718
FXUS65 KCYS 202001
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
101 PM MST FRI DEC 20 2024
KEY MESSAGES
- THE WEEKEND WILL CONTINUE MILD AND DRY WITH ANOTHER HIGH WIND EVENT
POSSIBLE FOR SUNDAY AND SUNDAY NIGHT ACROSS PORTIONS OF
SOUTHEAST WYOMING.
- SOMEWHAT COOLER TEMPERATURES WILL DEVELOP FOR MONDAY THROUGH CHRISTMAS
DAY WITH A CHANCE OF SNOW FOR THE SNOWY AND SIERRA MADRE
RANGES FOR MONDAY, AND AGAIN FOR THE MOUNTAINS AND NEARBY
LOWER ELEVATIONS FOR CHRISTMAS DAY.
SHORT TERM /THROUGH SATURDAY NIGHT/
ISSUED AT 1246 PM MST FRI DEC 20 2024
A RIDGE OF HIGH PRESSURE IS CURRENTLY IN PLACE OVER THE GREAT
BASIN REGION OF THE CONUS. TO THE EAST OF THIS FEATURE, A
LONGWAVE TROUGH IS PRESENT OVER THE GREAT LAKES. IN BETWEEN
THESE TWO FEATURES, A BROAD REGION OF NORTHWEST FLOW IS PRESENT
OVER THE HIGH PLAINS. A SURFACE PRESSURE GRADIENT IS PRESENT
OVER SOUTHEAST WYOMING BETWEEN THESE TWO RIDGE AND TROUGH
FEATURES, RESULTING IN HIGH WINDS OVER THE TYPICAL WIND-PRONE
REGIONS THIS AFTERNOON. WIND GUST OBSERVATIONS HAVE GENERALLY
REMAINED UNDER 50 KNOTS THIS AFTERNOON OUTSIDE OF ONE OR TWO
ISOLATED GUSTS. THEREFORE, THE HIGH WIND WATCH WILL REMAIN IN
EFFECT AS WE HAVE LIKELY REACHED THE PEAK OF THIS EVENT. WIND
GUSTS ARE EXPECTED TO DECREASE THROUGH THE LATER AFTERNOON AND
EARLY EVENING AS THE RIDGE TO OUR WEST BUILDS IN AND SURFACE
PRESSURE GRADIENTS DECREASE. EXPECT MILD WEATHER TO CONTINUE
THIS AFTERNOON WITH TEMPERATURES AROUND 15-20 DEGREES ABOVE
AVERAGE. AS WINDS DIMINISH OVERNIGHT AND GIVEN CLEAR SKIES IN
PLACE, DECENT RADIATIONAL COOLING WILL HELP KEEP LOW
TEMPERATURES COOLER, ONLY AROUND 5-10 DEGREES ABOVE AVERAGE.
ON SATURDAY, THE RIDGE AXIS WILL TRANSLATE EASTWARD THROUGH THE
DAY AND PASS THROUGH SOUTHEAST WYOMING AND WESTERN NEBRASKA.
EXPECT LIGHT WINDS, MAINLY CLEAR SKIES, AND TEMPERATURES RUNNING
AT LEAST 20 DEGREES ABOVE NORMAL FOR LATE DECEMBER. MANY
LOCATIONS WILL BE NEAR OR ABOVE RECORD HIGH LEVELS, WITH THE
BEST CHANCES FOR BREAKING RECORDS AT CHEYENNE, SCOTTSBLUFF, AND
LARAMIE. OVERNIGHT A COMPACT AREA OF LOW PRESSURE WILL TRAVERSE
THE NORTHERN HIGH PLAINS, BRINGING SOME CLOUDS BACK INTO THE
REGION. LOW TEMPERATURES WILL BE WARMER ON SATURDAY NIGHT THAN
FRIDAY NIGHT AS A RESULT OF THESE CLOUDS. PRESSURE GRADIENTS
WILL TIGHTEN ONCE AGAIN WITH THE APPROACH OF THIS SYSTEM AND
WIND SPEEDS WILL PICK UP LATE SATURDAY NIGHT, ESPECIALLY IN THE
WIND PRONE CORRIDORS. OVERALL FORECAST CONFIDENCE IS VERY HIGH
THROUGHOUT THE SHORT TERM WITH UPWARD ADJUSTMENTS TO TEMPERATURE
BLENDS AND WIND GUST FORECASTS BASED ON LOCAL MACHINE LEARNING
GUIDANCE.
LONG TERM /SUNDAY THROUGH THURSDAY/
ISSUED AT 1246 PM MST FRI DEC 20 2024
LONG TERM FORECAST REMAINS UNCHANGED WITH THE UPPER LEVEL RIDGE
SLOWLY PUSHING EASTWARD WITH THE NEXT PROGRESSIVE UPPER LEVEL
SHORTWAVE DIGS ACROSS MONTANA AND INTO THE DAKOTAS SUNDAY AFTERNOON,
WITH A SERIES OF SHORTWAVES DIGGING A BIT FURTHER SOUTHWARD ON THE
BACK END OF THE FIRST SHORTWAVE MONDAY MORNING THROUGH AT LEAST
MIDWEEK. MOSTLY DRY FORECAST EXPECTED ACROSS THE CWA FOR THE LATE
WEEKEND WITH THE PRIMARY PACIFIC SYSTEM BEING A BIT TOO FAR TO THE
NORTH TO CAUSE ANY REAL PRECIPITATION IMPACTS AND THE BETTER
MOISTURE ADVECTION REMAINS TO THE NORTH AND SOUTH OF THE CWA. ONLY
PRECIPITATION CONCERNS FOR SUNDAY FOCUS ON THE SMALL BANDS OF PWATS
INCHING NORTHWARD INTO THE SOUTHERN COUNTIES IN SOUTHEAST WYOMING
AND WESTERN NEBRASKA. HOWEVER, THE STRONG WESTERLY FLOW WILL LIKELY
AID IN THE DOWNSLOPING COMPONENT AND CONTINUE TO DRY OUT THE LOWER
LEVELS. WITH THAT BEING SAID, WINDS ARE PROGGED TO REMAIN ELEVATED
TO HIGH WIND POTENTIALS ON THE UNDERSIDE OF THE SHORTWAVE THAT IS
ATTEMPTING TO CLOSE OFF INTO A CUTOFF LOW AS EVIDENT WITH THE STRONG
700MB TO 500MB JET MAXES SUNDAY AFTERNOON AND EVENING. LOCAL IN-
HOUSE MODEL GUIDANCE IS IN AGREEMENT WITH THIS SOLUTION WITH AROUND
60% PROBABILITIES FOR HIGH WIND CRITERIA AROUND THE NORMAL WIND
PRONE AREAS, BUT COULD EVEN SEE HIGHER WINDS PUSHING A BIT FURTHER
EASTWARD WITH SOME SIGNALS FOR MOUNTAIN WAVE ACTIVITY. HOWEVER, NOT
GETTING A LOT OF SUPPORT FROM THE NBM V4.2 PROBABILITY OF EXCEEDING
ANY SIGNIFICANT WIND GUSTS OUTSIDE OF THE WIND PRONE AREAS WHERE 50%
TO 60% PROBABILITIES OF EXCEEDING 41 KNOTS EXIST.
NEXT FOCUS IN THE LONG TERM FORECAST WILL REMAIN CENTERED ON THE
EARLY TO MID PORTIONS OF THE WORK WEEK, WITH THE SERIES OF
SHORTWAVES PULSING ACROSS THE ZONE, KICKING UP PRECIPITATION CHANCES
WITH MUCH BETTER MOISTURE ADVECTION THAN WILL BE OBSERVED WITH THE
SUNDAY SYSTEM. PWATS INCREASE SIGNIFICANTLY DURING THIS TIME PERIOD,
WITH PWAT ANOMALIES INCREASING FROM +2.0 TO +3.0 SIGMA ABOVE
CLIMATOLOGY BY MONDAY EVENING, BEFORE SPREADING EASTWARD INTO
CENTRAL NEBRASKA AND JUST OUT OF REACH EARLY TUESDAY MORNING. MODELS
ARE IN RELATIVELY GOOD AGREEMENT, PLACING MOST PRECIPITATION ALONG
THE MOUNTAIN ZONES ACROSS THE SIERRA MADRES/SNOWY RANGE AND SOME
HIGHER TERRAINS INTO CARBON COUNTY. ALTHOUGH, THERE ARE SOME
CONCERNS IF PRECIPITATION WILL REACH THE LOWER ELEVATIONS INTO THE
I-25 CORRIDOR WITH SOME DECENT PWATS SPREADING EASTWARD INTO WESTERN
NEBRASKA WITH SOME LOWER END SNOW POTENTIALS SIMILAR TO A FEW DAYS
AGO. OTHERWISE, THE HOLIDAY FORECAST THROUGH THE REMAINDER OF THE
FORECAST PERIOD REMAINS ON TRACK WITH GOOD CHANCES FOR SNOW CONFINED
TO THE MOUNTAIN RANGES AND SOME LOWER END POPS ACROSS ALBANY AND
CARBON COUNTY. ALTHOUGH, AT THE TIME OF THIS FORECAST, PWATS ARE NOT
ALL THAT IMPRESSIVE WITH A BULK OF THE MOISTURE REMAINING TOO FAR TO
THE SOUTHEAST INTO SOUTHEASTERN COLORADO.
AVIATION /18Z TAFS THROUGH 18Z SATURDAY/
ISSUED AT 1016 AM MST FRI DEC 20 2024
VFR CONDITIONS EXPECTED AT ALL TERMINALS TODAY. EXTREMELY WINDY
CONDITIONS AT CYS THROUGH THE AFTERNOON WITH WINDS DROPPING
BELOW 20 KNOTS OVERNIGHT. EXPECT WESTERLY WINDS GENERALLY
DECREASING LATER IN THE DAY AT ALL TERMINALS. A MAINLY CLEAR
NIGHT AT ALL TERMINALS WITH VFR ONCE AGAIN ON SATURDAY.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WATCH UNTIL 8 PM MST THIS EVENING FOR WYZ106-110-116.
NE...NONE.
SHORT TERM...MAC
LONG TERM...MRD
AVIATION...MAC
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