851  
FXUS65 KCYS 261725  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1125 AM MDT WED APR 26 2017  
   
SHORT TERM
 
(TODAY THROUGH THURSDAY NIGHT)  
ISSUED AT 514 AM MDT WED APR 26 2017  
 
MAIN FORECAST CONCERN IN THE SHORT TERM WILL BE SNOWFALL IN THE  
MOUNTAINS AND NEARBY HIGH VALLEYS. WATER VAPOR IMAGERY SHOWS FAST  
NORTHWEST FLOW ACROSS THE PACNW AND INTO THE GREAT BASIN, AND 00Z  
MODELS REMAIN CONSISTENT SHOWING THIS STREAM OF MOISTURE AND  
ENERGY MOVING OVERHEAD THE NEXT COUPLE OF DAYS. THE MAIN JET WILL  
REMAIN TO OUR WEST AND SOUTH THOUGH, KEEPING US UNDER COLD  
CYCLONIC FLOW. A VIGOROUS SHORTWAVE TROUGH CURRENTLY JUST OFFSHORE  
OR/WA WILL APPROACH THE FORECAST AREA TODAY, ALONG WITH A LEADING  
VORT MAX. THESE FEATURES WILL MOVE OVERHEAD TONIGHT AND STALL OVER  
THE HIGH PLAINS WHILE THE STRONG UPPER JET CARVES OUT A DEEP  
TROUGH ALONG THE SPINE OF THE ROCKIES LATE THURSDAY. FOR TODAY,  
EXPECT MAINLY DRY CONDITIONS THROUGH THE MORNING WITH RAIN/SNOW  
SHOWERS DEVELOPING OVER THE MOUNTAINS BY EARLY AFTERNOON. SFC  
PRESSURE FALLS IN ADVANCE OF THE SHORTWAVE AND VORT MAX ARE  
EXPECTED ALONG THE MOUNTAINS, WITH SFC CONVERGENCE LOOKING TO  
STRENGTHEN JUST TO THE LEE OF THE LARAMIE RANGE. THEREFORE, COULD  
SEE A FEW SHOWERS AND STORMS DEVELOP ALONG THIS CONVERGENCE  
BOUNDARY IN WYOMING. EAST OF THE BOUNDARY LOOKS RELATIVELY STABLE  
IN THE LLVLS, BUT MODELS DO SHOW PERHAPS SUFFICIENT ELEVATED  
INSTABILITY ALONG WITH THE MIDLEVEL FORCING TO MAINTAIN A FEW  
SHOWERS INTO THE NEBRASKA PANHANDLE AS WELL.  
 
THE SFC TROUGH WILL SHIFT A BIT WESTWARD AND STRENGTHEN TONIGHT AS  
THE MORE VIGOROUS WAVE EDGES CLOSER, INDUCING LLVL UPSLOPE FLOW  
TONIGHT THROUGH THURSDAY. MAINTAINED CHANCE TO LIKELY POPS ACROSS  
THE PLAINS THROUGH THIS TIME FOR THE COMBINATION OF INCREASING  
UPPER FORCING AND UPSLOPE FLOW. RAIN/SNOW SHOWERS EXPECTED TONIGHT  
AND THURSDAY WILL GIVE WAY TO MAINLY ALL SNOW ON THURSDAY NIGHT.  
ALONG AND WEST OF THE LARAMIE RANGE, EXPECT OROGRAPHIC  
SHOWERS/STORMS THIS AFTERNOON WITH A BRIEF BREAK IN THE EARLY  
EVENING BEFORE THE STRONGER SHORTWAVE BRINGS INCREASING QG FORCING  
AND OROGRAPHIC LIFT TONIGHT THROUGH THURSDAY. SHOULD BE A GOOD  
BURST OF SNOW OVER THE HIGHER TERRAIN LATER THIS EVENING AND  
OVERNIGHT, WITH THE POTENTIAL FOR ADDITIONAL SNOWFALL IN  
CONVECTION THURSDAY AFTERNOON WITH THE SHORTWAVE OVERHEAD. TOTAL  
SNOW ACCUMULATION IN THE SNOWY AND SIERRA MADRE MOUNTAINS THROUGH  
THIS TIME SHOULD BE ROUGHLY 6 TO 10 INCHES WITH PERHAPS LOCALLY  
HIGHER AMOUNTS IN LOCATIONS THAT EXPERIENCE CONVECTION THURSDAY  
AFTERNOON. WENT AHEAD WITH A WINTER WEATHER ADVISORY FOR THESE  
MOUNTAINS FROM THIS EVENING THROUGH THURSDAY AFTERNOON. THE NEARBY  
LOWER ELEVATIONS COULD ALSO SEE A PERIOD OF SNOWFALL AS THE  
SHORTWAVE MOVES OVERHEAD AND SFC TROUGH SHIFTS EAST BACK TOWARDS  
THE PLAINS, WITH ACCUMULATIONS HERE LOOKING TO BE IN THE 1 TO 3  
INCH RANGE MAINLY TONIGHT. WARMING TEMPS THROUGH THE DAY THURSDAY  
COULD KEEP PRECIP ALL RAIN IN THE HIGH VALLEYS. AS MENTIONED  
ALREADY, THE SFC TROUGH WILL SHIFT EAST INTO THE PLAINS WITH  
SHORTWAVE PASSAGE, BUT LOOKS TO STALL ALONG THE LEE OF THE LARAMIE  
RANGE THROUGH THURSDAY NIGHT. THEREFORE, BEST SFC AND UPPER LEVEL  
DYNAMICS WILL TRANSLATE TO THE PLAINS, ALTHOUGH A FEW LIGHTER  
OROGRAPHIC SNOW SHOWERS REMAIN POSSIBLE AS WELL.  
   
LONG TERM
 
(FRIDAY THROUGH TUESDAY)  
ISSUED AT 514 AM MDT WED APR 26 2017  
 
STRONG 160KT UPPER JET WILL DIVE SE'WARD INTO THE N'ERN AND CENTRAL  
ROCKIES BY EARLY FRIDAY, CARVING OUT A DEEP TROUGH OVER THE W'ERN  
US. MODELS ARE IN PRETTY GOOD AGREEMENT IN CLOSING OFF AN UPPER LOW  
OVER NW CO ON FRIDAY AFTERNOON AND HAVING IT SINK SLOWLY S'WARD  
THROUGH EARLY SATURDAY. AT THE LOW LEVELS, AN INVERTED TROUGH WILL  
SET ROUGHLY FROM THE N LARAMIE RANGE SE'WARD INTO EXTREME NE CO. N  
OF THIS TROUGH, MOIST E'LY FLOW ALONG WITH GOOD OVERRUNNING WILL  
ALLOW AMPLE AMOUNTS OF PRECIPITATION ESPECIALLY EARLY FRIDAY AS  
THERE WILL STILL BE SOME UPPER DIFFLUENCE AND REMNANT MID LEVEL  
ENERGY FROM THE THURSDAY WAVE HANGING AROUND. 700 MB TEMPS RANGE  
FROM -7 TO -8 FRIDAY MORNING WHICH COMBINED WITH DECENT  
PRECIPITATION RATES SHOULD LOWER SNOW LEVELS TO 4500 TO 5000 FT.  
THINK THE AREAS FROM THE N LARAMIE RANGE TO DOUGLAS/LUSK COULD SEE  
SEVERAL INCHES OF SNOW BY MID DAY FRIDAY. AREAS TO THE SOUTH SUCH  
AS LARAMIE AND CHEYENNE EASTWARD TO SIDNEY MAY BE IN A LOCAL PRECIP  
MINIMA BASED AS BY THE TIME THE FLOW SWITCHES TO A MORE FAVORABLE  
UPSLOPE DIRECTION, THE BEST FORCING FOR ASCENT IS SAGGING TO THE  
SOUTH AND EAST AND FOCUSED MORE INTO CO. COULD STILL BE SOME LIGHT  
AMOUNTS OF SNOW OVER THE PLAINS E OF THE LARAMIE RANGE FRIDAY  
EVENING.  
 
UPPER TROUGH SHIFTS E'WARD SATURDAY INTO SUNDAY AS TRANSITORY  
RIDGING MOVES OVERHEAD. EARLY NEXT WEEK LOOKS ACTIVE ONCE AGAIN.  
WEAK SHORTWAVE PASSING TO THE N MAY SPARK SOME AFTERNOON SHOWERS  
MONDAY BEFORE YET ANOTHER TROUGH DIGS INTO THE NORTHERN/CENTRAL  
ROCKIES ON TUESDAY  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z THURSDAY MORNING)  
ISSUED AT 1125 AM MDT WED APR 26 2017  
 
MVFR CIGS OVER THE NORTHEAST NEB PANHANDLE SHOULD CLEAR BY EARLY  
AFTERNOON WITH SHOWERS GRADUALLY INCREASING OVER THE AREA FROM KRWL  
TO KCYS DURING THE AFTERNOON. SCATTERED MAINLY MVFR CIGS RETURNING  
AGAIN OVERNIGHT WITH SOME SNOW SHOWERS ESPECIALLY LATER TONIGHT FROM  
KRWL TO KCYS WITH LOCAL IFR CONDITIONS ASSOCIATED WITH THEM.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 514 AM MDT WED APR 26 2017  
 
NO FIRE WEATHER CONCERNS ARE ANTICIPATED THROUGH THE END OF THE  
WEEK DUE TO COOL TEMPERATURES AND DAILY CHANCES FOR RAIN AND SNOW  
SHOWERS.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM MDT  
THURSDAY FOR WYZ112-114.  
 
NE...NONE.  

 
 

 
 
SHORT TERM...RJM  
LONG TERM...DEL  
AVIATION...DEL  
FIRE WEATHER...RJM  
 
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