908  
FXUS65 KCYS 270441  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1041 PM MDT TUE MAY 26 2015  
   
UPDATE
 
 
ISSUED AT 925 PM MDT TUE MAY 26 2015  
 
THUNDERSTORM ACTIVITY CONTINUES TO WEAKEN ACROSS THE AREA THIS  
EVENING. THERE ARE STILL A FEW THUNDERSTORMS INTO NIOBRARA COUNTY  
IN EAST CENTRAL WYOMING BUT THOSE SHOULD DIE OFF IN THE NEXT HOUR  
OR SO WITH ISOLATED SHOWERS THE REST OF TONIGHT. NO CHANGES TO THE  
 

 
   
SHORT TERM
 
(TONIGHT - THURSDAY NIGHT)  
ISSUED AT 352 PM MDT TUE MAY 26 2015  
 
A WEAK SHORTWAVE TROUGH AND ASSOCIATED MID LEVEL VORT MAX CONTINUES  
TO MOVE EASTWARD ACROSS WESTERN WY THIS AFTN. THIS...COMBINED WITH  
LLVL CONVERGENCE ALONG THE LARAMIE RANGE IS PROVIDING SUFFICIENT  
FORCING FOR ISOLATED TO WIDELY SCATTERED CONVECTION ACROSS MUCH OF  
SOUTHEAST WY AND THE WESTERN NE PANHANDLE. 15 KT H5 FLOW RESULTS IN  
VERY MODEST EFFECTIVE BULK SHEAR VALUES...SO DO NOT EXPECT TO SEE  
ANY ORGANIZED SEVERE WEATHER TODAY DESPITE THE MARGINAL RISK ON THE  
LATEST SPC DAY 1 OUTLOOK. COULD SEE A FEW STORMS PRODUCE SMALL HAIL  
THOUGH WITH THE LATEST MESOANALYSIS SHOWING AROUND 1500 J/KG MLCAPE  
VALUES AND A RELATIVELY COOL AIR MASS STILL IN PLACE WITH SFC TEMPS  
IN THE LOW TO MID 60S. TORRENTIAL RAIN STILL A POSSIBILITY WITH PWAT  
VALUES ON THE ORDER OF 0.7 INCH...SO COULD SEE SOME LOCALIZED MINOR  
FLOODING ON SATURATED GROUND IF ANY STORMS HANG AROUND TOO LONG. THE  
THREAT FOR SHOWERS AND THUNDERSTORMS SHOULD DECREASE INTO TONIGHT...  
BUT GFS/NAM/ECM ALL HANG ON TO SOME WEAK QPF ACROSS OUR WESTERN AND  
NORTHERN ZONES AS THE SHORTWAVE AXIS LIFTS NORTHEAST OVERNIGHT. WILL  
HANG ON TO LOW-END POPS.  
 
MOIST SOUTHWEST FLOW ALOFT REMAINS IN PLACE ON WEDNESDAY...WITH LEE  
TROUGHING TAKING SHAPE ALONG THE WYO/NEB STATE LINE. MAIN CHALLENGE  
WILL BE THE EASTWARD PROGRESSION OF THIS FEATURE AS THIS WILL PLAY A  
MAJOR ROLE IN PCPN COVERAGE IN THE AFTN. UPPER DIFLUENCE ATOP WEAK  
LLVL CONVERGENCE WILL HELP TO INITIATE CONVECTION ONCE AGAIN DURING  
THE LATE MORNING THROUGH EARLY EVENING. AHEAD OF THE BOUNDARY...DEW  
POINTS ARE PROGGED TO BE IN THE 50S WITH MODEST H7-H5 LAPSE RATES  
AROUND 7 DEG C/KM. NAM CAPES BETWEEN 1000-2000 J/KG WOULD SUPPORT A  
FEW STRONGER STORMS ONCE AGAIN...SO THE SPC MARGINAL RISK LOOKS GOOD  
FOR THE PANHANDLE. OPTED NOT TO MENTION ANY SMALL HAIL ATTM AS THE  
POTENTIAL FOR ORGANIZED CONVECTION IS LIMITED. SOME WARM ADVECTION  
TOMORROW HELPING TO INCREASE H7 TEMPS TO 5-8 DEG C PER MOST OF OUR  
AVAILABLE GUIDANCE...SO SHOULD SEE A FEW MORE 70S FOR HIGHS. THE  
OVERALL PATTERN WILL REMAIN THE SAME INTO THU AS A POORLY ORGANIZED  
SHORTWAVE SHIFTS ACROSS WESTERN WY. CONVECTION IS LIKELY ONCE AGAIN  
IN THE AFTERNOON...THOUGH THE BETTER CHANCE FOR STRONGER STORMS WILL  
BE TO THE EAST WITH THE BETTER INSTABILITY.  
   
LONG TERM
 
(FRIDAY - TUESDAY)  
ISSUED AT 352 PM MDT TUE MAY 26 2015  
 
THE WET PATTERN WILL PERSIST ON FRIDAY AS AN UPPER SHORTWAVE  
PASSES ACROSS THE REGION AND INTERACTS WITH SFC UPSLOPE FLOW  
BEHIND A COOL FRONT THAT WILL PASS ACROSS EARLY IN THE DAY. THE  
RAIN WILL END FRIDAY NIGHT AS THE UPPER WAVE MOVES EAST AND DRIER  
AIR FILTERS INTO THE AREA. A RELATIVELY DRY WEEKEND LOOKING TO SET  
UP OVER THE AREA AS UPPER RIDGING MOVES ACROSS THE AREA THOUGH  
SOME WIDELY SCTD CONVECTION POSSIBLE MAINLY NEAR THE MTNS SUNDAY  
AS MOISTURE BEGINS RETURNING NORTHWARD IN RESPONSE TO LEE TROFFING  
OVER THE HIGH PLAINS. MONDAY AND TUESDAY WILL SEE MORE TYPICAL  
LATE SPRING WEATHER OVER THE CWA WITH AFTERNOON AND EVENING  
SHOWERS AND THUNDERSTORMS AS THE UPPER FLOW TURNS SW AHEAD OF THE  
NEXT UPPER TROF THAT WILL MOVE OVER THE WESTERN CONUS.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z WEDNESDAY NIGHT)  
ISSUED AT 1038 PM MDT TUE MAY 26 2015  
 
VFR CONDITIONS EXPECTED FOR ALL SOUTHEAST WYOMING AND NEBRASKA  
PANHANDLE AIRPORTS OVERNIGHT INTO WEDNESDAY. SHOWERS ARE WEAKENING  
NOW NORTH OF A LINE FROM WHEATLAND TO CHADRON LATE THIS EVENING  
AND SHOULD CONTINUE TO DO SO. CONVECTION EXPECTED TO RETURN  
WEDNESDAY AFTERNOON WITH TEMPERATURES CLIMBING BACK INTO THE 70S.  
ADDED VCTS WORDING FOR ALL TAFS. WILL NARROW IN ON TIMING AS THE  
EVENT GETS CLOSER.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 352 PM MDT TUE MAY 26 2015  
 
NO FIRE WEATHER CONCERNS WITH RECENT RAINFALL AND CONTINUED DAILY  
CHANCES FOR SHOWERS AND THUNDERSTORMS ACROSS MUCH OF THE AREA.  
 

 
   
HYDROLOGY
 
 
ISSUED AT 919 PM MDT TUE MAY 26 2015  
 
LATEST RIVER FORECAST HAS BEEN ISSUED. FORECASTS AT THE RIVER  
FORECAST POINTS ALONG THE NORTH PLATTE RIVER AND LARAMIE RIVER  
HAVE GENERALLY BEEN LOWERED AS MOST THUNDERSTORM ACTIVITY MISSED  
THE RUNOFF BASIN TODAY. ACTUAL RIVER CRESTS COULD CERTAINLY BE  
ADJUSTED DEPENDING ON EXACT LOCATION OF CONVECTION THE NEXT FEW  
DAYS BUT GIVEN THE RANDOM NATURE OF CONVECTIVE ACTIVITY...ANY NEW  
PRECIPITATION WILL NEED TO BE CLOSELY MONITORED.  
 

 
   
CLIMATE
 
 
ISSUED AT 352 PM MDT TUE MAY 26 2015  
 
CHEYENNE RECEIVED ANOTHER 0.29 INCH OF RAINFALL WITH A HEAVY STORM  
EARLIER THIS AFTERNOON. THIS BRINGS OUR MONTHLY TOTAL TO 5.74  
INCHES...BUMPING US TO THE 5TH WETTEST MAY ON RECORD. THE RECORD  
IS 6.66 INCHES IN 1904. CHANCES FOR SHOWERS AND THUNDERSTORMS WILL  
EXIST EVERY DAY THROUGH THE REST OF THE WEEK. THERE IS A SMALL  
CHANCE OF EXCEEDING THE ALL TIME RECORD BEFORE THE END OF THE  
MONTH IF ANY HEAVIER STORMS AFFECT THE CITY.  
 

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

 
 

 
 
UPDATE...SML  
SHORT TERM...CLH  
LONG TERM...RE  
AVIATION...GCC  
FIRE WEATHER...CLH  
HYDROLOGY...SML  
CLIMATE...CLH  
 
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