000 FXUS65 KCYS 231602 AFDCYS AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE CHEYENNE WY 902 AM MST MON NOV 23 2009 .UPDATE...CURRENT RADAR LOOP SHOWS SCATTERED SNOW SHOWERS...MAINLY ALONG AND SOUTH OF I80 THIS MORNING...STARTING TO DIMINISH TO ISOLATED SNOW SHOWERS OR FLURRIES AS A COLD FRONT PUSHES SOUTHEAST OF THE REGION. SNOW ACCUMULATIONS HAVE BEEN UP TO 1 INCH SO FAR THIS MORNING WITH 4 TO 6 INCHES REPORTED IN THE MOUNTAINS. FORECAST LOOKS ON TRACK...CONDITIONS EXPECTED TO IMPROVE BY THIS AFTERNOON WITH COLDER THAN NORMAL TEMPERATURES THROUGH TONIGHT. && .PREV DISCUSSION... /ISSUED 330 AM MST MON NOV 23 2009/ SHORT TERM...TODAY THROUGH TUESDAY NIGHT... LIGHT SNOW WAS FALLING OVER THE SNOWY RANGE AND AT TIMES OVER THE REST OF CARBON AND ALBANY COUNTIES. EARLIER THIS MORNING... KRWL HAD AN INCH OF NEW SNOW AND KSAA ABOUT ONE HALF INCH. THE RETURNS ON THE KCYS RADAR HAVE BEEN SLOWLY INCREASING SINCE 05Z. HOWEVER...AS OF 09Z THE INTENSITY AND COVERAGE OF THE LIGHT SNOW ON AREA RADARS WAS NOT GREAT. BAROCLINIC BAND ON SATELLITE IMAGERY WAS BECOMING LESS ORGANZIED EARLY THIS MORNING AS WELL. THE UPPER LOW EARLY THIS MORNING WAS STILL OVER SOUTH CENTRAL MONTANA WITH MOST OF THE ENERGY ACROSS SOUTHERN WYOMING ASSOCIATED WITH THE 300 MB JET. THE ASSOCIATED WAS LOCATED FROM NEAR KLSK TO BETWEEN KLAR AND KCYS AS OF 09Z. STILL A LARGE AREA OF 2 TO 3 MB THREE HOURLY SURFACE RISES BEHIND THE FRONT AT THAT TIME. THE FRONT SHOULD MOVE THROUGH THE REST OF THE CWA BY 14Z. MODELS DEVELOP THE MID AND UPPER LEVEL LOW OVER NORTHWEST KANSAS BY 00Z WITH THE SURFACE LOW OVER EASTERN KANSAS. WITH THAT MOVEMENT AND LIFT FROM THE 300 MB JET...MID LEVEL FRONTOGENESIS AND SURFACE FORCING BELIEVE THAT LIGHT SNOW OR FLURRIES WILL SPREAD OVER MUCH OF THE CWA BY MID MORNING. BASED ON CURRENT RADAR AND SATELLITE TRENDS HAVE LOWERED THE AMOUNTS TO LESS THAN AN ADDITIONAL INCH THROUGH THE MORNING. LARGER AMOUNTS STILL EXPECTED IN THE SNOWY RANGE WHERE OROGRAPHICS WILL ENHANCE THE SNOWFALL. THE REST OF TODAY WILL BE WINDY AND COOLER WITH SOME SNOW SHOWERS. THE LAPSE RATES ARE STILL EXPECTED TO STEEPEN WITH THE COLD TEMPERATURES ALOFT. MID LEVEL CONVERGENT AREA THROUGH THE AFTERNOON WOULD FAVOR BANDS OF SNOW SHOWERS BETWEEN KEAN AND KIBM AND OUTSIDE OF THE MOUNTAINS HAVE THE HIGHEST POPS IN THAT AREA. HEIGHTS ALOFT RISE OVER THE REGION TONIGHT AND TUESDAY AS THE STORM SYSTEM MOVES FURTHER EAST ON THE PLAINS. SURFACE HIGH PRESSURE WILL ALSO BE OVER THE AREA...CENTERED OVER WESTERN WYOMING. THE RESULT SHOULD BE DRY AND COOL CONDITIONS THROUGH THAT TIME AS WELL AS A MINIMUM OF CLOUD COVER. MODELS ARE ALL SIMILAR IN DEPICTING A SHORTWAVE TROUGH MOVING INTO THE NORTHERN PLAINS TUESDAY NIGHT. THE FEATURE WILL PUSH A SHALLOW COLD FRONT INTO THE EAST PART OF THE CWA AFTER 06Z WEDNESDAY. AT THIS TIME HAVE PLACED THE FRONT FROM KPBF TO KDGW BY 12Z WEDNESDAY. HAVE ADJUSTED THE WINDS TO MORE NORTHERLY BEHIND THE FRONT. THE GFS AND ECMWF DEVLOP LIGHT SNOW OR FLURRIES BEHIND THE FRON THE IN THE NORTHEAST THIRD OF THE CWA AFTER 06Z WEDNESDAY. FOR NOW HAVE BUMPED UP POPS A BIT FOR LATER TUESDAY NIGHT IN THAT PART OF THE CWA. LONG TERM...WEDNESDAY THROUGH SUNDAY PREFERRED THE ECMWF IN THE EXTENDED PERIOD...WHICH SEEMS THE MOST CONSISTENT MODEL. THE GFS AND ECMWF ARE SIMILAR EARLY ON...BUT THEN BEGIN TO DIFFER BY FRIDAY EVENING. THE 00Z GFS IS SLOWER AND DEEPER WITH THE UPPER TROUGH MOVING ACROSS THE ROCKIES AND INTO THE PLAINS THAN THE ECMWF AND ALSO ITS PREVIOUS RUN. NW CYCLONIC FLOW WILL BE OVER THE CWA ON WED BETWEEN AN UPPER RIDGE OVER THE WRN U.S. AND AN UPPER LOW MOVING INTO THE CENTRAL MISSISSIPPI VALLEY. SOME THICKER CLOUDS WILL OCCUR OVER THE NE PORTION OF THE CWA DURING THE DAY...BUT WILL DECREASE TOWARDS EVENING. AN UPPER RIDGE WILL BE OVER THE FORECAST AREA ON THANKSGIVING DAY RESULTING IN DRY AND VERY MILD CONDITIONS. SW FLOW WILL DEVELOP ALOFT ON BLACK FRIDAY AS THE UPPER RIDGE AXIS MOVES EAST AND AN UPPER TROUGH MOVES OVER THE CENTRAL AND SOUTHERN ROCKIES AND DEEPENS. VERY MILD CONDITIONS WILL CONTINUE ACROSS THE AREA FRIDAY...BUT THEN A COLD FRONT WILL MOVE ACROSS THE CWA LATE FRI NIGHT/EARLY SAT WHICH WILL COOL TEMPS SIGNIFICANTLY FOR SAT AND SUN. THE UPPER TROUGH WILL ALSO MOVE ACROSS THE CWA ON SAT. NOT VERY MUCH MOISTURE IS ASSOCIATED WITH THIS SYSTEM...SO LEFT VERY LOW POPS IN THE FORECAST. SEEMS EL NINO MAY BE STARTING TO INFLUENCE THE WEATHER PATTERNS OVER THE FORECAST AREA. THE FLOW APPEARS TO SPLIT SAT NIGHT PER ECMWF WITH NORTH UPPER FLOW OVER THE CWA THE RESULT ON SUN. AN UPPER LOW THEN DEVELOPS IN THE SOUTHERN PORTION OF THE SPLIT...OVER THE DESERT SW. HIGH TEMPERATURES WILL BE AROUND NORMAL FOR WED...10 TO 15 DEGREES ABOVE NORMAL FOR THANKSGIVING AND BLACK FRIDAY...AROUND NORMAL SAT...AND 5 TO 8 DEGREES BELOW NORMAL FOR SUN. AVIATION... THE STORM SYSTEM MOVING ACROSS THE CENTRAL ROCKIES TODAY WILL PRODUCE AT LEAST PERIODS OF MVFR CEILINGS AND VISIBILITIES IN SNOW OVER MUCH OF THE CWA. THE SNOWY RANGE WILL BE OBSCURED FOR MOST OF THE DAY. IN ADDITION...NORTHERLY SURFACE WINDS WILL GUST AS HIGH AS 35 KNOTS OVER THE EAST PART OF THE CWA TODAY. ICING WILL BE A CONCERN OVER THE CWA TODAY ESPECIALLY BETWEEN 8000 FEET MSL AND 12000 FEET MSL. VFR CONDITIONS WILL RETURN TO THE CWA THIS EVENING AS THE STORM SYSTEM MOVES ONTO THE PLAINS. WINDS WILL ALSO GRADUALLY DECREASE EARLY TONIGHT. A SHALLOW SURFACE COLD FRONT WILL MOVE OVER THE EAST PART OF THE CWA LATER TUESDAY NIGHT AND MAY PRODUCE MVFR OR IFR CEILINGS BEHIND THE FRONT AS WELL AS SOME FLURRIES. FIRE WEATHER... FIRE WEATHER CONCERNS WILL BE MINIMAL INTO THE MID PART OF THE WEEK. COOL TEMPERATURES AND HIGHER RELATIVE HUMIDITIES WILL PERSIST THROUGH THAT TIME ALONG WITH SOME LIGHT SNOW TODAY. NORTHERLY WINDS WILL GUST AS HIGH AS 40 MPH OVER MUCH OF THE AREA TODAY. THE WARMEST AND DRIEST DAYS THIS WEEK WILL BE THANKSGIVING DAY AND FRIDAY. && .CYS WATCHES/WARNINGS/ADVISORIES... WY...NONE. NE...NONE. && $$ SHORT TERM/AVIATION... LONG TERM...