115
FXUS65 KCYS 312118
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
318 PM MDT SAT MAY 31 2025
KEY MESSAGES
- WARMER TEMPERATURES AND DRIER CONDITIONS WILL PERSIST THROUGH
THE WEEKEND.
- TROPICAL MOISTURE WILL MOVE INTO THE AREA FOR MONDAY AS A
STRONG PACIFIC COLD FRONT MOVES SOUTHEAST INTO WYOMING. THIS
WILL SET THE STAGE FOR MODERATE TO HEAVY RAINFALL AND STRONG
THUNDERSTORMS MONDAY AFTERNOON THROUGH MONDAY NIGHT.
- COOLER AND WETTER WEATHER WILL PREVAIL FOR TUESDAY AND
WEDNESDAY BEFORE A WARMING TREND DEVELOPS FOR THURSDAY THROUGH
SATURDAY. CHANCES FOR LATE DAY SHOWERS AND THUNDERSTORMS WILL
CONTINUE EACH DAY.
SHORT TERM /THROUGH MONDAY/
ISSUED AT 315 PM MDT SAT MAY 31 2025
PLEASANT WEATHER TO START OFF THE WEEKEND WITH TEMPERATURES WELL
INTO THE 70S FOR MOST LOCATIONS AND A FEW LOW 80S FOR PORTIONS
OF WESTERN NEBRASKA. RECENT KCYS RADAR LOOP SHOWS SOME SHOWERS
DEVELOPING NEAR THE SIERRA MADRE AND SNOWY RANGES WITH A FEW
ISOLATED THUNDERSTORMS FURTHER SOUTH INTO FAR NORTHERN COLORADO.
CAN'T RULE OUT A BRIEF THUNDERSTORM OR TWO DEVELOPING NEAR THE
MOUNTAINS INTO EARLY THIS EVENING, SO ADDED A 20 PERCENT CHANCE
OF SHOWERS AND THUNDER OVER THE MOUNTAINS AND ADJACENT HIGH
VALLEYS/PLAINS. THIS ACTIVITY IS FORECAST TO QUICKLY DIMINISH
NEAR SUNSET.
A BETTER CHANCE FOR THUNDERSTORMS IS EXPECTED ON SUNDAY WITH
WARMER TEMPERATURES. ALTHOUGH THE UPPER LEVEL RIDGE AXIS IS
FORECAST TO BUILD OVER THE AREA AS THE MIDLEVEL LOW PRESSURE
SYSTEM TO OUR EAST QUICKLY DIGS SOUTH...A POTENT UPPER LEVEL
VORTICITY MAXIMUM IS EXPECTED TO TRACK SOUTHEAST INTO THE
EASTERN WYOMING PLAINS SUNDAY AFTERNOON. THIS FEATURE, AND SOME
SURFACE COVERGENCE, SHOULD BE ENOUGH TO TRIGGER SOME SCATTERED
SHOWERS AND THUNDERSTORMS WITH MLCAPE BETWEEN 500 TO 1000 J/KG
DURING THE AFTERNOON. NOT MUCH 0-6KM SHEAR, SO NOT LOOKING AT
ANY SEVERE THUNDERSTORMS AT THIS TIME, BUT THERE COULD BE A FEW
BRIEF STRONGER THUNDERSTORMS INTO SUNDAY EVENING. EXPECT THIS
ACTIVITY TO PUSH EASTWARD INTO THE PLAINS OF WESTERN NEBRASKA
SUNDAY EVENING. OTHERWISE, SHOULD BE A PLEASANT AND WARM DAY FOR
THE FIRST DAY OF JUNE WITH HIGHS IN THE 80S. SOME OF THE LOWER
ELEVATIONS BELOW 4500 FEET MAY APPROACH 90 SUNDAY AFTERNOON.
COMPLICATED WEATHER PATTERN EXPECTED ON MONDAY, WHICH INCLUDES
THE POSSIBILITY OF SEVERE WEATHER, FLASH FLOODING, AREAS OF
MODERATE TO HEAVY RAINFALL, AND MUCH COOLER TEMPERATURES BEHIND
A PACIFIC FRONT. VISIBLE SATELLITE LOOP SHOWS AN UPPER LEVEL
LOW OFF THE SOUTHERN COASTLINE OF CALIFORNIA AND A DISSIPATING
TROPICAL SYSTEM NEAR THE SOUTHERN END OF BAJA CALIFORNIA. THIS
UPPER LEVEL LOW IS FORECAST TO ACCELERATE NORTHEAST AS THE NEXT
PACIFIC TROUGH MOVES ONSHORE. IN ADDITION, TROPICAL MOISTURE
WILL LIFT NORTHWARD AHEAD OF THIS UPPER LEVEL LOW WITH
INCREASING LOW TO MIDLEVEL MOISTURE EXPECTED OVER THE HIGH
PLAINS AND THE INTERMOUNTAIN WEST. MEANWHILE, MODELS SHOW THE
PACIFIC UPPER LEVEL TROUGH AND ASSOCIATED STRONG COLD FRONT (FOR
THIS TIME OF THE YEAR) TRACKING EAST AND THEN SOUTHEAST OVER
SOUTHEAST WYOMING AND WESTERN NEBRASKA. NAEFS HAS BEEN VERY
CONSISTENT IN SHOWING PWATS AND SPECIFIC HUMIDITY OVER THE 99TH
PERCENTILE OVER A LARGE PORTION OF THE AREA WITH SOME AREAS NEAR
A 30 YEAR MAXIMUM FOR EARLY JUNE. ALL MODELS SHOW PLENTY OF FORCING
WITH UPSLOPE FLOW, FRONTOGENESIS, AND SURFACE CYCLOGENESIS NEAR
THE WYOMING/COLORADO BORDER. AND THIS IS IN ADDITION TO FAVORABLE
THERMODYNAMIC PROFILES SOUTHEAST OF A LINE FROM LARAMIE TO
CHADRON. THERE IS A SLIGHT RISK FOR SEVERE THUNDERSTORMS FOR FAR
SOUTHEAST WYOMING AND THE SOUTHERN NEBRASKA PANHANDLE IN ADDITION
TO A SLIGHT RISK FOR EXCESSIVE RAINFALL ALONG AND SOUTH OF THE
NORTH PLATTE RIVER VALLEY. HOWEVER, ALL THIS DEPENDS ON THE THE
SPEED AND MOVEMENT OF BOTH THE PACIFIC UPPER LEVEL LOW (NEAR
SOUTHERN CALIF) AND THE PACIFIC COLD FRONT/ASSOCIATED UPPER LEVEL
TROUGH. IF THE COLD FRONT IS EVEN FASTER THAN PREDICTED, SEVERE
THREAT AND EXCESSIVE RAINFALL THREAT MAY SHIFT SOUTH (SLOWER AND
FURTHER NORTH RESPECTIVELY). ALL MODES OF SEVERE WEATHER ARE POSSIBLE
ALONG THE I-80 CORRIDOR FROM LARAMIE EASTWARD TO THE SOUTHERN
NEBRASKA PANHANDLE. HOWEVER, THE WINDOW FOR DISCRETE CELLS APPEARS
TO BE PRETTY SMALL AS FORCING AND LINEAR UPSCALE- GROWTH TAKES
OVER AS WE HEAD INTO THE LATE AFTERNOON AND EARLY EVENING HOURS.
ALSO, SHEAR APPEARS TO BE LIMITED UNTIL MID TO LATE AFTERNOON.
MODEL SOUNDINGS CONTINUE TO SHOW NEARLY SATURATED TROPICAL-LIKE
SOUNDINGS UP TO THE TROPOPAUSE THROUGH MONDAY NIGHT. COULD SEE
SOME MUCH NEEDED RAINFALL AMOUNTS OVER 1 INCH TO POSSIBLY 2 INCHES
IF THE SURFACE COLD FRONT DOESN'T PUSH THROUGH TOO FAST ON MONDAY.
KEPT POP ABOVE 60 PERCENT WITH SCATTERED TO NUMEROUS THUNDERSTORMS.
INCREASED HIGH TEMPERATURES A FEW DEGREES FROM CHEYENNE OVER THE
SIDNEY DUE TO THE TYPICAL MODEL COLD BIAS OBSERVED AHEAD OF STRONG
SURFACE COLD FRONTS THIS TIME OF THE YEAR. HOWEVER, TEMPERATURES
ARE EXPECTED TO QUICKLY LOWER INTO THE 40S AND 50S BEHIND THE
FRONT.
LONG TERM /MONDAY NIGHT THROUGH FRIDAY NIGHT/
ISSUED AT 212 PM MDT SAT MAY 31 2025
MONDAY NIGHT/TUESDAY...IN THE WAKE OF THE COLD FRONT, IT LOOKS LIKE
WIDESPREAD SHOWERS AND SOME THUNDERSTORMS, ESPECIALLY MONDAY
EVENING. COOLER TEMPERATURES IN THE WAKE OF THE SHORTWAVE TROUGH
ALOFT AND COLD FRONT FOR TUESDAY. LOOKS LIKE ENOUGH LOW AND MID
LEVEL MOISTURE IN THE WEST FLOW ALOFT FOR SCATTERED TO NUMEROUS
SHOWERS AND THUNDERSTORMS.
WEDNESDAY...TEMPERATURES WILL REMAIN ON THE COOL SIDE BENEATH ZONAL
FLOW ALOFT AND WITH ANOTHER SHORTWAVE TROUGH ALOFT PASSAGE. WITH
ADEQUATE LOW AND MID LEVEL MOISTURE, WE EXPECT SCATTERED TO NUMEROUS
AFTERNOON AND EVENING SHOWERS AND THUNDERSTORMS.
THURSDAY...WEST FLOW ALOFT CONTINUES AND WITH SOME DRYING NOTED IN
THE LOW AND MID LEVELS, COVERAGE OF SHOWERS AND THUNDERSTORMS WILL
BE LESS, WITH WARMER TEMPERATURES EXPECTED.
FRIDAY...THE SLOW WARMING TREND CONTINUES BASED ON 700 MB
TEMPERATURE TRENDS. LOOKS LIKE ADEQUATE LOW AND MID LEVEL MOISTURE
FOR SCATTERED LATE DAY SHOWERS AND THUNDERSTORMS.
SATURDAY...A BROAD TROUGH ALOFT MOVES OVERHEAD WITH THE FLOW TURNING
NORTHERLY. LOOKS LIKE ADEQUATE LOW AND MID LEVEL MOISTURE FOR
SCATTERED LATE DAY SHOWERS AND THUNDERSTORMS. 700 MB TEMPERATURE
TRENDS SUGGEST THE CONTINUATION OF THE WARMING TREND.
AVIATION /18Z TAFS THROUGH 18Z SUNDAY/
ISSUED AT 1126 AM MDT SAT MAY 31 2025
NORTHWEST FLOW ALOFT WILL PREVAIL AS A RIDGE ALOFT BEGINS TO
ASSERT ITSELF. SKIES WILL BE MOSTLY CLEAR. WINDS WILL GUST TO
25 KNOTS AT CHEYENNE, AND THE NEBRASKA PANHANDLE TERMINALS
UNTIL 00Z.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...TJT
LONG TERM...RUBIN
AVIATION...RUBIN
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