847  
FXUS65 KRIW 231951  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
151 PM MDT MON OCT 23 2017  
   
SHORT TERM
 
MONDAY NIGHT THROUGH THURSDAY  
 
WE DON'T HAVE A LOT OF ISSUES IN THE FIRST 36 HOURS OF THE FORECAST  
SO I WILL NO TALK A LOT ABOUT THEM. EXPECT NEAR TO SLIGHTLY ABOVE  
NORMAL TEMPERATURES. WIND SHOULD DECREASE AFTER SUNSET TONIGHT WITH  
LIGHT TO MODERATE WINDS FOR ALL AREAS TOMORROW. SO ALL IN ALL, A  
FAIRLY NICE DAY.  
 
THINGS TURN MORE INTERESTING ON WEDNESDAY. A STRONG COLD FRONT WILL  
BE MOVING TOWARD THE AREA FROM THE NORTH. THE FIRST AREA TO SEE  
EFFECTS WILL LIKELY BE THE ABSAROKAS AND CODY FOOTHILLS WHERE  
INCREASING 700 MILLIBAR WINDS MAY MIX TO THE SURFACE AND BRING SOME  
LOCALLY STRONG WINDS. IT IS BORDERLINE FOR HIGH WINDS THOUGH, SO WE  
WILL HOLD OFF ON ANY HIGHLIGHTS. THE OTHER CONCERN IS POSSIBLE  
CRITICAL FIRE CONDITIONS. THE TIGHTENING PRESSURE GRADIENT AHEAD OF  
THE FRONT WILL INCREASE SOUTHWEST FLOW ACROSS THE FAVORED ROCK  
SPRINGS THROUGH NATRONA COUNTY CORRIDOR. TEMPERATURES ARE ALSO  
EXPECTED TO CLIMB INTO THE 70S AND RELATIVE HUMIDITY FALLING TOWARD  
10 PERCENT. THERE IS A GOOD CHANCE A FIRE WEATHER WATCH WOULD BE  
NEEDED ACROSS NATRONA COUNTY. THERE IS MORE UNCERTAINTY FOR JOHNSON  
COUNTY THOUGH, SINCE WIND WILL BE LIGHTER AND MAY NOT BECOME STRONG  
ENOUGH UNTIL LATER IN THE DAY WHEN TEMPERATURES DROP AS THE COLD  
FRONT APPROACHES FROM THE NORTH. IT WILL BE A WARM DAY IN MANY  
AREAS, WITH MANY OF THE LOWER ELEVATIONS SEEING HIGH TEMPERATURES  
INTO THE 70S.  
 
THE AFOREMENTIONED COLD FRONT WILL BEGIN TO MOVE INTO NORTHERN  
WYOMING WEDNESDAY NIGHT AND ACROSS THE AREA ON THURSDAY AND IT WILL  
HAVE THREE MAIN EFFECTS. THE FIRST EFFECT WILL BE SOME STRONG AND  
POSSIBLY HIGH WINDS ACROSS AREAS FAVORED BY STRONG COLD ADVECTION  
WITH NORTH TO NORTHWESTERLY FLOW, MAINLY THE NORTHERN BIG HORN BASIN  
AND NORTHERN JOHNSON COUNTY. WE BUMPED UP WINDS SIGNIFICANTLY AS A  
RESULT. THE SECOND WILL BE A PERIOD OF PRECIPITATION AS THE FRONT  
MOVES THROUGH. IT WOULD LIKELY START AS RAIN BUT THEN CHANGE TO SNOW  
AS SURFACE AND 700 MILLIBAR TEMPERATURES PLUMMET. THE SYSTEM HAS  
LITTLE MOISTURE TO WORK WITH AND IS A QUICK HITTER, SO WE DO NOT  
EXPECT A LOT OF SNOW. HOWEVER, THE TIMING AROUND THE MORNING COMMUTE  
COULD MAKE THINGS INTERESTING.  
 
THE MAIN EFFECT WILL BE THE MUCH COLDER TEMPERATURES, WHICH WILL BE  
A SLAP IN THE FACE. ALL AREAS EAST OF THE DIVIDE WILL SEE AT LEAST A  
20 DEGREE DROP IN HIGH TEMPERATURES WHEN COMPARED TO WEDNESDAY. THE  
MOST DRAMATIC DROP WILL BE IN EASTERN PORTIONS OF THE COUNTY WARNING  
AREA WHERE TEMPERATURES COULD BE AS MUCH AS 35 DEGREES COLDER THAN  
ON WEDNESDAY AFTERNOON. WITH A BRISK NORTH TO NORTHWESTERLY BREEZE,  
IT WILL FEEL EVEN COLDER.  
   
LONG TERM
 
THURSDAY THROUGH MONDAY  
 
MEAN LONGWAVE RIDGE HOLDS BETWEEN 130-135W THROUGH THE PERIOD  
KEEPING US IN A NNW-NW FLOW MUCH OF THE PERIOD. OUR THURSDAY SYSTEM  
IS PASSING OFF TO THE EAST AND SOUTH TO START THIS PERIOD. COLD  
SURFACE HIGH WILL LIKELY BE OVERHEAD/SLIGHTLY EAST OF US AROUND 00Z  
FRIDAY. COLDEST TEMPERATURES OF THE FALL SEASON ARE QUITE POSSIBLE  
FRIDAY MORNING, ESPECIALLY (MAINLY) EAST OF THE DIVIDE. ANY NEW  
LIGHT SNOW COVER (FROM OUR THURSDAY SYSTEM) WILL JUST INCREASE THOSE  
ODDS. MANY LOW LYING/SNOW COVERED AREAS COULD SEE TEENS. CHILLY  
AIRMASS IS SHORT LIVED THROUGH WITH WARMING ALOFT MOVING IN QUICKLY  
FRIDAY THROUGH AT LEAST EARLY SUNDAY. ANOTHER SWD MOVING SHORTWAVE  
MAY AFFECT US SUNDAY NIGHT OR MONDAY OF NEXT WEEK. SOME SIGNIFICANT  
DIFFERENCES IN TIMING AND LOCATION THIS FAR OUT BUT MEAN RIDGE  
LOCATION SUPPORTS ANOTHER POTENTIAL DISTURBANCE DROPPING DOWN THE  
FRONT SIDE OF THE RIDGE (12Z EURO IS A DAY LATER BUT NOW AT LEAST  
SHOWS THIS SYSTEM PRODUCING SNOW HERE BUT NOT UNTIL LATER MONDAY  
NIGHT INTO TUESDAY). THIS SYSTEM THAT THE GFS SHOWS QUITE WELL IS  
CURRENTLY WAY OVER IN ASIA AND MOVES ACROSS THE PACIFIC THIS WEEK.  
ANOTHER STRONG COLD FRONT MAY MOVE DOWN FROM THE NORTH NEXT SUNDAY  
NIGHT/EARLY MONDAY WITH BRIEF SNOW POTENTIALLY, ESPECIALLY NORTH  
HALF/UPSLOPE AND NRN MOUNTAIN AREAS (NOT UNLIKE OUR UPCOMING LATE  
WED NGT/THUR SYSTEM). SO COLD START TO THE EXTENDED THAN WARMING UP  
OVER THE WEEKEND BEFORE DROPPING SHARPLY, ESPECIALLY EAST OF THE  
DIVIDE, SUNDAY NIGHT/MONDAY. SO 40S AND SOME 50S FRIDAY WITH TEMPS  
WARMING INTO THE 60S (50S FOR SOME BASINS) IN MANY AREAS EAST OF THE  
DIVIDE SATURDAY AND SUNDAY (BASIN AREAS MAY BEGIN TO STRUGGLE THOUGH  
WITH INVERSIONS STARTING TO HAVE AN EFFECT, ESPECIALLY SATURDAY)  
WITH MAINLY 50S WEST. EAST SLOPE FOOTHILL AREAS WILL BE QUITE NICE  
THIS COMING WEEKEND WITH 40S AND 50S (MAYBE EVEN A FEW LOWER 60S  
DOWN LOW). MOST OF THE MIDDLE TO HIGHER MOUNTAINS (ABOVE 9000 FEET  
AND UP) WILL SEE 40S TO LOWER 50S.  
 

 
   
AVIATION
 
00Z ISSUANCE  
 
VFR CONDITIONS WILL PREVAIL THROUGH TUESDAY. GUSTY WEST TO NORTHWEST  
WIND AREAS WILL DECREASE AFTER SUNSET.  

 
   
FIRE WEATHER
 
 
A RIDGE OF HIGH PRESSURE WILL BRING DRY WEATHER THROUGH WEDNESDAY.  
GUSTY BREEZES THIS AFTERNOON WITH DECREASE AFTER SUNSET. TOMORROW  
WILL BE A DRY AND WARMER DAY. ALTHOUGH RELATIVE HUMIDITY MAY FALL  
INTO THE TEENS AT TIMES, WIND SHOULD REMAIN LIGHT TO MODERATE FOR  
MOST AREAS. MIXING AND SMOKE DISPERSAL WILL BE GENERALLY FAIR TO  
GOOD.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...HATTINGS  
LONG TERM...SKRBAC  
AVIATION...SKRBAC  
FIRE WEATHER...HATTINGS  
 
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