757  
FXUS65 KRIW 201021  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
421 AM MDT SUN OCT 20 2019  
   
SHORT TERM
 
(TODAY THROUGH TUESDAY)  
ISSUED AT 415 AM MDT SUN OCT 20 2019  
 
SATELLITE IMAGERY EARLY THIS MORNING SHOWS THE UPPER LOW OVER THE  
CENTRAL/SOUTHERN BIGHORN MOUNTAINS. RADAR IMAGERY EARLY THIS  
MORNING SHOWS PERSISTENT SNOW SHOWERS IN THE NORTHWEST FLOW ACROSS  
WESTERN WYOMING, WHILE AN AREA OF RAIN AND SNOW EXPANDING IN  
COVERAGE NEAR THE UPPER LOW. THERE WAS EVEN A LIGHTNING STRIKE OR  
TWO ACROSS NORTHEAST FREMONT COUNTY AROUND 2 AM. THIS UPPER LOW IS  
PROGGED TO PUSH INTO THE NEBRASKA PANHANDLE BY 18Z, AND THEN TO  
NORTH-CENTRAL NEBRASKA BY 00Z MONDAY.  
 
THE ACTIVITY OVER THE WEST WILL CONTINUE TO DECREASE IN COVERAGE  
AND INTENSITY AS THE MORNING PROGRESSES. NO CHANGES TO WINTER  
HIGHLIGHTS OVER THE WEST.  
 
THE BEST DYNAMICS WILL BE OVER THE FAR EASTERN SECTIONS OF THE  
FORECAST AREA ASSOCIATED WITH THE UPPER LOW BEFORE IT AND THE  
DYNAMICS PULL AWAY AROUND MIDDAY. IN THE AFTERNOON, DESPITE THE  
BULK OF THE DYNAMICS PUSHING AWAY, MODELS CONTINUE TO SHOW  
INSTABILITY ISOLATED TO SCATTERED SNOW SHOWERS PUSHING SOUTHEAST  
ACROSS THE AREA MAINLY EAST OF THE DIVIDE. THE HIGH RESOLUTION  
MODELS CONTINUE TO IMPACT THE CASPER AREA WITH THIS SHOWER  
ACTIVITY. SNOW COULD BE HEAVY IN THESE SHOWERS. DESPITE  
TEMPERATURES IN THE MID TO UPPER 30S EARLY THIS MORNING, EXPECT  
ANY RAIN TO CHANGE QUICKLY TO SNOW FROM DYNAMICAL COOLING AND A  
LOW WET-BULB ZERO TEMPS. THUS WITH SNOWFALL, POSSIBLY HEAVY AT  
TIMES, IN COMBINATION WITH STRONG WIND HAVE ELECTED TO ISSUE A  
WINTER WEATHER ADVISORY UNTIL 6 PM TODAY FOR JOHNSON AND NATRONA  
COUNTIES. ONCE THE PRECIPITATION CHANGES TO SNOW, EXPECT ALL SNOW  
THROUGH THE EVENT. ROAD IMPACTS REMAIN IN QUESTION DUE TEMPS IN  
THE 30S, BUT SUSPECT THE RATE OF THE SNOWFALL THIS MORNING SHOULD  
MAKE BECOME SLICK THIS MORNING, BEFORE LIKELY IMPROVING IN THE  
AFTERNOON. HOWEVER, THE HEAVY SNOW SHOWERS THIS AFTERNOON COULD  
RESULT IN WET ROADS QUICKLY BECOME SLICK AND SNOW COVERED AGAIN.  
THE HIGH WIND WARNING REMAINS IN EFFECT FOR JOHNSON COUNTY.  
 
TONIGHT, MODELS SHOW A SHORTWAVE IN THE STRONG NORTHWEST FLOW  
PULLING ACROSS THE AREA. THERE IS ALSO SOME UPPER JET FORCING  
WHICH WILL ALLOW FOR WIDESPREAD SNOWFALL OVER THE FAR  
WEST/NORTHWEST LAST TONIGHT INTO MONDAY MORNING. SNOW  
ACCUMULATIONS SHOULD BE LIGHT, BUT MAIN CONCERN IN THIS PATTERN IS  
FOR GRAND TARGHEE AND POSSIBLY THE ALPINE AREA GETTING HEAVIER  
SNOW THAN WHAT MODEL PRECIPITATION AMOUNTS WOULD SUGGEST.  
 
BY MIDDAY MONDAY INTO THE AFTERNOON, THE FORECAST AREA BEGINS TO  
BE ON THE ANTI-CYCLONIC SIDE OF THE UPPER FLOW WHICH SHOULD  
DECREASE THE COVERAGE OF SNOW SIGNIFICANTLY.  
 
TUESDAY, PERSISTENT MOIST NORTHWEST FLOW WILL CONTINUE PERIODS OF  
SNOW OVER THE NORTHWEST.  
   
LONG TERM
 
(TUESDAY NIGHT THROUGH SATURDAY)  
ISSUED AT 415 AM MDT SUN OCT 20 2019  
 
A COLD FRONT WILL MOVE INTO THE STATE ON WEDNESDAY. WITH THIS  
SYSTEM, THE SHOWERS IN THE NORTHWEST WILL PUSH EAST OF THE DIVIDE,  
SPREADING FURTHER SOUTH INTO PORTIONS OF CENTRAL WYOMING. THE  
SHOWERS WILL BE IN THE REGION THROUGH THURSDAY. GUSTY WINDS WILL  
ALSO ACCOMPANY THIS NEXT SYSTEM ACROSS MUCH OF THE AREA. THURSDAY  
LOOKS TO BE THE COLDEST MORNING WITH THE MODELS SHOWING H7  
TEMPERATURES AT -8 TO -14 C FOR SURFACE TEMPS IN THE TEENS AND LOW  
TO MID 20S. THE SHOWERS WILL DIMINISH LATER IN THE DAY FOR DRIER  
CONDITIONS.  
 
FRIDAY WILL SEE SIMILAR MORNING LOWS, HOWEVER IT WILL BE A FAIRLY  
DRY DAY. MODELS ARE INDICATING A NEW SYSTEM MOVING INTO THE NORTH ON  
SATURDAY, BUT IT THERE IS TOO MUCH UNCERTAINTY THIS EARLY IN THE  
FORECAST PERIOD.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)  
ISSUED AT 415 AM MDT SUN OCT 20 2019  
 
WEST OF THE CONTINENTAL DIVIDE...KRKS, KJAC, KBPI, KPNA TERMINAL  
SITES.  
 
TODAY WILL SEE SCATTERED SNOW SHOWERS IN NW WY WITH ISOLATED SNOW  
SHOWERS ELSEWHERE. A GUSTY WIND WILL BE COMMON AT THE TERMINAL  
SITES, DIMINISHING THIS EVENING. SNOW SHOWERS WILL INCREASE IN  
COVERAGE OVER THE WEST AFTER 03Z, CONTINUING THROUGH 12Z MONDAY. THE  
TERMINAL SITES WILL HAVE VFR CONDITIONS. KJAC MAY SEE MVFR  
CONDITIONS AT TIMES DUE TO REDUCED VISIBILITY AND LOWER CEILINGS.  
MOUNTAINS WILL BE OBSCURED AT TIMES.  
 
EAST OF THE CONTINENTAL DIVIDE...KCPR, KLND, KRIW, KCOD, KWRL  
TERMINAL SITES.  
 
AT 12Z, AREAS OF SNOW WILL OCCUR ALONG AND EAST OF A LINE FROM KCOD  
TO KRIW TO KCPR. HERE MVFR CONDITIONS WILL PREVAIL WITH LOCAL IFR  
CONDITIONS. THIS AREA OF SNOW WILL CONTINUE THROUGH 21Z BEFORE  
DECREASING BY 00Z. EXPECT MOUNTAINS TO BE FREQUENTLY OBSCURED TODAY.  
A GUSTY WIND WILL BE COMMON TODAY, DECREASING THIS EVENING. VERY  
WINDY CONDITIONS WILL OCCUR AT KBYG AIRPORT TODAY WITH WIND GUSTS AS  
HIGH AS 50 KNOTS.  
 
AFTER 00Z, SCATTERED SNOW SHOWERS WILL OCCUR WITH LOCAL MVFR  
CONDITIONS THROUGH 06Z MONDAY, THEN DECREASING SNOW SHOWERS AFTER  
06Z.  
 
PLEASE SEE THE AVIATION WEATHER CENTER AND/OR CWSU ZDV AND ZLC FOR  
THE LATEST INFORMATION ON ICING AND TURBULENCE FORECASTS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 415 AM MDT SUN OCT 20 2019  
 
UNSEASONABLY COLD AND BLUSTERY TODAY AND MONDAY. THE SNOW WILL END  
ACROSS MUCH OF THE WEST BY MIDDAY, BUT SOME SIGNIFICANT SNOWFALL  
AND STRONG WIND IS EXPECTED ACROSS JOHNSON AND NATRONA COUNTIES  
TODAY. THE SNOW OVER THE EAST WILL END BY EARLY EVENING, BUT  
ANOTHER ROUND OF SNOW WILL IMPACT THE WEST BEGINNING AROUND  
MIDNIGHT LASTING THROUGH MONDAY MORNING. HOWEVER ACCUMULATIONS  
WILL BE LIGHTER THAN WHAT OCCURRED WITH THE PAST SYSTEM. ANOTHER  
STRONG STORM SYSTEM WILL IMPACT THE AREA TUESDAY NIGHT AND  
WEDNESDAY WITH THE BULK OF THE SNOWFALL ACROSS NORTHERN AND  
CENTRAL WYOMING.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL NOON MDT TODAY FOR WYZ001-002-  
013>015-023-024-027.  
 
WINTER STORM WARNING UNTIL NOON MDT TODAY FOR WYZ012.  
 
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ010-  
011-020-022.  
 
HIGH WIND WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ010.  
 
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ008-  
009.  
 

 
 

 
 
SHORT TERM...MURRELL  
LONG TERM...SWANSON  
AVIATION...ROSS  
FIRE WEATHER...MURRELL  
 
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