702  
FXUS65 KRIW 251238  
AFDRIW  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE RIVERTON WY  
638 AM MDT TUE APR 25 2017  
   
SHORT TERM
 
(THIS AFTERNOON THROUGH WEDNESDAY)  
ISSUED AT 636 AM MDT TUE APR 25 2017  
 
UPDATED TO UPGRADE THE BUFFALO AREA AND NRN JOHNSON TO A WINTER  
STORM WARNING. SNOW CONTINUES TO PILE UP WITH HEAVY SNOW AND  
STRONG WIND CONTINUING. MORE HEAVY SNOW THIS MORNING BEFORE  
TAPERING OFF.  
 
WITH THE CONTRAST IN THE WEATHER PATTERN...WE WILL AGAIN DIVIDE THE  
FORECAST INTO WEST AND EAST OF THE DIVIDE THIS MORNING.  
 
WEST OF THE DIVIDE...THE LOW THAT IS BRINGING THE PRECIPITATION  
CONTINUES TO DRIFT EAST-NORTHEASTWARD ACROSS THE AREA NOW, MOVING  
ACROSS NATRONA COUNTY AS I WRITE THIS. THE BEST LIFT HAS SHIFTED  
TO THE EAST OF THE AREA, HOWEVER THE POCATELLO RADAR CONTINUES TO  
SHOW MORE PRECIPITATION MOVING INTO THE AREA. THE MODELS CONTINUE  
TO SHOW SHOWERS MOVING THROUGH THE AREA THROUGH THE MORNING SO WE  
WILL CONTINUE THE ADVISORIES AND SPECIAL WEATHER STATEMENTS RIDE  
FOR NOW. THE SHOWERS SHOULD DECREASE IN INTENSITY LATER IN THE DAY  
WITH A LULL, NOT REALLY A BREAK BUT A LULL IN THE ACTIVITY FROM  
THIS AFTERNOON THROUGH WEDNESDAY MORNING. FOLLOWING THAT THE NEXT  
IN THE SEEMINGLY NEVER ENDING SERIES OF FRONTS AND TROUGHS  
APPROACHES AND WILL BRING THE NEXT CHANCE OF RAIN AND SNOW TO THE  
MOUNTAINS. WITH THIS SYSTEM, TIMING IS STILL A BIT UNCERTAIN WITH  
THE NAM A BIT FASTER THAN THE GFS WITH THE BEST QPF. WE MADE FEW  
CHANGES FOR NOW AND SHOULD BE ABLE TO FINE TUNE IT MORE AS WE MOVE  
CLOSER TO THE EVENT. THESE SHOWERS WILL LIKELY CONTINUE THROUGH  
THURSDAY AS WELL WITH SOME WANING IN THE ACTIVITY ON THURSDAY  
NIGHT. AT THIS TIME, IT LOOKS FAIRLY LIKELY THAT MORE HIGHLIGHTS  
MAY BE NEEDED STARTING LATER ON WEDNESDAY. TEMPERATURES, AS  
EXPECTED, WILL CONTINUE TO AVERAGE BELOW NORMAL.  
 
EAST OF THE DIVIDE...ONCE AGAIN WE HAVE THAT DIFFICULT DECISION OF A  
FEW DEGREES OR A FEW HUNDRED FEET OF ELEVATION MAKING A BIG  
DIFFERENCE IN THE FORECAST. THINGS LOOK OK FOR NOW IN AROUND BUFFALO  
WITH SNOW CHANGING OVER RIGHT ON SCHEDULE. QUITE A BIT OF QPF,  
ALREADY AROUND EIGHT TENTHS AT THE BUFFALO AIRPORT AT THIS TIME.  
THAT BEING SAID, A LOT OF THE QPF WAS LOST TO RAIN ALREADY. HOWEVER,  
TEMPERATURES ARE GETTING RATHER CLOSE TO THAT FREEZING MARK. WARM  
GROUND TEMPERATURES ARE KEEPING PAVEMENT WET RIGHT NOW, BUT THAT MAY  
CHANGE. THIS COULD BE A SITUATION WHERE A FEW HUNDRED FEET OF  
ELEVATION COULD MAKE A DIFFERENCE BETWEEN 6 TO 8 INCHES OF SNOW AND  
ONLY 1 OR 2 IN JOHNSON COUNTY. FOR NOW, WE WILL LET THE ADVISORIES  
RIDE BUT WE COULD MAKE A GAME TIME DECISION TO UPGRADE. ANOTHER AREA  
OF CONCERN IS THE CODY FOOTHILLS, A PLACE WE HAVE BEEN BURNED ON A  
FEW TIMES THIS YEAR. RIGHT NOW, PRECIPITATION IS STILL MAINLY RAIN  
BUT THIS COULD CHANGE. WE WILL STICK TO THE SPS FOR NOW. ELSEWHERE,  
ANY SNOW AMOUNTS SHOULD REMAIN BELOW ADVISORY LEVELS. THIS WILL  
ESPECIALLY BE THE CASE IN PLACES WHERE CHANGEOVER OCCURS LATER WHERE  
THE LATE APRIL SUN WILL KEEP PAVED SURFACES MAINLY WET.  
 
MOST OF THE MODELS SHOW THE STEADIEST PRECIPITATION ENDING BY NOON  
AS LOW PRESSURE MOVES AWAY INTO THE PLAINS STATES. ALMOST ALL  
PRECIPITATION SHOULD END THIS EVENING WITH ALMOST ALL AREAS MAINLY  
DRY AFTER MIDNIGHT. AT THIS POINT, WEDNESDAY LOOKS LIKE THE BREAK  
BETWEEN TWO SYSTEMS. THE NAM ESPECIALLY SHOWS A MAINLY DRY DAY. EVEN  
THE GFS HAS MAINLY DRY CONDITIONS. THE DAY SHOULD TURN OUT LIKE  
MONDAY, WITH A FEW AFTERNOON SHOWERS AROUND BUT MOST AREAS RAIN FREE  
MOST OF THE TIME. TEMPERATURES WILL BE WARMER THAN TODAY, BUT STILL  
AVERAGE BELOW NORMAL.  
 
THE NEXT SYSTEM WILL THEN MOVE IN FOR THURSDAY WITH ANOTHER CHANCE  
OF PRECIPITATION. AND YES, THIS COULD MEAN SNOW AS WELL FOR MANY  
AREAS. 700 MILLIBAR TEMPERATURES ARE EXPECTED TO DROP THROUGH THE  
DAY, REACHING MINUS 6 TO MINUS 8 BY 00Z FRIDAY. IF THERE IS ONE  
SAVING GRACE, A BULK OF THE POSSIBLE SNOW MAY FALL DURING THE DAY  
WHEN THE SUN MAY PREVENT MUCH OF A PROBLEM ON THE ROADS. LOW  
PRESSURE DEVELOPING OVER COLORADO COULD BRING MORE SNOW, BUT MORE  
LIKELY ON FRIDAY. MY COLLEAGUE WILL HAVE MORE ON THAT.  
   
LONG TERM
 
(FRIDAY THROUGH MONDAY)  
ISSUED AT 636 AM MDT TUE APR 25 2017  
 
COLD LONGWAVE TROUGH WILL BE WELL ENTRENCHED ACROSS THE AREA TO  
START THIS PERIOD WITH POTENTIAL FOR SIGNIFICANT SNOW IN PARTS OF  
CENTRAL WYOMING. MODELS CONTINUE TO STRUGGLE WITH THE DETAILS AND  
MOST OF THE GUIDANCE HAS A RATHER UNORGANIZED UPPER LOW BUT THERE'S  
STILL A PERIOD IN THERE WHERE IT'S QUITE FAVORABLE BASED ON MEAN  
TROUGH OVER THE AREA. BOTTOM LINE: STILL A DECENT SHOT OF SOME  
ACCUMULATING SNOW WHICH WILL LIKELY START AT THE END OF THE SHORT  
TERM PERIOD AND CARRY OVER INTO THE START OF THIS PERIOD. CONDITIONS  
IMPROVE QUICKLY LATER FRIDAY NIGHT OR SATURDAY AS THE UPPER LOW  
DROPS WELL TO THE SOUTH AND EAST SOMEWHERE BETWEEN THE TX PANHANDLE  
AND THE KS AREA. STILL SOME COLD AIR ALOFT FOR SNOW SHOWERS IN AND  
NEAR THE MOUNTAINS ON SATURDAY BUT OTHERWISE, MOST AREAS WILL SEE  
LIMITED PCPN BY SATURDAY BUT IT'LL BE CHILLY FOR LATE APRIL.  
SHORTWAVE RIDGING MOVES OVER HEAD SUNDAY BUT NEXT SHORTWAVE  
APPROACHES THE FAR WEST LATE SUNDAY FOR AN INCREASING CHANCE OF MTN  
SNOW SHOWERS AND VALLEY RAIN SHOWERS IN THE AFTERNOON. THE NEXT  
DIGGING TROUGH MOVES IN MONDAY POSSIBLY CLOSING OFF OVER NRN UT OR  
SWRN WY ON TUESDAY. DECENT POTENTIAL FOR MORE WIDESPREAD SNOW EAST  
OF THE DIVIDE. LOWERED TEMPS SOME BUT PROBABLY NOT ENOUGH BASED ON  
CURRENT THINKING.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z WEDNESDAY MORNING)  
ISSUED AT 636 AM MDT TUE APR 25 2017  
 
WEST OF THE DIVIDE...KBPI/KJAC/KPNA/KRKS ROUTES  
 
SCATTERED TO NUMEROUS MVFR/IFR SNOW SHOWERS WILL REMAIN VICINITY AND  
NORTH OF A KAFO-KDUB LINE THROUGH 15Z TUESDAY, WITH A DRIER  
WESTERLY FLOW PREVAILING ACROSS SW WYOMING. A COLD FRONT WILL  
THEN SPREAD A LINE OF RAIN AND SNOW SHOWERS FROM CENTRAL WYOMING  
SOUTH AND WEST ACROSS THE INTERSTATE 80 CORRIDOR, VICINITY KRKS  
15Z-18Z TUESDAY, WITH SNOW SHOWERS ALSO PUSHING SOUTH INTO KPNA-  
KBPI IN THE AFTERNOON. A RIDGE OF HIGH PRESSURE WILL BUILD IN  
TUESDAY EVENING, WITH DECREASING SNOW SHOWERS FROM THE NORTH,  
SCATTERED SNOW SHOWERS LINGERING MAINLY VICINITY KJAC AND  
SURROUNDING MOUNTAINS BY 12Z TUESDAY WITH VFR CONDITIONS  
PREVAILING ELSEWHERE.  
 
EAST OF THE DIVIDE...KCOD/KCPR/KLND/KRIW/KWRL ROUTES  
 
AN UPPER LEVEL LOW PRESSURE SYSTEM WILL CONTINUE TO INTENSIFY OVER  
NORTHEAST WYOMING EARLY THIS MORNING WITH A LARGE BAND OF HEAVIER  
PRECIPITATION, WIDESPREAD MFVR/IFR CONDITIONS, NORTH OF THE LOW  
PRESSURE SYSTEM VICINITY AND NORTH OF A 50SM NORTH OF KCPR-KTHP  
LINE. RAIN AND SNOW SHOWERS WILL BE MORE SCATTERED SOUTH OF THIS  
LINE THROUGH AROUND 12Z. A COLDER NORTHERLY FLOW WILL PUSH SOUTH  
BEHIND THE LOW PRESSURE SYSTEM WITH SNOW LEVELS EXPECTED TO LOWER TO  
VALLEY FLOORS ACROSS NORTH AND CENTRAL WYOMING 12Z-15Z, AND MAINLY  
IFR SNOW SPREADING SOUTH OF A KCPR-KLND LINE BY 15Z. SNOW MAY  
BECOME MIXED WITH RAIN THROUGH LATE TUESDAY MORNING AND TUESDAY  
AFTERNOON. DRIER AIR AND IMPROVING CONDITIONS WILL GRADUALLY  
PREVAIL FROM THE NORTH AND WEST TUESDAY EVENING.  

 
   
FIRE WEATHER
 
 
ISSUED AT 636 AM MDT TUE APR 25 2017  
 
A COOL AND WET PATTERN LOOKS TO PERSIST FOR MUCH OF THE WEEK. LOW  
PRESSURE WILL BRING RAIN AND SNOW TO MANY AREAS EAST OF THE DIVIDE  
TODAY WITH LINGERING SHOWERS ACROSS MANY AREAS WEST OF THE DIVIDE. A  
GUSTY NORTH TO NORTHWEST WIND WILL OCCUR THROUGH THE DAY ACROSS THE  
NORTHERN HALF OF THE STATE. MIXING AND SMOKE DISPERSAL WILL BE  
GENERALLY FAIR TO POOR. TOMORROW WILL BE DRIER AND MILDER EAST OF  
THE DIVIDE BUT ANOTHER FRONT WILL BRING ANOTHER CHANCE OF RAIN AND  
SNOW TO THE WESTERN VALLEYS AND MOUNTAINS WEDNESDAY AFTERNOON AND  
NIGHT.  
 

 
   
RIW WATCHES/WARNINGS/ADVISORIES
 
 
WINTER WEATHER ADVISORY UNTIL NOON MDT TODAY FOR WYZ001-002-012-  
014-015-024.  
 
WINTER WEATHER ADVISORY UNTIL 6 PM MDT THIS EVENING FOR WYZ008-  
009.  
 
WINTER STORM WARNING UNTIL 6 PM MDT THIS EVENING FOR WYZ010.  
 

 
 

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