Issued by NWS Omaha/Valley, NE
000 FXUS63 KOAX 222108 AFDOAX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE OMAHA/VALLEY NE 308 PM CST SUN NOV 22 2009 .SHORT TERM...TONIGHT THROUGH WEDNESDAY SERIES OF SYSTEMS TO AFFECT THE REGION OVER THE NEXT SEVERAL DAYS ARE NOW EVIDENT IN THE CONUS. SUBJECTIVE 12Z UPPER AIR ANALYSIS INDICATES UPPER TROUGH EXTENDING FROM NRN AB/SASK THROUGH THE MT/DAKOTAS BORDER AND TOWARD SERN NM. STRONGEST 500MB HT FALLS AHEAD OF THAT TROUGH WERE CENTERED IN NRN MB...AT 120M. UPPER LOW WAS ALSO DIGGING ASHORE IN THE PAC NW...WITH 500MB HT FALLS OF 150MBA LONG THE COAST AND 1.5PVU ANALYSIS INDICATING SYSTEM ALREADY REACHING ID AT 19Z. 850MB LOW WAS CENTERED IN NRN MB/SASK...WITH SECONDARY 850MB LOW IN WRN KS AND COLD FRONT EXTENDING BETWEEN...ALONG WITH MOISTURE POOLING IN ERN NEB AHEAD OF THE FRONT. MOISTURE/FORCING ARE ENOUGH FOR A FEW SPRINKLES/LIGHT SHOWERS IN ERN NEB...WITH GREATER COVERAGE FURTHER E IN IA. SFC LOW AT 19Z WAS CENTERED IN S CNTRL KS...WITH TROUGH AXIS EXTENING NWD THROUGH CNTRL/NERN NEB TOWARD SWRN MN. MAIN FORECAST CONCERN LIES IN EVOLUTION OF SYSTEMS OVER NEXT FEW DAYS..PARTICULARLY WITH SECOND SYSTEM. POTENTIAL FOR VERY LIGHT PRECIP SHOULD CONTINUE INTO TNGT. HAVE USED DZ MENTION MOST PLACES...WITH A LT RAIN MENTION IN THE E AFTER MIDNIGHT. ALSO MENTIONED PATCHY FOG IN THE WRN HALF OF THE CWA AS WINDS SHOULD DIMINISH SOMEWHAT OVERNIGHT AS FRONT WASHES OUT...WITH AMPLE LOW- LEVEL MOISTURE IN PLACE. KEPT -RA MENTION IN THE N TMRW MRNG AND EVERYWHERE IN THE AFTN...THOUGH THINK POTENTIAL IS SMALL...AS MODELS ARE FAIRLY CONSISTENT IN KEEPING PRECIP GOING ALONG/E OF THE MO RIVER AS WELL AS DEVELOPING AREA OF PRECIP CLOSER TO THE DEEPENING UPPER LOW IN WRN/CNTRL NEB. STILL...COULD VERY WELL BE SANDWICHED BETWEEN THE TWO FOR MUCH OF THE DAY WITH LITTLE PRECIP HERE AT ALL. UPPER LOW IS NOW CONSISTENTLY PROGGED TO CLOSE OFF IN THE SD/NEB HIGH PLAINS BY 00Z TUES...DIGGING INTO SERN NEB/NERN KS BY 12Z TUES AND LIFTING INTO ERN IA BY 00Z WED. 12Z NAM WAS THE SOLE OUTLIER AS A SLOWER/FURTHER W SOLUTION...BUT WITH GOOD AGREEMENT BETWEEN ECMWF/GFS/GEM SOLUTIONS...LEANED TOWARD THE COMPROMISE AMONG THEM. WITH INCREASED CONFIDENCE IN TIMING/TRACK...HAVE INCREASED TO CAT POPS ON MON NT AND LIKELIES ON TUES. TEMPERATURE PROFILE ABOVE THE SFC WOULD SUPPORT A CHANGEOVER TO SNOW ON MON NT AS PRECIP OVERSPREADS CWA...BUT SFC TEMPS ARE SO WARM AND MOISTURE SO HIGH THAT FROZEN PRECIP MAY STRUGGLE TO REACH THE GROUND. STRONGEST LIFT PER MID-LEVEL FGEN DOES NOT ALIGN WELL WITH COLD AIR INTRUSION...WITH COLDER MID-LEVEL TEMPS NOT REALLY REACHING THE CWA UNTIL AFTER 12Z WED AS SHORTWAVE MOVING AROUND THE MAIN UPPER LOW PROVIDES A REINFORCING SHOT OF COLD AIR. DYNAMICAL COOLING WOULD HELP TURN PROFILE TOWARD SNOW...BUT NOT SURE IT WILL BE ENOUGH. HPC GUIDANCE HAS STARTED TO LEAN TOWARD LIGHTER SNOW AMOUNTS WITH SIMILAR REASONING. OVERALL...KEPT SNOW FCST SIMILAR TO GRIDS YESTERDAY...WITH SOME LIGHT ACCUM ON MON NT INTO EARLY TUES. HAVE SLOWED PROGRESS OF SYSTEM OUT ON TUES/TUES NT. KEPT TUES COLD WITH SFC COLD-AIR ADVECTION...AS WELL AS CLOUDS/PRECIP...HOLDING DIURNAL CURVE DOWN /AND POSSIBLY CREATING FALLING TEMPS MUCH OF THE DAY/. .LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY THE LONG TERM PERIOD WILL BE CHARACTERIZED BY RELATIVELY COOL WEATHER THROUGH THE END OF THE WEEK...WITH A POTENTIAL WARMUP FOR THE WEEKEND. DRY WEATHER IS FORECAST THANKSGIVING THROUGH SUNDAY AS WELL. A DEEP LONGWAVE TROUGH IN THE MISSISSIPPI VALLEY AND GREAT LAKES WILL BEGIN THE EXTENDED FORECAST WEDNESDAY NIGHT AND THURSDAY. GFS AND ECMWF ARE CONSISTENT WITH THIS FEATURE...POINTING TO HIGH CONFIDENCE FOR MUCH COOLER TEMPERATURES FOR THE MIDDLE OF THE COUNTRY. BOTH MODELS SUGGEST AN EMBEDDED SHORTWAVE COULD PRODUCE A ROUND OF LIGHT SNOW WEDNESDAY NIGHT JUST TO OUR EAST...WITH FLURRIES POSSIBLE IN EASTERN NEBRASKA. 850 TEMPERATURES ARE FORECAST TO DIP TO -6C BY THURSDAY MORNING...WITH COOL ADVECTION CONTINUING ON THURSDAY. HAVE LOWS IN THE 20S WITH HIGHS BARELY REACHING 40 FOR MOST OF THE CWA...BUT SEVERAL GFS ENSEMBLE MEMBERS WOULD KEEP TEMPS IN THE 30S. COOL WEATHER CONTINUES FRIDAY AS SKIES CLEAR AND WINDS DIMINISH WITH SURFACE HIGH SETTLING OVER THE REGION. COULD SEE TEMPS DROP WELL INTO THE TEENS FRIDAY MORNING...WITH MINIMAL MIXING KEEPING AFTERNOON HIGHS IN THE 30S...ESPECIALLY IN THE EAST. SOUTHERLY WINDS RETURN FRIDAY NIGHT AND SATURDAY ON BACK SIDE OF RETREATING SURFACE HIGH...HELPING TO PUSH TEMPS BACK INTO THE 40S OR LOWER 50S. MODELS DIVERGE SATURDAY AFTERNOON INTO SUNDAY...WITH GFS DROPPING ANOTHER WAVE/LOW INTO THE NORTHERN PLAINS SATURDAY AFTERNOON...WHICH PUSHES A COLD FRONT THROUGH OUR CWA. THE ECMWF SLIDES A SURFACE FRONT THROUGH THE CWA AS WELL...BUT ITS UPPER AIR PATTERN CONTINUES A ZONAL OR SOUTHWEST FLOW. IN SENSIBLE WEATHER TERMS...BOTH SUGGEST COOLER WEATHER ON SUNDAY WITH HIGHS BACK TOWARD NORMAL AND RELATIVELY SMALL CHANCES FOR PRECIPITATION. && .AVIATION... TAF SITES KOFK/KOMA/KLNK 18Z TAFS SFC TROUGH APPEARS TO HAVE STALLED OUT ACROSS CENTRAL NEBRASKA AND IS EXPECTED TO WASH OUT THIS AFTERNOON IN THE VCNTY OF KOFK. FOR KOFK...MVFR CEILINGS AND VISIBILITIES THRU 23/07Z FOLLOWED BY IFR CEILNGS. WILL LIKELY SEE LIFR CEILINGS ON AND OFF THRU THE REMAINDER OF THE FCST PERIOD IN THE VCNTY OF KOFK. FOR KOMA...VFR CONDS UNTIL 23/01Z WHEN VSBY DROPS TO MVFR. CEILINGS EXPECTED TO DROP TO IFR BY 23/10Z AND REMAIN SO THRU THE FCST PD. FOR KLNK...VFR TO MVFR CEILINGS BY 22/20Z AND MVFR VSBYS BY 23/03Z AS WELL AS IFR CEILINGS FOR THE REMAINDER OF THE FCST PD. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...NONE. IA...NONE. && $$ SHORT TERM...MAYES LONG TERM...DERGAN AVIATION...REESE
