482 FXUS65 KRIW 121808 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 1108 AM MST SAT JAN 12 2013 .SHORT TERM...SATURDAY THROUGH MONDAY NIGHT GOOD MORNING AND WELCOME TO THE FREEZER. THE HEAVIEST SNOW HAS MOVED ON TO THE EAST INTO THE DAKOTAS. HOWEVER...A FILLING UPPER LEVEL LOW WILL CONTINUE TO PRODUCE CLOUDS AS WELL AS AREAS OF LIGHT SNOW OVERNIGHT AND EARLY THIS MORNING. ALMOST ALL OF THE AREAS OF STEADY LIGHT SNOW SHOULD END EARLY. HOWEVER...AREAS OF SNOW SHOWERS AND FLURRIES MAY CONTINUE INTO THE AFTERNOON WITH A PERSISTENT TROUGH PLACED OVER THE AREA AND ASSOCIATED CYCLONIC CURVATURE. ACROSS THE AREA IT WILL BE QUITE COLD WITH HIGHS STRUGGLING TO REACH 10 ABOVE. CLOUD COVER WILL BE THE X FACTOR FOR LOWS TONIGHT. LATEST MODELS KEEP HIGHER HUMIDITY ALOFT SO WE RAISED THE LOW TEMPERATURES JUST A BIT...STILL WELL BELOW NORMAL HOWEVER. ON SUNDAY IT LOOKS LIKE EVERYONE WILL STAY IN THE VERY COLD TEMPERATURES WITH SNOW SHOWERS ALONG THE MOUNTAINS. WITH MODELS SHOWING SOME CLEARING SUNDAY NIGHT TEMPERATURES SHOULD BE LOWEST EARLY MONDAY MORNING WITH MANY AREAS DROPPING BELOW MINUS 20. MONDAY LOOKS TO BE ANOTHER VERY COLD DAY UNDER CONTINUING NORTHERLY FLOW. A SHORTWAVE MOVING SOUTH WILL HELP KEEP THE CHANCE OF SNOW SHOWERS ACROSS NORTHWESTERN WYOMING. EVERYONE ELSE SHOULD REMAIN DRY. THE NEXT CHANCE OF A DECENT WEATHER MAKER MOVES IN FOR MONDAY NIGHT AS A FAST MOVING SYSTEM DROPS IN FROM THE NORTH-NORTHWEST OUT OF CANADA. THE SYSTEM DOES NOT SEEM TO HAVE A LOT OF MOISTURE TO WORK WITH BUT A DECENT AMOUNT OF DYNAMICS SO WE BUMPED UP POPS FOR MONDAY NIGHT...ESPECIALLY ACROSS THE NORTHERN PORTIONS OF THE COUNTY WARNING AREA. .LONG TERM...TUESDAY THROUGH SATURDAY ALBERTA CLIPPER DIVES INTO THE NORTHERN PLAINS ON TUESDAY...INCREASING NW FLOW ACROSS THE AREA WITH A MOIST UPGLIDE PATTERN ACROSS THE NORTH GRADUALLY SHIFTING EAST THROUGH THE DAY. NO CHANGES TO THE FORECAST HERE WITH CHANCES OF SNOW ACROSS THE NORTH EXCEPT IN THE THE CODY FOOTHILLS WHERE STRONGER DOWNSLOPE WINDS WILL KEEP THINGS DRY. HEIGHTS INCREASE OVER AREA THROUGH WEDNESDAY AS EASTERN PACIFIC RIDGE EXPANDS INTO THE INTERMOUNTAIN WEST. DRY AND WARMER AIR ALOFT AND DECREASING NW FLOW WILL RESULT IN STEEPENING INVERSIONS OVER THE WESTERN VALLEYS AND BASINS ON WEDNESDAY. FORECAST TEMPERATURES CONTINUE TO BE WEIGHTED HEAVILY TOWARD HPC BIAS-CORRECTED GUIDANCE WHICH IS SLOWEST TO ERODE THESE INVERSIONS. UPPER RIDGE FORECAST TO REMAIN ALONG WEST COAST THROUGH THE REST OF THIS PERIOD WITH BROAD TROUGH DOWNSTREAM EAST OF THE ROCKIES. THIS WILL LEAVE WYOMING IN DRY NW FLOW. GFS IS MORE AGGRESSIVE WITH CLIPPERS IN THIS FLOW PUSHING ARCTIC FRONTAL BOUNDARY FURTHER WEST ACROSS THE NORTHERN HIGH PLAINS WHILE ECMWF KEEPS THIS BOUNDARY WELL TO THE NORTH AND EAST. GFS HAS BEEN TRENDING FURTHER NORTH WITH THE FRONTAL BOUNDARY...AND FORECAST IS WEIGHTED TOWARD MORE CONSISTENT ECMWF. THUS...DRY AND WARMER WEATHER ON TAP FOR THE MOUNTAINS AND WIND CORRIDORS WHILE COLDER AIR REMAINS TRAPPED IN THE SNOW-COVERED WESTERN VALLEYS AND CENTRAL BASINS WEDNESDAY THROUGH SATURDAY. && .AVIATION.../18Z ISSUANCE/ LINGERING SNOWFALL WILL KEEP PERIODS OF MVFR CONDITIONS AT THE MAJORITY OF AREA TERMINALS INTO THE AFTERNOON HOURS. CONDITIONS EXPECTED TO IMPROVE AFTER 20Z FOR AREAS EAST OF THE DIVIDE. ANOTHER WEAK SYSTEM WILL IMPACT WESTERN WYOMING LEAVING LIGHT SNOWFALL OVER THE MOUNTAINS. VCSH HAS BEEN INCLUDED AT SOME TERMINALS WEST OF THE DIVIDE TO ACCOUNT FOR ANY DEVELOPMENT WITH THIS DISTURBANCE. CLOUD COVER IS EXPECTED TO REMAIN FAIRLY WIDESPREAD THROUGH THE NIGHT WHICH WILL ATTEMPT TO STOP ANY FOG DEVELOPMENT. && .FIRE WEATHER... THE HIGHER MOUNTAINS OF THE NORTH AND WEST WILL CONTINUE TO HAVE AREAS OF LIGHT SNOW THROUGH THE WEEKEND WITH A LINGERING TROUGH. THE LOWER ELEVATIONS WILL BECOME VERY COLD AND AREAS OF FLURRIES WILL BE POSSIBLE WITH A GENERAL TREND FOR DECREASING CLOUDS. WINDS WILL TAPER OFF AS WELL THROUGH THE NIGHT...ESPECIALLY IN THE LOWER ELEVATIONS AS TEMPERATURE INVERSIONS BEGIN TO SET UP. RELATIVE HUMIDITY WILL BE ELEVATED OVER THE WIDESPREAD FRESH SNOWFALL AND UNDER THE INVERSIONS WHERE THE COLDEST AIR WILL BE. LOW MIXING HEIGHTS AND POOR SMOKE DISPERSAL WILL EXTEND THROUGH THE WEEKEND. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...HATTINGS LONG TERM...AEM AVIATION...BRANHAM FIRE WEATHER...HATTINGS