580
FXUS65 KCYS 292206
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
306 PM MST WED JAN 29 2025
KEY MESSAGES
- THERE IS A SLIGHT CHANCE FOR SLUSHY SNOW ACCUMULATIONS IN CHEYENNE
COUNTY THURSDAY MORNING.
- MILD TEMPERATURES CONTINUE INTO SATURDAY FOR AREAS ALONG AND
EAST OF I-25, BUT AREAS TO THE WEST WILL REMAIN COLD,
ESPECIALLY AT NIGHT.
- WIDESPREAD STRONG WINDS RETURN FRIDAY INTO SATURDAY WITH MILD
TEMPERATURES CONTINUING.
- CONSIDERABLE UNCERTAINTY REMAINS CONCERNING TEMPERATURES AND
THE PRECIPITATION POTENTIAL FOR SUNDAY ONWARD.
SHORT TERM /THROUGH FRIDAY/
ISSUED AT 301 PM MST WED JAN 29 2025
THE SYNOPTIC WEATHER PATTERN REMAINS MINIMALLY CHANGED OVER THE LAST
24 HOURS. GOES SATELLITE IMAGERY SHOWS THE MEANDERING DISORGANIZED
UPPER LEVEL LOW CONTINUING TO SPIN OVER THE FOUR CORNERS REGION AS
IT GRADUALLY DRIFTS EASTWARD. THE JET STREAM IS STILL JUST OFF TO
OUR NORTH AND EAST, WITH FAST MOVING CLOUD COVER VISIBLE OVER THE
NORTHERN PLAINS. OUR AREA REMAINS UNDER THE DEFORMATION ZONE IN
BETWEEN THESE TWO FEATURES, CONTRIBUTING TO THE LIGHT WINDS AND
TRANQUIL WEATHER PATTERN WE HAVE ENJOYED THIS WEEK. MILD
TEMPERATURES CONTINUE FOR THE HIGH PLAINS, WHILE THE WESTERN VALLEYS
REMAIN IMPACTED BY THE SHARP SURFACE INVERSION, ALTHOUGH IT HAS
ERODED SLIGHTLY SINCE YESTERDAY. WITH ANOTHER NIGHT OF CLEAR SKIES
AND LIGHT WINDS, DROPPED TEMPERATURES WELL BELOW GUIDANCE ONCE AGAIN
FOR RAWLINS, SARATOGA, AND LARAMIE FOR THURSDAY MORNING. WE WILL
ALSO NEED TO WATCH BORDEAUX FOR SOME HIGH WIND POTENTIAL TONIGHT.
GFS BASED IN-HOUSE GUIDANCE SHOWS ABOUT A 40% CHANCE FOR HIGH WINDS
HERE INTO THURSDAY MORNING, BUT THERE IS SOME CONCERN THAT THE GFS
MAY BE OVERESTIMATING THE STRENGTH OF THE SURFACE HIGH OVER INTERIOR
WY, WHICH THE IN-HOUSE GUIDANCE IS RESPONDING TO. AS A RESULT, DO
NOT HAVE THE CONFIDENCE FOR ANY HIGH WIND PRODUCTS AT THIS TIME.
THE UPPER LEVEL LOW WILL FINALLY EJECT INTO THE PLAINS TONIGHT INTO
TOMORROW MORNING, AND THERE IS A LOW CONFIDENCE POTENTIAL FOR SLUSHY
SNOW ACCUMULATION IN THE FAR SOUTHEAST PART OF THE FORECAST AREA,
AROUND SIDNEY AND CHEYENNE COUNTY. THIS IS AN UNUSUAL SETUP FOR SNOW
ACROSS THE AREA. THE UPPER LEVEL LOW IS DISORGANIZED AND DECAYING,
AND THE SURFACE LOW IS VERY WEAK, IF IT IS PRESENT AT ALL. HOWEVER,
GUIDANCE SHOWS AN EXTREMELY NARROW TROWAL DEVELOPING OVER THE HIGH
PLAINS ON THE NORTHERN FRINGE OF THE UPPER LEVEL LOW THURSDAY
MORNING WHICH IS EXPECTED TO PRODUCE A CORRESPONDING EXTREMELY
NARROW BAND OF PRECIPITATION. LIFT ACTUALLY LOOKS FAIRLY STRONG
WITHIN THIS BAND, BUT DRY AIR IS PRESENT BOTH ALOFT AND IN THE
BOUNDARY LAYER. THE MEDIAN POSITION OF THIS BAND IS ROUGHLY OVER THE
I-76 CORRIDOR, AND THUS MOSTLY OUTSIDE OF OUR FORECAST AREA, BUT
SEVERAL ENSEMBLE MEMBERS SHIFT THIS NARROW BAND JUST 25 TO 50 MILES
NORTH, WHICH COULD PUT DECENT PRECIPITATION OVER SIDNEY AND POINTS
SOUTHEASTWARD. SEVERAL SLUSHY INCHES OF SNOW ACCUMULATION ARE NOT
OUT OF THE QUESTION, BUT THE PROBABILITY IS FAIRLY LOW (ABOUT 20-
30%). OTHER THAN THAT, BREEZY NORTHERLY WINDS WILL DEVELOP AND KEEP
HIGHS ACROSS THE AREA SLIGHTLY COOLER, BUT STILL NEAR TO ABOVE
AVERAGE FOR THE HIGH PLAINS.
HEADING INTO FRIDAY, WE'LL SEE THE BEGINNING OF THE END OF THE
PERIOD OF LIGHT WINDS WE HAVE BEEN ENJOYING AS THE UPPER LEVEL LOW
MOVES OFF TO THE EAST AND A STRONG JET PUSHES INLAND FROM THE WEST
COAST. THE RIDGE AXIS WILL BE MOVING ACROSS THE AREA FRIDAY,
SUPPORTING VERY MILD TEMPERATURES. INCREASING WINDS SHOULD FINALLY
MIX OUT THE INVERSION WEST OF THE LARAMIE RANGE AND BOOST
TEMPERATURES TO ABOVE NORMAL VALUES. WINDS WILL ALSO BE ON THE
INCREASE FOR THE WIND PRONE AREAS DURING THE DAY FRIDAY. HIGH WIND
HEADLINES WILL LIKELY BE NEEDED, BUT IT IS A LITTLE EARLY STILL TO
ISSUE NOW. MORE DETAILS ON THE WIND EVENT CAN BE FOUND IN THE LONG
TERM DISCUSSION BELOW.
LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/
ISSUED AT 301 PM MST WED JAN 29 2025
THE LONG TERM WILL BE ACTIVE DURING THE BEGINNING OF THE PERIOD
AS WE SEE ZONAL FLOW SET UP ACROSS THE REGION AND BRING A SURGE
OF BOTH STRONG WINDS AND MOISTURE TO THE AREA THROUGH THE START
OF NEXT WEEK. BEYOND THIS THOUGH, UNCERTAINTY SKYROCKETS AS
ENSEMBLES STILL DIVERGE SIGNIFICANTLY ON HOW TO RESOLVE BOTH
THE UPPER AND LOWER LEVELS, RESULTING IN A SPREAD ACROSS MOST
FORECAST PARAMETERS, PARTICULARLY TEMPERATURES, PRECIPITATION,
AND WINDS LEADING TO LOW CONFIDENCE IN THE FORECAST BEYOND THE
WEEKEND.
FOR THIS LONG TERM PERIOD, HAVE STARTED OVERNIGHT FRIDAY INTO
SATURDAY MORNING TO ACCOUNT FOR THE EXPECTED WEEKEND WIND EVENT
FOR THE REGION. TAKING A LOOK AT MODELS ALONGSIDE IN HOUSE
GUIDANCE, THE STRONGEST CONDITIONS LOOK TO OCCUR DURING THE
BEGINNING OF THIS TIMEFRAME FROM 00-12Z ON SATURDAY, WITH THE IN
HOUSE MODELS INDICATING A 60-80% PROBABILITY OF WIND GUSTS 60+
MPH FOR OUR USUAL WIND PRONE LOCATIONS AS THE JET MAX
STRENGTHENS DURING THIS TIME PERIOD. THE GFS PLACES AN 80 KNOT
LOW LEVEL JET AT 700 MB OVER THE REGION, AND WITH FAVORABLE
SUBSIDENCE TAKING PLACE, EXPECT THESE WINDS TO MIX DOWN AND
PROMOTE THE HIGH WIND EVENT. MOVING JUST BEYOND THESE THROUGH
THE REST OF THE TIME PERIOD, MODELS DO CONTINUE TO KEEP THE
ZONAL ORIENTED JET ALOFT OVER OUR REGION, BUT MIXING INTO THE
MID TO LOWER ELEVATIONS WON'T BE QUITE AS STRONG AS THE
BEGINNING OF THE PERIOD. LIKELY WILL CONTINUE TO FUEL BREEZY
CONDITIONS FOR THE CWA, BUT CURRENTLY NOT EXPECTING NEAR THE
HIGH WIND CRITERIA THAT STARTS THE PERIOD, WITH IN HOUSE
GUIDANCE ALSO IN AGREEMENT.
THIS PATTERN WILL ALSO FAVOR A STOUT MOISTURE FLOW INTO THE
REGION, WITH BOTH THE GEFS AND ECMWF ENSEMBLE OVERSPREADING
150-200% OF NORMAL PRECIPITABLE WATER ACROSS THE REGION
BEGINNING SATURDAY MORNING AND CONTINUING THROUGH EARLY NEXT
WEEK. THAT BEING SAID, DON'T EXPECT EITHER A SIGNIFICANT WINTER
SYSTEM OR A LOWER ELEVATION WASHOUT FROM THIS ACTIVITY, AS
SURFACE LEVEL QPF TOTALS OUTSIDE OF THE HIGHER TERRAIN WILL BE
LESS THAN A TENTH OF AN INCH WIDESPREAD. THIS IS LIKELY DUE TO
THE LACK OF SIGNIFICANT FORCING AND FLOW KEEPING THE MAJORITY OF
THIS ACTIVITY UPSLOPE ON THE WINDWARD SIDE OF THE MOUNTAINS
WHERE THE MAJORITY OF POTENTIAL PRECIPITATION WILL OCCUR.
MONDAY THROUGH TUESDAY UNCERTAINTY SPIKES WITH THE FORECAST
HOWEVER, AS MODELS AND ENSEMBLES CONTINUE TO DISAGREE ON HOW TO
EVOLVE THIS FLOW IN THE END OF THE LONG TERM. BASED ON THE
POSITIONING OF THE JET OVERHEAD ALONGSIDE THE INFLUENCE OF A
DEVELOPING LOW OFF THE BRITISH COLUMBIA COASTLINE, CONDITIONS
COULD RANGE TO CONTINUED NOTABLY WARMER THAN AVERAGE, SLIGHTLY
ABOVE, OR POSSIBLY CLOSER TO NORMAL, ALONGSIDE MORE
PRECIPITATION FOR THE REGION. ENSEMBLE CLUSTERS ARE GENERALLY
SPLIT AROUND 30/30/30% FOR EACH SOLUTION, LEADING TO SPLIT
CONFIDENCE ALL THE WAY. THE HIGH FOR CHEYENNE ON MONDAY RANGES
BETWEEN 32 TO 62 DEGREES, SHOWING THE HIGH LEVEL OF UNCERTAINTY
PRESENT. THE MAJORITY OF THE LONG TERM REMAINS THE NBM FOR THIS
FORECAST UPDATE DUE TO THE UNCERTAINTY, BUT HAVE MADE SOME
NOTABLE CHANGES TO WINDS TO ACCOUNT FOR THE HIGH CONFIDENCE IN
STRONGER WINDS ON SATURDAY INTO SUNDAY.
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1036 AM MST WED JAN 29 2025
AVIATION CONCERNS REMAIN MINIMAL FOR MOST TERMINALS OVER THE
NEXT 24 HOURS, WITH VFR CONDITIONS ALONGSIDE WINDS GENERALLY 10
KNOTS OR LESS. KSNY WILL HAVE A CHANCE OF LIGHT SNOW TOMORROW AS
A BAND SETS UP JUST TO THE SOUTH OF THE TERMINAL. HIGH
RESOLUTION GUIDANCE CONTINUES TO BE SPREAD ON THE POSSIBILITY OF
ACTIVITY HERE, BUT THERE IS MODERATE TO HIGH CONFIDENCE THAT
HEAVIER SNOW WILL REMAIN TO THE SOUTH. ADDED A PROB30 FOR LIGHT
SNOW BETWEEN 12-18Z TO ACCOUNT FOR A LIGHT SNOW SHOWER OR TWO
MOVING INTO THE SITE AND BRINGING MVFR CONDITIONS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...NONE.
NE...NONE.
SHORT TERM...MN
LONG TERM...CG
AVIATION...CG
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