774 FXUS63 KTOP 300534 AFDTOP AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TOPEKA KS 1134 PM CST TUE JAN 29 2013 .DISCUSSION... SEE PREV DISCUSSION. && .AVIATION... DEFORMATION BAND OF SNOW HAS FORMED TO THE WEST OF THE TERMINALS...AND THE RAP AND NAM CONTINUE TO SHOW THIS BAND MOVING ACROSS NORTHEAST KANSAS OVERNIGHT. TIMING IS SEVERAL HOURS SLOWER FROM THE PREV FORECAST WITH SNOW LIKELY PERSISTING AT TOP AND FOE UNTIL 14Z. MODELS ALSO SUGGEST A LACK OF ICE IN THE TOP OF THE CLOUD INITIALLY. WITH SEVERAL REPORTS OF PL UPSTREAM...HAVE INTRODUCED A MIX OF -SNPL UNTIL THE BETTER DEFORMATION BAND MOVES IN AND SATURATES THE DENDRITIC GROWTH ZONE FOR A PERIOD OF MODERATE SNOW. CONFIDENCE IS HIGH THAT THERE WILL BE IFR AND LIFR CONDITIONS DURING THE NEXT 8 TO 12 HOURS. WOLTERS && .PREV DISCUSSION... /957 PM CST TUE JAN 29 2013/ A BAND OF SNOW HAS DEVELOPED ACROSS SOUTHWESTERN AND CENTRAL KANSAS WITHIN THE DEFORMATION ZONE OF THE UPPER TROUGH. THE LATEST RAP AND NAM PROGS SUGGEST THIS BAND OF SNOW WILL CONTINUE TO MOVE EAST AND NORTHEAST ACROSS THE NORTHERN TWO THIRDS OF THE FORECAST AREA...WITH THE HEAVIEST BAND SETTING UP NORTH OF AN ABILENE TO HOLTON LINE. MODELS HAVE ALSO TRENDED SOUTH WITH THE SNOW ACCUMULATIONS AND SHOW A COUPLE INCHES POSSIBLE ALONG INTERSTATE 70. WITH MODELS STILL SHOWING DECENT FRONTOGENETICAL FORCING AND THE DEFORMATION BAND HAVING ALREADY FORMED...HAVE EXPANDED THE ADVISORY A LITTLE FURTHER SOUTH TO INCLUDE DICKINSON...GEARY...MORRIS AND WABAUNSEE COUNTIES. WOLTERS /556 PM CST TUE JAN 29 2013/ 21Z RAP AND 18Z NAM HAVE STARTED TO SHOW SOME INDICATION OF A DECENT FRONTOGENETICAL BAND DEVELOPING MAINLY DURING THE 06Z TO 12Z TIME FRAME. WITH RECENT RADAR TRENDS SHOWING A BAND STARTING TO FORM ACROSS WESTERN KS...AM BEGINNING TO THINK THAT MODELS ARE DOING A REASONABLE JOB DEPICTING THE SYSTEM AS IT LIFTS OUT OVERNIGHT. CONFIDENCE IS INCREASING THAT THERE WILL BE SNOW. SNOW AMOUNTS SEEM TO BE IN THE BALLPARK INITIALLY. WITH SOME UNCERTAINTY FROM THE PREV FORECAST ABOUT MESOSCALE FORCING...THINK THAT FORECAST SNOW AMOUNTS ARE PROBABLY NOT ON THE LOW SIDE. THERE ARE STILL SOME QUESTIONS WITH SOME INDICATIONS OF MID LEVEL DRY AIR COMING IN AT THE DENDRITIC GROWTH ZONE AND A GENERAL LACK OF INSTABILITY OF CONDITIONAL INSTABILITY THAT COULD ACT TO KEEP SNOW AMOUNT ON WITHIN THE FORECASTED VALUES. IF ANYTHING WILL NEED TO WATCH THINGS PROGRESS AND POTENTIALLY EXPAND THE ADVISORY IF INDEED A BAND OF MODERATE SNOW MOVES ACROSS THE AREA. MODELS CONTINUE TO SHOW A STRENGTHENING PRESSURE GRADIENT WITH NORTH AND NORTHWEST WINDS GUSTING UP TO 35 MPH. WOLTERS /328 PM CST TUE JAN 29 2013/ THE ABRUPT RETURN TO WINTER CONTINUES TODAY ACROSS THE FORECAST AREA...AFTER A ROUND OF MORNING SHOWERS AND THUNDERSTORMS FOR EASTERN PORTIONS OF THE STATE. THE DEEP LONGWAVE TROF CONTINUES TO MOVE EASTWARD ACROSS THE ROCKY MOUNTAINS AND INTO THE HIGH PLAINS. ENERGY ROTATING THROUGH THE TX PANHANDLES AIDING IN ENHANCING A NEGATIVE TILT TO THE SOUTHERN STREAM AS IT LIFTS INTO OUR AREA THIS EVENING AND OVERNIGHT. HAVE EXPANDED THE WINTER WEATHER ADVISORY BOTH WEST AND SOUTH A FEW COUNTIES. STILL APPEARS AS IF FAR NE COUNTIES WILL GET THE HIGHER SNOW AMOUNTS WHERE BAND OF FRONTOGENESIS TRACKS WEST TO EAST GENERALLY NORTH OF THE INTERSTATE...AS DOES THE MID LEVEL DEFORMATION ZONE. HARD TO SEE A TIME WHEN ALL INGREDIENTS COME TOGETHER FOR A BANDED HEAVY SNOW EVENT...ALTHOUGH AROUND 06Z NORTH OF THE MHK AREA DO SEE SOME FRONTOGENETIC FORCING ALIGNED WITH SOME NEGATIVE EPV...THEREFORE INCREASED SNOW TOTALS FOR THIS AREA. 2-3 INCH LINE RUNS GENERALLY ALONG THE INTERSTATE WITH DIMINISHING AMOUNTS SOUTH AND HIGHER NUMBERS NORTH AND EAST. STARTED ADVISORY WEST AT 6PM FOLLOWED BY AN 11PM START FOR COUNTIES FARTHER EAST. OF CONCERN ARE THE WINDS THAT ACCOMPANY THIS SYSTEM AS THE SNOW FALLS OVERNIGHT AND INTO THE EARLY COMMUTE TOMORROW MORNING. SNOW WILL REDUCE VISIBILITIES AND MAY MAKE ROADS DIFFICULT TO KEEP CLEAR...SO THAT EVEN A FEW INCHES OF SNOW MAY BRING TRAVEL PROBLEMS. SNOW SHOULD END BY 9AM AND WILL LIKELY END A FEW HOURS SOONER OUT WEST AND CAN ADJUST ADVISORY ENDING AS NEEDED. THURSDAY THROUGH NEXT TUESDAY...DRY WEATHER WILL LIKELY CONTINUE THROUGH THE REMAINDER OF THE FORECAST PERIOD AS COLD AND DRY AIR PLUNGES SOUTHWARD INTO THE CENTRAL PLAINS. NORTHWEST FLOW ALOFT ON THE EASTERN EDGE OF A STRONGLY AMPLIFIED RIDGE OVER THE WESTERN CONUS WILL PREVENT THE FORMATION OF ANY STRONG SURFACE TROUGH AND SUBSEQUENT WARM AIR ADVECTION THROUGH THE REST OF THE WORK WEEK. THE FIRST PUSH OF COLD AIR WILL ALSO LIKELY BE REINFORCED BY A SECOND PUSH OF COLD AIR ON THURSDAY NIGHT...WHICH MODELS CURRENTLY PROG TO BE CHARACTERIZED BY 850 MB TEMPERATURES AROUND -15 DEGREES C. THE COLDEST MORNING AT THIS TIME LOOKS TO BE FRIDAY MORNING...WHEN THE SURFACE HIGH ASSOCIATED WITH THE ARCTIC AIRMASS BECOMES CENTERED OVER NORTHEAST KANSAS. CURRENTLY THE FORECAST FOR FRIDAY MORNING REFLECTS SLIGHTLY LOWER TEMPS THAN THE PREVIOUS FORECAST SUGGESTED DUE TO THE FACT THAT SNOW FROM TUESDAY NIGHT/WED MORNING WILL LIKELY LINGER PREVENTING THE POLAR AIR FROM MODIFYING MUCH. GIVEN THAT SNOW WILL LIKELY STILL BE ON THE GROUND AND THAT SKIES WILL CLEAR AND WINDS WILL BE CALM...IN RESPONSE TO THE SURFACE HIGH...EXPECT FRIDAY MORNING TO BE VERY CHILLY...WITH LOWS IN THE SINGLE DIGITS TO LOWER TEENS. BY SATURDAY THE SURFACE HIGH WILL SLIDE EASTWARD AND SOUTHERLY RETURN FLOW WILL COMMENCE ON THE BACKSIDE OF THE HIGH. CONCURRENTLY THE AFOREMENTIONED WESTERN CONUS RIDGE MAY SHIFT EVER SO SLIGHTLY TO THE EAST...ALLOWING THE COLD AIR ASSOCIATED WITH THE BROAD HUDSON BAY LOW TO ALSO SHIFT EAST. THE BOTTOM LINE FOR THE WEEKEND AND INTO NEXT WEEK IS A GRADUAL WARMING TREND AS SURFACE WINDS WILL BE WESTERLY TO SOUTHWESTERLY...WHICH WILL INTRODUCE A SLIGHT DOWNSLOPE COMPONENT...AIDING IN SURFACE TEMP WARMING. AT THIS POINT MAX TEMPS LOOK TO RUN ABOUT 10 DEGREES ABOVE NORMAL FROM SUNDAY THROUGH NEXT TUESDAY...BUT THIS COULD CHANGE A FEW DEGREES EITHER WAY DEPENDING ON HOW FAST THE SNOW MELTS. JL && .TOP WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY TIL 7AM WED FOR KSZ008-009-020>022-034>037. WINTER WEATHER ADVISORY TIL 9AM WED KSZ010>012-023-024-026-038>040. && $$