117 FXUS65 KRIW 252108 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 208 PM MST MON FEB 25 2013 .SHORT TERM...TONIGHT THROUGH THURSDAY NEW...COLD STORM SYSTEM IS ALREADY SPREADING VERY LIGHT SNOW INTO THE NW AND THIS WILL SPREAD ACROSS THE REST OF THE FAR WEST OVER THE NEXT COUPLE HOURS. SYSTEM IS FAIRLY ENERGETIC WITH A -35C COLD CORE AND IMPRESSIVE HEIGHT FALLS ON THE MORNING RAOBS ALONG WITH THE BACK SIDE JET. SYSTEM SHOULD DIG OVERNIGHT AND PROVIDE A MODEST SNOW EVENT TO THE FAR WEST INTO TUESDAY MORNING. SNOW RATIOS WILL PLAY A CRITICAL ROLE HERE AND AM GOING IN THE HIGH TEENS TO AROUND 20-1. COLD FRONT SLIDES SOUTH...EAST OF THE DIVIDE LATER TONIGHT INTO TUESDAY MORNING WITH A BRIEF SHOT OF SNOW DEVELOPING IN MANY AREAS. THE FAR SOUTH ALSO GETS AN EVENING SHOT WITH THE WLY FRONT AND THEN ANOTHER ROUND IN ERN SWEETWATER LATER TUESDAY MORNING INTO TUESDAY AFTERNOON. JET STREAK MAY PROVIDE SOME DECENT SUPPORT IN THE 06-12Z TIMEFRAME TO GET SNOW GOING IN THE CENTRAL ZONES EARLIER THAN ONE WOULD THINK. THEN WE GET A QUICK SHOT OF QG FORCING AND MARGINAL UPSLOPE TUESDAY MORNING FOR SOME WIDESPREAD LIGHT TO LOCALLY MODERATE SNOW FROM THE WIND RIVER BASIN OVER TO CASPER...THEN SAGGING SOUTH INTO OUR FAR ERN AND SRN ZONES AFTER 18Z. CASPER AND CASPER MTN HAVE THE POTENTIAL FOR AN ADVISORY EVENT BEGINNING AS EARLY AS 09-12Z WITH A CHANCE OF WIDESPREAD SNOW BREAKING OUT IN THE JET STREAK SUPPORT AREA JUST TO OUR EAST AS EARLY AS 03-06Z WITH ODDS INCREASING AFTER THAT. EVENING CREW WILL HAVE TO WATCH THIS CLOSELY AND ISSUE AN ADVISORY EARLIER IF THIS BEGINS SETTING UP. OTHERWISE...HAVE PUT ADVISORY AMOUNTS IN TOWARDS CPR AND CPR MTN ON TUESDAY. CONDITIONS IMPROVE TUESDAY NIGHT WITH WEAK RIDGING MOVING IN THROUGH WEDNESDAY. STILL ENOUGH MOISTURE IN THE FLOW FOR A FEW MTN FLURRIES AHEAD OF OUR WEAKER SYSTEM DROPPING SOUTH WEDNESDAY NIGHT AND THURSDAY MORNING. PRETTY GOOD BET OF SOME LIGHT SNOW SHOWERS/FLURRIES IN THE MOUNTAINS WITH THIS SYSTEM WITH A LESSER CHANCE IN THE LOWER ELEVATIONS BUT JUST A LITTLE MORE STRENGTH WITH THIS SYSTEM AND MORE SNOW SHOWERS WILL AFFECT THE LOWER ELEVATIONS. .LONG TERM...THURSDAY NIGHT THROUGH MONDAY JUST SOME RESIDUAL LIGHT SNOW OR FLURRIES CAN BE EXPECTED IN THE NORTHWEST MTNS AND THE BIG HORN MTNS THURSDAY NIGHT AND FRIDAY MORNING AS THE LAST OF A SERIES OF PROGRESSIVELY WEAKER WEATHER SYSTEMS PARADE SOUTHEAST AND AWAY FROM THE AREA. A WARMING TREND WILL CONTINUE FRIDAY THROUGH SUNDAY AS A RIDGE BUILDS IN FROM THE WEST BEHIND THE LAST SHORTWAVE. HIGH TEMPERATURES WILL BE IN THE 40S THIS WEEKEND AT THE LOWER ELEVATIONS EAST OF THE DIVIDE AND THE UPPER 30S WEST. AN ALBERTA CLIPPER TYPE WEATHER SYSTEM WILL TRACK SOUTHEAST ACROSS WY ACCORDING TO THE GFS/ECMWF BY 12Z MONDAY. OUT AHEAD OF THE THIS APPROACHING FEATURE...SNOWFALL WILL LIKELY BREAK OUT IN WESTERN WY SUNDAY WITH THE SNOW SPILLING OVER THE DIVIDE SUNDAY NIGHT AND THEN FOCUSED MAINLY EAST OF THE DIVIDE BY MONDAY NIGHT. A WEAK LOW LEVEL UPSLOPE FLOW WILL BECOME ESTABLISHED MONDAY EAST OF THE DIVIDE BETWEEN SURFACE CYCLOGENESIS OVER THE EAST SLOPE OF THE SOUTHERN ROCKIES AND A SURFACE HIGH IN CANADA. RIGHT NOW THE GFS/ECMWF ARE STILL TREATING THIS UPPER LEVEL FEATURE AS AN OPEN WAVE SO NO DIRECT INDICATION SO FAR THAT THIS WILL BE A HUGE SNOW MAKER. .AVIATION.../00Z ISSUANCE/ WEST OF THE CONTINENTAL DIVIDE...LIGHT SNOW WILL CONTINUE TO DEVELOP OVER THE NORTHWEST WY MOUNTAINS AFTER 21Z. THE SNOW WILL EXPAND ACROSS ALL OF THE WESTERN MOUNTAINS AFTER 00Z WITH MVFR TO IFR CONDITIONS PREVAILING THROUGH 12Z TUESDAY. THE FAR WEST VALLEYS WILL ALSO SEE SOME SNOW WITH MVFR CONDITIONS PREVAILING. THE KJAC TERMINAL SITE WILL BE IMPACTED BY THIS SNOW WITH SOME IFR CONDITIONS. EAST OF THE CONTINENTAL DIVIDE...VFR CONDITIONS WILL THROUGH 06Z TUESDAY. AFTER 06Z TUE...SOME LIGHT SNOW WILL DEVELOP OVER THE NORTH AND CONTINUE THROUGH 12Z TUE WITH AREAS OF MVFR CONDITIONS. EXPECT WINDY WEATHER AT THE KCPR TERMINAL SITE FOR THE REST OF TODAY. .FIRE WEATHER... ANOTHER STORM SYSTEM WILL BRING SNOW TO THE WEST TONIGHT AND TUESDAY MORNING AND EAST OF THE DIVIDE LATER TONIGHT THROUGH MUCH OF TUESDAY. CONDITIONS WILL IMPROVE TUESDAY NIGHT WITH VALLEY AND BASIN INVERSIONS RETURNING WEDNESDAY. A WEAKER SYSTEM WILL PASS THROUGH WEDNESDAY NIGHT AND THURSDAY FOR MAINLY MOUNTAIN SNOW SHOWERS. A LARGER RIDGE OF HIGH PRESSURE IS EXPECTED TO BUILD IN FOR FRIDAY THROUGH THE WEEKEND WITH DRY CONDITIONS WITH FAIRLY STRONG INVERSIONS FOR THE CENTRAL AND WESTERN BASINS AND VALLEYS. && .RIW WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL 11 AM MST TUESDAY WYZ012-023. && $$ SHORT TERM...SKRBAC LONG TERM...LIPSON AVIATION...LIPSON FIRE WEATHER...SKRBAC