333  
FXUS65 KCYS 291139  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
539 AM MDT TUE JUL 29 2014  
   
SHORT TERM
 
(TODAY THROUGH THURSDAY NIGHT)  
ISSUED AT 400 AM MDT TUE JUL 29 2014  
 
MORNING WATER VAPOR SATELLITE IMAGERY SHOWS A WELL ORGANIZED  
UPPER-LEVEL LOW DEVELOPING OVER SOUTHERN NV/UT WITHIN A GENERAL  
WEAKNESS IN A LARGER SCALE RIDGING PATTERN. ABUNDANT MONSOONAL  
MOISTURE CONTINUES TO SPREAD NORTHWARD INTO THE CENTRAL ROCKIES  
IN ADVANCE OF THIS FEATURE WITH ISOLATED SHOWERS NOW DEVELOPING  
OVER SOUTHEAST WY AND THE NORTHERN PANHANDLE. CONVECTION SHOULD  
ONLY INCREASE IN COVERAGE WITH TIME AS LARGE SCALE ASCENT SPREADS  
ACROSS THE AREA. MOIST LLVL UPSLOPE STRENGTHENS DRAMATICALLY BY  
18Z BENEATH STRONG DIVERGENCE ALOFT ASSOCIATED WITH A 100 KT JET  
STREAK OVER THE NORTHERN PLAINS. EXCELLENT MOISTURE IS IN PLACE  
WITH PWAT VALUES AROUND 1.5 INCHES AND WIDESPREAD SFC DEWPOINTS  
IN THE 50S TO NEAR 60F PER RECENT OBS. BELIEVE CONVECTION SHOULD  
BECOME QUITE NUMEROUS BY MID AFTN. INTRODUCED CATEGORICAL POPS  
AFTER 21Z ALONG AND JUST EAST OF THE LARAMIE RANGE WITH THE  
UPSLOPE ENHANCEMENT.  
 
GFS K-INDEX VALUES OF 35 TO 40 C AND STRONG UVVS POINT TO HEAVY  
RAIN POTENTIAL THIS AFTN AND EVE. GFS AND NAM BUFKIT SOUNDINGS  
SUPPORT EFFICIENT RAIN PRODUCTION WITH TALL/SKINNY CAPE PROFILES  
AND DEEP SATURATION AFTER 21Z. WHILE THE RESIDENCE TIME OF  
FAVORABLE DYNAMICS MAY NOT SUPPORT A SIGNIFICANT FLOODING  
RISK...STORMS WILL BE SLOW MOVING WITH AVERAGE 700-300 MILLIBAR  
WINDS ONLY AROUND 10 KT. PLUS THE GFS/NAM/ECMWF MODELS ALL AGREE  
WITH QPF VALUES BETWEEN 1 AND 2 INCHES ALONG AND ON EITHER SIDE OF  
THE LARAMIE RANGE. WPC STILL PAINTS A MDT RISK FOR EXCESSIVE  
RAINFALL IN OUR SOUTHERN ZONES. WENT AHEAD AND HOISTED A FLASH  
FLOOD WATCH FOR THE MOUNTAINS AND SOME OF THE ADJACENT VALLEYS/HIGH  
PLAINS. NOT TOO CONFIDENT THAT AREAS FARTHER EAST WILL SEE HIGHER  
AMOUNTS AS CONVECTION MAY BE LARGELY TERRAIN DRIVEN. LEFT THOSE  
AREAS OUT OF THE WATCH FOR THE TIME BEING...BUT THE DAY SHIFT MAY  
WISH TO REVISIT.  
 
CONVECTION SHOULD DECREASE IN COVERAGE AND INTENSITY BY SUNRISE  
WED AS STRONGER DYNAMICS SHIFT SOUTH AND EAST. ECMWF AND NAM ARE  
SLOWER TO MOVE THINGS OUT WITH SOME HIGHER QPF CARRYING OVER INTO  
THE 18Z TO 00Z TIME FRAME ON WED AFTN...SO WILL NEED TO MONITOR  
FOR A TEMPORAL EXTENTION OF THE FLASH FLOOD THREAT. OTHERWISE...  
TEMPERATURES TODAY AND WED WILL RATHER COOL WITH WIDESPREAD CLOUDS  
AND PCPN. H7 TEMPS ONLY AROUND 5-7C ON WED SUGGESTS COOLER THAN  
CONSENSUS MOS INDICATES...ONLY LOOKING AT A HIGH AROUND 65F HERE  
IN CYS. WARMER AND DRIER FOR THU AS RIDGING RE-ESTABLISHES ITSELF  
OVER THE ROCKY MOUNTAIN REGION. PCPN CHANCES WILL BE CONFINED TO  
THE MOUNTAINS.  
   
LONG TERM
 
(FRIDAY THROUGH TUESDAY)  
ISSUED AT 400 AM MDT TUE JUL 29 2014  
 
A VERY TYPICAL EARLY AUGUST PATTERN TAKING SHAPE DURING THE EXTENDED  
PERIOD...AS UPPER-LEVEL RIDGE AXIS OVER THE INTERMOUNTAIN WEST IS  
PERIODICALLY INFILTRATED BY SHORTWAVE ENERGY AND ASSOCIATED POCKETS  
OF MONSOONAL MOISTURE. IT BECOMES MORE DIFFICULT THIS TIME OF YEAR  
TO FEEL CONFIDENT IN REMOVING DIURNALLY DRIVEN CONVECTIVE CHANCES.  
 
THE FIRST SHORTWAVE WILL MOVE INTO WRN WYOMING FRIDAY MORNING  
REACHING WRN ZONES FOR FRIDAY AFTERNOON. BEST CHANCES FOR CONVECTION  
WILL BE FOR AREAS IN CLOSEST PROXIMITY OF THIS WAVE WEST OF  
INTERSTATE 25. PROGS SBCAPES OF 200-400 J/KG SUGGEST ANY  
THUNDERSTORM DEVELOPMENT WOULD BE NON-SEVERE. WEAK STEERING FLOW  
WILL ONLY MOVE THIS SHORTWAVE TO NORTHEAST WYOMING/WRN SOUTH DAKOTA  
BY LATE SATURDAY. INSTABILITY AXIS WILL REMAIN PARKED ALONG THE  
FRONT RANGE AND ADJACENT ERN PLAINS. CONVECTIVE CHANCES AGAIN HAVE  
BEEN CONFINED GENERALLY WEST OF INTERSTATE 25 ON SATURDAY.  
 
MEDIUM RANGE GUIDANCE IS CONSISTENT IN SLINGING ANOTHER PIECE OF  
SHORTWAVE ENERGY THRU THE FOUR CORNERS TOWARDS THE COWBOY STATE ON  
SUNDAY. THE GFS IS QUICKEST AND STRONGEST WITH THIS ENERGY WHILE THE  
ECMWF OFFERS A SLIGHTLY SLOWER AND WEAKER SOLUTION. IN EITHER CASE  
ITS EFFECTS REALLY WONT BE FELT UNTIL LATE SUNDAY AND MORE SO ON  
MONDAY AS COLD FRONT SLIPS SOUTH THRU THE CWFA. THIS WILL BRING THE  
NEXT CHANCE FOR SHOWER AND THUNDERSTORM ACTIVITY. DEPENDING UPON THE  
TIMING OF THIS FTR...IT MAY LINGER AND/OR HAVE THE MOST IMPACT ON  
TUESDAY. FOR NOW...HAVE BEEN FAIRLY LIBERAL WITH CONVECTIVE CHANCES  
FOR MON/TUE WITH THE EXPECTATIONS THAT THESE WILL BE REFINED AS  
SOLUTIONS CONVERGE.  
 
TEMPERATURES WILL BE THE WARMEST ON SUNDAY AS HIGHS CLIMB BACK INTO  
THE 80S AT ALL LOCATIONS. COOLER TEMPERATURES ANTICIPATED BEHIND THE  
COLD FROPA MON/TUE...WITH HIGHS FALLING BACK INTO THE 70S FOR MOST  
LOCATIONS.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 538 AM MDT TUE JUL 29 2014  
 
MOIST UPSLOPE FLOW WILL COMBINE WITH A GOOD SUPPLY OF MONSOONAL  
MOISTURE TO PRODUCE A PERIOD OF POOR AVIATION CONDITIONS...  
ESPECIALLY AT KRWL...KLAR AND KCYS. BEFORE THIS CONVECTION  
DEVELOPS...THERE MAY BE A PERIOD OF MVFR/IFR CIGS/VSBYS THIS  
MORNING PRIMARILY AT WESTERN NEBRASKA PANHANDLE SITES. THIS SHOULD  
LIFT BETWEEN 16-18Z. SHOWERS AND THUNDERSTORMS SHOULD KICK OFF  
FIRST NR KRWL AS EARLY AS LATE THIS MORNING. THIS AREA OF  
CONVECTION WILL BECOME MORE WIDESPREAD THRU THE AFTERNOON  
AFFECTING KLAR AND KCYS. VERY HEAVY RAIN IS EXPECTED TO ACCOMPANY  
THIS ACTIVITY. SOME LOCATIONS WILL SEE UPWARDS OF 1-2 INCHES OF  
RAIN TODAY AND TONIGHT. THIS ACTIVITY MAY MAKE IT INTO THE WRN  
NEBRASKA PANHANDLE AIRFIELDS THIS EVENING. EXPECT GENERALLY JUST A  
DECREASE INTO MVFR WITH THESE SHOWERS/THUNDERSTORMS...BUT COULD  
SEE IFR VSBYS IN THE HEAVIEST ACTIVITY. THIS ACTIVITY WILL  
CONTINUE...BUT LESSEN IN COVERAGE SOME TONIGHT.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 400 AM MDT TUE JUL 29 2014  
 
A STRONG STORM SYSTEM COMBINED WITH MONSOON MOISTURE WILL GIVE  
WAY TO WIDESPREAD SHOWERS AND THUNDERSTORMS ON TUESDAY AND  
WEDNESDAY. THE GREATEST COVERAGE WILL BE ALONG AND ON EITHER SIDE  
OF THE LARAMIE RANGE WHERE A GENERAL 1 TO 2 INCHES OF RAIN CAN BE  
EXPECTED. COOLER TEMPERATURES AND NEW MOISTURE WILL MITIGATE ANY  
FIRE WEATHER CONCERNS THROUGH MID WEEK.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...FLASH FLOOD WATCH FROM NOON MDT TODAY THROUGH LATE TONIGHT FOR  
WYZ103-106-112-114>118.  
 
NE...NONE.  
 

 
 

 
 
SHORT TERM...HAMMER  
LONG TERM...HAHN  
AVIATION...HAHN  
FIRE WEATHER...HAMMER  
 
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