508  
FXUS65 KCYS 291807  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1207 PM MDT FRI JUL 29 2016  
   
UPDATE
 
 
ISSUED AT 1145 AM MDT FRI JUL 29 2016  
 
LOW-LEVEL CUMULUS FIELD IS EXPANDING RAPIDLY IN BOTH COVERAGE, AND  
VERTICAL EXTENT OVER THE LARAMIE RANGE. THE OVERALL ENVIRONMENT IS  
ALREADY QUITE FAVORABLE FOR SEVERE THUNDERSTORM DEVELOPMENT, W/THE  
LATEST SPC MESOSCALE ANALYSIS SHOWING STEEPENING LOW/MID-LVL LAPSE  
RATES AND RESULTANT MUCAPES OVER 2000 J/KG WITH MINIMAL CIN. MOIST  
BOUNDARY LAYER IN PLACE ALONG/EAST OF THE LARAMIE RANGE WITH UPPER  
50S DEWPOINTS CURRENTLY OBSERVED AT KCYS, AND EFFECTIVE BULK SHEAR  
IS MORE THAN SUFFICIENT FOR SUPERCELLS AT 40 KTS. THIS COMBINED W/  
EXCELLENT LOW-LEVEL CONVERGENCE WILL MORE THAN LIKELY SUPPORT MORE  
WIDESPREAD ACTIVITY AS WE HEAD INTO THE AFTERNOON. AGREE WITH HRRR  
SOLUTIONS SHOWING ROBUST CONVECTION ALONG A CHEYENNE TO TORRINGTON  
LINE AT 22Z. INTRODUCED LIKELY POPS OVER MUCH OF SOUTHEAST WY THIS  
AFTERNOON. ALL OTHER ASPECTS OF THE FORECAST ARE IN GOOD SHAPE.  
 

 
   
SHORT TERM
 
(TODAY THROUGH SUNDAY)  
ISSUED AT 300 AM MDT FRI JUL 29 2016  
 
TODAY...STILL BELIEVE WE WILL SEE SOME FOG DEVELOP DURING THE LATE  
NIGHT AND EARLY MORNING HOURS BASED ON CURRENT AND PROJECTED  
TEMPERATURE AND DEWPOINT SPREADS, ESPECIALLY ONCE SOME RESIDUAL LOW  
AND MIDDLE CLOUDS DISSIPATE WITH THE PASSING SHOWERS ACROSS FAR  
SOUTHEAST WYOMING AND THE SOUTHERN NEBRASKA PANHANDLE.  
 
AGREE WITH THE STORM PREDICTION CENTER OUTLOOK OF MARGINAL RISK  
ALONG AND EAST OF A DOUGLAS TO LARAMIE LINE THIS AFTERNOON AND  
EVENING BASED ON THE EVENTS OF THE PAST FEW DAYS, AS WELL AS THE  
PROXIMITY OF A LOW AND MID LEVEL THETA-E RIDGE AXIS OF INSTABILITY  
RESIDING NORTH TO SOUTH ACROSS FAR SOUTHEAST WYOMING AND THE  
NEBRASKA PANHANDLE. LOW LEVEL CONVERGENCE ALONG THE LARAMIE RANGE  
EXPECTED TO HELP IGNITE ISOLATED TO WIDELY SCATTERED COVERAGE OF  
THUNDERSTORMS THIS AFTERNOON, AND WITH PROJECTED CAPES OF 1000 TO  
2000 J/KG AND WIND SHEAR IN EXCESS OF 40 KNOTS, EXPECT ISOLATED  
STRONG TO SEVERE STORMS TO DEVELOP IN THE MARGINAL RISK AREA, MOST  
LIKELY SOUTH OF A CHEYENNE TO ALLIANCE LINE WHERE INSTABILITY WILL  
BE MAXIMIZED. GUIDANCE MAXIMUMS CLOSE AND WILL FOLLOW THESE.  
 
TONIGHT...STORMS EXPECTED TO DECREASE IN COVERAGE AND INTENSITY THIS  
EVENING WITH THE LOSS OF DAYTIME HEATING WITH MORE LATE NIGHT FOG  
DEVELOPING ACROSS PARTS OF WESTERN NEBRASKA BASED ON PROJECTED  
BOUNDARY LAYER PROGS.  
 
SATURDAY...WITH LESS LOW AND MID LEVEL MOISTURE AVAILABILITY AND  
WARMER TEMPERATURES AT MID LEVELS OF THE ATMOSPHERE, EXPECT LESS  
COVERAGE OF AFTERNOON AND EVENING THUNDERSTORMS ALONG WITH WARMER  
TEMPERATURES AT NAM AND GFS GUIDANCE TEMPERATURES SUGGEST.  
 
SATURDAY NIGHT...A QUIETER NIGHT WITH MINIMAL CHANCE OF SHOWERS AND  
THUNDERSTORMS DUE TO LACK OF FORCING MECHANISMS AND LIFT. BOUNDARY  
LAYER PROGS SUGGEST LATE NIGHT FOG POSSIBLE FROM CHADRON TO SIDNEY.  
 
SUNDAY...A WEAK SHORTWAVE PROGGED TO MOVE ACROSS NORTHERN COLORADO  
WILL COMBINE WITH ADEQUATE MID LEVEL MOISTURE TO PRODUCE ISOLATED  
AFTERNOON AND EVENING THUNDERSTORMS, WITH LIMITED COVERAGE DUE TO  
RELATIVELY WARM TEMPERATURES ALOFT NEAR 16 CELSIUS. WARMING TREND  
CONTINUES PER THICKNESSES AND WARMING TEMPERATURES ALOFT AND HAVE  
COMPROMISED BETWEEN THE NAM AND GFS MOS MAXIMUM TEMPERATURES.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 330 AM MDT FRI JUL 29 2016  
 
THERE IS GENERAL CONSENSUS WITH THE 00Z MEDIUM RANGE MODELS PROGGING  
THE SUBTROPICAL UPPER HIGH CENTER TO SHIFT EAST FROM THE FOUR CORNERS  
TO THE SOUTH CENTRAL GREAT PLAINS BY MIDWEEK. THE FLOW ALOFT WILL  
BECOME SOUTHWEST, OPENING THE DOOR FOR SOME MONSOONAL MOISTURE.  
HOWEVER, DIURNAL CONVECTIVE COVERAGE WILL BE ISOLATED TO WIDELY  
SCATTERED AT BEST AND CONFINED TO THE HIGHER TERRAIN AND PORTIONS  
OF THE PLAINS. THE ECMWF CONTINUES ITS WETTER TREND COMPARED TO  
THE GFS, AND COMPROMISED. MONDAY AND TUESDAY WILL BE WARMER THAN  
AVERAGE WITH HIGHS IN THE 80S TO MID 90S. A RATHER POTENT UPPER  
TROUGH WILL TRACK EAST ALONG THE NORTHERN TIER CONUS WEDNESDAY  
WHICH WILL PUSH A COOL FRONT THROUGH THE CWA. THE FLOW ALOFT WILL  
BE MORE WESTERLY WHICH WILL CUT OFF THE MONSOONAL MOISTURE.  
TEMPERATURES WILL MODERATE BACK TO NORMAL VALUES FOR EARLY AUGUST  
WITH HIGHS IN THE 80S.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)  
ISSUED AT 1145 AM MDT FRI JUL 29 2016  
 
MOSTLY VFR CONDITIONS THROUGH THE TAF PERIOD. SCATTERED  
THUNDERSTORMS WILL DEVELOP ALONG THE LARAMIE RANGE OVER THE NEXT  
FEW HOURS AND MOVE SOUTHEAST. INCLUDED VCTS AT MOST SITES THROUGH  
THE EARLY EVENING. THE BEST CHANCE OF MVFR/VFR VIS IN HEAVY RAIN  
WILL BE AT CYS. WINDS WILL GENERALLY BE BELOW 20 KTS, EXCEPT IN  
THE VICINITY OF TSTMS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 300 AM MDT FRI JUL 29 2016  
 
LOWERING AFTERNOON HUMIDITIES THROUGH THE WEEKEND, AND WITH WINDS  
AND GUSTS SLOWLY INCREASING EACH DAY, CONCERNS WILL INCREASE  
ESPECIALLY BY SUNDAY ALONG AND WEST OF INTERSTATE 25.  
 

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

 
 

 
 
UPDATE...CLH  
SHORT TERM...RUBIN  
LONG TERM...MAJ  
AVIATION...ZF  
FIRE WEATHER...RUBIN  
 
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