLE
WEDNESDAY AFTERNOON THROUGH EARLY THURSDAY MORNING, WITH ONLY A
TRACE OF SNOW ACCUMULATING WEST OF THE LARAMIE RANGE AND 2 TO 4
INCHES OF SNOW ACCUMULATION IN THE MOUNTAINS.
PRECIPITATION CHANCES WILL CONTINUE THURSDAY WITH THE DEVELOPMENT OF
THE UPPER-LEVEL SHORTWAVE, BUT THE UPPER-LEVEL PATTERN BECOMES QUITE
MESSY INTO THURSDAY AFTERNOON. THE UPPER-LEVEL SHORTWAVE WILL DEEPEN
ACROSS THE INTERMOUNTAIN WEST THROUGH EARLY FRIDAY MORNING, BUT
STRONG 500MB CYCLONIC VORTICITY ADVECTION (CVA) NORTHEAST OF THE
BASE OF THE SHORTWAVE WILL ACT TO ACCELERATE THE NORTHERN PORTION OF
THE LOW, WITH THE SOUTHERN PORTION STAYING STEADY. THE NORTHERN
PORTION OF THE LOW LOOKS TO PINCH TOGETHER, RESULTING IN THE
SHORTWAVE WEAKENING SIGNIFICANTLY AS THE ATMOSPHERE ATTEMPTS TO
REORGANIZE AFTER THE TROUGH GETS PINCHED OFF. BOTH THE GFS AND ECMWF
SUGGEST THIS MESSY UPPER-LEVEL FLOW FOR FRIDAY INTO SATURDAY, WITH A
BROAD, WEAKER SHORTWAVE TROUGH DEVELOPING FRIDAY EVENING AND
STARTING TO ADVECT OFF TO THE EAST. THIS INCREASES CONFIDENCE IN A
MESSY UPPER-LEVEL PATTERN DOMINATING THE MID-WEEK WEATHER. LUCKILY,
WITH THE MESSY DISTURBANCES ALOFT, SYNOPTIC SUPPORT FOR ASCENT WILL
CONTINUE THROUGHOUT MID-WEEK, ENABLING PRECIPITATION CHANCES TO
CONTINUE. PRECIPITATION CHANCES START TO TAPER OFF ON FRIDAY AS THE
UPPER-LEVEL SHORTWAVE FINALLY MOVES EAST OF THE REGION AND A RIDGE
DEVELOPS ACROSS MUCH OF THE INTERMOUNTAIN WEST. 700MB FLOW WILL
REMAIN MESSY THROUGH THE MIDDLE OF THE WEEK AND INTO THE WEEKEND
AHEAD OF THE RIDGE DEVELOPING EARLY SATURDAY MORNING. ANOTHER SYSTEM
ATTEMPTS TO MOVE INTO THE WESTERN CONUS SATURDAY AFTERNOON IN THE
GFS, BUT SIGNIFICANT DISAGREEMENT IS PRESENT BETWEEN LONG RANGE
MODELS. THEREFORE, FORECAST UNCERTAINTY INCREASES THROUGH THE
WEEKEND.
AVIATION /18Z TAFS THROUGH 18Z TUESDAY/
ISSUED AT 1130 AM MDT MON APR 27 2026
TRICKY FORECAST FOR THIS TAF PERIOD WITH VARYING CIGS AND VIS, WIND
SPEED AND DIRECTION CHANGES, ALSO PRECIP TYPE AND TIMING. SO, THIS
AFTERNOON EXPECT THE BEGINNING OF ISOLATED TO SCATTERED SNOW SHOWERS,
RAIN SHOWERS, AND/OR THE POSSIBILITY OF A FEW THUNDERSTORMS, BEST
CHANCES AT KRWL, KLAR, AND KCYS. AS TEMPERATURES COOL THIS EVENING,
PRECIPITATION WILL MAKE THE TRANSITION TO ALL SNOW ALONG WITH FG
DEVELOPING. BY 13Z TUESDAY, WEATHER CONDITIONS WILL IMPROVE EVER SO
SLIGHTLY ACROSS THE SOUTHEAST WYOMING TERMINALS AND AROUND 15Z FOR
THE NEBRASKA SITES.
CYS WATCHES/WARNINGS/ADVISORIES
WY...WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 3 PM MDT
TUESDAY FOR WYZ112-114.
NE...NONE.
SHORT TERM...RV
LONG TERM...AM
AVIATION...RZ
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