558
FXUS65 KCYS 020925
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
325 AM MDT SAT MAY 2 2026
KEY MESSAGES
- WARMER AND DRIER WEATHER WILL CONTINUE THROUGH SUNDAY, LEADING
TO NEAR CRITICAL FIRE WEATHER CONDITIONS.
- THE POTENTIAL FOR COOL TEMPERATURES AND WIDESPREAD
PRECIPITATION CONTINUES TO INCREASE FOR MONDAY AFTERNOON
THROUGH WEDNESDAY MORNING. THUNDERSTORMS, BENEFICIAL RAINFALL,
AND ACCUMULATING SNOW ARE ALL POSSIBLE, BUT THE DETAILS ARE
STILL UNCERTAIN.
- DRIER, WARMER, AND WINDIER WEATHER RETURNS TO THE AREA FOR THE
SECOND HALF OF THE WORK WEEK.
SHORT TERM /THROUGH SUNDAY NIGHT/
ISSUED AT 320 AM MDT SAT MAY 2 2026
GOES WATER VAPOR IMAGERY SHOWS AN EXTREMELY DRY AIRMASS ALOFT MOVING
FROM NORTH TO SOUTH ACROSS OUR AREA THIS MORNING. THIS AIRMASS IS
LOCATED ON THE EASTERN PERIPHERY OF A NARROW RIDGE BUILDING INTO THE
NORTHERN ROCKIES REGION THIS MORNING. AS THE RIDGE STRENGTHENS
ALOFT, WE CAN EXPECT TEMPERATURES ON THE RISE, GAINING ABOUT 10F FOR
TODAY'S HIGHS COMPARED TO YESTERDAY. WHILE SURFACE DEWPOINTS
AREN'T TERRIBLE CURRENTLY, THE DRIER AIR ALOFT WILL BEGIN TO MIX
DOWN TO THE SURFACE BY MID MORNING. PRECIPITABLE WATER WILL
DROP TO AROUND 0.1 TO 0.2" THIS AFTERNOON, WHICH WILL BE AROUND
THE 2.5 PERCENTILE FOR MUCH OF THE AREA. LOOK FOR DEWPOINTS TO
DROP INTO THE TEENS TO SINGLE DIGITS, PUSHING RH DOWN TO AROUND
8 TO 12%. WE WILL HAVE VERY DEEP, WELL-MIXED BOUNDARY LAYERS AND
POTENT INVERTED-V SOUNDINGS THIS AFTERNOON. THE VERY DRY
AIRMASS WILL ELEVATE FIRE WEATHER CONCERNS, BUT THE WINDS WILL
REMAIN MARGINAL. A LIGHT NORTHWEST BREEZE IS EXPECTED TO DEVELOP
THIS AFTERNOON, WITH CONSISTENT GUSTS AROUND 15 TO 25 MPH. A
HANDFUL OF GUSTS UP TO 30 MPH ARE PROBABLE TODAY OVER THE HIGH
PLAINS, BUT CURRENTLY THIS IS NOT EXPECTED TO BE CONSISTENT
ENOUGH TO WARRANT A RED FLAG WARNING. WE WILL NEED TO WATCH
CONDITIONS CLOSELY THROUGH THE DAY IN THE CASE THAT WINDS END UP
STRONGER THAN ANTICIPATED.
A SHORTWAVE TROUGH WILL PASS WELL TO OUR NORTH THIS AFTERNOON. A
WEAK SURFACE HIGH PRESSURE SYSTEM WILL SETTLE IN OVER THE NORTHERN
PLAINS BEHIND THIS SYSTEM, PUSHING INTO OUR AREA THIS EVENING. WINDS
WILL TURN NORTHEAST OVER THE PLAINS AND WE SHOULD SEE POSITIVE
MOISTURE ADVECTION IN THE LOWER LEVELS. THE MOISTURE SHOULD PUSH UP
AGAINST THE LARAMIE RANGE BY SUNDAY MORNING, BUT THEN RETREAT
SLIGHTLY DURING THE DAY SUNDAY. GUSTY WESTERLY WINDS AND CONTINUED
VERY DRY AIR WILL PREVAIL FOR THE SOUTHEAST WYOMING I-80 CORRIDOR.
WHILE FUELS ARE IN GREENUP FOR MOST OF THIS AREA, THE BREEZY AND DRY
CONDITIONS MAY SPREAD INTO LARAMIE COUNTY, WHERE THE EXTREME LACK OF
RECENT PRECIPITATION HAS STUNTED THE SPRING GREENUP. WE MAY HAVE
LOCALLY CRITICAL FIRE WEATHER CONDITIONS IN LARAMIE COUNTY,
DEPENDING ON HOW FAR THE STALLED BOUNDARY RETREATS TO THE EAST
DURING THE DAY. SUNDAY WILL BE ANOTHER WARM DAY ACROSS THE AREA, BUT
MID TO UPPER LEVEL MOISTURE IS EXPECTED TO RECOVER NICELY. A BROAD
UPPER LEVEL CLOSED LOW MOVING INTO THE WEST COAST WILL CONTRIBUTE
SOME PACIFIC MOISTURE, WHILE ANOTHER WEAK SHORTWAVE ALOFT WILL MOVE
DOWN FROM THE NORTHWEST SUNDAY AFTERNOON. THE LATTER FEATURE IS
EXPECTED TO COME WITH OVERRUNNING ISENTROPIC LIFT AHEAD OF THE
TROUGH AXIS, WHICH WILL BE WELL-TIMED WITH PEAK HEATING IN THE MID
AFTERNOON HOURS. AREAS ALONG AND NORTH OF THE NORTH PLATTE RIVER
WILL HAVE BETTER LOW-LEVEL MOISTURE AS WELL. THE SYNOPTIC LIFT WILL
KICK OFF WIDELY SCATTERED SHOWERS AND THUNDERSTORMS THAT SHOULD BE
ABLE TO TAP INTO MODEST CONVECTIVE INSTABILITY IN THE 200 TO 500
J/KG RANGE. WHILE MOST OF THE ACTIVITY WILL BE UP IN SOUTH DAKOTA
AND NORTHEAST WYOMING, POPS IN THE 20 TO 40% RANGE SPREAD INTO
PORTIONS OF OUR AREA ALONG AND NORTH OF A ROUGHLY DOUGLAS TO
ALLIANCE LINE. ANY SHOWERS OR THUNDERSTORMS WILL HAVE THE POTENTIAL
TO PRODUCE GUSTY WINDS. FURTHER SOUTH, WE MAY SEE SOME ISOLATED HIGH-
BASED SHOWERS AND PERHAPS A FEW RUMBLES OF THUNDER, BUT MEASURABLE
RAINFALL IS UNLIKELY.
LONG TERM /MONDAY THROUGH FRIDAY/
ISSUED AT 320 AM MDT SAT MAY 2 2026
THE PRIMARY OF THE MEDIUM RANGE FORECAST IS THE PRECIPITATION
POTENTIAL FOR MONDAY AFTERNOON THROUGH WEDNESDAY MORNING. A VERY
COMPLEX SYNOPTIC SETUP IS EXPECTED TO DEVELOP DURING THIS PERIOD.
FIRST, AN EXPANSIVE UPPER LEVEL CLOSED LOW IS EXPECTED TO SLOWLY
MEANDER INLAND AND BECOME STRETCHED OUT ACROSS THE SOUTHWESTERN
CONUS. PLENTIFUL PACIFIC MOISTURE WILL BE PULLED INTO THE AREA, AND
THEN STRETCHED OUT FROM WEST TO EAST MORE OR LESS ALONG THE
I-80 CORRIDOR FROM CALIFORNIA TO NEBRASKA. MEANWHILE, A VERY
LARGE AND UNSEASONABLY STRONG UPPER LEVEL TROUGH REMAINS PARKED
OVER THE HUDSON BAY REGION. MODELS ARE IN GOOD AGREEMENT SHOWING
THIS FEATURE RETROGRADING WESTWARD MONDAY INTO TUESDAY, WHICH
WILL ALLOW FOR A FAIRLY POTENT VORT-MAX TO DIVE SOUTHWARD ALONG
THE EASTERN SIDE OF THE NORTHERN ROCKIES. IN AN UNUSUAL TWIST
FOR THIS YEAR, MODEL GUIDANCE IS TRENDING TOWARDS THE SCENARIO
IN WHICH THE LIFT ASSOCIATED WITH THE NORTHERN BRANCH SYSTEM
ARRIVES WHILE PLENTIFUL MOISTURE FROM THE OTHER SYSTEM IS STILL
OVERHEAD. THIS SCENARIO WOULD HAVE THE POTENTIAL TO ACTUALLY
DENT (BUT NOT EVEN CLOSE TO ELIMINATE) THE ONGOING EXTREME
DROUGHT CONDITIONS. THE OVERALL PICTURE AMONGST THE MAJOR
ENSEMBLE MEMBERS MAY BE THE BEST SIGNAL FOR WIDESPREAD
BENEFICIAL MOISTURE WE HAVE SEEN SINCE LAST FALL, BUT THE
OFFICIAL FORECAST HEDGES ON THE CONSERVATIVE SIDE. WE'LL FIRST
BREAK DOWN THE OVERALL EVOLUTION EXPECTED OF THIS SYSTEM, AND
THEN GET INTO SOME QPF AND SNOWFALL PROBABILITIES BELOW.
MONDAY WILL BE A TRANSITION DAY ACROSS THE AREA. THERE IS FAIRLY
HIGH CONFIDENCE IN AREAS ALONG THE I-80 CORRIDOR SEEING WARM
TEMPERATURES AROUND 10F ABOVE SEASONAL AVERAGES. FURTHER NORTH,
MONDAY'S HIGHS HAVE MORE UNCERTAINTY DUE TO THE EXPECTED DAYTIME
ARRIVAL OF A STRONG SURFACE COLD FRONT. EVEN FURTHER SOUTH, AN
EARLIER FRONTAL ARRIVAL MAY MEAN WE SEE A FAIRLY EARLY HIGH
TEMPERATURE, WITH COOLING OCCURRING DURING THE MID TO LATE
AFTERNOON HOURS. DECENT FRONTOGENESIS WILL BE MOVING INTO A
MODESTLY UNSTABLE ENVIRONMENT MONDAY AFTERNOON, WHICH SHOULD
KICK OFF THE EVENT WITH SCATTERED SHOWERS AND THUNDERSTORMS.
MOST MODEL GUIDANCE SHOWS THE FRONT SLOWING DOWN AS IT PUSHES UP
AGAINST THE MOUNTAINS OF SOUTHERN WYOMING AND NORTHERN
COLORADO, PROVIDING THE POTENTIAL FOR A LONGER DURATION WINDOW
OF LIFT MONDAY NIGHT THROUGH THE DAY ON TUESDAY. TEMPERATURES
WILL CONTINUE TO DROP THROUGH THIS PERIOD AHEAD OF ANOTHER VORT-
MAX DROPPING DOWN FROM THE NORTH WHICH SHOULD ARRIVE TUESDAY
AFTERNOON OR EVENING. MODELS ARE NOW IN FAIRLY GOOD AGREEMENT
SHOWING THE CLOSED LOW OVER THE SOUTHWEST GETTING ABSORBED BY
THE PARENT TROUGH TUESDAY NIGHT INTO WEDNESDAY MORNING. IN TERMS
OF OUR OUTCOME ON THE GROUND, WE SHOULD SEE SNOW LEVELS
STARTING OFF AROUND 9 TO 10 KFT MONDAY AFTERNOON, BUT THIS WILL
RAPIDLY DROP OVERNIGHT AND THROUGH THE DAY TUESDAY. THE LATEST
LREF HAS 700-MB TEMPERATURES DOWN TO -4C OVER CHEYENNE BY
DAYBREAK TUESDAY, WITH HIGH CONFIDENCE IN VALUES BETWEEN -5 AND
-8C DURING MOST OF THE DAYTIME HOURS TUESDAY AND INTO WEDNESDAY
MORNING. THIS WOULD BE COLD ENOUGH TO RAIN CHANGING TO OR MIXING
WITH SNOW FOR THE ENTIRE AREA. THERE IS STILL A BIT OF
UNCERTAINTY IN THE TIMING. IF MOST OF THE SNOW FALLS DURING THE
DAY, THE SNOW ACCUMULATION EXPECTATIONS WILL BE CONSIDERABLY
LESS DUE TO THE VERY STRONG EARLY MAY SUN, WHEREAS SNOWFALL AT
NIGHT WOULD BE MUCH MORE LIKELY TO ACCUMULATE. AS A RESULT, WE
WON'T GET INTO TOO MUCH DETAIL ON THE POTENTIAL SNOWFALL
AMOUNTS. THE CURRENT MOST LIKELY SCENARIO WOULD MEAN
ACCUMULATING SNOW ABOVE ABOUT 5500 FT IN ELEVATION.
WITH GOOD LOW-LEVEL UPSLOPE EAST TO NORTHEASTERLY FLOW AND THE
PRIMARY LIFTING MECHANISM TIED TO THE FRONTAL BOUNDARY STALLING
AGAINST THE TERRAIN, THE AREA IN THE VICINITY OF THE SNOWY AND
LARAMIE RANGES WILL HAVE THE BEST CHANCE AT SEEING DROUGHT-DENTING
MOISTURE FROM THIS SYSTEM. CURRENTLY, CHEYENNE HAS AN 80% CHANCE OF
SEEING 0.5" OR MORE OF PRECIPITATION, AND EVEN A 50% CHANCE FOR AN
INCH OF LIQUID! LARAMIE'S PROBABILITIES ARE A LITTLE LOWER, SINCE
THE AREA DOES NOT DO WELL WITH EASTERLY LOW-LEVEL FLOW.
PROBABILITIES ALSO DECREASE RAPIDLY ALONG AND NORTH OF THE NORTH
PLATTE RIVER. CURRENT NBM PROBABILITIES FOR SCOTTSBLUFF ARE FOR A
75% CHANCE FOR 0.25", A 50% CHANCE FOR 0.5", AND A 15% CHANCE FOR 1
INCH OR MORE. UNFORTUNATELY, THE LUSK TO CHADRON AREA IS UNLIKELY TO
SEE MUCH MOISTURE FROM THIS SYSTEM WITH THE BEST DYNAMICS POSITIONED
SOUTH AND WEST OF THE AREA, BUT THE MOST LIKELY SCENARIO DELIVERS
BETWEEN 0.05 AND 0.25" TO THIS AREA. NBM PROBABILITIES ARE ACTUALLY
CONSERVATIVE RELATIVE TO THE CURRENT ENSEMBLE SUITE, BUT THAT IS A
COMFORTABLE PLACE TO BE AT THIS TIME. THIS SYSTEM IS QUITE
COMPLICATED AND DISORGANIZED, AND ENSEMBLE SYSTEMS ARE GENERALLY
UNDER-DISPERSED. THE CURRENT OFFICIAL FORECAST IS NEAR THE ENSEMBLE
25TH PERCENTILE DUE TO THESE CONCERNS, AND THE TENDENCY OF EVERY
STORM SYSTEM THIS SEASON TO FIZZLE ONCE WE GET WITHIN A FEW DAYS.
A FEW RAIN AND SNOW SHOWERS MAY LINGER INTO WEDNESDAY WITH
TEMPERATURES REMAINING 10 TO 15F BELOW SEASONAL AVERAGES. RIDGING
WILL BUILD BACK INTO THE WESTERN CONUS FOR THE END OF THE UPCOMING
WORK WEEK. WE MAY SEE A PERIOD OF WINDY CONDITIONS WEDNESDAY NIGHT
THROUGH THURSDAY AS THIS TRANSITION OCCURS. CURRENT PROBABILITIES
FOR HIGH WINDS IN THE WIND PRONE AREAS ARE AROUND 20 TO 40%. WARM
AIR ADVECTION WILL RETURN QUICKLY DURING THIS PERIOD AS WELL. WE
SHOULD SEE TEMPERATURES CLIMB BACK TO NEAR SEASONAL AVERAGES ON
THURSDAY, AND THEN ABOVE AVERAGE BY FRIDAY.
AVIATION /06Z TAFS THROUGH 06Z SUNDAY/
ISSUED AT 1125 PM MDT FRI MAY 1 2026
VFR CONDITIONS EXPECTED FOR THE FORECAST PERIOD. NORTHWEST WINDS
WILL OCCASIONALLY GUST AROUND 20 KNOTS SATURDAY AFTERNOON AND
EARLY EVENING. WINDS WILL EASE AFTER SUNSET AGAIN, AND MAY BE
VARIABLE AT TIMES.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MN
LONG TERM...MN
AVIATION...MN
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