235  
FXUS65 KCYS 261155  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
555 AM MDT THU APR 26 2018  
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 309 AM MDT THU APR 26 2018  
 
NO MAJOR HEADLINES OVER THE NEXT 24 TO 36 HOURS OTHER THEN GUSTY  
NORTH WINDS AT 35 TO 45 MPH NOW THROUGH LATE-MORNING. CAUTION IS  
ADVISED ON WEST TO EAST ORIENTED ROADS DUE TO CROSS-WINDS. WIND  
WILL REDUCE THROUGH THE AFTERNOON WITH CLOUDS CLEARING.  
 
A QUICK MOVING SHORTWAVE TROUGH IS SHIFTING OVER THE HIGH PLAINS  
THIS MORNING AND HAS USHERED IN A COLD FRONT AND GUSTY NORTH  
WINDS. PEAK WIND GUSTS THUS FAR HAVE BEEN NEAR 35 TO 40 MPH FOR  
THE HIGH PLAINS OF SOUTHEAST WY AND WESTERN PANHANDLE OF NE.  
AREAS ALONG AND WEST OF THE LARAMIE RANGE HAVE WEAKER WINDS AS THE  
H7-H5 GRADIENTS FARTHER WEST ARE LOWER. THE ELEVATED WINDS SHOULD  
PERSIST THROUGH THE MID- TO LATE-MORNING HOURS AS SOME DOWNWARD  
MOMENTUM TRANSFER OCCURS. LIGHT PRECIPITATION IS ALSO NOTED IN THE  
GREATEST MID- AND UPPER-LEVEL LIFT ZONE OF THE TROUGH AXIS. HOWEVER,  
LIMITED AVAILABLE MOISTURE IN THE BOUNDARY LAYER IS KEEPING  
REALIZED SURFACE PRECIPITATION MINIMAL. PATCHY LIGHT SNOW FLURRIES  
ABOVE 7000FT AND ISOLATED LIGHT MIST/DRIZZLE WILL BE POSSIBLE FOR  
THE LOWER ELEVATIONS BUT OVERALL COVERAGE AND ACCUMULATION WILL  
BE LOW TO NONEXISTENT. HIGHEST CONFIDENCE IN ANY ACCUMULATION OF  
SNOW WOULD BE THE HIGHEST ELEVATIONS OF THE NORTHERN LARAMIE RANGE  
AND PERHAPS SOME OF THE SNOWY RANGE. PRECIPITATION WILL END BY  
NOON AS THE TROUGH SHIFTS SOUTHEAST OF THE REGION WITH CLEARING  
SKIES THROUGH THE AFTERNOON.  
 
CLEAR SKIES TONIGHT INTO FRIDAY MORNING WHILE WINDS SHIFT BACK TO  
THE WEST. DECENT RADIATIONAL COOLING SET-UP WILL BE IN PLACE  
FRIDAY MORNING OTHER THEN THE SLIGHTLY WARMING DOWNSLOPE WINDS  
POSSIBLY IN PLACE. LOWS WILL DROP TO NEAR FREEZING FOR MOST  
LOCATIONS IN LOWER ELEVATIONS AND 20S FOR THE HIGHER TERRAIN.  
   
LONG TERM
 
(FRIDAY THROUGH WEDNESDAY)  
ISSUED AT 309 AM MDT THU APR 26 2018  
 
A WARM & GENERALLY DRY WEEKEND AHEAD FOR MUCH OF SOUTHEAST WYOMING  
AND THE WESTERN NEBRASKA PANHANDLE. THE GFS & ECMWF REMAIN IN GOOD  
AGREEMENT WITH HIGH AMPLITUDE UPPER-LEVEL RIDGING OVER THE CENTRAL  
ROCKIES AND ADJACENT HIGH PLAINS ON SATURDAY. THIS RIDGE IS LIKELY  
TO BEGIN BREAKING DOWN BY SUNDAY, BUT ITS EFFECTS WILL CONTINUE TO  
BE FELT THROUGH THE ENTIRE WEEKEND. H7 TEMPERATURES AVERAGING FROM  
+6C TO +8C, COUPLED WITH SUBSIDENCE ALOFT SHOULD SUPPORT AFTERNOON  
HIGHS WELL INTO THE 70S AND EVEN LOW 80S ACROSS MUCH OF THE CWA ON  
BOTH SATURDAY AND SUNDAY. DEEP MIXING COMBINED WITH DECENT LOW-LVL  
HEIGHT GRADIENTS WILL CONTRIBUTE TO GUSTY SOUTHEASTERLY WIND ALONG  
AND EAST OF THE LARAMIE RANGE ON SATURDAY AFTERNOON.  
 
FORECAST SOUNDINGS SUGGEST A DRY BOUNDARY LAYER ON SATURDAY, WHICH  
SEEMS LIKELY TO LIMIT PRECIPITATION CHANCES CONSIDERABLY. HOWEVER,  
WE MAY START TO SEE AN INCREASE IN SOUTHWEST FLOW ALOFT IN ADVANCE  
OF A SHORT WAVE DIGGING INTO THE PACIFIC NW. THIS MAY YIELD ENOUGH  
FORCING AND MID-LEVEL MOISTURE TO GENERATE SOME SHOWER OR THUNDER-  
STORM ACTIVITY OVER THE HIGHER TERRAIN IN THE AFTERNOON, BUT WOULD  
EXPECT THIS TO BE VERY ISOLATED AND WITH THE DRY PROFILES, IT WILL  
BE DIFFICULT TO GET ANY OF THIS SPREADING ONTO THE PLAINS. OVERALL  
INSTABILITY PROFILES ARE QUITE MODEST, BUT WITH VERY STEEP LOW/MID  
LEVEL LAPSE RATES WOULD EXPECT CAPES TO SUPPORT AT LEAST A LOW-END  
CONVECTIVE POTENTIAL. WE CANNOT ENTIRELY RULE OUT SOME ACTIVITY ON  
SUNDAY OVER A LARGER AREA, BUT DESPITE STRONGER FORCING, AVAILABLE  
MOISTURE SEEMS EVEN MORE SCARCE.  
 
A MUDDLED PATTERN LATE IN THE PERIOD DURING THE MON-WED TIME FRAME  
WITH UPPER-LEVEL TROUGHING TAKING CONTROL. MODEL DISCREPANCIES ARE  
SIGNIFICANT, BUT THE GENERAL CONSENSUS IS FOR AN UNSETTLED PATTERN  
WITH COOLER TEMPERATURES & DAILY CHANCES FOR PRECIPITATION. WE ARE  
GOING TO HAVE TO CLOSELY MONITOR THE EVOLUTION OF THIS PATTERN FOR  
MID NEXT WEEK, AS MULTIPLE SURGES OF COOLER AIR COULD COOL THERMAL  
PROFILES SUFFICIENTLY FOR SNOW OVER THE PLAINS. DESPITE WHAT LOOKS  
TO BE RATHER FRAGMENTED MID/UPPER LEVEL ENERGY, THE GFS/ECMWF BOTH  
AGREE ON A MORE DISTINCT DISTURBANCE EJECTING NORTHEAST ACROSS THE  
FOUR CORNERS ON WEDNESDAY. THE MODELS ALSO SUGGEST A POSSIBLE COLD  
FRONTAL PASSAGE DURING THIS TIME, RESULTING IN NORTH-NORTHEAST LOW  
LEVEL FLOW. THIS SHOULD BE PROGRESSIVE, BUT IT HAS POTENTIAL TO BE  
ONE OF OUR HEAVIER SNOW MAKERS BASED ON CURRENT PROJECTIONS.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)  
ISSUED AT 550 AM MDT THU APR 26 2018  
 
AS A GENERAL RULE, VFR CONDITIONS SHOULD PREVAIL THROUGH THE EARLY  
MORNING HOURS W/ A FEW POCKETS OF LOWER CEILINGS BEHIND THE RECENT  
COLD FRONT. CLOUD BASES WILL GENERALLY BE IN THE 5K-10K FOOT RANGE  
OVER THE NEXT FEW HOURS, ALTHOUGH THE SOUTHEAST WY TERMINALS COULD  
SEE A PERIOD OF NEAR-MVFR CONDITIONS W/ BKN-OVC SKIES AT, OR A BIT  
BELOW 3500 FEET AGL. ISOLATED SNOW SHOWERS COULD IMPACT KRWL, KLAR  
AND KCYS THROUGH ABOUT 15Z W/ DRY CONDITIONS LATER. GUSTY WIND NOW  
AFFECTING HIGH PLAINS AREAS WILL PERSIST TODAY, BUT WILL GRADUALLY  
DECREASE IN MAGNITUDE OVER THE NEXT FEW HOURS. VFR CONDITIONS WILL  
BE THE RULE FOR ALL TERMINALS AFTER 18Z.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 454 AM MDT THU APR 26 2018  
 
GUSTY NORTH WINDS OF 30 TO 40 MPH ARE ONGOING THIS MORNING FOR THE  
HIGH PLAINS IN WY AND WESTERN NE. THESE WILL CONTINUE THROUGH LATE  
MORNING AND THEN SUBSIDE THROUGH THE AFTERNOON AS HUMIDITY LEVELS  
DROP. TEMPERATURES WILL BE COOLER TODAY AREA-WIDE AND OVERALL  
MINIMUM HUMIDITY VALUES WILL BE HIGHER THEN YESTERDAY. THIS WILL  
LIMIT OVERALL FIRE WEATHER CONCERNS. FRIDAY WILL BE WARMER AND  
DRIER AS HUMIDITY VALUES FALL INTO THE 10 TO 20 PERCENTILES.  
LUCKILY, WINDS WILL BE QUITE LIGHT AND AGAIN FIRE WEATHER CONCERNS  
WILL BE LOW.  
 
A FEW HIGHER TERRAIN SHOWERS AND ISOLATED THUNDERSTORMS COULD OCCUR  
SATURDAY WITH THE HIGH PLAINS REMAINING DRY.  
 
NEXT BETTER CHANCE OF WIDESPREAD WETTING PRECIPITATION WILL BE MONDAY  
 

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

 
 

 
 
SHORT TERM...JSA  
LONG TERM...CLH  
AVIATION...CLH  
FIRE WEATHER...JSA  
 
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