902  
FXUS65 KCYS 111236  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
636 AM MDT WED SEP 11 2024  
   
KEY MESSAGES  
 
- SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED THIS  
AFTERNOON WITH LOCALLY HEAVY RAINFALL AND GUSTY WINDS  
POSSIBLE.  
 
- CRITICAL FIRE WEATHER CONDITIONS ARE EXPECTED FOR MOST OF THE  
AREA ON THURSDAY WITH STRONG WINDS GUSTING 40 TO 50 MPH. FIRE  
WEATHER WATCHES HAVE BEEN ISSUED.  
 
 
   
SHORT TERM /THROUGH THURSDAY NIGHT/  
 
ISSUED AT 400 AM MDT WED SEP 11 2024  
 
A POTENT EARLY SEASON SHORTWAVE TROUGH CURRENTLY MOVING ONSHORE IN  
THE PACIFIC NORTHWEST WILL BE THE MAIN PLAYER DRIVING A FAIRLY  
DYNAMIC NEXT 48 HOURS OR SO OF WEATHER. AN INITIAL SHORTWAVE  
DISTURBANCE/VORT-MAX IS ALREADY MOVING OUT AHEAD OF THE MAIN  
PARENT TROUGH, CURRENTLY LOCATED OVER WESTERN WYOMING. SYNOPTIC  
LIFT AHEAD OF THIS SYSTEM IS PRODUCING INCREASING CLOUD COVER  
ACROSS WYOMING, WHICH IN TURN HAS LEAD TO A FAIRLY WARM START TO  
OUR WEDNESDAY. CLOUD COVER WILL EXPAND EASTWARD THROUGH THE DAY  
INTO WESTERN NEBRASKA, OVERALL LEADING TO TEMPERATURES SLIGHTLY  
COOLER THAN THE LAST FEW DAYS. THIS INITIAL WAVE HAS ALSO  
TAPPED INTO IMPROVED MID- LEVEL MOISTURE, AND IS HELPING TO  
INCREASE COLUMN WATER VAPOR THROUGH THE DAY. AS A RESULT OF THE  
HIGHER MOISTURE CONTENT, EXPECT MORE ACTIVE SHOWER AND  
THUNDERSTORM ACTIVITY TODAY, WITH A MUCH BETTER CHANCE OF  
RAINFALL REACHING THE GROUND. FORECAST SOUNDINGS FOR THE  
AFTERNOON STILL SHOW A FAIRLY DRY BOUNDARY LAYER, BUT WITH  
ENOUGH MOISTURE ALOFT THAT THE CLOUD MASS SHOULDN'T HAVE TROUBLE  
REACHING THE GROUND. WHILE A FEW SHOWERS MAY BE AROUND LATER  
THIS MORNING, THUNDERSTORM ACTIVITY SHOULD BEGIN BETWEEN ABOUT  
NOON AND 2PM AND CONTINUE WELL INTO THE EVENING HOURS. MODEL  
GUIDANCE HAS TRENDED A LITTLE BIT MORE DISORGANIZED WITH THE  
MID-LEVEL FRONTAL BOUNDARY ALONG THE SHORTWAVE TROUGH AXIS THIS  
PM, WHICH REDUCES THE PROBABILITY OF A MORE ORGANIZED LINEAR  
SYSTEM. HOWEVER, A FEW HIRES MODELS STILL SHOW STORMS  
LINEARIZING. OVERALL, LOOKING AT PRIMARILY A THREAT FOR STRONG  
GUSTY WINDS AND ISOLATED HEAVY RAINFALL SINCE PARAMETERS REMAIN  
MARGINAL FOR MORE ORGANIZED SEVERE THUNDERSTORMS.  
 
AS THE PARENT TROUGH BARRELS ACROSS THE NORTHWEST TOWARDS CENTRAL  
IDAHO BY THURSDAY MORNING, EXPECT THE DRY SLOT OF THE EXTRA-  
TROPICAL CYCLONE TO POSITION ITSELF OVER OUR AREA. MID-LEVEL  
MOISTURE WILL QUICKLY DEPART BETWEEN MIDNIGHT AND DAWN ON  
THURSDAY. WYOMING PRECIPITABLE WATER VALUES AS LOW AS 0.25 TO  
0.35" MAY SHOW UP BY MIDDAY THURSDAY. STRONG WINDS ALOFT  
ROUNDING THE BASE OF THE TROUGH WILL MOVE OVER THE AREA. THE  
POTENT TROUGH ALOFT WILL ALSO SUPPORT RAPID LEE CYCLOGENESIS  
OVER NORTH CENTRAL WY/SOUTHEAST MT TONIGHT INTO THURSDAY. IN  
FACT, THE NAEFS MEAN SHOWS SLP APPROACHING CLIMATOLOGICAL  
MINIMUMS ACROSS MUCH OF THIS AREA. A SURFACE TROUGH TRAILING OUT  
OF THE SURFACE LOW PRESSURE CENTER IS EXPECTED TO DEVELOP IN  
CENTRAL WY BY EARLY MORNING, AND THEN GRADUALLY PROGRESS  
EASTWARD ACROSS THE FORECAST AREA THROUGH THE DAY, REACHING THE  
WY/NE BORDER BY MID AFTERNOON. EXPECT SOUTHERLY WINDS AHEAD OF  
THIS BOUNDARY AND SOUTHWESTERLY WINDS BEHIND, ALONG WITH VERY  
DRY AIR. STRONG MIXING SHOULD HELP GET THESE WINDS DOWN TO THE  
SURFACE, AND MOST OF WY COULD BE LOOKING AT WIND GUSTS OF 40+  
MPH. ALONG WITH CRITICAL AFTERNOON RH BEHIND THE BOUNDARY, THIS  
WILL LEAD TO A FAIRLY CONCERNING FIRE WEATHER SETUP ACROSS THE  
AREA. THERE IS SOME UNCERTAINTY ON HOW FAR AND HOW FAST THE DRY  
AIR WILL PROGRESS EASTWARD, WHICH WILL IMPACT HOW MUCH OF THE NE  
PANHANDLE SEES CRITICAL FIRE WEATHER CONDITIONS. FIRE WEATHER  
WATCHES HAVE BEEN ISSUED FOR THE ENTIRE AREA FOR WHICH FUELS ARE  
LISTED AS CRITICAL. THE LAST PIECE OF THE PUZZLE FOR THURSDAY'S  
FORECAST WILL BE A NARROW THREAT FOR THUNDERSTORMS. WHILE MOST  
OF THE AREA SHOULD BE IN THE DRY SLOT, MODELS SHOW A NARROW  
TONGUE OF ELEVATED MOISTURE MOVING JUST HEAD OF THE SURFACE  
TROUGH. STRONG ISENTROPIC LIFT IN THIS REGION MAY HELP SUPPORT  
CONVECTION IN FAR EAST CENTRAL WY AND THE NORTHERN NEBRASKA  
PANHANDLE THURSDAY AFTERNOON AND EVENING. HOWEVER, IT IS ALSO  
POSSIBLE THIS FAVORABLE ASCENT REGION REMAINS JUST UP TO THE  
NORTHEAST PRIMARILY IN SD. FOR NOW, HAVE SOME SLIGHT CHANCE TO  
CHANCE POPS IN THE AREA, BUT WITH A FAIRLY DYNAMIC SETUP THANKS  
TO THE STRONG UPPER LEVEL TROUGH, WE'LL NEED TO KEEP AN EYE ON  
THIS FOR SOME LOCALLY STRONG TO SEVERE WINDS, IF THE STORMS CAN  
DEVELOP.  
 
 
   
LONG TERM /FRIDAY THROUGH TUESDAY/  
 
ISSUED AT 400 AM MDT WED SEP 11 2024  
 
THE UPPER-LEVEL PATTERN IS EXPECTED TO REMAIN SOMEWHAT ACTIVE IN  
THE EXTENDED FORECAST PERIOD W/ GENERAL LONG-WAVE TROUGHING MOST  
LIKELY PERSISTING THROUGH EARLY TO MID NEXT WEEK. THE POST-FROPA  
COOL DOWN ON FRIDAY WILL BE SHORT LIVED W/ A SLIGHT TREND TOWARD  
WARMER TEMPERATURES OVER THE WEEKEND AS THE THERMAL RIDGE BEGINS  
TO BUILD BACK INTO THE REGION. HIGHLY ACTIVE QUASI-ZONAL MID AND  
UPPER-LEVEL FLOW COULD HELP HOLD TEMPERATURES BACK SLIGHTLY, BUT  
DAYTIME HIGHS MAY STILL REACH THE UPPER 80S TO NEAR 90 DEG F FOR  
THE WESTERN NE PANHANDLE ON SUNDAY. THE NEXT SUBSTANTIAL SHOT OF  
COOLER AIR SHOULD ARRIVE ON TUESDAY AS THE NEXT TROUGH DIGS INTO  
THE GREAT BASIN. DESPITE THE VERY ACTIVE PATTERN ALOFT, PROFILES  
REMAIN VERY DRY AND ANY CHANCES FOR CONVECTION SHOULD BE MINIMAL  
UNTIL LATE IN THE FORECAST PERIOD AHEAD OF THE NEXT LARGER SCALE  
DISTURBANCE ALOFT.  
 
 
   
AVIATION /12Z TAFS THROUGH 12Z THURSDAY/  
 
ISSUED AT 632 AM MDT WED SEP 11 2024  
 
IN GENERAL, VFR PREVAILS. SCATTERED HIGH-BASED SHOWERS AND A FEW  
THUNDERSTORMS ARE EXPECTED THIS AFTERNOON, ROUGHLY BETWEEN 18Z &  
03Z. GUSTY & ERRATIC SURFACE WINDS WILL BE THE PRIMARY HAZARD TO  
AVIATION INTERESTS. WIND GUSTS UP TO 40 KNOTS MAY BE POSSIBLE AT  
KCDR LATER THIS AFTERNOON THROUGH THE EVENING W/ A STRENGTHENING  
LOW-LEVEL JET.  
 
 
   
FIRE WEATHER  
 
ISSUED AT 400 AM MDT WED SEP 11 2024  
 
ELEVATED FIRE WEATHER CONDITIONS ARE EXPECTED THIS AFTERNOON.  
SOUTHERLY WINDS GUSTING 25 TO 30 MPH WITH MIN RH BETWEEN 15 AND 20%  
WILL BE PRESENT IN THE NEBRASKA PANHANDLE, PORTIONS OF EAST CENTRAL  
WY, AND IN CARBON COUNTY VALLEYS. ADDITIONALLY, AFTERNOON CONVECTIVE  
ACTIVITY MAY BRING LIGHTNING AND GUSTY WINDS. SOME WETTING RAINFALL  
WILL BE POSSIBLE, BUT THE COVERAGE OF WETTING RAINS MAY NOT BE VERY  
HIGH.  
 
WIDESPREAD CRITICAL FIRE WEATHER CONDITIONS ARE INCREASINGLY LIKELY  
FOR THURSDAY. STRONG SOUTHWEST TO SOUTH WINDS AND MIN RH BETWEEN 10  
AND 15% FOR ALL SE WYOMING VALLEYS AND FAR WESTERN NEBRASKA WILL  
LEAD FAVORABLE CONDITIONS FOR RAPID FIRE SPREAD. WINDS COULD GUST AS  
HIGH AS 40 TO 50 MPH. FIRE WEATHER WATCHES HAVE BEEN ISSUED FOR MOST  
OF THE AREA FOR 12PM TO 8PM THURSDAY.  
 
 
   
CYS WATCHES/WARNINGS/ADVISORIES  
 
WY...FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY  
EVENING FOR WYZ417>423-425-427>433.  
NE...FIRE WEATHER WATCH FROM THURSDAY AFTERNOON THROUGH THURSDAY  
EVENING FOR NEZ435>437.  
 
 
 
 
 
SHORT TERM...MN  
LONG TERM...CLH  
AVIATION...CLH  
FIRE WEATHER...MN  
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