319  
FXUS65 KRIW 190501  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
1001 PM MST THU JAN 18 2018  
   
SHORT TERM
 
(THIS EVENING THROUGH SUNDAY)  
ISSUED AT 1226 PM MST THU JAN 18 2018  
 
ACTIVE WEATHER PERIOD IS ABOUT TO BEGIN FIRST IN THE NWRN CORNER  
STARTING MAINLY AFTER 06Z TONIGHT AS MOIST SW FLOW AHEAD OF  
DEVELOPING FRONT/FRONTOGENESIS AND IN THE POTENTIAL RIGHT ENTRANCE  
REGION OF A ANTI-CYCLONICALLY CURVED JET. BEST SHOT IS AIMED AT  
YNP LATE TONIGHT WORKING TOWARDS THE TETONS LATE TONIGHT INTO  
FRIDAY MORNING. NOT A LONG DURATION EVENT BUT THERE WILL LIKE BE  
A HEAVIER SNOW PERIOD OF 6 HOURS WITH SNOWFALL RATES AROUND AN  
INCH PER HOUR. OTHER 'LIGHTER' PERIODS AND IT ADDS UP TO A 5 TO 10  
INCH EVENT FOR THE NW MTNS WITH LOCALLY HIGHER AMOUNTS AND A 3 TO  
7 INCH EVENT FOR MOST OF THE LOWER ELEVATIONS. A QUICK PERIOD OF  
LIGHT TO MODERATE SNOW WILL FALL IN THE JACKSON VALLEY DURING THE  
DAY FRIDAY BUT NOT CONFIDENT ON AN ADVISORY THERE YET AND WILL LET  
THE NEXT CREW LOOK AT THIS. A QUICK SHOT OF ACCUMULATING SNOW  
WILL ALL FALL IN THE STAR VALLEY BY MID- MORNING THROUGH FRIDAY  
AFTERNOON WITH SOME POTENTIAL FOR ADVISORIES DOWN THERE  
EVENTUALLY. AHEAD OF THIS STORM SYSTEM, THE SW WINDS WILL BE  
INCREASING ACROSS THE WIND CORRIDOR LATER TONIGHT INTO FRIDAY  
MORNING WITH SOME HIGH WINDS EXPECTED BUT MAINLY HIGHER ELEVATION  
SENSORS AND OF COURSE OUTER DR. IN CASPER. WILL ISSUE AN SPS FOR  
SOME HIGH WIND IN THOSE AREAS AND GUSTS 40-55 MPH ELSEWHERE.  
THINGS GET MUCH MORE INTERESTING EAST OF THE DIVIDE, EARLY  
SATURDAY THROUGH SATURDAY NIGHT. AS THE MAIN UPPER LOW DIGS SE SRN  
UT SATURDAY, STRONG FRONTOGENESIS DEVELOPS OVER CENTRAL WY WITH  
AN IMPRESSIVE H7- H5 QG FRONTOGENESIS/H6 DEFORMATION SIGNATURE  
HOVERING OVER FREMONT AND NATRONA COUNTIES THROUGH THE DAY  
SATURDAY. COUPLE LET WITH THE ANTICYCLONIC TAIL OF A STRONG JET  
CREATING MODERATE TO STRONG UPPER DIVERGENCE AND WE'RE SETTING THE  
STAGE FOR SOME WIDESPREAD SIGNIFICANT SNOW WITH POTENTIAL FOR  
HEAVY SNOW BANDS. THE HEAVIEST SNOW WE'RE LOOKING AT RIGHT NOW  
STRETCHES FROM THE SWRN CORNER OF SWEETWATER COUNTY NE TO NATRONA  
COUNTY INCLUDING THE CASPER AREA. WILL BE ISSUING WINTER STORM  
WATCHES FOR THOSE AREAS FROM 09Z SATURDAY THROUGH 12Z SUNDAY.  
FUTURE HIGHLIGHTS WILL LIKELY BE NEEDED NORTH AND WEST OF THESE  
AREAS IN CENTRAL WY. IT'S STILL WORTH WATCHING CLOSELY THE LANDER  
FOOTHILLS AND RIVERTON AREA JUST BECAUSE OF THE POTENTIAL UPPER  
JET COMING IN ALIGNMENT WITH THE FRONTOGENESIS/H6 DEFORMATION  
SIGNATURE. WILL HIT THE AREA WITH SOLID ADVISORY AMOUNTS FOR NOW  
AND LET THE NEXT CREW ALSO KEEP A WATCH ON THESE DEVELOPMENTS.  
FURTHER EAST, A 6 TO 10 INCH EVENT FOR CASPER AND VICINITY WITH 4  
TO 8, 5 TO 10 IN ERN AND SRN SWEETWATER COUNTY LOOKS PRETTY GOOD.  
THE NE WIND WILL BE INCREASING DOWN THERE TOO LATE SATURDAY INTO  
SATURDAY NIGHT. SLOW IMPROVEMENT FROM NW TO SE EARLY SUNDAY INTO  
SUNDAY MORNING AND CHILLY.  
   
LONG TERM
 
(SUNDAY NIGHT THROUGH THURSDAY)  
ISSUED AT 1226 PM MST THU JAN 18 2018  
 
OVERALL, THE MR MODELS (EXCEPT THE CA) WITH RESPECT TO THE EXTENDED  
FORECAST ARE IN DECENT AGREEMENT INTO/THROUGH TUESDAY NIGHT BEFORE  
DIFFERENCES IN UPPER LEVEL WAVE TRANSLATION SPEED DIFFERENCES SHOW  
UP. THROUGH THIS TIME PERIOD, FROM SUNDAY NIGHT THROUGH TUESDAY  
NIGHT, SHORTWAVE RIDGING FOLLOWING THE WEEKEND'S STORM SYSTEM WILL  
QUICKLY GET MASHED DOWN MONDAY AFTERNOON/EVENING ACROSS WESTERN WY  
FROM AN EMBEDDED SHORTWAVE TROF WITH MODEST MOISTURE AND DYNAMICS  
ACCOMPANYING THE DISTURBANCE. LIGHT TO OCCASIONALLY MODERATE  
SNOWFALL EXPECTED FROM MONDAY AFTERNOON THROUGH MONDAY NIGHT WITH  
THIS SYSTEM...BECOMING LIGHT SNOW OR FLURRIES FROM TUESDAY INTO  
WEDNESDAY MORNING. THEN, THE DIFFERENCES IN TRANSLATION SPEED BEGIN  
TO APPEAR WITH THE EC FASTER THAN THE GFS. THE EC SUBSEQUENTLY  
ALLOWS MORE SIGNIFICANT MOISTURE/PRECIPITATION BACK INTO WRN WY SOME  
(NOW) 6 HRS EARLIER THAN THE GFS ON WEDNESDAY AS THE NEXT  
SIGNIFICANT TROF APPROACHES FROM THE WEST. SOME TEMPORAL  
DIFFERENCES, TOO, BEGIN SHOW UP AND SLOWLY DIVERGE THROUGH THE END  
OF THE FORECAST PERIOD. WHILE BOTH MDLS DIG THE END OF THE WEEK'S  
(NEXT) PROGRESSIVE TROF INTO/ACROSS THE WRN/SWRN CONUS TO SOME  
EXTENT, THE SLOWER AND MORE NORTHERN BIASED GFS ALLOW BETTER AND  
MORE BULLISH DEVELOPMENT OF THE RESULTING PRECIP/SNOW THURSDAY NIGHT  
THROUGH FRIDAY WHILE THE SOMEWHAT SPLIT AND SOUTHERN BIASED EC MOVES  
LESS PRECIP/SNOW THROUGH THE REGION QUICKER. THERE WILL SURELY BE  
MANY BACK AND FORTHS BETWEEN THE MODELS OVER THE NEXT SEVERAL DAYS  
WITH REGARD TO THESE DIFFERENCES WITHIN A PROGRESSIVE UPPER LEVEL  
PATTERN TO WATCH FOR.  
 

 
   
AVIATION
 
(FOR THE 06Z TAFS THROUGH 06Z SATURDAY)  
ISSUED AT 1000 PM MST THU JAN 18 2018  
 
WEST OF THE CONTINENTAL DIVIDE...KJAC, KBPI, KPNA AND KRKS  
 
SNOW WILL MOVE INTO NW WY OVERNIGHT AND CONTINUE THROUGH FRIDAY  
NIGHT. KJAC WILL BE IMPACTED BY 12Z FRIDAY. MVFR TO IFR CONDITIONS  
WILL OCCUR IN NW WY WITH MOUNTAINS OBSCURED. THE SNOW WILL DEVELOP  
OVER SW WY TOWARD 18Z FRIDAY AND INCREASE IN COVERAGE BY 00Z  
SATURDAY. EXPECT MVFR TO IFR CONDITIONS TO OCCUR ALONG WITH  
MOUNTAINS OBSCURED. AT KRKS, THE SNOW WILL HOLD OFF UNTIL ABOUT 06Z  
SATURDAY, THUS KEEPING THEM IN THE VFR CATEGORY THROUGH 06Z  
SATURDAY. AREAS OF LLWS WILL OCCUR IN THE WEST THROUGH FRIDAY  
AFTERNOON.  
 
EAST OF THE CONTINENTAL DIVIDE...KCPR, KCOD, KRIW, KLND, AND KWRL  
 
VFR CONDITIONS TO PREVAIL THROUGH THE FORECAST PERIOD FOR ALL TAF  
SITES. SURFACE SOUTHWEST WINDS AT 20 TO 30 KNOTS WITH GUSTS TO 40  
KNOTS WILL CONTINUE VICINITY 50NM NE KRKS TO KCPR THROUGH FRIDAY  
MORNING. ADDITIONALLY, AREAS OF LLWS WILL OCCUR OVER THE AREA  
THROUGH FRIDAY AFTERNOON.  
 
PLEASE SEE INDIVIDUAL TERMINAL SITES FOR MORE DETAILS. ADDITIONALLY,  
THE AVIATION WEATHER CENTER WILL HAVE THE LATEST INFORMATION ON  
ICING AND TURBULENCE FORECASTS.  
 

 
   
FIRE WEATHER
 
 
ISSUED AT 1226 PM MST THU JAN 18 2018  
 
STRONG SOUTHWEST WINDS WILL BLOW AND ACTUALLY INCREASE TONIGHT FROM  
JEFFREY CITY TO CASPER AND CONTINUE QUITE STRONG INTO AT LEAST  
FRIDAY MORNING. THE MOUNTAINS AND LEE OF THE MOUNTAIN RANGES WILL  
ALSO SEE GUSTY TO STRONG WINDS TONIGHT INTO FRIDAY. SNOW WILL  
DEVELOP IN THE NORTHWEST LATE TONIGHT THROUGH FRIDAY AND DROP INTO  
FAR SOUTHWEST WYOMING DURING THE DAY FRIDAY INTO FRIDAY EVENING. THE  
SNOW WILL THEN SHIFT EAST OF THE DIVIDE LATE FRIDAY NIGHT INTO  
SATURDAY WITH AREAS OF SIGNIFICANT SNOW IN CENTRAL WYOMING. MIXING  
WILL BE FAIR TO LOCALLY GOOD IN MOST AREAS FRIDAY AND GENERALLY POOR  
SATURDAY.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH LATE SATURDAY  
NIGHT FOR WYZ019-020-022-028>030.  
 
WINTER WEATHER ADVISORY FROM 11 PM THIS EVENING TO 5 PM MST  
FRIDAY FOR WYZ001-002-012.  
 

 
 

 
 
SHORT TERM...SKRBAC  
LONG TERM...BRAUN  
AVIATION...BRAUN/AR  
FIRE WEATHER...SKRBAC  
 
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