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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