396  
FXUS65 KCYS 020046  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
646 PM MDT MON SEP 1 2014  
   
SHORT TERM
 
(THIS EVENING THROUGH WEDNESDAY NIGHT)  
ISSUED AT 422 PM MDT MON SEP 1 2014  
 
MADE NO CHANGES TO THE EARLIER FORECAST UPDATE FOR THE NEXT 12HRS  
OTHER THAN TO BUMP UP MAX TEMPS A FEW DEGREES ACROSS THE PLAINS.  
ISOLATED TO SCATTERED SHOWERS AND STORMS DEVELOPED MAINLY ALONG  
THE COLD FRONT AND PINE RIDGE EARLIER THIS AFTERNOON...WITH THE  
STRONGEST ACTIVITY CURRENTLY PUSHING EAST-NORTHEAST OUT OF THE  
CWA. A FEW STORMS THAT DEVELOPED OVER THE BIG HORNS ARE NOW RACING  
SOUTHEAST TOWARD THE CWA...WITH OTHER WEAKER SHOWERS MOVING OFF  
THE LARAMIE RANGE AND OVER THE WYO/NEB PLAINS. DRIER AIR  
CONTINUING TO MOVE IN FROM THE WEST WILL LIMIT OVERALL  
INSTABILITY SO EXPECT THIS ACTIVITY TO REMAIN ON THE WEAKER SIDE.  
THE EXCEPTION MAY BE IN THE SOUTHERN PANHANDLE WHERE DEW POINTS  
REMAIN IN THE MID 40S WITHIN AN ENVIRONMENT THAT HAS NOT QUITE  
BEEN WORKED OVER YET. SO COULD STILL SEE GUSTY WINDS FROM MORE  
ROBUST CONVECTION THAT SHOULD DEVELOP HERE OVER THE NEXT FEW  
HOURS.  
 
THE SHORTWAVE WILL SHIFT EAST OF THE AREA LATE THIS EVENING WITH  
THE UPPER LEVEL JET LIFTING TO THE NORTH. NAM FORECAST SOUNDINGS  
STILL HINT AT THE POSSIBILITY OF PATCHY STRATUS TONIGHT MAINLY FOR  
THE LOW RIVER VALLEYS IN THE PANHANDLE SO WILL KEEP SOME CLOUDS IN  
THE FORECAST FOR THESE AREAS TONIGHT. OTHERWISE...MUCH DRIER AND  
WARMER AIR WILL ADVECT INTO THE CWA AS THE JET LIFTS NORTH AND AN  
UPPER LEVEL RIDGE BUILDS OVERHEAD FOR THE NEXT COUPLE OF DAYS.  
TUESDAY AND WEDNESDAY LOOK TO BE MOSTLY SUNNY...BREEZY...AND DRY  
ACROSS THE FORECAST AREA...WITH THE MAIN CONCERN TRANSITIONING TO  
FIRE WEATHER. WENT AHEAD AND UPGRADED THE FIRE WEATHER WATCH TO A  
RED FLAG WARNING FOR ZONES 301...LOWER ELEVATIONS OF  
302...304...AND 309. AFTER FURTHER REVIEW...LEFT 303 AND 308 OUT  
OF THE WARNING AS FUELS HAVE BEEN DEEMED NON-SUPPORTIVE FOR LARGE  
FIRE GROWTH. HUMIDITIES ACROSS MUCH OF THE CWA WILL DROP INTO THE  
TEENS WITH GUSTS OF 30 TO 40 MPH EXPECTED ALONG AND WEST OF THE  
LARAMIE RANGE. FURTHER EAST...FORECAST SOUNDINGS SHOW THAT DEEP  
MIXING WITHIN THE BOUNDARY LAYER WILL BE DELAYED TO THE LATER  
AFTERNOON SO WINDS SHOULD BE WEAKER WITH GUSTS OF 20 TO 25 MPH AT  
TIMES IN THE LATER AFTERNOON. SOUNDINGS SHOW THAT WEDNESDAY WILL  
SEE A DEEPER BOUNDARY LAYER OVER THE CWA FOR MOST OF THE DAY...SO  
MORE WIDESPREAD GUSTY WINDS AND DRY HUMIDITIES ARE ANTICIPATED  
WITH AN EXPANSION OF THE RED FLAG WARNING QUITE POSSIBLE. WILL LET  
LATER SHIFTS REFINE TIMING AND LOCATION OF POTENTIAL CRITICAL  
CONDITIONS FOR WEDNESDAY. TEMPERATURES WILL WARM BACK TO ABOVE  
NORMAL READINGS FOR THIS TIME OF YEAR ON WEDNESDAY.  
   
LONG TERM
 
(THURSDAY THROUGH SUNDAY)  
ISSUED AT 422 PM MDT MON SEP 1 2014  
 
FRONTAL PASSAGE IS STILL PROGGED FOR THURS MORNING WITH A 15-20  
DEGREE DROP IN TEMPS ON THURS COMPARED TO WED. EAST TO  
SOUTHEASTERLY SFC WINDS DEVELOP BY THURS NIGHT AND COMBINED WITH  
INCREASING LARGE SCALE ASCENT/ISENTROPIC LIFT...SHOWERS COULD  
DEVELOP ACROSS THE CWA. THE ECMWF CONTINUES THE TREND FROM  
YESTERDAYS MODEL SOLN OF BEING MORE AGGRESSIVE ON QPF FOR THURS  
NIGHT...ESPECIALLY OVER THE PANHANDLE. THE GFS AND CANADIAN ARE  
QUITE A BIT DRIER SO KEPT POPS IN THE SLIGHT CHANCE CATEGORY FOR  
NOW. SFC HIGH REMAINS ANCHORED OVER THE NORTHERN PLAINS THROUGH AT  
LEAST SAT SO LLVL UPSLOPE WILL CONTINUE TO THE EAST OF THE LARAMIE  
RANGE...KEEPING TEMPS SLIGHTLY BELOW NORMAL. WEAK SHORTWAVES WILL  
MOVE THROUGH THE FLOW...HOWEVER TIMING IS UNCERTAIN AT THIS POINT.  
UNTIL THE MODELS COME INTO BETTER AGREEMENT ON THE LOCATION OF BEST  
FORCING AND QPF...IT IS BEST TO KEEP POPS IN THE 20-30 PERCENT RANGE  
FOR FRI AND SAT. IT SHOULD BE NOTED THAT NONE OF THE LONG RANGE  
MODELS INDICATE A SUBSTANTIAL AMOUNT OF PRECIP FOR FRI-SAT...ONLY A  
FEW TENTHS. IT DOES APPEAR THAT THE AIRMASS WILL BE MORE UNSTABLE  
OVER SOUTHEAST WY...SO BEST CHANCE OF THUNDER WILL BE THERE.  
SOUTHWESTERLY FLOW ALOFT STRENGTHENS BY SUN AND WITH A LEE TROUGH  
DEVELOPING OVER THE PLAINS...SLIGHT WARMING WITH ENSUE.  
 

 
   
AVIATION
 
(FOR THE 00Z TAFS THROUGH 00Z TUESDAY AFTERNOON)  
ISSUED AT 632 PM MDT MON SEP 1 2014  
 
A FEW SHOWERS LINGER AROUND MAINLY WRN NEBRASKA PANHANDLE  
TERMINALS AT ISSUANCE. MOST CONVECTION HAS BEEN WEAK THUS FAR AND  
RECENT RADAR RETURNS SUGGEST THAT THESE SHOWERS WILL CONTINUE TO  
WEAKEN OVR THE NEXT FEW HOURS. EXPECT SKIES TO GRADUALLY CLEAR  
OVERNIGH RETURNING...WITH VFR CONDITIONS PREVAILING THRU TUESDAY.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 422 PM MDT MON SEP 1 2014  
 
ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS WILL CONTINUE FOR  
AREAS ALONG AND EAST OF THE LARAMIE RANGE THROUGH THIS EVENING.  
MUCH DRIER CONDITIONS WILL SETTLE IN FOR TUESDAY AND WEDNESDAY  
ACROSS THE DISTRICT...WITH WINDY CONDITIONS EXPECTED TO CONTINUE  
IN AREAS ALONG AND WEST OF THE LARAMIE RANGE DURING THE AFTERNOON  
HOURS. CRITICAL FIRE WEATHER CONDITIONS ARE LIKELY FOR LOWER  
ELEVATIONS ALONG AND WEST OF THE LARAMIE RANGE AS A RESULT...WITH  
FUELS SUPPORTIVE OF LARGE FIRE GROWTH IN ZONES  
301...302...304...AND 309. THEREFORE...UPGRADED THE FIRE WATCH TO  
A RED FLAG WARNING FOR THESE ZONES STARTING NOON ON TUESDAY AND  
CONTINUING THROUGH 7 PM. CRITICAL FIRE WEATHER CONDITIONS ARE  
POSSIBLE AS WELL ON WEDNESDAY FOR THESE SAME AREAS....AND COULD  
ALSO EXTEND FURTHER EAST INTO THE EASTERN WYOMING PLAINS.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...RED FLAG WARNING FROM NOON TO 7 PM MDT TUESDAY FOR WYZ301-302-  
304-309.  
 
NE...NONE.  

 
 

 
 
SHORT TERM...RJM  
LONG TERM...FINCH  
AVIATION...HAHN  
FIRE WEATHER...RJM  
 
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