Issued by NWS Cheyenne, WY
000 FXUS65 KCYS 122348 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 550 PM MDT TUE MAY 12 2009 .UPDATE... MAJORITY OF STRONG CONVECTION HAS EXITED THE CWA TO THE EAST WITH ONLY WEAKER LIGHT SHOWERS REMAINING. SOME GUSTY WINDS NOTED WITH A FEW OF THESE WEAK ECHOES SO WILL ADD MENTION OF THIS OVER THE PANHANDLE INTO EARLY THIS EVENING. OTHERWISE NO CHANGES. .PREVIOUS DISCUSSION .SHORT TERM...TONIGHT THROUGH WEDNESDAY NIGHT... SOME SHOWERS AND THUNDERSTORMS HAVE FORMED SINCE 1830Z MAINLY TO THE EAST OF THE LARAMIE RANGE. THE STRONGEST STORM AS OF 1930Z WAS NEAR KBFF BUT HAS WEAKENED SOME SINCE 19Z. POTENTIAL STILL EXISTS FOR STRONGER AND EVEN SEVERE STORMS ESPECIALLY ALONG AND EAST OF A LINE FROM KHRS TO KSNY. THAT AREA HAS BEEN RECOVERING FROM THE PASSAGE OF THE SHORTWAVE TROUGH THIS MORNING WITH BOUNDARY LAYER WINDS RETURNING TO MORE SOUTHERLY AND SURFACE DEW POINTS IN THE MID 40S. THE NAM AND SREF CONTINUE TO INDICATE A MORE UNSTABLE AND MOIST ENVIRONMENT THAN THE GFS THROUGH THE EARLY EVENING. THE STRONGER ACTIVITY WILL FOCUS ALONG THE SURFACE LOW PRESSURE TROUGH CURRENTLY EXTENDING BACK INTO THE EAST PART OF THE CWA FROM NORTH CENTRAL NEBRASKA. THE ACTIVITY WILL ALSO MOVE QUICKLY OFF TO THE EAST AND SHOULD BE EAST OF THE CWA BY 03Z. STRONG WIND GUSTS AND HAIL ARE STILL THE MAIN WEATHER THREAT FROM THE STRONGER STORMS. AN ENERGETIC SHORTWAVE TROUGH WILL MOVE ACROSS THE CWA TONIGHT AND WEDNESDAY MORNING WITH THE ASSOCIATED SURFACE COLD FRONT MOVING THROUGH THE ENTIRE CWA BY 06Z. SOME SHOWERS WERE OVER NORTHERN WYOMING EARLY THIS AFTERNOON AND THOSE MAY CLIP THE FAR NORTH PART OF THE CWA INTO WEDNESDAY MORNING. OTHERWISE...WEDNESDAY WILL BE COOLER AND WINDY...BUT GENERALLY DRY OVER THE CWA. THE 700 MB WINDS ARE BETWEEN 40 AND 50 KNOTS UP THROUGH MID AFTERNOON WEDNESDAY AND SO WILL GO AHEAD AND ISSUE A WIND ADVISORY FOR THE WESTERN NEBRASKA PANHANDLE FOR WEDNESDAY. WINDS MAY DIMINISH SOME AFTER 21Z OVER THE CWA AS THE SURFACE PRESSURE GRADIENT RELAXES. THE SURFACE HIGH WILL MOVE OVER THE HIGH PLAINS BY 12Z THURSDAY AND WILL PRODUCE A MOSTLY CLEAR AND COOL NIGHT WEDNESDAY NIGHT. .LONG TERM...THURSDAY THROUGH MONDAY. TEMPERATURES SHOULD REBOUND RATHER QUICKLY AFTER WEDNESDAY WITH HIGHS IN THE LOWER 70S. WESTERLY UPPER LEVEL FLOW WILL REMAIN ACROSS THE AREA ON THURSDAY. THE ECMWF SHOWS A WEAK UPPER LEVEL SHORTWAVE MOVING ACROSS MONTANA ON LATE THURSDAY INTO FRIDAY. TEMPERATURES ON FRIDAY MAY BE SLIGHTLY COOLER COMPARED TO THURSDAY SINCE THE UPPER LEVEL FEATURE WILL NOT MOVE THROUGH SOUTHEASTERLY WYOMING UNTIL THE AFTERNOON. THUS EXPECT HIGHS IN THE UPPER 60S TO AROUND 70. THERE WILL ALSO BE A SLIGHT CHANCE OF THUNDERSTORMS ON FRIDAY AFTERNOON AND INTO THE EARLY EVENING. SATURDAY WILL BE COOLER AFTER THE PASSAGE OF THE WEAK DISTURBANCE WITH HIGHS IN THE MID TO UPPER 60S. THE REMAINDER OF THE WEEKEND AND INTO EARLY NEXT WEEK WILL BE WARM AND MOSTLY DRY AS HIGH PRESSURE BUILDS OVER THE WESTERN UNITED STATES. BY MONDAY...THE TEMPERATURES WILL WARM TO THE LOWER TO MID 70S. WITH THE WARMER TEMPERATURES THROUGH EARLY NEXT WEEK...THERE MAY BE SOME HYDROLOGY CONCERNS PARTICULARLY WITH THE ADDITIONAL SNOWMELT. THERE ARE SOME UNCERTAINTY IN THE FORECAST AFTER MONDAY AS THE ECMWF SHOWS A WEAK BACKDOOR COLD FRONT MOVING ACROSS EASTERN PORTIONS OF WYOMING. && .AVIATION... SOME SHOWERS AND THUNDERSTORMS WILL MOVE EAST OVER THE EAST PART OF THE CWA THROUGH 03Z. BRIEF MVFR CEILINGS AND VISIBILITIES WILL BE ASSOCIATED WITH THE ACTIVITY. OTHERWISE...VFR CONDITIONS CAN BE EXPECTED THROUGH 12Z THURSDAY. STRONG WESTERLY WINDS WILL BE THE MAIN WEATHER CONCERN THROUGH EARLY THIS EVENING AND THEN AGAIN LATE TONIGHT AND WEDNESDAY. AT THE SURFACE WEST WINDS WILL GUST AS HIGH AS 45 KNOTS. WITH THE JET STREAM OVER THE CWA LATE TONIGHT AND WEDNESDAY...MOUNTAIN WAVE ACTIVITY WILL BE POSSIBLE MAINLY ON THE LEE OF THE SNOWY RANGE. && .FIRE WEATHER... THE WARM...DRY AND WINDY CONDITIONS WILL CONTINUE OVER MUCH OF THE SOUTHEAST WYOMING PART OF THE CWA THROUGH THE EARLY EVENING. IN FACT...SOME RELATIVE HUMIDITIES WILL STILL BE IN THE TEENS IN PARTS OF SOUTHEAST WYOMING THROUGH 01Z. THE FUELS OVER THE CWA ARE STILL ON THE GREEN SIDE DUE TO THE TIME OF YEAR AND RECENT PRECIPITATION. A COLD FRONT WILL MOVE ACROSS THE CWA THROUGH 06Z WITH COOLER TEMPERATURES AND RESULTING HIGHER RELATIVE HUMIDITIES EXPECTED FOR TONIGHT AND WEDNESDAY. WEST WINDS WILL STILL GUST AS HIGH AS 50 MPH OVER THE CWA FOR MUCH OF WEDNESDAY...BUT FIRE WEATHER CONCERNS WILL BE LESS THAN THOSE OF TODAY DUE TO THE COOLER TEMPERATURES. && .HYDROLOGY... WATER LEVELS ON THE LITTLE SNAKE RIVER BETWEEN SAVERY AND BAGGS WILL REMAIN HIGH FOR THE NEXT SEVERAL DAYS. THE COOLER TEMPERATURES EXPECTED SHOULD LOWER SNOWMELT RATES AND RUNOFF. FORECASTS FOR THE RIVER GAGE AT DIXON KEEPS THE STAGE A FOOT OR 2 BELOW ACTION STAGE THROUGH THE WEEKEND. WITH THE WARMER WEATHER RETURNING FOR EARLY NEXT WEEK...RIVER LEVELS SHOULD RISE ONCE AGAIN. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...WIND ADVISORY FROM 8 AM WEDNESDAY TO 6 PM WEDNESDAY FOR NEZ001- NEZ002-NEZ003-NEZ019-NEZ020-NEZ021-NEZ054-NEZ055. && $$ SHORT TERM/AVIATION...WEILAND LONG TERM....MG
