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000 FXUS63 KTOP 210552 AFDTOP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TOPEKA KS 1152 PM CST FRI NOV 20 2009 .UPDATE... UPDATE FOR 06Z AVIATION. && .DISCUSSION... SEE PREVIOUS DISCUSSION. && .AVIATION... A FEW ROUNDS OF GROUND FOG ALREADY PASSING OVER TOP ASOS...BUT IFR VISIBILITIES HAVE STRUGGLED TO STAY PERSISTENT. SURFACE RIDGE OVER THE AREA WITH TEMPS WELL BEYOND CROSSOVER LEVELS SUGGEST LIFR FG STILL LIKELY AT ALL SITES OVERNIGHT...AT LEAST INTERMITTENTLY. INCREASING SOUTHERLY WINDS WILL BRING INCREASING MOISTURE ABOVE WOULD KEEP LIMITING CEILINGS IN PLACE FOR MUCH OF SATURDAY...THOUGH DIFFERENCES IN THE LEVEL AND DURATION OF THIS IS IN QUESTION. GIVEN NARROW BAND OF LOWER CEILINGS TO THE SOUTH...WILL BRING THINGS UP TO MVFR LEVELS FOR THE AFTERNOON AND EVENING. 65 && .PREV DISCUSSION... /ISSUED 306 PM CST FRI NOV 20 2009/ DISCUSSION... SHORT TERM (THROUGH SATURDAY)... THE PRIMARY FORECAST CONCERN IN THE SHORT TERM IS THE POSSIBILITY OF DENSE FOG ONCE AGAIN LATE TONIGHT AND INTO SATURDAY MORNING. THE CENTRAL PLAINS ARE CURRENTLY TRAPPED BETWEEN STORM SYSTEMS AS A SIGNIFICANT RAIN MAKER IS IN PLACE OVER TEXAS...THE TROUGH PRODUCING OUR WET WEATHER EARLIER THIS WEEK HAS MOVED OFF TO THE NORTHEAST... AND A LARGE TROUGH IS NOW MOVING ON TO NORTHERN PORTIONS OF THE WEST COAST. AT THE SURFACE A BROAD AREA OF HIGH PRESSURE IS SITUATED ACROSS NORTHERN KANSAS...PROVIDING DRY SINKING AIR...LIGHT WINDS...AND CLEAR SKIES THIS AFTERNOON. THE LIGHT WINDS WILL CONTINUE THROUGH THE OVERNIGHT HOURS. HIGH CLOUDS SHOULD BE CONFINED TO SOUTHEASTERN PORTIONS OF KANSAS...SO RADIATIONAL COOLING WILL BE STRONG OVER THE I-35 CORRIDOR AND POINTS NORTH AND WEST. FORECAST SOUNDINGS INDICATE THAT A STRONG INVERSION WILL FORM OVER THESE AREAS AND TEMPS WILL FALL BELOW THE CROSSOVER TEMPERATURE AND ESSENTIALLY SHOULD REACH 100 PERCENT RH THROUGH THE LOWEST 1000 FEET BY EARLY MORNING. FOG WILL LIKELY DEVELOP WITH SOME DENSE FOG POSSIBLE NEAR SUNRISE. ANTICIPATE THE DEPTH OF MOISTURE TO INCREASE FROM SOUTH TO NORTH OVERNIGHT WHICH MAY PROMOTE ADDITIONAL LOW STRATUS AND FOG DEVELOPMENT. CONFIDENCE IN THE OVERALL DENSITY OF FOG...AND LOCATION OF POTENTIAL DENSE FOG IS NOT HIGH AT THE MOMENT SO HAVE HELD OFF ON ISSUING A DENSE FOG ADVISORY UNTIL THE DETAILS SORT THEMSELVES OUT A LITTLE BETTER. SATURDAY TEMPERATURES WILL BE MILD ONCE AGAIN...BUT CLOUD COVER WILL BE MORE PREDOMINANT THAN TODAY. CURRENTLY LOOKS LIKE THE FOG WILL LIFT INTO A STRATUS DECK AND PERSIST THROUGH A GOOD PART OF THE DAY WITH MOISTURE ADVECTION ALOFT FROM THE SOUTH. GFS IS ATTEMPTING TO OUTPUT SOME LIGHT PRECIP...BUT LIFT APPEARS MARGINAL AND OVERALL MOISTURE DEPTH IS LACKING. MAY SEE A BIT OF DRIZZLE BUT DO NOT EXPECT ACCUMULATING PRECIP. BARJENBRUCH LONG TERM (SATURDAY NIGHT THROUGH FRIDAY)... SATURDAY NIGHT AND SUNDAY NIGHT...AN UPPER LEVEL TROUGH OVER THE WESTERN CONUS WILL FILL AS IT MOVES EAST ACROSS THE PLAINS. LOW-LEVEL WAA OF RESIDUAL MOISTURE WILL CAUSE DRIZZLE AND AREAS OF FOG TO FORM SATURDAY NIGHT INTO SUNDAY MORNING. THERE MAY BE ENOUGH ASCENT AHEAD OF THE WEAKENING UPPER TROUGH FOR ISOLATED RAIN SHOWERS OR SPRINKLES THROUGH THE DAY SUNDAY. SUNDAY HIGHS WILL BE DEPENDENT ON CLOUD COVER...IF SKIES BECOME PARTLY CLOUDY DURING THE AFTERNOON THEN HIGHS MAY BE IN THE MID TO UPPER 50S. HOWEVER...IF WE KEEP THE LOW STRATUS THROUGH THE DAY THEN HIGHS WILL BE MUCH COOLER...MAY ONLY SEE THE UPPER 40S TO AROUND 50. MONDAY THROUGH TUESDAY NIGHT...A SECOND UPPER LEVEL TROUGH WILL MOVE ONSHORE ACROSS THE PACIFIC NORTHWEST AND DIG SOUTHEAST ACROSS THE PLAINS. THE 12Z RUN OF THE EC DIGS THE 5H TROUGH FARTHER WEST ACROSS THE HIGH PLAINS LATE MONDAY AFTERNOON THEN LIFTS THE AMPLIFIED UPPER TROUGH EAST AND NORTHEAST ACROSS THE STATE OF KS. MEANWHILE...THE 12Z GFS DIGS THE UPPER LEVEL TROUGH ACROSS THE CENTRAL PLAINS...SOUTHEAST INTO THE MID MS RIVER VALLEY. THE 12Z RUN OF THE NAM LOOKS TO BE SOMEWHERE BETWEEN THE EC AND GFS SOLUTIONS. IF THE EC SOLUTION WERE TO VERIFY WE WOULD HAVE A BETTER CHANCE FOR RAIN MONDAY AFTERNOON...CHANGING OVER TO SNOW THROUGH THE NIGHT ACROSS THE NORTHERN COUNTIES OF THE CWA...THOUGH THE BEST TROWAL SET UP WOULD BE NORTH OF THE CWA ACROSS EASTERN NE. THE GFS SOLUTION WOULD BE MUCH DRIER WITH THE MOST OF THE FORCING AND ASCENT REMAINING NORTH AND EAST OF THE CWA. THE NAM MODEL SOLUTION SHOWS THE UPPER TROUGH DIGGING SOUTHEAST ACROSS NORTHERN KS...SO THERE WOULD BE A BETTER CHANCE FOR RAIN POSSIBLY MIXING WITH SNOW ACROSS THE NORTHERN COUNTIES OF THE CWA LATE MONDAY NIGHT. I PLACED IN A MIX OF RAIN AND SNOW ACROSS NORTH CENTRAL KS MONDAY NIGHT IN CASE THE NAM AND EC CONTINUE TO CONVERGE ON THEIR CURRENT SOLUTIONS. HIGHS ON TUESDAY WILL ONLY REACH THE MID 40S TO LOWER 50S DUE TO CLOUD COVER AND PRECIP CHANCES. THE END OF NEXT WEEK COULD BE TURNING SHARPLY COOLER AS BOTH THE EC AND GFS SHOW A LONGER WAVE LENGTH UPPER LEVEL TROUGH DEVELOPING ACROSS THE CENTRAL CONUS. IF WE KEEP NORTHWEST FLOW ALOFT WE MAY NOT SEE MUCH IN THE WAY OF PRECIPITATION DURING THIS PERIOD. HIGHS WEDNESDAY THROUGH FRIDAY WILL BE IN THE MID 40S TO AROUND 50 WITH OVERNIGHT LOWS IN THE MID 20S TO LOWER 30S. GARGAN && .TOP WATCHES/WARNINGS/ADVISORIES...NONE. && $$
