Issued by NWS Cheyenne, WY
000 FXUS65 KCYS 131958 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 230 PM MDT WED MAY 13 2009 .SHORT TERM...TONIGHT THROUGH FRIDAY... WINDS HAVE BEEN SLOWLY DIMINISHING OVER THE WYOMING PART OF THE CWA EARLY THIS AFTERNOON AS THE LOW LEVEL GRADIENTS RELAX. HOWEVER... THE WINDS WILL CONTINUE TO GUST AS HIGH AS 50 MPH THROUGH 00Z ALONG AND EAST OF THE LARAMIE RANGE. MEANWHILE...OVER THE PANHANDLE THE WINDS WILL CONTINUE TO STRONG INTO THE EARLY EVENING HOURS. MOST LOCATIONS IN THAT PART OF THE CWA HAVE HAD GUSTS BETWEEN 45 AND 55 MPH WITH A FEW LOCATIONS REPORTING EVEN STRONGER WINDS. WILL EXTEND THE WIND ADVISORY FOR THE PANHANDLE UNTIL 01Z. SURFACE HIGH PRESSURE WILL MOVE QUICKLY OVER THE CWA AND ONTO THE PLAINS TONIGHT. THE RESULT WILL BE LIGHTER WINDS FOR MUCH OF THE NIGHT AND COOL TEMPERATURES DUE TO THE DRY ATMOSPHERE. SOUTHERLY RETURN FLOW IN THE BOUNDARY LAYER WILL DEVELOP OVER THE CWA AS THE NIGHT GOES ON WITH GUSTY WINDS AFTER 06Z IN THE LARAMIE VALLEY AND POINTS WESTWARD. SOME CIRRUS WILL ALSO SPREAD OVER THE CWA TONIGHT. THURSDAY WILL BE WARMER AND WINDY DUE TO THE SOUTHERLY SURFACE PRESSURE GRADIENT AND WESTERLY FLOW ALOFT. THE LOW LEVEL MOISTURE INCREASES OVER THE EAST PART OF THE CWA THURSDAY AFTERNOON AND THE NAM DEPICTS SOME QPF IN THAT AREA. BUT THE AIR MASS SHOULD BE CAPPED OVER ESPECIALLY THE EAST PART OF THE CWA. FOR NOW WILL LEAVE LOW POPS MAINLY OVER AND NEAR THE SNOWY RANGE THURSDAY AFTERNOON AND EARLY EVENING. THURSDAY NIGHT WILL BE A MUCH MILDER NIGHT AHEAD OF THE NEXT SHORTWAVE TROUGH AND ASSOCIATED PACIFIC COLD FRONT. THE GFS IS SEVERAL HOURS FASTER WITH THOSE FEATURES THAN THE OTHER MODELS AND WILL USE THE SREF FOR TIMING. THE FRONT SHOULD MOVE ACROSS THE CWA LATE THURSDAY AFTERNOON AND EARLY THURSDAY NIGHT. THE SHORTWAVE TROUGH WILL MOVE QUICKLY ACROSS THE NORTHERN AND CENTRAL ROCKIES LATE THURSDAY NIGHT AND FRIDAY MORNING. THE NEW AIR MASS LOOKS TO BE DRY WITH ALL MODELS DEVELOPING VERY LITTLE IN THE WAY OF QPF EVEN WITH BOUNDARY LAYER NORTHERLY WINDS. WILL KEEP LOW POPS OVER THE CWA FOR NOW ON FRIDAY WITH THE COOLER TEMPERATURES BEING THE MAIN RESULT OF THE FRONTAL AND TROUGH PASSAGE. .LONG TERM...FRIDAY NIGHT THROUGH WEDNESDAY... COOLER AND DRIER AIR WILL SPREAD OVER THE CWA FRIDAY NIGHT BEHIND COLD FRONT AND EXPECT ANY PCPN TO HAVE MOVED OUT OF THE CWA AT THAT TIME. MILD AND DRY SATURDAY THEN UPPER RIDGING OVER THE WESTERN CONUS WILL BUILD TOWARD THE REGION SUNDAY INTO EARLY NEXT WEEK RESULTING IN WARM AND CONTINUED DRY WEATHER. CHANGES MAY BEGIN MID PART OF NEXT WEEK AS NEXT UPPER TROUGH MOVES OVER THE WESTERN CONUS AND UPPER FLOW BEGINS TO BACK OVER THE REGION BRINGING A LITTLE COOLER AIR AND PERHAPS SOME CONVECTION THOUGH BETTER CHANCE LOOKS TO BE JUST BEYOND THIS TIME. && .AVIATION... VFR CONDITIONS WILL PREVAIL OVER THE CWA THROUGH FRIDAY. WINDS AND THE ASSOCIATED TURBULENCE WILL BE THE MAIN ELEMENT AFFECTING AVIATION INTERESTS DURING THAT TIME. STRONG WEST OT NORTHWEST WINDS AT THE SURFACE WITH GUSTS TO 45 KNOTS WILL AFFECT THE CWA MAINLY ALONG AND EAST OF THE LARAMIE RANGE THROUGH 01Z. IN ADDITION... MOUNTAIN WAVE ACTIVITY CAN BE EXPECTED TO CONTINUE THROUGH THAT TIME TO THE LEE OF THE SNOWY AND LARAMIE RANGES. SOUTHERLY SURFACE WINDS INCREASE LATE TONIGHT AND THURSDAY MORNING OVER THE CWA WITH GUSTS TO 35 KNOTS LIKELY FOR MUCH OF THURSDAY. A COLD FRONT MOVES ACROSS THE CWA LATE THURSDAY AFTERNOON THROUGH FRIDAY MORNING AND WILL SHIFT THE WINDS TO MORE NORTHERLY. SOME SHOWERS CAN ALSO BE EXPECTED ON FRIDAY BEHIND THE FRONT WITH CLOUD BASES GNERALLY BETWEEN 5 AND 8 THOUSAND FEET AGL. && .FIRE WEATHER... STRONG NORTHWEST WINDS WILL CONTINUE OVER THE CWA THROUGH THE EARLY EVENING. EVEN WITH THE COOLER TEMPERATURES...THE ATMSOPHERE IS VERY DRY WITH RELATIVE HUMIDITIES AS OF 1930Z BETWEEN 10 AND 20 PERCENT. WINDS WILL DECREASE AND THE RELATIVE HUMIDITY WILL INCREASE TONIGHT...HOWEVER RECOVERY WILL BE POOR WITH VALUES IN THE WEST PART OF THE CWA ONLY BETWEEN 40 AND 50 PERCENT BY SUNRISE. SOUTHERLY WINDS WILL INCREASE OVER THE CWA ON THURSDAY WITH GUSTS UP TO 40 MPH. THOSE SAME SOUTH WINDS WILL HELP INCREASE THE LOW LEVEL MOISTURE AND THE MINIMUM RELATIVE HUMIDITY CALUES SHOULD BE BETWEEN 18 AND 24 PERCENT IN THE AFTERNOON. A COLD FRONT WILL MOVE ACROSS THE REGION LATE THURSDAY AFTERNOON AND EARLY THURSDAY NIGHT. THE FRONT WILL SHIFT THE WINDS TO MORE NORTHERLY AND WILL BRING IN ANOTHER COOLER AIR MASS FOR FRIDAY. SOME SHOWERS ARE POSSIBLE ON FRIDAY BEHIND THE FRONT...BUT ANY RAINFALL AMOUNTS WILL BE VERY LIGHT. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...WIND ADVISORY UNTIL 7 PM WEDNESDAY FOR NEZ001-NEZ002-NEZ003- NEZ019-NEZ020-NEZ021-NEZ054-NEZ055. && $$ WEILAND/EMANUEL
