RSS FeedsIssued by NWS Riverton, WY
000 FXUS65 KRIW 230935 AFDRIW AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RIVERTON WY 235 AM MST MON NOV 23 2009 .SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT A STRONG PACIFIC COLD FRONT PLOWED ACROSS THE CWA EARLIER THIS EVENING LEAVING IN ITS WAKE 2 TO 3 INCHES OF SNOW ACROSS MUCH OF SWEETWATER COUNTY. THE ASSOCIATED TROUGH AXIS WILL TRACK ACROSS THE AREA THIS MORNING ALONG WITH THE ASSOCIATED Q VECTOR FORCING. SOME BOUNDARY LAYER MOISTURE WILL SPILL OVER EAST OF THE DIVIDE BUT MOST OF THIS MOISTURE SHOULD REMAIN NORTH AND EAST OF THE OWL CREEK MTNS THIS MORNING. PRESENTLY...A LARGE AREA OF VIRGA IS EVIDENT ON RADAR EAST OF THE DIVIDE THAT SEEMS TO BE ASSOCIATED WITH THE SOUTHBOUND CANADIAN COLD FRONT AS THE MORE SOUTHERN REFLECTIVITY ELEMENTS ARE MOVING EAST AND THE NORTHERN MOST ELEMENTS ARE MOVING SOUTH CAUSING FRONTAL CONVERGENCE. SOME OF THIS SNOW COULD BE REACHING THE GROUND OVER EASTERN FREMONT COUNTY WHERE SLIGHTLY STRONGER ECHOES ARE BEING DETECTED. THE THREAT OF SNOWFALL SHOULD PERSIST THE LONGEST IN THE CASPER AREA WHERE Q VECTOR FORCING WILL PERSIST THE LONGEST. A SECONDARY SHORTWAVE TROUGH ON THE BACK SIDE OF THE MAIN LONG WAVE TROUGH WILL PUSH SOUTH ACROSS WYOMING TODAY. ISENTROPIC LIFT IN WESTERN WY AHEAD OF THIS NEXT FEATURE SHOULD PROVIDE WESTERN WY WITH A BRIEF PERIOD OF LIGHT SNOW THIS MORNING. WILL KEEP LOW CHANCES OF LIGHT SNOW GOING FOR THE REMAINDER OF THE DAY TODAY MAINLY ACROSS WESTERN WY ALONG WITH LESSER CHANCES IN THE BIG HORN MTNS TO ACCOUNT FOR THIS SECONDARY TROUGH TO MOVE THROUGH WITH DEEP MOISTURE LINGERING ACROSS WESTERN WY TODAY. CLOUDS WILL LINGER FOR MOST OF THE DAY IN THE CASPER AREA TODAY ALONG WITH A POSSIBLE FLURRY AS DEEP MOISTURE WILL LINGER THERE THROUGH LATE THIS AFTERNOON. SIGNIFICANT DRYING WILL TAKE PLACE ELSEWHERE. TONIGHT WILL FEATURE A COLD CLEAR NIGHT WITH SOME BELOW ZERO READINGS IN THE WEST. SHOULD SEE SOME PATCHY FOG EARLY TUESDAY MORNING IN THE FAR WEST VALLEYS ONCE WARM AIR BEGINS TO ADVECT INTO THE AREA ALOFT FROM THE WEST. TUESDAY MORNING WILL FEATURE A TRANSITORY RIDGE BEFORE THE NEXT UPSTREAM TROUGH NOW LOCATED AT 150W OFF THE PACIFIC COAST TRAVELS UP AND OVER THE RIDGE NOW...ALONG THE PACIFIC COAST...AND COMES DIVING SOUTHEAST OUT OF ALBERTA AS AN ALBERTA CLIPPER AND CLIPPING OUT NORTHEAST ZONES BY TUESDAY NIGHT. THE MODELS CONTINUE TO OSCILLATE BETWEEN MISSING OUR CWA ALTOGETHER WITH THIS FEATURE TO AFFECTING NORTHERN WY AND MOST AREAS EAST OF THE DIVIDE AND THIS WILL PROBABLY CONTINUE UNTIL THE TROUGH RIDES OVER THE RIDGE. WILL GO WITH THE IDEA OF GIVING THE BIG HORN MTNS THE HIGHEST CHANCE OF SNOWFALL WITH THIS FEATURE AND WILL UP THE WINDS IN JOHNSON COUNTY TUESDAY NIGHT THROUGH WEDNESDAY. ANOTHER CLEAR CALM NIGHT FOR WEDNESDAY NIGHT IS IN STORE WITH MORE AIR ADVECTING BACK INTO THE AREA ALOFT ONCE AGAIN FOR STRENGTHENING TEMPERATURE INVERSIONS. .LONG TERM...THURSDAY THROUGH MONDAY THE EXTENDED WILL BEGIN WITH A RIDGE OVER THE FORECAST AREA THURSDAY AND THURSDAY NIGHT. THIS WILL RESULT IN DRY CONDITIONS AND ABOVE AVERAGE TEMPERATURES THURSDAY. MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT IN A LONGWAVE TROUGH PUSHING INTO THE WEST COAST THURSDAY NIGHT...AND THEN EAST INTO THE INTERMOUNTAIN WEST/GREAT BASIN FRIDAY. A MAJOR COLD FRONT IS ALSO EXPECTED TO PUSH THROUGH THE FORECAST AREA LATE FRIDAY/FRIDAY NIGHT. HOWEVER...MEDIUM RANGE MODELS ARE HAVING MUCH DIFFICULTY IN DETERMINING WHERE THE BEST ENERGY/SHORTWAVES WILL MOVE ACROSS THE ROCKIES...AND THUS WHERE THE BULK OF THE PRECIP WILL OCCUR. 00Z GFS IS MUCH MORE BULLISH ON DEVELOPING UPSLOPE CONDITIONS SATURDAY/SATURDAY NIGHT WHILE GEM AND ECMWF KEEP THE FLOW MORE NORTHWEST...WITH MUCH LESS PRECIPITATION. HAVING SAID THAT...HAVE INCREASED POPS SLIGHTLY FOR THIS SYSTEM...ESPECIALLY FOR FRIDAY NIGHT WEST...AND THEN EVERYWHERE ON SATURDAY. WILL CONTINUE WITH SLIGHT POPS MOST EVERYWHERE ON SUNDAY...DUE TO THE UNCERTAINTY OF THIS SYSTEM. HAVE COOLED TEMPERATURES DOWN FOR THE WEEKEND...AS ECMWF AND GFS HAVE BEEN CONSISTENT IN BRINGING IN AT LEAST -10 DEG CELSIUS 700MB TEMPS FOR SATURDAY AND SUNDAY...WHICH ROUGHLY TRANSLATES TO AROUND 40 DEGREES FAHRENHEIT AT 5000 FEET IF ATMOSPHERE IS FULLY MIXED. THUS...IF CLOUD COVER AND/OR PRECIPITATION BECOMES MORE APPARENT...THE CURRENT FORECAST MAX TEMPS FOR THIS WEEKEND WILL NEED TO BE LOWERED. && .AVIATION... A WEATHER SYSTEM WILL CONTINUE MOVE THROUGH THE AREA TODAY. SNOW SHOWERS WILL OCCUR OVER THE MOUNTAINS WITH MVFR CONDITIONS AT TIMES ALONG WITH MOUNTAIN OBSCURATION. THE SNOW SHOWERS WILL BE ENDING AROUND 00Z TUE. THE LOWER ELEVATIONS WILL SEE VFR CONDITIONS TODAY INTO THIS EVENING. SOME MVFR CONDITIONS WILL OCCUR IN EAST CENTRAL WY DUE TO SNOW SHOWERS...FROM KBYG TO KCPR...UNTIL 18Z...THEN VFR CONDITIONS WILL PREVAIL THROUGH 00Z TUE. && .FIRE WEATHER... SOME SNOW WILL LINGER MAINLY IN THE CASPER AREA THIS MORNING BEFORE THE PACIFIC WEATHER SYSTEM EXITS TO THE EAST. SOME LIGHT SNOW WILL PERSIST IN WESTERN WYOMING TODAY AS A SECONDARY COLD FRONT PUSHES SOUTH ACROSS THE AREA. HIGH PRESSURE WILL BUILD INTO THE AREA TONIGHT FOR CLEAR AND COLD CONDITIONS ALONG WITH STRONG BASIN AND VALLEY INVERSIONS. DRY WEATHER WILL BE THE RULE THROUGH MID WEEK WITH THE EXCEPTION OF AN ALBERTA CLIPPER AFFECTING MAINLY JOHNSON COUNTY AND THE BIG HORN MTNS WITH A CHANCE OF LIGHT SNOW AND INCREASING NORTH WINDS TUESDAY NIGHT AND WEDNESDAY. STRONG INVERSIONS CAN BE EXPECTED THURSDAY MORNING EAST OF THE DIVIDE AND WEDNESDAY AND THURSDAY MORNINGS WEST OF THE DIVIDE. && .RIW WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...LIPSON LONG TERM...WM AVIATION...AR FIRE WEATHER...LIPSON
