FXUS63 KTOP 020558 AFDTOP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TOPEKA KS 1158 PM CST MON DEC 1 2008 .UPDATE... UPDATED FOR THE 06Z TAFS. && .DISCUSSION... SEE PREVIOUS FORECAST DISCUSSION. && .AVIATION... FOR THE 06Z TAFS...VFR CONDITIONS ARE EXPECTED OVER THE NEXT 24 HRS. SOUTHERLY WINDS WILL BECOME GUSTY THIS MORNING AS SFC HIGH PRESSURE CONTINUES OFF TO THE EAST OF THE FORECAST AREA. VFR CLOUDS WILL BE ON THE INCREASE TODAY...BUT ONLY MID TO HIGH LEVEL CLOUDS ARE EXPECTED. A COLD FRONT IS EXPECTED TO MOVE THROUGH THE FORECAST AREA TOMORROW NIGHT...BUT AFTER THE VALID TIME FOR THIS FORECAST. CAVANAUGH && .PREV DISCUSSION... /ISSUED 735 PM CST MON DEC 1 2008/ UPDATE... UPDATED FOR THE 00Z TAFS. DISCUSSION... SEE PREVIOUS FORECAST DISCUSSION. AVIATION... FOR THE 00Z TAFS...VFR CONDITIONS ARE EXPECTED OVER THE NEXT 24 HRS. SFC WINDS ARE EXPECTED TO BACK AROUND FROM THE WEST TO THE SOUTHWEST BY MIDNIGHT AS HIGH PRESSURE MOVES EAST OF THE FORECAST AREA. OTHERWISE WINDS ARE EXPECTED TO REMAIN UP SUFFICIENTLY TO PREVENT RADIATIONAL FOG DEVELOPMENT OVER TAF SITES TONIGHT. CAVANAUGH PREV DISCUSSION... /ISSUED 315 PM CST MON DEC 1 2008/ DISCUSSION... MORNING UPPER AIR DATA AND RECENT WATER VAPOR IMAGERY DEPICT A TRANSITION IN THE UPPER FLOW OCCURRING WITH 60-100M 12 HOUR 500MB HEIGHT RISES IN NORTHERN SECTIONS OF THE PLAINS AND ROCKIES AT 12Z...WITH SHORTWAVE ENERGY MOVING EAST INTO THE WESTERN CANADIAN PROVINCES AND PACIFIC NORTHWEST THIS AFTERNOON. HIGH CLOUDS AHEAD OF THESE WESTERN WAVES WERE SPILLING OVER THE ROCKIES AND INTO THE HIGH PLAINS BY 20Z. MID TO LOW LEVEL TEMPS WERE RATHER COOL AT KTOP...BUT WERE AROUND 20C WARMER IN THE NORTHERN ROCKIES. RESIDUAL LOW/MID LEVEL MOISTURE HAS SLOWLY DIMINISHED TODAY AS THE WARM AIR BEGINS TO MOVE IN...BUT MID AFTERNOON TEMPS WERE STILL STRUGGLING TO BREACH THE MIDDLE 30S IN MUCH OF THE LOCAL AREA. THE UPPER HEIGHT RISES ARE PROGGED TO TRANSLATE INTO THE CENTRAL PLAINS TONIGHT AS HIGH CLOUDS FILTER IN. STRONG WARM AIR ADVECTION WILL OCCUR IN THE MID LEVELS...INCLUDING AROUND 12C WARMING AT 850MB. WEAK SURFACE RIDGING WILL MOVE ACROSS THE CWA AND WITH A FAIR AMOUNT OF CLEAR SKIES ALLOW TEMPS TO FALL QUICKLY IN THE EVENING. INCREASING MIXING OF THE WARMING AIR ALOFT MAY KEEP TEMPERATURE FALLS IN CHECK AFTER MIDNIGHT...WITH WARMING GETTING A JUMP ON PROVIDING A MUCH WARMER BUT STILL BREEZY LATE FALL DAY FOR TUESDAY. JUST HOW WARM IS SOMEWHAT IN QUESTION WITH MOS VALUES SEEMS TO BE ON THE UPPER END OF WHAT DAYTIME MIXING CAN BRING TO THE GROUND IN THE STRONG INVERSION AND SOME AMOUNT OF CIRRUS TO OFFSET LOW SUN ANGLE INSOLATION. HAVE KEPT VALUES NEAR THOSE OF THE PREVIOUS FORECAST. 65 SOME ACCUMULATING SNOWS ARE POSSIBLE LATE TUESDAY NIGHT AND WEDNESDAY AS THE NEXT COLD FRONT MOVES THROUGH THE FORECAST AREA. RAISED POPS WITH THE HIGHER VALUES AROUND 50 PERCENT ACROSS THE NORTHEAST WHERE MOISTURE AND FORCING ARE MOST LIKELY TO MATCH UP. MODELS HAVE BEEN MOST CONSISTENT IN SHOWING A BAND OF SNOW DEVELOPING ACROSS THIS AREA. THE MAIN REASONING FOR RAISING POPS IS TO ACCOUNT FOR THE STRONG FRONTOGENESIS IN THE MID LEVELS BEHIND THE FRONT. MOISTURE CONTINUES TO BE THE LIMITING FACTOR WITH THIS FRONT...BUT THINK FORCING WILL BE STRONG ENOUGH WITH A NARROW AXIS OF MOISTURE FOR SNOW TO FALL. BECAUSE OF THE LIMITED MOISTURE AND PROGRESSIVE NATURE OF THE FRONT...SNOW AMOUNTS SHOULD BE RELATIVELY LIGHT. HAVE AROUND AN INCH ACROSS THE NORTHEAST WHERE THERE IS A GREATER POTENTIAL FOR AN ORGANIZED SNOW AND TO SET UP. MODELS BRING THE COLD FRONT THROUGH LATE TUESDAY NIGHT WITH STRONG CAA OCCURRING ON THE NORTH WINDS. THEREFORE TEMPS WILL NOT SHOW MUCH OF A DIURNAL WARM UP IN THE AFTERNOON. TEMPS WILL LIKELY BE NEARLY STEADY ACROSS EAST CENTRAL KS WHERE CLOUD COVER WILL LAST LONGER. ALSO WITH THE PRECIP WELL BEHIND THE FRONT AND THE STRONG CAA BRINGING TEMPS DOWN...HAVE GONE WITH ALL SNOW IN THE WEATHER GRIDS. THERE COULD BE A BRIEF PERIOD OF MIXED PRECIP AS PRECIP INITIATES...HOWEVER THIS WILL LIKELY BE SHORT LIVED AS FORECAST SOUNDINGS QUICKLY COOL BELOW FREEZING ONCE PRECIP DOES BEGIN. DO NOT EXPECT A BIG WARM UP THROUGH THE REMAINDER OF THE WEEK AS NORTHWEST FLOW BRINGS PERIODIC COLD FRONTS THROUGH THE FORECAST AREA. ANOTHER REINFORCING SURGE OF COOL AIR IS LIKELY ON THURSDAY AS A SHORTWAVE DIVED FROM THE NORTHERN HIGH PLAINS INTO THE TN VALLEY. MODELS INDICATE SOME ISENTROPIC UPGLIDE AND FRONTOGENESIS WITH THIS SHORTWAVE THURSDAY NIGHT. THOUGH MOISTURE AGAIN IS NOT OVERLY IMPRESSIVE...THINK FORCING COULD BE STRONG ENOUGH TO AT LEAST GET SOME FLURRIES TO FLY ACROSS CENTRAL KS...AND HAVE ADDED THIS TO THE FORECAST. OTHERWISE WILL NOT MENTION ANY PRECIP THOUGH SUNDAY. THE ECMWF AND GFS ENSEMBLE MEAN START TO SHOW A TRANSITION FROM NORTHWEST FLOW TO A LONGWAVE TROUGH SETTING UP OVER THE ROCKIES EARLY NEXT WEEK. ECMWF BRINGS ANOTHER COLD FRONT THROUGH ON MONDAY AS A SHORTWAVE DIVES SOUTH FROM THE PACIFIC NORTHWEST INTO THE FOUR CORNERS REGION. BECAUSE OF THIS ADDED SLIGHT CHANCE POPS TO MONDAY. WOLTERS AVIATION... LINGERING LOW LEVEL MOISTURE WILL LIKELY KEEP SOME AMOUNT OF CLOUD JUST ABOVE MVFR HEIGHTS THIS AFTERNOON AS DIURNAL HEATING HELPS RAISE CLOUD LEVELS. NORTHWEST WINDS WILL SLOWLY SLACKEN AND BACK DURING THE AFTERNOON...WITH SOUTHWEST WINDS INCREASING OVERNIGHT INTO TUESDAY MORNING. THE DEGREE TO WHICH THIS OCCURS COMPARED TO THE INCREASING LOW LEVEL JET WILL NEED TO BE WATCHED AS BREAKS IN THE INVADING CIRRUS MAY ALLOW SURFACE WINDS TO BE QUITE LIGHT...RESULTING IN MINOR LOW LEVEL WIND SHEAR DURING THE LATE NIGHT AND POST DAWN HOURS. 65 && .TOP WATCHES/WARNINGS/ADVISORIES...NONE. && $$ |
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