RSS FeedsIssued by NWS Riverton, WY
000 FXUS65 KRIW 241004 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 304 AM MST TUE NOV 24 2009 .SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT NORTHWEST WINDS ARE STILL BLOWING ACROSS THE WIND RIVER BASIN ALONG THE WIND RIVER CORRIDOR. THESE WINDS SHOULD RETREAT NORTHWEST TOWARD CROWHEART AND DUBOIS AS THE NOCTURNAL INVERSION DEEPENS THIS MORNING. WEST WINDS IN THE CODY FOOTHILLS WILL LIKELY PERSIST TODAY AS THE BUILDING 1038MB SURFACE HIGH BUILDS INTO SOUTHWEST WY KEEPING THE SURFACE GRADIENT IN PLACE FOR AREAS EAST OF THE DIVIDE. WILL KEEP PATCHY FOG IN THE WESTERN VALLEYS AND BASINS FOR THIS MORNING...NOT FORMING UNTIL AFTER 12Z SINCE THE STUBBORN TRAPPED SC DECK IN NW WY STILL HAS TO DISSIPATE AND LOWEST TEMP/DEW POINT DEPRESSIONS WILL NOT BE REALIZED UNTIL SUFFICIENT RADIATIONAL COOLING TAKES PLACE AFTER THE DISSIPATION OF THE STRATEGY DECK. EVEN IF THE LOW CLOUDS DO NOT COMPLETELY CLEAR OUT OVER THE WESTERN VALLEYS...SOME FOG COULD STILL FORM. DJ WAS ALTERNATING BETWEEN FOG AND LOW CLOUDS EARLIER THIS EVENING. ANY FOG THAT FORMS WILL NOT BE WIDESPREAD SINCE THERE IS NOT A SUFFICIENT DRY LAYER ABOVE THE INVERSION. SHOULD SEE SOME BELOW ZERO TEMP READINGS EARLY THIS MORNING IN THE WESTERN VALLEYS AND BASINS WITH FRESH SNOW COVER IN PLACE. THE TROUGH CURRENTLY RIDING UP AND OVER THE RIDGE...THAT WILL BE IN PLACE TODAY...IS NOW OVER ALBERTA AND WILL APPROACH OUR NORTHEAST ZONES AS AN ALBERTA CLIPPER. THE CLIPPER WILL SPREAD MOST OF ITS Q VECTOR FORCING ACROSS THE NORTHERN PLAINS WHICH THE MODELS HAVE BEEN CONSISTENTLY ADVERTISING DURING THE LAST COUPLE OF DAYS SO WILL TREAT THIS SYSTEM AS ONE THAT GIVES OUR NORTHEAST ZONES A GLANCING BLOW IN THE FORM OF INCREASING NNW WIND AND SPOTTY LIGHT SNOW ACROSS JOHNSON COUNTY AND THE BIG HORN MTNS FROM ABOUT 06Z WEDNESDAY THROUGH 18Z WED. SOME MOISTURE IS INDICATED FROM 700 TO 500MB AS WELL AS AT THE BOUNDARY LEVEL WITH THIS FEATURE BUT DYNAMICS ARE LACKING. CONSIDERABLE LOW CLOUDS ARE A SURE BET. THE WIND RIVER/BIG HORN BASINS WILL EXPERIENCE A TEMPORARY WEAKENING OF THE INVERSION AS COLDER AIR ALOFT PASSES BY OVERHEAD AND TO THE NORTHEAST. WESTERN BASINS AND VALLEYS WILL KEEP AN INVERSION DAY AND NIGHT THROUGH AT LEAST THURSDAY NIGHT WITH CENTRAL BASINS EXPERIENCING A REINFORCING INVERSION BY WEDNESDAY NIGHT. ONCE THE ALBERTA CLIPPER EXITS TO THE EAST...THE FOOTHILLS/MOUNTAINS AND THE SOUTHERN WIND CORRIDOR WILL WARM UP NICELY FOR THANKSGIVING DAY AS SUFFICIENT MIXING FROM SOUTHWEST WINDS COINCIDENT WITH LEE SIDE SURFACE TROUGH WILL WARM AREAS UP LIKE CPR WITH HIGHS IN THE 50S. THE GFS INDICATES H7 TEMPS TO WARM TO AROUND 5C BY THURSDAY EVE. BASINS AND VALLEYS ON THU WILL REMAIN TRAPPED. .LONG TERM...FRIDAY THROUGH TUESDAY A TROUGH WILL PUSH ACROSS THE WEST INTO THE ROCKIES FRIDAY/FRIDAY NIGHT...REMAINING OVER THE AREA THROUGH THE HOLIDAY WEEKEND. MEDIUM RANGE MODELS ARE SHOWING THE BULK OF THE ENERGY WITH THE INITIAL PUSH OF THE LONGWAVE TROUGH...REMAINING WEST/NORTHWEST OF THE AREA. MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT IN SOME DECENT ENERGY ON THE BACKSIDE OF THIS TROUGH DIGGING FRIDAY NIGHT THROUGH SATURDAY NIGHT INTO THE FOUR CORNERS REGION/DESERT SOUTHWEST. THE 00Z ECMWF DIGS IT FARTHER WEST/SOUTHWEST THAN THE GFS. BY SATURDAY NIGHT...THE LONGWAVE TROUGH IS PROJECTED BY THE MEDIUM RANGE MODELS TO BE EFFECTIVELY SPLIT...WITH A CIRCULATION OVER THE SOUTHERN ROCKIES...AND ANOTHER ONE OVER THE NORTHERN HIGH PLAINS. THIS LONGWAVE TROUGH IS THEN PROJECTED TO SLOWLY EJECT EAST SUNDAY AND MONDAY...WITH THE SOUTHERN PART BECOMING CUT OFF OVER THE SOUTHERN PLAINS. BEST CHANCES FOR SNOW WITH THIS TROUGH SHOULD BE FRIDAY NIGHT AND SATURDAY OVER THE WEST...AS THE ENERGY ON THE BACKSIDE OF THE TROUGH BEGINS TO DIG. DEPENDING UPON THE EXACT TRACK WITH THE DIGGING ENERGY...IT COULD ALLOW FOR SOME UPSLOPE CONDITIONS TO DEVELOP EAST OF THE DIVIDE SATURDAY/SATURDAY NIGHT. CURRENTLY...IT DOES NOT APPEAR ANY SIGNIFICANT SNOWFALL IS EXPECTED OVER THE FORECAST AREA WITH THIS SYSTEM...BUT WILL OF COURSE NEED TO BE WATCHED. ALTHOUGH PRECIPITATION REMAINS UNCERTAIN WITH THIS SYSTEM...THE COLD FRONT PUSHING ACROSS THE AREA LATE FRIDAY AND FRIDAY NIGHT IS NOT. DRY CONDITIONS ARE EXPECTED MONDAY...WITH A RIDGE OVER THE AREA. HOWEVER THIS WILL BE SHORTLIVED...AS MEDIUM RANGE MODELS SHOW A TROUGH PUSHING SOUTHEAST OUT OF BRITISH COLUMBIA MONDAY NIGHT/TUESDAY...WITH THE GFS SLOWER THAN THE ECMWF. THE WARMEST TEMPERATURES IN THE EXTENDED WILL BE FRIDAY...AHEAD OF THE COLD FRONT PUSHING ACROSS THE AREA LATE FRIDAY/FRIDAY NIGHT. TEMPERATURES SATURDAY AND SUNDAY SHOULD BE SLIGHTLY BELOW AVERAGE...WITH A WARMING TREND MONDAY AND TUESDAY. WENT WITH THE SLOWER SOLUTION OF THE ECMWF WITH NEXT WEEKS TROUGH...AND THUS WITH WARMER TEMPS THAN MEX MOS. && .AVIATION... VFR CONDITIONS TO PREVAIL AT ALL TERMINALS THROUGH TUESDAY WITH THE EXCEPTION OF OCCASIONAL MVFR CEILINGS AT KJAC. BOUNDARY LAYER MOISTURE PREVALENT ENOUGH TO GENERATE LOW CLOUDS IN THE FAR WEST VALLEYS. SHOULD SEE KJAC CEILING IMPROVE TO VFR BETWEEN 14Z AND 17Z TUESDAY. ALSO EXPECT FREQUENT MOUNTAIN TOP OBSCURATIONS THROUGH THE FORECAST PERIOD ACROSS NORTHWEST WYOMING IN PESKY NORTHWEST FLOW. GUSTY WIND AT KCOD...KRKS...AND KRIW WILL DECREASE EARLY TUESDAY MORNING. MEANWHILE...SURFACE GRADIENT WILL BECOME MORE FAVORABLE FOR GUSTY SOUTHWEST WIND AT KCPR. INTRUSION OF SURFACE HIGH PRESSURE BY MIDDAY TUESDAY WILL BEGIN TO RELAX THIS GRADIENT BY 00Z/WEDNESDAY. THIS SHOULD BRING DECREASING WIND TO KCPR BY SUNSET TUESDAY. NEXT UPPER LEVEL SYSTEM WILL QUICKLY SKIRT AREAS EAST OF THE DIVIDE TUESDAY EVENING. FOR TERMINAL SITES...EXPECT ONLY INCREASING MID-LEVEL CLOUDS WITH NO PRECIPITATION IN ASSOCIATION WITH THIS CLIPPER SYSTEM. && .FIRE WEATHER... STRONG VALLEY AND BASIN INVERSIONS WILL BE IN PLACE THROUGH THURSDAY NIGHT. THE ONE MAIN INTERRUPTION TO THIS PATTERN WILL BE AN ALBERTA CLIPPER THAT WILL AFFECT MAINLY THE BIG HORN MOUNTAINS AND THE LOWER ELEVATIONS OF JOHNSON COUNTY TUESDAY NIGHT AND WEDNESDAY MORNING IN THE FORM OF SPOTTY LIGHT SNOW...CONSIDERABLE LOW CLOUDS AND INCREASED NORTH NORTHWEST WINDS WITH THE ADJACENT WIND RIVER AND BIG HORN BASINS EXPERIENCING A PARTIAL WEAKENING OF THE INVERSION. THE HIGHER ELEVATIONS AND AREAS FROM THE GREEN MOUNTAINS TO CASPER WILL WARM UP INTO THE 50S ON THANKSGIVING DAY. && .RIW WATCHES/WARNINGS/ADVISORIES...NONE. && $$ SHORT TERM...LIPSON LONG TERM...WM AVIATION...CNJ FIRE WEATHER...LIPSON
