486  
FXUS65 KCYS 180501  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
1000 PM MST SAT FEB 17 2018  
   
SHORT TERM
 
(TONIGHT - MONDAY NIGHT)  
ISSUED AT 252 PM MST SAT FEB 17 2018  
 
AN EXTREMELY ACTIVE PERIOD OF WEATHER ACROSS SOUTHEAST WYOMING AND  
THE WESTERN NEBRASKA PANHANDLE OVER THE NEXT 24-48 HOURS. CONCERNS  
REMAIN FOCUSED ON STRONG WINDS THROUGH TONIGHT, AND THE THREAT FOR  
SIGNIFICANT SNOWFALL ON SUNDAY AND MONDAY.  
 
A FEW WIND GUSTS AROUND 60 MPH HAVE BEEN OBSERVED AROUND ARLINGTON  
THIS AFTERNOON, BUT GENERALLY SPEAKING MOST AREAS HAVE REMAINED AT  
OR BELOW 50 MPH WITH FAIRLY MODEST FLOW ALOFT. WE STILL ANTICIPATE  
A DRAMATIC UP-TICK IN WIND SPEEDS OVERNIGHT AS A FAIRLY STRONG SFC  
LOW TRACKS ACROSS NORTHEAST WY INTO WESTERN SD. H7 AND H85 CAG-CPR  
GRADIENTS CLIMB TO BETWEEN 80 AND 90 METERS AS THIS HAPPENS, ALONG  
WITH H7-H8 FLOW OF 55-65 KNOTS OVER MUCH OF SOUTHEAST WY AND 65-75  
KNOTS OVER THE N. LARAMIE RANGE. SIGNIFICANT DOWNWARD OMEGA SHOULD  
SUPPORT WIDESPREAD STRONG WIND GUSTS OVER THE WIND PRONE AREAS, AS  
WELL AS SOME ADJACENT PLAINS/VALLEY AREAS AS WELL. WE EXTENDED OUR  
HIGH WIND WARNINGS THROUGH 16Z AS FLOW ALOFT REMAINS ELEVATED INTO  
MID SUNDAY MORNING. AFTER THAT, THE HIGH WIND THREAT SHOULD SLOWLY  
DIMINISH WITH AN APPROACHING COLD FRONT AND WEAKENING GRADIENTS. A  
BLUSTERY DAY IS LIKELY SUNDAY ALONG/W OF THE LARAMIE RANGE, BUT IT  
APPEARS WINDS WILL REMAIN BELOW CRITERIA AT THIS TIME. NEXT COUPLE  
OF SHIFTS WILL WANT TO RE-EVALUATE, HOWEVER.  
 
ATTENTION THEN SHIFTS TO OUR WINTER STORM POTENTIAL. THERE IS SOME  
POTENTIAL FOR SNOW TO BEGIN AS EARLY AS MID SUNDAY MORNING, MAINLY  
ACROSS NORTHERN CONVERSE COUNTY W/ THE INITIAL PASSAGE OF THE COLD  
FRONT. THIS INITIAL PERIOD OF SNOW MAY BE FAIRLY HEAVY, WITH MODEL  
GUIDANCE SUGGESTING VERY STRONG FRONTOGENESIS ALONG W/ A FAVORABLE  
POSITION OF THE UPPER JET. THAT SAID, WE UPGRADED THOSE AREAS TO A  
WINTER STORM WARNING WITH THIS PACKAGE AND OPTED TO INCLUDE HIGHER  
ELEVATIONS IN THE N. LARAMIE RANGE AND FERRIS/SEMINOE MOUNTAINS AS  
WELL. SPECIAL THANKS TO WFOS UNR AND RIW FOR THE COORDINATION THIS  
AFTERNOON IN MAKING A DECISION TO UPGRADE. OTHERWISE, THIS APPEARS  
LIKELY TO BE A WIDESPREAD SIGNIFICANT SNOWFALL AS THE RRQ OF A 120  
KNOT H25 JET TRAVERSES THE CWA. SNOW IS LIKELY TO SPREAD SOUTHEAST  
ACROSS THE AREA THROUGH THE DAY, AND IN GENERAL BECOME HEAVIEST IN  
THE SUNDAY NIGHT/MONDAY TIME FRAME WITH IMPRESSIVE FRONTOGENESIS &  
STRONG UPPER LEVEL DYNAMIC SUPPORT. CONSENSUS GUIDANCE AND WPC ARE  
ALL LOOKING VERY REASONABLE WITH WIDESPREAD 8-12 INCH AMOUNTS WITH  
LOCALLY HIGHER TOTALS IN THE MOUNTAINS. SLIGHTLY LOWER AMOUNTS ARE  
EXPECTED FROM THE CHEYENNE AREA INTO THE S. PANHANDLE, BUT WE WILL  
STILL LIKELY HAVE ADVISORY LEVEL AMOUNTS. NAM SOUNDINGS ALSO WOULD  
SUGGEST SOME POTENTIAL FOR A PERIOD OF LIGHT FREEZING DRIZZLE LATE  
SUNDAY NIGHT FOR THESE AREAS, WHILE THE GFS IS COLDER AND SUGGESTS  
PREDOMINANTLY SNOW. WILL NEED TO KEEP AN EYE ON THIS AS WELL. KEPT  
WINTER STORM WATCHES GENERALLY AS-IS, BUT DECIDED TO INCLUDE AREAS  
FROM TORRINGTON/GOSHEN COUNTY TOWARD ALLIANCE/BOX BUTTE COUNTY FOR  
EXPECTED AMOUNTS IN THE 4-8 INCH RANGE THROUGH MONDAY NIGHT.  
 
DANGEROUS WIND CHILLS ARE ALSO LIKELY ON SUNDAY NIGHT, BUT MORE SO  
MONDAY NIGHT WITH SNOW ENDING AND DEEPER COLD AIR IN PLACE.  
   
LONG TERM
 
(TUESDAY - SATURDAY)  
ISSUED AT 252 PM MST SAT FEB 17 2018  
 
NO MAJOR FORECAST CONCERNS THROUGH THE REMAINDER OF NEXT WEEK. THE  
UPPER-LEVEL PATTERN FAVORS A FEW PASSING WEAK DISTURBANCES, BUT WE  
EXPECT THESE TO BE FAIRLY DRY SYSTEMS WITH LIMITED CHANCES FOR ANY  
PRECIPITATION.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SUNDAY EVENING)  
ISSUED AT 1000 PM MST SAT FEB 17 2018  
 
STRONG WESTERLY WINDS WITH GUSTS 35-50 KT WILL CONTINUE THROUGH  
SUNDAY MORNING ALONG AND WEST OF INTERSTATE 25. MODERATE TO SEVERE  
MOUNTAIN WAVE TURBULENCE CAN BE EXPECTED. VFR WILL PREVAIL AT ALL  
TERMINALS UNTIL SUNDAY AFTERNOON AND EARLY EVENING WHEN CIG/VIS  
LOWER TO MVFR-IFR AS AN ARCTIC COLD FRONT PROGRESSES SOUTH ACROSS  
SOUTHEAST WYOMING AND WESTERN NEBRASKA. SNOW DEVELOPS FROM NORTH TO  
SOUTH DURING THE AFTERNOON AND EVENING. WINDS SHIFT TO THE NORTH-  
NORTHEAST WITH GUSTS AROUND 25 KT.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 313 AM MST SAT FEB 17 2018  
 
STRONG WINDS CONTINUE TODAY AHEAD OF AN APPROACHING ARCTIC FRONT  
MOVING INTO THE AREA FROM THE NORTH. WILL SEE WIDESPREAD STRONG  
WINDS THROUGH THE DAY TODAY INTO THIS EVENING. BY SUNDAY LATE  
MORNING, WE BEGIN TO SEE THE FRONT MOVE INTO CONVERSE AND NIOBRARA  
COUNTIES WITH WINDS SHIFTING NORTH AND NORTHEAST BEHIND THE FRONT.  
WIDESPREAD MODERATE SNOW AND MUCH COLDER AIR MOVING IN BEHIND THE  
FRONT. JUST ABOUT EVERY LOCATION IN SOUTHEAST WYOMING AND NEBRASKA  
PANHANDLE ARE GOING TO SEE SNOW ACCUMULATIONS WITH THE MOST  
SIGNIFICANT ALONG AND NORTH/WEST OF A LINE FROM CHADRON TO  
WHEATLAND TO BUFORD. SNOW CONTINUES INTO TUESDAY BEFORE ENDING.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING  
FOR WYZ106>117.  
 
HIGH WIND WARNING UNTIL 9 AM MST SUNDAY FOR WYZ104>107-109-110-  
113-115>117.  
 
WINTER STORM WARNING FROM 9 AM SUNDAY TO MIDNIGHT MST MONDAY  
NIGHT FOR WYZ101-103>105.  
 
HIGH WIND WARNING UNTIL 9 AM MST SUNDAY FOR WYZ101-103.  
 
WINTER STORM WATCH FROM SUNDAY MORNING THROUGH MONDAY EVENING  
FOR WYZ102.  
 
NE...WINTER STORM WATCH FROM SUNDAY EVENING THROUGH MONDAY EVENING  
FOR NEZ002-003-095-096.  
 

 
 

 
 
SHORT TERM...CLH  
LONG TERM...CLH  
AVIATION...MAJ  
FIRE WEATHER...GCC  
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab WY Page
The Nexlab NE Page Main Text Page