000 FXUS63 KIND 051659 AFDIND AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE INDIANAPOLIS IN 1159 PM EST THU DEC 5 2013 .UPDATE... THE AVIATION SECTION HAS BEEN UPDATED BELOW. && .SYNOPSIS... ISSUED AT 433 AM EST THU DEC 5 2013 A COLD FRONT WILL TRACK SOUTH INTO THE TENNESSEE VALLEY TODAY. A SERIES OF DISTURBANCES MOVING ALONG THIS BOUNDARY BEGINNING LATER THIS AFTERNOON INTO FRIDAY WILL SET THE STAGE FOR WHAT WILL BE THE FIRST SIGNIFICANT WINTER STORM OF THE SEASON ACROSS MUCH OF CENTRAL INDIANA. AFTER A BRIEF BREAK...ANOTHER WINTRY SYSTEM WILL IMPACT CENTRAL INDIANA SUNDAY INTO MONDAY. HIGH PRESSURE WILL BRING DRY AND VERY COLD CONDITIONS FOR THE MIDDLE OF NEXT WEEK. && .NEAR TERM /THIS AFTERNOON/... ISSUED AT 923 AM EST THU DEC 5 2013 RADAR TRENDS SHOW AN AREA OF FREEZING RAIN OVER EAST CENTRAL ILLINOIS PUSHING NORTHEAST TOWARD LAFAYETTE AND KOKOMO. TEMPERATURES IN NW INDIANA CONTINUE TO FALL IN THE WAKE OF THE COLD FRONT...AND COLDER AIR IS EXPECTED TO ARRIVE AS THE DAY PROGRESSES. THUS HAVE EXPANDED THE WINTER WEATHER ADVISORY FOR NORTHWEST PARTS OF CENTRAL INDIANA...AS LIGHT ICING DUE TO THE FREEZING RAIN MAY RESULT IN SOME ICY SURFACES. AS COLDER AIR ARRIVES THIS AFTERNOON...A TRANSITION TO ALL SNOW WILL BE EXPECTED. HAVE TRENDED TEMPERATURES AS FALLING THIS AFTERNOON DUE TO THE EXPECTED COLD AIR ADVECTION. && .SHORT TERM /TONIGHT THROUGH SATURDAY NIGHT/... ISSUED AT 433 AM EST THU DEC 5 2013 MAIN FORECAST CHALLENGES REMAIN FOCUSED ON THE IMPENDING WINTER STORM AND DETAILING SPECIFIC IMPACTS WITH PRECIP TYPE AND SNOW/ICE ACCUMS. MODEL GUIDANCE HAS TIGHTENED UP A BIT MORE EARLY THIS MORNING AND WHILE SOME SUBTLE FLUCTUATIONS REMAIN POSSIBLE IN TRACK AND LOCATION OF THE HEAVIEST SNOWFALL...CONFIDENCE IS HIGH ENOUGH AT THIS POINT TO UPGRADE HEADLINES FROM THE WATCH IN PLACE. MORE DISCUSSION ON THIS BELOW. FRONTAL BOUNDARY WILL SAG SLOWLY SOUTH THROUGH THE TENNESSEE VALLEY AND INTO THE SOUTHERN APPALACHIANS BY FRIDAY. WINTRY PRECIPITATION WILL DEVELOP AND IMPACT THE REGION AS TWO DISTINCT WAVES TRAVERSE THE BOUNDARY TONIGHT AND ON FRIDAY AS PROGRESSIVELY COLDER AIR SPREADS SOUTH ACROSS CENTRAL INDIANA. WINTER STORM WITH TWO PHASES WILL BE IN ITS INFANCY THIS EVENING WITH PRECIP ARRIVING. A STRONG LOW LEVEL JET WILL PASS THROUGH THE TENNESSEE VALLEY OVERNIGHT AND WITH MID LEVEL FRONTOGENESIS AND A SHARPENING BAROCLINIC ZONE OVER THE REGION...BROAD AREA OF OVERRUNNING PRECIP WILL BECOME WIDESPREAD. MODEL GUIDANCE HAS LARGELY COME IN MORE AGGRESSIVE WITH THE COLDER AIR THROUGH THE BOUNDARY LAYER OVER AS THE NIGHT PROGRESSES OVER THE LAST FEW RUNS. MODEL SOUNDINGS SHOW A SUBTLE LAYER OF DRIER AIR INFILTRATING THE BOUNDARY LAYER INITIALLY THAT MAY TAKE A LITTLE TIME TO MOISTEN UP VIA EVAPORATIVE COOLING PROCESSES. THIS WOULD SUPPORT SLEET MIXING IN WITH RAIN AND SNOW THROUGH THE EVENING...WITH PRECIP LIKELY FALLING AS ALL SNOW ALONG AND NORTH OF INTERSTATE 70 AFTER MIDNIGHT. FURTHER SOUTH...LIGHT RAIN WILL GRADUALLY TRANSITION TO A MIX OF PRIMARILY SLEET AND SNOW OVERNIGHT...WITH THE SNOW/MIX LINE ALONG OUR FAR SOUTHERN BORDER BY DAYBREAK FRIDAY. WITH A MORE PRONOUNCED WARM LAYER OVER SOUTHERN COUNTIES TONIGHT AND SURFACE TEMPS LIKELY TO FALL BELOW FREEZING BY MIDNIGHT...HAVE INTRODUCED A PERIOD WITH FREEZING RAIN MIXING IN WITH SLEET AND SNOW LATE TONIGHT IN A THIN BAND FROM WASHINGTON NORTHEAST TO NEAR SEYMOUR AND GREENSBURG. BOUNDARY LAYER WILL LIKELY COOL SUFFICIENTLY TO SUPPORT MAINLY SNOW EVEN ACROSS SOUTHERN COUNTIES AROUND OR SHORTLY AFTER DAYBREAK FRIDAY. TAKING INTO CONSIDERATION SNOWFALL RATIOS LIKELY AT 10 TO 1 AND POSSIBILITY THAT SLEET WILL CUT DOWN ON SNOWFALL AMOUNTS OVER MUCH OF THE REGION TO SOME DEGREE...POTENTIAL FOR 1 TO 2 INCHES OF SNOW BY DAYBREAK FRIDAY WITH LOCALLY HIGHER AMOUNTS NEAR OR JUST SOUTH OF THE I-70 CORRIDOR. SHOULD THE CHANGEOVER HAPPEN A BIT QUICKER OVERNIGHT...SNOW TOTALS WOULD END UP BEING HIGHER OVER THE SOUTHERN HALF OF THE FORECAST AREA. LIGHT ICING REMAINS A POSSIBILITY OVER SOUTHERN COUNTIES AS WELL WITH SLEET AND POCKETS OF FREEZING RAIN MIXING IN. PRECIP RATES WILL SLOW DOWN TEMPORARILY FRIDAY MORNING BEFORE ROUND 2 ARRIVES AS ANOTHER WAVE LIFTS OUT OF THE SOUTHERN PLAINS AND RIDES NORTHEAST INTO THE OHIO VALLEY BY THE AFTERNOON. UPPER DYNAMICS... MID LEVEL FRONTOGENESIS AND DEFORMATION REMAIN EXTREMELY IMPRESSIVE AND WILL BE THE MAIN CATALYSTS IN BRINGING WIDESPREAD SNOWFALL ACROSS MUCH OF THE FORECAST AREA BY MIDDAY FRIDAY. APPEARS THE LOW LEVEL JET ACCOMPANYING THE SECOND WAVE WILL BE STRONGER THAN THE ONE PASSING TO OUR SOUTH TONIGHT. COMBINED WITH A RENEWED SURGE OF FRONTOGENETICAL FORCING NORTH OF THE FRONTAL BOUNDARY AND THE REGION RESIDING WITHIN THE FAVORABLE RIGHT REAR QUAD OF A 170-180KT UPPER JET DURING THE AFTERNOON...EXPECT SNOW TO BECOME LOCALLY HEAVY OVER THE SOUTHERN HALF OF THE FORECAST AREA BY THE AFTERNOON. THE PRESENCE OF AN INCREASING DENDRITIC GROWTH ZONE TO GO ALONG WITH NEGATIVE EPV AND THE DEFORMATION AXIS STRONGLY SUGGESTIVE OF A BAND OR FEW BANDS OF HEAVIER ACCUMS SETTING UP SW TO NE FROM NEAR VINCENNES E/NE TO BLOOMINGTON/BEDFORD...TO COLUMBUS/SEYMOUR. WITH HIGHER CONFIDENCE IN SIGNIFICANT IMPACTS AND CRITERIA BEING MET OVER THE SOUTHERN TWO ROWS OF COUNTIES...WILL UPGRADE TO A WARNING. TOTAL SNOW ACCUMS OF 6 TO 7 INCHES WITH LOCALLY HIGHER AMOUNTS ARE EXPECTED. FURTHER NORTH WITH SNOWFALL AMOUNTS OF 3 TO 6 INCHES...WILL TRANSITION THE WATCH TO AN ADVISORY AND ADD ANOTHER ROW OF COUNTIES NORTH. ACROSS FAR NORTHERN SECTIONS OF THE FORECAST AREA...1 TO 2 INCHES OF SNOW WILL BE POSSIBLE BY FRIDAY EVENING. THE REMAINDER OF THE SHORT TERM WILL BE COLD AND MAINLY DRY AS ARCTIC HIGH PRESSURE PASSES THROUGH THE REGION. MOISTURE WILL QUICKLY RETURN NORTH LATE SATURDAY NIGHT AS AN INVERTED TROUGH SETS UP ACROSS THE TENNESSEE VALLEY. MAY SEE NORTHERN FRINGE OF THE LIGHT SNOW EXPAND INTO FAR SOUTHERN COUNTIES TOWARDS DAYBREAK SUNDAY. THE ACTIVE WINTRY PATTERN CONTINUES. TEMPS...GENERALLY UNDERCUT MOS GUIDANCE THROUGH THE PERIOD. FRESH SNOW COVER WILL PRODUCE VERY COLD TEMPS FRIDAY NIGHT WITH SKIES CLEARING. MANY LOCALES MAY APPROACH 10 DEGREES. HELD HIGHS IN THE 20S ON FRIDAY WITH WIDESPREAD SNOW...WITH HIGHS ONLY IN THE LOW/MID 20S SATURDAY. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... ISSUED AT 433 AM EST THU DEC 5 2013 ENSEMBLES ARE IN GOOD AGREEMENT ON THE SLOW PROGRESSION OF A LARGE SCALE UPPER TROUGH THROUGH THE PERIOD...WHICH IS EXPECTED TO EXTEND FROM THE GREAT LAKES BACK INTO THE SOUTHERN PLAINS BY THE MIDDLE OF NEXT WEEK. MAJORITY OF THE ENSEMBLES EJECT A DECENT AMOUNT OF ENERGY WILL EJECT OUT OF THE TROUGH ACROSS THE PLAINS AND INTO THE GREAT LAKES BY SUNDAY AND EARLY MONDAY. MOST OF THE MEMBERS ARE STILL CLUSTERED AROUND A TENNESSEE TO WESTERN OHIO SURFACE LOW TRACK...BUT SOME MEMBERS ARE BEGINNING TO HINT AT AN INVERTED TROUGH EXTENDING NORTHWEST OF THE SURFACE LOW OR A MORE STRETCHED OUT AREA OF LOW PRESSURE. THIS IS PROBABLY A REFLECTION OF THE UPPER SYSTEM. NEVERTHELESS...ALL MEMBERS INDICATE THE 850MB LOW WILL PASS WELL TO THE NORTHWEST OF THE LOCAL AREA...SO THIS LOOKS MORE LIKE A MIXED EVENT THAN JUST SNOW. WILL CONTINUE TO CARRY POPS SUNDAY AND MONDAY...WITH A WINTRY MIX OVER ABOUT THE SOUTHEAST TWO THIRDS OF THE FORECAST AREA SUNDAY AND SUNDAY NIGHT. COLD ADVECTION SHOULD CHANGE ANY REMAINING PRECIPITATION TO SNOW LATER SUNDAY NIGHT AND INTO MONDAY. POTENTIAL CONTINUES FOR SNOW AND ICE ACCUMULATIONS WITH THIS SYSTEM. ENSEMBLES INDICATE LITTLE THREAT FOR PRECIPITATION AFTER MONDAY AS BROAD UPPER TROUGH GRADUALLY SHIFTS EAST. && .AVIATION /DISCUSSION FOR THE 05/18Z TAFS/... ISSUED AT 1200 PM EST THU DEC 5 2013 POOR FLYING CONDITIONS TO DEVELOP ACROSS MOST OF THE SITES AND PERSIST THROUGH THE PERIOD. SOME SHOWERY PRECIPITATION HAS ALREADY DEVELOPED AND IS MOVING THROUGH THE AREA. DEPENDING ON LOCATION THIS APPEARS TO BE -RA/-FZRA MIXED WITH SLEET. THIS SHOULD BE THE PREDOMINANT PRECIPITATION TYPE THROUGH EARLY EVENING AT IND/HUF AND THROUGH LATE EVENING AT BMG. LAF WILL LIKELY BE COLD ENOUGH WITHIN THE FIRST FEW HOURS OF THE PERIOD FOR MOST ANYTHING THAT OCCURS THERE TO FALL AS SNOW. PRECIPITATION WILL INCREASE IN COVERAGE AND INTENSITY OVERNIGHT AND GRADUALLY CHANGE TO ALL SNOW. THIS TRANSITION APPEARS LIKELY TO OCCUR BY 01-02Z AT HUF/IND...WITH A MORE PROLONGED MIXING PERIOD AT BMG. HOWEVER...EVEN BMG SHOULD BE ALL SNOW BY LATE TONIGHT. A SECOND WAVE WILL MOVE INTO THE AREA NEAR THE END OF THE TAF PERIOD FOR MOST SITES...MID MORNING TOMORROW...AND CONTINUE INTO THE AFTERNOON. THIS WILL LIKELY CAUSE WIDESPREAD IFR CONDITIONS OR WORSE IN MODERATE SNOW. LAF WILL ESCAPE THE WORST OF THE CONDITIONS AND IS LIKELY TO REMAIN MVFR THROUGH MUCH OF THE PERIOD. WINDS WILL GRADUALLY BECOME NORTHERLY DURING THE PERIOD...WITH SPEEDS LIKELY DECREASING SLIGHTLY THROUGH TONIGHT. && .IND WATCHES/WARNINGS/ADVISORIES... WINTER WEATHER ADVISORY UNTIL MIDNIGHT EST FRIDAY NIGHT FOR INZ021-028>031-035>049-051>057. WINTER STORM WARNING FROM 10 PM THIS EVENING TO MIDNIGHT EST FRIDAY NIGHT FOR INZ060>065-067>072. && $$ SYNOPSIS...RYAN NEAR TERM...PUMA SHORT TERM...RYAN LONG TERM....JAS AVIATION...NIELD VISIT US AT HTTP://WWW.WEATHER.GOV/IND FOLLOW US ON TWITTER AND YOUTUBE AT: WWW.TWITTER.COM/NWSINDIANAPOLIS WWW.YOUTUBE.COM/NWSINDIANAPOLIS