699  
FXUS63 KIWX 022001  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
301 PM EST MON MAR 2 2015  
   
SYNOPSIS
 
 
ISSUED AT 253 PM EST MON MAR 2 2015  
 
CLOUDS WILL INCREASE OVERNIGHT...LEADING TO A RETURN OF WINTRY  
WEATHER ON TUESDAY. UNDER CLOUDY SKIES TONIGHT...TEMPERATURES DROP  
QUICKLY BEFORE RISING TO NEAR FREEZING TUESDAY MORNING. A WINTRY  
MIX OF PRECIPITATION WILL SPREAD NORTH LATE TONIGHT AND  
TUESDAY...STARTING AS SNOW...CHANGING TO SLEET AND FREEZING RAIN  
TUESDAY MORNING. MOST AREAS WILL SEE LIGHT RAIN BY AFTERNOON.  
 
LOWS TONIGHT WILL BE IN THE UPPER TEENS AFTER MIDNIGHT...RISING  
TO NEAR FREEZING BY DAYBREAK TUESDAY. HIGHS TUESDAY WILL BE IN THE  
LOWER 30S.  
 

 
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY)  
ISSUED AT 253 PM EST MON MAR 2 2015  
 
COMPLEX AND CHALLENGING FORECAST BEGINNING OVERNIGHT INTO TUESDAY  
MORNING. MODELS IN GENERAL AGREEMENT ON THE TRACK AND DEPTH OF THE  
SURFACE LOW DRIVING INTO THE CENTRAL PLAINS AND NORTHERN GREAT  
LAKES DURING THE DAY TUESDAY. ISENTROPIC ASCENT OVER THE OHIO  
RIVER VALLEY WILL HELP BUILD A PRONOUNCED WARM LAYER BY DAYBREAK  
TUESDAY AND THIS WILL ALLOW LIGHT PRECIPITATION TO FORM. THERE IS  
POTENTIAL FOR FREEZING RAIN...MIXED WITH SLEET AT THE ONSET...WITH  
MODELS SUGGESTING WARM AIR TO MIX DOWN BY MID-DAY...ENDING THE  
FROZEN/FREEZING PRECIP.  
 
IT IS THE INTERIM PERIOD FROM DAYBREAK THROUGH NOON THAT IS CAUSING  
THE GREATEST DIFFICULTY. INSOLATION HAS INCREASED DRAMATICALLY OVER  
THE LAST FEW WEEKS AND WE ARE EXPERIENCING A LOT OF SNOWMELT THIS  
AFTERNOON. NOT SURE IF THE ROAD SURFACE TEMPERATURES WILL BE COLD  
ENOUGH TO SUPPORT SIGNIFICANT ACCUMULATION OF ICE...BUT AS WE HAVE  
SEEN HERE...A LIGHT GLAZE OF ICE CAN BE VERY DANGEROUS.  
 
THE OTHER CONCERN IS THAT SOME OF THE MODEL SOUNDINGS HINT THAT THE  
SURFACE TEMPERATURES...ESPECIALLY IN THE NORTHEAST MAY REMAIN BELOW  
FREEZING. WITH ENOUGH UNCERTAINTY...HAVE OPTED TO COVER THE ENTIRE  
WARNING AREA WITH A WINTER WEATHER ADVISORY FOR THE PERIOD OF 11Z TO  
18Z ON TUESDAY. AS WE GET CLOSER TO ONSET OF THE EVENT...THE  
ADVISORY WILL NEED TO BE ADJUSTED TO REFLECT THE CHANGING  
ENVIRONMENT.  
 
ON TOP OF ALL THAT...AS THE RAIN FALLS ON THE SNOW FIELD A FAVORABLE  
BOUNDARY LAYER ENVIROMENT WILL BE SET UP FOR FOG FORMATION. WINDS  
MAY BE ENOUG TO KEEP THE VISIBILITY FROM DROPPING TOO MUCH...BUT  
WITH THE SNOW FIELD AND RECENT COLD...EXPECT TO SEE AT LEAST SOME  
ADVECTIVE FOG FORMATION AS THE PRECIPITATION FALLS.  
 

 
   
LONG TERM
 
(TUESDAY NIGHT THROUGH MONDAY)  
ISSUED AT 253 PM EST MON MAR 2 2015  
 
FORECAST PERIOD BEGINS WITH COLD FRONT PASSAGE ASSOCIATED WITH  
EXITING SYSTEM. FRONT EXPECTED TO BE ENTERING THE FORECAST AREA AT  
THE START OF THE PERIOD AND BE SOUTH OF THE CWA BY 12Z WED. HIGH  
PRESSURE CENTER MOVES INTO THE DAKOTAS AND PLACES OUR REGION IN A  
PROLONGED COLD AIR ADVECTION PATTERN WHICH WILL RESULT IN CONTINUED  
FALLING TEMPS WED MORNING AND LITTLE DIURNAL RECOVERY IN THE  
AFTERNOON.  
 
COLD AIR MASS THEN CONTINUES TO BUILD INTO THE REGION AND WILL  
HAVE LOWS NEAR ZERO BOTH THURSDAY AND FRIDAY MORNING WITH HIGHS  
ONLY IN THE TEENS THURSDAY. LIGHT LAKE EFFECT SNOW SHOWERS  
EXPECTED IN THE NW CWA WITH FAIRLY UNIDIRECTIONAL W/NW FLOW BELOW  
4KFT INVERSION HEIGHTS. INITIAL ARCTIC INTRUSION WILL BE RATHER  
SHALLOW AND SURFACE BASED WHICH SHOULD KEEP LES LIGHT ON  
WEDNESDAY.  
 
THERMAL TROUGH THEN ARRIVES WED NITE AND NW WINDS GAIN A LITTLE  
MORE OF A NORTHERLY COMPONENT WHICH HAS POTENTIAL TO BRING A  
SINGLE BAND OVER THE AREA...BUT WINDS BEGIN TO BACK TO MORE  
WESTERLY FLOW DURING THE DAY THURSDAY AND INCREASE SHEAR BELOW  
INVERSION TO DISRUPT BANDING AND BRING IT TO AN END THURSDAY  
AFTERNOON/EVENING.  
 
QUIET AND WARMER WEATHER REMAINDER OF EXTENDED...SURFACE HIGH  
PRESSURE SHIFTS OFF TO THE EAST BRINGING RETURN FLOW TO THE  
REGION. UPPER TROF AXIS ALSO SHIFTS EAST WITH 160M HEIGHT RISES IN  
ITS WAKE. TEMPS WILL WARM FROM THE 20S ON FRIDAY INTO THE 30S FOR  
THE WEEKEND. WEAK SYSTEMS WILL TRAVERSE THE NORTHERN GREAT LAKES  
REGION AND BRING SMALL CHANCES FOR PRECIP PRIMARILY NORTH OF OUR  
FORECAST AREA...SO WILL CONTINUE WITH DRY FORECAST IN THIS TIME  
PERIOD PENDING A STRONGER SIGNAL FROM MODELS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)  
ISSUED AT 253 PM EST MON MAR 2 2015  
 
(FOR THE 18Z TAFS THROUGH 18Z TUESDAY AFTERNOON)  
ISSUED AT 1228 PM EST MON MAR 2 2015  
 
VERY COMPLICATED AVIATION FORECAST BEGINNING AFTER 10Z. VFR  
CONDITIONS TO PREVAIL FOR THE FIRST HALF OF THE FORECAST PERIOD.  
INCREASING CLOUD COVER AND LOWER AS ISENTROPIC LIFT BEGINS TO  
OVERSPREAD THE REGION. MVFR CONDITIONS DEVELOP AND SPREAD QUICKLY  
FROM SOUTHWEST TO NORTHEAST AFTER 10Z.  
 
ISENTROPIC LIFT WILL HELP TO DRIVE WARM AIR OVER THE SUB-FREEZING  
NEAR SURFACE BOUNDARY AND THIS WILL SET THE STAGE FOR A PERIOD OF  
LIGHT SNOW...TRANSITIONING TO A PERIOD OF ICE PELLETS...FREEZING  
RAIN AND THEN OVER TO ALL RAIN BEYOND THE TAF PERIOD.  
 
ADDITIONALLY WITH SOME MELTING TODAY...COULD SEE AREAS OF FOG  
FORMING ACROSS THE AREA. HAVE INTRODUCED THE FOG IN THE  
TAF...POSSIBLY COULD SEE LIFR CONDITIONS AS THE BOUNDARY LAYER  
SATURATES OVER THE SNOW PACK.  
 
ALSO CONCERNED THAT THE WINDS WILL BE INCREASING JUST ABOVE THE  
INVERSION. THIS COULD LEAD TO WINDSHEAR POTENTIAL LATE IN THE  
FORECAST.  
 

 
   
IWX WATCHES/WARNINGS/ADVISORIES
 
 
IN...WINTER WEATHER ADVISORY FROM 6 AM EST /5 AM CST/ TO 1 PM EST  
/NOON CST/ TUESDAY FOR INZ003>009-012>018-020-022>027-  
032>034.  
 
MI...WINTER WEATHER ADVISORY FROM 6 AM TO 1 PM EST TUESDAY FOR  
MIZ077>081.  
 
OH...WINTER WEATHER ADVISORY FROM 6 AM TO 1 PM EST TUESDAY FOR OHZ001-  
002-004-005-015-016-024-025.  
 
LM...NONE.  

 
 

 
 
SYNOPSIS...LEWIS  
SHORT TERM...LEWIS  
LONG TERM...JAL  
AVIATION...LEWIS  
 
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