National Weather Service Raw Text Product

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

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