505  
FXUS65 KCYS 211143  
AFDCYS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHEYENNE WY  
443 AM MST MON JAN 21 2019  
   
SHORT TERM
 
(TODAY THROUGH EARLY WEDNESDAY)  
ISSUED AT 355 AM MST MON JAN 21 2019  
 
CURRENT IR SATELLITE LOOP SHOWS THE NEXT PACIFIC STORM SYSTEM,  
WHICH IS FORECAST TO IMPACT SOUTHEAST WYOMING AS EARLY AS NOON  
TODAY, CURRENTLY MOVING EAST ACROSS THE GREAT BASIN REGION. THE  
BROAD AND POSITIVELY TILTED TROUGH WILL CONTINUE TO MOVE EAST THIS  
MORNING INTO UTAH/NW COLORADO/SW WYOMING EARLY THIS AFTERNOON.  
MODEL SHOW THIS SYSTEM ATTEMPTING TO CLOSE OFF FROM THE MEAN FLOW  
ALOFT AS EARLY AS THIS AFTERNOON AS IT MOVES EASTWARD SOMEWHERE  
ALONG THE WYOMING/COLORADO BORDER. CURRENT ADVISORIES AND WINTER  
STORM WARNINGS LOOK GOOD WEST OF I-25 AND DID NOT MAKE ANY CHANGES  
TO THIS PORTION OF THE FORECAST WITH 2 TO 5 INCHES OF SNOW  
EXPECTED IN THE LOWER ELEVATIONS AND 6 TO 14 INCHES IN THE  
MOUNTAINS. THE MAIN DISTURBANCE AND ASSOCIATED DYNAMICS WILL BE  
LOCATED ACROSS CENTRAL WYOMING BEFORE THE ENERGY DIGS SOUTHWARD  
TONIGHT, SO AREAS NORTH OF A RAWLINS TO LUSK LINE SHOULD SEE THE  
HIGHEST SNOW ACCUMULATIONS. WINDS WILL NOT BE TOO BAD WEST OF  
I-25, BUT GUSTS UP TO 35-40 MPH ARE STILL ANTICIPATED FOR A  
PERIOD OF TIME THIS AFTERNOON INTO THIS EVENING. WINDS WILL BE A  
FAR GREATER CONCERN ACROSS THE EASTERN PLAINS, ESPECIALLY TONIGHT  
AND EARLY TUESDAY. FOR THIS REASON, ADDED NIOBRARA COUNTY TO THE  
WINTER STORM WARNING SINCE SIGNIFICANT BLOWING SNOW IS EXPECTED  
FROM DOUGLAS TO LUSK. HIGH TEMPERATURES TODAY WILL LIKELY OCCUR  
EARLY IN THE DAY, WITH TEMPERATURE READINGS LOWERING IN THE  
AFTERNOON AS THE FRONT MOVES THROUGH THE AREA.  
 
FURTHER SOUTH AND EAST, INCLUDING MOST OF THE I-80 CORRIDOR AND  
WESTERN NEBRASKA, WILL HAVE TO CLOSELY MONITOR THE REDEVELOPMENT  
OF THE SURFACE AND UPPER LEVEL LOW AS IT SLIDES EASTWARD INTO  
CENTRAL AND EASTERN COLORADO. INITIALLY, GOOD OVERRUNNING JUST  
ABOVE THE SURFACE AND SOME FRONTOGENESIS/850-700 CONVERGENCE WILL  
PROVIDE AMPLE LIFT FOR MODERATE TO OCCASIONALLY HEAVY SNOW ALONG  
AND EAST OF I-25. NOT TERRIBLY CONCERNED ABOUT PROLONGED HEAVY  
SNOWFALL AT THIS TIME SINCE THE GULF OF MEXICO MOISTURE SOURCE IS  
CUT OFF. HOWEVER, CAN'T RULE IT OUT EITHER DUE TO DYNAMIC LIFT  
AND HIGH SNOW RATIOS. SNOW ACCUMULATION FORECAST WILL BE VERY  
TRICKY ALONG/EAST OF INTERSTATE 25 DUE TO THE VICINITY OF THE  
DEVELOPING UPPER LEVEL LOW SOMEWHERE NEAR THE  
NEBRASKA/COLORADO/KANSAS BORDER. THIS AREA WILL ALSO HAVE SOME  
STRONG UPPER LEVEL DIFLUENCE FOR A TIME THIS EVENING, POSSIBLY  
ENHANCING SNOWFALL ACCUMULATIONS ACROSS EXTREME SOUTHEAST WYOMING  
AND THE SOUTHERN NEBRASKA PANHANDLE. MODELS HAVE STRUGGLED WITH  
THESE FINE DETAILS, WITH THE CURRENT GFS NOW SHOWING MAINLY AN  
OPEN WAVE TROUGH MOVING ACROSS THE AREA WHILE THE ECMWF AND  
CANADIAN BOTH SHOW A DEVELOPING LOW ACROSS KANSAS AND NEBRASKA.  
GIVEN HOW CLOSE THE SOUTHERN NEBRASKA PANHANDLE IS TO THIS  
DEVELOPING LOW, DECIDED TO UPGRADE THIS AREA TO A WINTER STORM  
WARNING. EVEN IF SNOW AMOUNTS OF 6 INCHES AREN'T OBSERVED, THE  
COMBINATION OF SEVERAL INCHES OF SNOW AND WINDS GUSTING AROUND 45  
MPH THROUGH TUESDAY AFTERNOON WILL RESULT IN DANGEROUS TRAVEL  
CONDITIONS IN BLOWING SNOW IN THIS AREA. IN ADDITION, SOME UPSLOPE  
ENHANCEMENT IS LIKELY ON THE NORTHERN END OF THE CHEYENNE RIDGE  
THROUGH TUESDAY MORNING. THERE IS THE POTENTIAL FOR THIS WARNING  
AREA TO SHIFT WEST AS WELL, SINCE THE LAST FEW RUNS OF THE NAM  
HAVE CONTINUED TO SHOW HIGH SNOWFALL RATES INTO CHEYENNE,  
WHEATLAND, AND PINE BLUFFS. HOWEVER, MOST MODELS AND ENSEMBLE  
FORECAST SHOW A GENERAL 2 TO 4 INCHES ACROSS EXTREME SOUTHEAST  
WYOMING, WITH AMOUNTS CLOSER TO 1 OR 2 INCHES RIGHT ALONG THE  
COLORADO BORDER. DECIDED TO ISSUE A WINTER WEATHER ADVISORY FOR  
THE REMAINING AREAS ACROSS THE EASTERN PLAINS OF WYOMING AND THE  
REST OF THE NEBRASKA PANHANDLE. EVEN THOUGH IT WILL BE VERY WINDY  
IN THE ADVISORY AREA, THERE TENDS TO BE A NOTABLE DIFFERENCE IN  
VISIBILITY BETWEEN AN INCH OR TWO OF BLOWING SNOW COMPARED TO  
EVENTS WITH 4+ INCHES IN BLOWING SNOW. FOR NOW, BANNER, KIMBALL,  
AND CHEYENNE COUNTIES HAVE THE BEST CHANCE TO SEE VISIBILITIES  
AROUND ONE QUARTER TO ONE HALF MILE TONIGHT INTO TUESDAY MORNING.  
 
BY EARLY TO MID TUESDAY MORNING, CONDITIONS WILL SLOWLY IMPROVE  
FROM WEST TO EAST. THE 00Z ECMWF IS THE SLOWEST SOLUTION, SHOWING  
THE SNOW LINGERING THROUGH EARLY TUESDAY AFTERNOON ACROSS THE  
SOUTHERN NE PANHANDLE. WITH GUSTY NORTH WINDS CONTINUING, BLOWING  
SNOW MAY BE A CONCERN THROUGH THE DAY ALONG AND EAST OF INTERSTATE  
25 INTO THE NEBRASKA PANHANDLE WITH GUSTS APPROACHING 50 MPH IN A  
FEW PLACES. TEMPERATURES WILL RISE VERY LITTLE THROUGH THE DAY,  
WITH HIGHS IN THE 20S TO PERHAPS NEAR 30 OVER THE LOWER ELEVATIONS  
IN WESTERN NEBRASKA. COLD TEMPERATURES WILL CONTINUE TUESDAY  
NIGHT, BUT DO NOT EXPECT BITTER COLD SINCE INTERVALS OF LOW TO  
MIDLEVEL CLOUDS ARE EXPECTED THROUGH THE NIGHT.  
 
THERE IS THE POTENTIAL FOR STRONG WINDS TO REDEVELOP ACROSS THE  
WIND PRONE AREAS OF SOUTHEAST WYOMING LATE TUESDAY NIGHT AND INTO  
WEDNESDAY MORNING. ALL MODELS SHOW A STRENGTHENING PRESSURE  
GRADIENT AND INCREASING SUBSIDENCE ALONG THE SPINE OF THE  
MOUNTAINS. MAY NEED HIGH WIND HEADLINES OVER THE NEXT 24 TO 36  
HOURS FOR AT LEAST THE BORDEAUX AND ARLINGTON AREAS.  
   
LONG TERM
 
(WEDNESDAY THROUGH SUNDAY)  
ISSUED AT 247 AM MST MON JAN 21 2019  
 
AN ACTIVE FEW DAYS IS EXPECTED IN THIS LONG TERM FORECAST AS LARGE  
SCALE TROUGHING CONTINUES OVER THE EASTERN 2/3RDS OF THE CONUS.  
SHORTWAVE RIDGING WILL BE IN PLACE OVER WESTERN WYOMING TO START  
WEDNESDAY WITH THE POTENTIAL FOR STRONG WINDS. AN ACTIVE NORTHERN JET  
WILL BRING A SHORTWAVE TROUGH RIGHT ON THE HEELS OF THE PREVIOUS  
SYSTEM LATE WEDNESDAY NIGHT. MODELS ARE SOMEWHAT SPLIT ON THE  
COVERAGE OF PRECIPITATION THURSDAY MORNING, BUT GIVEN THE STRONG  
LIFT AND FAVORABLE OROGRAPHICS, SOME SNOW SEEMS LIKELY FOR WYOMING  
AND NEBRASKA. SOME CHILLY OVERNIGHT LOW TEMPERATURES ARE ALSO  
EXPECTED WITH STRONG NORTHERLY WINDS AND COLD ADVECTION. SNOW SHOULD  
END BY EARLY AFTERNOON THURSDAY THANKS TO THE PROGRESSIVE NATURE OF  
THE UPPER LEVEL FLOW. ANOTHER SHORTWAVE RIDGE AND AREA OF HIGH  
PRESSURE WILL QUICKLY DEVELOP BEHIND THE DEPARTING TROUGH FRIDAY  
MORNING. THIS WILL LIKELY SET THE STAGE FOR A HIGH WIND EVENT  
THROUGH THE MORNING AND AFTERNOON ON FRIDAY. 50 TO 60 DECAMETER  
HEIGHT RISES AT 500 MB IN COMBINATION WITH 50 TO 60 KNOT WINDS WILL  
MIX STRONG GUSTS DOWN TO THE SURFACE. THE WESTERLY DOWNSLOPE FLOW  
SHOULD ALSO WARM THINGS UP SLIGHTLY WITH TEMPERATURES ROCKETING INTO  
THE MID 40S FROM THE LOW TEENS THE NIGHT BEFORE.  
 
MID RANGE MODELS SHOW NO SIGNS OF STOPPING AS THE ACTIVE POLAR JET  
AND ASSOCIATED WAVE TRAIN BRINGS A CYCLICAL PATTERN OF COLD ARCTIC  
FRONT AND SNOW FOLLOWED BY HIGH WIND AND WARMER TEMPERATURES THROUGH  
THE WEEKEND AND INTO EARLY NEXT WEEK. ALL INDICATIONS ARE THAT THIS  
TIME PERIOD WILL CONTINUE TO BE VERY ACTIVE WITH A PLETHORA OF  
WEATHER HAZARDS FOR SOUTHEASTERN WYOMING AND WESTERN NEBRASKA.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 438 AM MST MON JAN 21 2019  
 
A COMPLEX FORECAST IS EXPECTED FOR THE NEXT 24 HOURS AS AN  
APPROACHING PACIFIC STORM SYSTEM MOVES INTO THE AREA LATER THIS  
AFTERNOON AND EVENING. EARLY MORNING UPSLOPE FOG WAS OCCURRING  
ACROSS THE NEBRASKA PANHANDLE WITH LOW CEILINGS AND VISIBILITY  
NEAR 1/4 MILE. THIS SHOULD CONTINUE THROUGH EARLY MORNING AND  
LIFT BY 18Z. LOWER CEILINGS WILL REMAIN AS PLENTIFUL MOISTURE  
STREAMS IN. CEILINGS AND MODERATE SNOW WILL DEVELOP NEAR RWL  
BETWEEN 18 AND 21Z WITH POTENTIAL FOR VERY LOW VISIBILITY AND LIFR  
CONDITIONS. SNOW WILL SPREAD EAST WITH STRONG NORTHERLY WIND  
GUSTS BEHIND THE ARCTIC FRONT. EXPECT WINDS OF 30-40 KTS WITH  
BLOWING SNOW AND VISIBILITIES AS LOW AS 1/4 MILE AT TIMES. SNOW  
WILL SPREAD EAST ONTO THE PLAINS AND CONTINUE THROUGH 12Z TUESDAY  
MORNING. EXPECT CONDIITONS TO GRADUALLY IMPROVE AFTER THAT.  
REFINEMENTS WILL BE MADE TO THE TIMING OF THE HEAVIEST SNOW BUT  
EXPECT WIDESPREAD LIFR CONDIITONS MONDAY NIGHT AND EARLY TUESDAY.  
AVIATORS TAKE CAUTION AS VISIBILITIES WILL BE LOW WITH STRONG  
TURBULENCE AND ICING LIKELY.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 259 AM MST MON JAN 21 2019  
 
NO FIRE WEATHER CONCERNS EXPECTED THIS WEEK. A PACIFIC STORM  
SYSTEM WILL PUSH ACROSS THE REGION TODAY AND TONIGHT RESULTING IN  
VERY WINDY CONDITIONS AND WIDESPREAD SNOW AND BLOWING SNOW. A  
RELATIVELY COLD PATTERN IS EXPECTED TO REMAIN OVER THE AREA  
THROUGH THE WEEK WITH OCCASIONAL SNOW SHOWERS.  
 

 
   
CYS WATCHES/WARNINGS/ADVISORIES
 
 
WY...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 11 AM MST  
TUESDAY FOR WYZ106>108-116>119.  
 
WINTER STORM WARNING FROM 6 PM THIS EVENING TO 11 AM MST TUESDAY  
FOR WYZ102.  
 
WINTER WEATHER ADVISORY FROM 11 AM THIS MORNING TO 11 AM MST  
TUESDAY FOR WYZ105-109>115.  
 
WINTER STORM WARNING FROM 11 AM THIS MORNING TO 11 AM MST  
TUESDAY FOR WYZ101-103-104.  
 
NE...WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 11 AM MST  
TUESDAY FOR NEZ002-003-019-021-095-096.  
 
WINTER STORM WARNING FROM 6 PM THIS EVENING TO 11 AM MST TUESDAY  
FOR NEZ020-054-055.  
 

 
 

 
 
SHORT TERM...TJT  
LONG TERM...AL  
AVIATION...AL  
FIRE WEATHER...TJT  
 
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