765
FXUS65 KCYS 221134
AFDCYS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHEYENNE WY
534 AM MDT FRI SEP 22 2023
SHORT TERM
(TODAY - SATURDAY NIGHT)
ISSUED AT 413 AM MDT FRI SEP 22 2023
AN ACTIVE PATTERN AHEAD OVER THE NEXT 24 TO 48 HOURS ACROSS SOUTH-
EAST WYOMING & THE WESTERN NEBRASKA PANHANDLE. THE PRIMARY CONCERN
FOR THIS AFTERNOON AND EVENING WILL BE THE POTENTIAL FOR STRONG TO
SEVERE THUNDERSTORMS ACROSS EAST CENTRAL WYOMING INTO THE NORTHERN
NEBRASKA PANHANDLE AS THE WARM FRONT SURGES NORTHWARD. STRONG NON-
CONVECTIVE WINDS BECOME THE PRIMARY FOCUS LATE TONIGHT THROUGH MID
DAY SATURDAY AS A STRONG BORA DEVELOPS W/ THE COLD FRONTAL PASSAGE
ACROSS THE CWA.
WIDESPREAD CONVECTION IS ALREADY ONGOING EARLY THIS MORNING ACROSS
CENTRAL AND EASTERN PORTIONS OF THE CWA, ON THE NOSE OF PERSISTENT
700-MB WARM AIR ADVECTION AND RESULTANT FRONTOGENESIS. THIS SHOULD
EXIT THE CWA BY MID-MORNING, BUT IN THE MEANTIME COULD LEAD TO THE
POTENTIAL FOR SOME MARGINALLY SEVERE HAIL WITH MUCAPES AROUND 1000
J/KG, BUT EFFECTIVE BULK SHEAR UNDER 30 KNOTS SHOULD LIMIT OVERALL
LONGEVITY/ORGANIZATION OF UPDRAFTS. AS THE DAY PROGRESSES, INTENSE
WARM AIR ADVECTION ALOFT WILL SUPPORT THE WARM FRONT SURGING NORTH
THROUGH THE AFTERNOON, EVENTUALLY STALLING ACROSS EAST CENTRAL WYO
INTO THE NORTHERN NEB PANHANDLE DURING THE MID/LATE AFTERNOON. THE
AIR MASS IN ADVANCE OF THIS FRONT (ROUGHLY ALONG & NORTH OF A LINE
FROM DOUGLAS TO ALLIANCE) WILL BE VERY FAVORABLE FOR SEVERE STORMS
WITH DEW POINTS IN THE LOW/MID 50S, AND VERY STEEP MID-LEVEL LAPSE
RATES SUPPORTING SBCAPES OF 1500-2000 J/KG. SHEAR PROFILES WILL BE
EXTREMELY IMPRESSIVE AS A 50+ KNOT 500-MB SPEED MAX TRAVERSES MUCH
OF THE AREA IN ADVANCE OF A VIGOROUS TROUGH. THIS, COUPLED W/ VERY
STRONG DIRECTIONAL SHEAR WITH EASTERLY SURFACE WINDS VEERING SOUTH
BETWEEN 700-500 MB WILL SUPPORT EFFECTIVE BULK SHEAR NEAR 60 KNOTS
WITH AROUND 150-200 M2/S2 OF EFFECTIVE SRH. THERE IS NO DOUBT THIS
IS A HIGHLY UNUSUAL ENVIRONMENT FOR LATE SEPTEMBER W/ THE OVER ALL
PARAMETER SPACE APPEARING VERY FAVORABLE FOR SUPERCELLS CAPABLE OF
ALL FACETS OF SEVERE WEATHER. CONVECTIVE COVERAGE IS UNCERTAIN YET
AGAIN, BUT DYNAMIC FORCING ASSOCIATED WITH INTENSE UPPER DIFLUENCE
AND THE LEFT-EXIT REGION OF A 115+ KNOT 250-MILLIBAR JET, ORIENTED
PERFECTLY ALONG THE WARM FRONT SHOULD EASILY CONTRIBUTE TO CI NEAR
THE BOUNDARY. EXPECT A BIT OF A MIXED STORM MODE, GIVEN THE FAIRLY
STRAIGHT HODOGRAPHS/LARGELY UNIDIRECTIONAL FLOW ALOFT. EXPECT SOME
CELL MERGERS/SPLITS AS WELL AS SOME ORGANIZED LINE SEGMENTS, BUT A
THREAT FOR VERY LARGE/DESTRUCTIVE HAIL, AS WELL AS A FEW TORNADOES
WILL ACCOMPANY SUPERCELLS ACROSS OUR NORTHERN ZONES TODAY. SPC HAS
HIGHLIGHTED THIS AREA IN A SLGT RISK WITH A 15% HATCHING FOR HAIL,
AND A 5% TORNADO.
AS THE CONVECTIVE THREAT WANES INTO THE MID EVENING HOURS, OVERALL
FOCUS WILL QUICKLY SHIFT TO THE INCREASING WIND SPEEDS OVER SOUTH-
EAST WYOMING AS AN INTENSE COLD FRONT BLASTS EASTWARD LATER FRIDAY
EVENING INTO EARLY SATURDAY, SUPPORTING A CLASSIC BORA-DRIVEN HIGH
WIND EPISODE. CARBON/ALBANY COUNTIES WILL BE THE FIRST TO SEE WIND
GUSTS INCREASE BY MID-EVENING AS H7/H85 CAG-CPR GRADIENTS SURGE TO
50+ METERS AFTER 03Z, PEAKING BETWEEN 70-75 METERS BETWEEN 06Z AND
12Z SATURDAY BEFORE SLOWLY DECREASING. LATEST RANDOM FOREST MODELS
FOR ARLINGTON SUGGEST A DRAMATIC UPTICK IN PROBABILITIES AFTER 03Z
WITH A PEAK NEAR 80 PERCENT AROUND 09Z SATURDAY. POSSIBLE MOUNTAIN
WAVE ACTIVITY OFF THE SNOWYS COULD LEAD TO SOME SPILLAGE OF HIGHER
GUSTS INTO THE LARAMIE VALLEY OVERNIGHT AS WELL. MOST INTENSE WIND
SPEEDS FOR THE LARAMIE RANGE AND ADJACENT PORTIONS OF I-25 SEEM TO
OCCUR PRIMARILY AFTER 06Z WITH INTENSE COLD ADVECTION ALOFT AIDING
IN RAPIDLY STEEPENING LAPSE RATES ALONG W/A DISTINCT OMEGA COUPLET
INDICATING SEVERE MOUNTAIN WAVES. FORECAST SOUNDINGS FOR KCYS SHOW
A SIGNIFICANT MOUNTAIN TOP INVERSION, WITH 55-65 KNOT FLOW PRESENT
NEAR THE TOP OF THE MIXED LAYER. FURTHERMORE, A DRAMATIC WEST-EAST
SURFACE PRESSURE GRADIENT ON THE ORDER OF 6 TO 8 HPA COULD DEVELOP
ALONG THE SPINE OF THE LARAMIE RANGE, WITH A CORE OF 65-75 KNOT H7
TO H8 FLOW CO-LOCATED WITH EXTREME DOWNWARD OMEGA VALUES. AS SUCH,
80-90+ MPH WIND GUSTS MAY BE EASILY ACHIEVABLE ACROSS THE SOUTHERN
LARAMIE RANGE/ADJACENT FOOTHILLS, WITH 70-80 MPH GUSTS POSSIBLE IN
CHEYENNE AS WELL. RANDOM FOREST MODELS FOR CHEYENNE, BORDEAUX, AND
BUFORD ALL SHOW DRAMATIC SIGNALS WITH PARAMETER SPACE ANALOGS EVEN
SUPPORTING POTENTIAL FOR 75+ MPH GUSTS. STRONGEST GUSTS WILL OCCUR
OVERNIGHT INTO THE EARLY/MID MORNING, WITH WINDS SLOWLY DECREASING
THROUGH THE DAY. HIGH WIND WATCHES HAVE BEEN UPGRADED TO WARNINGS,
VALID FROM THIS EVENING/OVERNIGHT THROUGH 21Z SATURDAY.
LONG TERM
(SUNDAY - THURSDAY)
ISSUED AT 413 AM MDT FRI SEP 22 2023
OVERVIEW: LONG STRETCH OF QUIET WEATHER WITH WARMING TEMPERATURES
AND GENERAL BREEZINESS IS EXPECTED THROUGH MUCH OF NEXT WEEK. WINDS
COULD STAY ELEVATED ENOUGH ACROSS THE REGION AND WITH THE DRY
CONDITIONS SOME FIRE WEATHER CONCERNS MAY DEVELOP MONDAY INTO
TUESDAY. OUTSIDE OF THAT EXPECT A QUIET WEATHER WEEK WITH THE
POTENTIAL FOR PRECIPITATION CHANCES TO RETURN TO THE FORECAST TOWARD
NEXT FRIDAY (DAY 7)
DISCUSSION: MINIMAL CHANGES MADE TO THE LONG TERM FORECAST PERIOD
WITH LARGE AMPLITUDE RIDGING BUILDING INTO THE REGION. SLIGHT
ADJUSTMENTS WERE MADE TO THE WIND AND WIND GUST FORECAST FOR MONDAY
AND TUESDAY IN ADDITION TO SLIGHT TEMPERATURE ADJUSTMENTS. MODELS
ARE LOCKED IN WITH THIS LARGE RIDGE SITTING ACROSS MUCH OF THE
INTERIOR WEST THROUGH MUCH OF THE UPCOMING WEEK. THIS WILL TRANSLATE
TO DRY AND QUIET CONDITIONS UNDER MOSTLY SUNNY SKIES. THE MAIN
WEATHER HAZARD WILL BE THE POTENTIAL OF SOME FIRE WEATHER CONDITIONS
DEVELOPING ACROSS PORTIONS OF THE REGION MONDAY AND TUESDAY AS WINDS
STAY GUSTY IN THE 20 TO 30 MPH RANGE. THE RIDGE WILL EVENTUALLY MOVE
JUST ENOUGH EAST WHICH WILL AID IN DECREASING THE WIND SPEEDS BY MID
WEEK AND WITH THE RIDGE OVERHEAD TEMPERATURES ARE PROGGED TO RESPOND
WITH 80F TEMPERATURES RETURNING TO THE FORECAST FOR THE NEBRASKA
PANHANDLE AND ALONG THE NORTH PLATTE RIVER VALLEY WITH WIDESPREAD
70S EXPECTED ELSEWHERE.
THE PATTERN HOLDS BEFORE WE BEGIN TO SWITCH THE FLOW BACK TO THE SW
AS THE RIDGE IS PUSHED FURTHER EAST BY THE NEXT DEVELOPING STORM
ENTERING THE PACIFIC NORTHWEST. LOTS OF UNCERTAINTY AMONGST THE LONG
RANGE MODELS AND THE ENSEMBLE MEMBERS WITH THIS NEXT STORM, BUT
PRECIPITATION CHANCES COULD RETURN THE FORECAST BY THE END OF NEXT
WEEK.
AVIATION
(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 547 PM MDT THU SEP 21 2023
THE TERMINAL FORECAST OVER THE NEXT 12-24 HOURS WILL BE AN ACTIVE
SCENARIO FOR MOST SITES. VCTS AND VCSH ARE EXPECTED TO SLOWLY MOVE
FROM SOUTHWEST TO NORTHEAST BETWEEN 0Z-6Z, WITH KCDR SEEING THE
LONGEST WINDOW OF PRECIPITATION INTO THE OVERNIGHT HOURS. KLAR AND
KRWL WILL REMAIN VFR OVERNIGHT, AND WINDS GUSTS PICKING UP BY
TOMORROW MORNING TO 25-35 KNOTS. KCYS WILL SEE THE POTENTIAL FOR
VCTS TO WIND DOWN EARLY THIS EVENING, AND WEAK UPSLOPE FLOW WILL
CREATE LOW CIGS OVERNIGHT, ULTIMATELY IN THE FORM OF IFR/LIFR
THROUGH APPROXIMATELY 15Z FRIDAY.
THE NE PANHANDLE TERMINALS WILL ALSO BE IMPACTED BY THE LOW CIGS
THIS EVENING AND OVERNIGHT. FLIGHT CONDITIONS WILL TRANSITION FROM
MVFR TO IFR/LIFR BETWEEN 6Z-15Z, AND THE POTENTIAL FOR REDUCTION
IN VIS ALSO WILL BECOME APPARENT CLOSE TO THE 12Z-15Z TIMEFRAME
FOR THESE TERMINALS. ADDITIONALLY, ONCE THE VCSH AND VCTS PUSH
NORTHEAST, VRB WINDS WITH GUSTS TO LESS THAN 12 KNOTS WILL BE
EXPECTED.
FIRE WEATHER
ISSUED AT 413 AM MDT FRI SEP 22 2023
NO FIRE WEATHER CONCERNS W/ COOLER TEMPERATURES & MINIMUM RHS WELL
OUTSIDE OF CRITICAL THRESHOLDS. SCATTERED SHOWERS AND STORMS EARLY
THIS MORNING FOR MOST DISTRICTS, BECOMING MORE FOCUSED ACROSS EAST
CENTRAL WYO INTO THE NORTHERN NEB PANHANDLE DURING THE MID TO LATE
AFTERNOON HOURS. SEVERE STORMS ARE POSSIBLE W/ VERY LARGE HAIL AND
DAMAGING WINDS, AS WELL AS A FEW TORNADOES. WIDESPREAD STRONG WIND
GUSTS ARE EXPECTED OVERNIGHT THROUGH SATURDAY, ESPECIALLY OVER THE
SOUTHEAST WYOMING WIND CORRIDORS AND ADJACENT PORTIONS OF I25. SEE
HIGH WIND WARNINGS FOR MORE DETAILS.
CYS WATCHES/WARNINGS/ADVISORIES
WY...HIGH WIND WARNING FROM 9 PM THIS EVENING TO 3 PM MDT SATURDAY
FOR WYZ106-107-110-115.
HIGH WIND WARNING FROM MIDNIGHT TONIGHT TO 3 PM MDT SATURDAY FOR
WYZ116-117.
HIGH WIND WARNING FROM 2 AM TO 3 PM MDT SATURDAY FOR WYZ118.
NE...NONE.
SHORT TERM...CLH
LONG TERM...AW
AVIATION...AW
FIRE WEATHER...CLH
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