045  
FXUS65 KCYS 291653  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1053 AM MDT THU JUL 29 2021  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 330 AM MDT THU JUL 29 2021  
 
LATEST WV IMAGERY/UPPER AIR ANALYSIS SHOWED THE CENTER OF THE UPPER  
RIDGE FROM EASTERN CO THROUGH KS. MONSOONAL MOISTURE WAS CIRCULATING  
NORTHWARD THROUGH WESTERN CO INTO ALL BUT SOUTHEAST WY. A FRONT  
EXTENDED FROM SOUTH CENTRAL THROUGH SOUTHEAST WY INTO NORTHERN NE.  
WINDS BEHIND THE FRONT WERE NORTHEASTERLY AND GUSTY, WITH DEW POINTS  
IN THE MID 50S TO LOWER 60S.  
 
THIS FRONT IS PROGGED TO PUSH SOUTH OF I-80 EARLY THIS MORNING. HIGH  
TEMPERATURES BEHIND THE FRONT WILL BE 5-10 DEGREES COOLER THAN  
WEDNESDAY. MODERATE EASTERLY WINDS WILL PROVIDE THE SETUP FOR  
OROGRAPHIC FORCING AS WELL AS INCREASING LOW LEVEL MOISTURE. SCATTERED  
CONVECTION WILL DEVELOP THIS AFTERNOON. THERMODYNAMICS WILL BE MARGINAL  
FOR SEVERE STORMS, WITH MORE OF A STRONG WIND THREAT AND LESS OF A  
HAIL THREAT DUE TO LONG SKINNY CAPE FORECAST SOUNDINGS. LOCALLY HEAVY  
RAIN WILL ACCOMPANY SOME OF SHOWERS AND STORMS. STORM MOTION WILL BE  
NORTH TO NORTHEAST ~25 KT. PRECIPITABLE WATER VALUES WILL RANGE FROM  
0.8" TO 1.3". THE DAY 1 EXCESSIVE RAINFALL OUTLOOK (ERO) HAS A MARGINAL  
RISK WEST OF A CHEYENNE TO DAWES-BOX BUTTE COUNTY LINE. SCATTERED  
SHOWERS AND THUNDERSTORMS WILL LINGER INTO THE LATE EVENING SOUTH OF  
A RAWLINS TO ALLIANCE LINE, AND PAST MIDNIGHT TO THE NORTH.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 330 AM MDT THU JUL 29 2021  
 
MODEL CONSENSUS HAS THE NW-SE ORIENTED UPPER RIDGE EXTENDING FROM THE  
NORTHERN ROCKIES TO THE NORTHERN GULF COAST THROUGH THE WEEKEND. A  
DIGGING UPPER TROUGH OVER THE EASTERN CONUS WILL AMPLIFY THE RIDGE  
OVER THE ROCKIES AND HIGH PLAINS EARLY NEXT WEEK. PRECIPITABLE WATER  
(PW) VALUES WILL REMAIN BETWEEN 1" AND 1.3" FRIDAY THROUGH SATURDAY.  
LOCALLY HEAVY RAINFALL WILL BE THE PRIMARY CONCERN, WITH THE DAY 2  
(FRIDAY/FRIDAY NIGHT) ERO PLACING THE MARGINAL RISK ALONG AND WEST  
OF A LINE FROM DOUGLAS TO CHEYENNE. A SLIGHT RISK FOR EXCESSIVE RAINFALL  
WAS INTRODUCED OVER MUCH OF ALBANY, SOUTHEAST CARBON AND FAR WESTERN  
LARAMIE COUNTIES. THIS INCLUDES THE MULLEN BURN SCAR WHERE HOURLY  
RAINFALL RATES COULD EXCEED AN INCH. LATER SHIFTS MAY NEED TO CONSIDER  
A FLASH FLOOD WATCH WITHIN THE SLIGHT RISK AREA.  
 
MOST MODELS SHOW PW VALUES DECREASING TO 0.6" TO 1" SUNDAY THROUGH  
MONDAY AS SOME DRIER AIR ALOFT TRIES TO SPREAD SOUTH INTO THE CWA. THIS  
SHOULD LOWER THE FLASH FLOOD RISK OVER THE BURN SCARS. THERE WILL BE  
A DECREASE IN AREAL COVERAGE OF SHOWERS AND THUNDERSTORMS TUESDAY THROUGH  
WEDNESDAY AS THE UPPER RIDGE BUILDS OVER THE REGION ACCOMPANIED BY  
DRIER AIR ALOFT (PW'S LOWER TO 0.4" TO 0.75").  
 
HIGH TEMPERATURES WILL COOL INTO THE 70S AND 80S THIS WEEKEND, FOLLOWED  
BY SLIGHT WARMING EARLY NEXT WEEK WITH 80S TO LOWER 90S.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)  
ISSUED AT 1050 AM MDT THU JUL 29 2021  
 
LATEST CURRENT RADAR IMAGERY INDICATES SOME LIGHT CONVECTION  
PULSING ACROSS THE NORTH AND EASTERN PORTIONS OF THE CWA.  
EXPECTING MOSTLY VFR TO MVFR CONDITIONS THROUGH THE EARLY MORNING  
HOURS, OUTSIDE OF KCYS CURRENTLY AT IFR. SHOULD SEE KCYS CEILINGS  
LIFT TO AROUND MVFR CONDITIONS OVER THE NEXT FEW HOURS.  
OTHERWISE, MAIN CONCERNS STILL EXIST WITH THUNDERSTORM POTENTIAL  
THROUGH THE LATE NIGHT HOURS. A FAIR AMOUNT OF UNCERTAINTY WITH  
THESE SYSTEMS AS THE HIRES MODELS HAVE BEEN FAIRLY INCONSISTENT.  
EARLY RUNS INDICATED A DECENT AMOUNT OF WIDESPREAD CONVECTION  
DEVELOPING ACROSS SOUTHEASTERN WYOMING, AND PUSHING EASTWARD INTO  
THE NEBRASKA PANHANDLE. HOWEVER, THE MOST RECENT RUNS HAVE BACKED  
OFF SOME OF THE THUNDERSTORM ACTIVITY WEST OF I-25, AND PRIMARILY  
SOUTHWARD INTO COLORADO, LIKELY DUE TO THE CLOUD DECK OVER THE  
REGION. AS A RESULT, WENT AHEAD AND DID NOT UPDATE THE VCTS IN THE  
TAFS. WILL LIKELY NEED TO EVALUATE LATER MODEL RUNS TO DETERMINE  
THE EXACT TIMING AND LOCATION OF ANY IMPACTS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 330 AM MDT THU JUL 29 2021  
 
A PATTERN CHANGE TOWARD COOLER TEMPERATURES AND INCREASING CHANCES FOR  
SHOWERS AND THUNDERSTORMS WILL COMMENCE TODAY AND PERSIST THROUGH THE  
WEEKEND AS THE RIDGE OF HIGH PRESSURE SHIFTS TO THE SOUTHEAST. MINIMUM  
HUMIDITIES THE NEXT FEW DAYS WILL INCREASE TO 25 TO 35 PERCENT. PERIODS  
OF HEAVY RAIN WILL RAISE THE POTENTIAL FOR LOCALIZED FLASH FLOODING,  
PARTICULARLY OVER THE BURN SCARS.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...NONE.  
NE...NONE.  

 
 

 
 
SHORT TERM...MAJ  
LONG TERM...MAJ  
AVIATION...MD  
FIRE WEATHER...MAJ  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab WY Page
The Nexlab NE Page Main Text Page