256  
FXUS63 KIWX 111145  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
645 AM EST MON DEC 11 2017  
   
SYNOPSIS
 
 
ISSUED AT 418 AM EST MON DEC 11 2017  
 
A FAST MOVING CLIPPER SYSTEM WILL BRING LIGHT SNOW TO FAR NORTHERN  
INDIANA AND LOWER MICHIGAN TODAY. ACCUMULATIONS WILL RANGE FROM  
JUST A DUSTING TO AS MUCH AS 2 INCHES ACROSS LOWER MICHIGAN.  
BETTER CHANCES FOR SNOW AND HEAVY LAKE EFFECT SNOW ARRIVE TONIGHT  
AND CONTINUE INTO TUESDAY AND TUESDAY NIGHT. SEVERAL INCHES OF  
ACCUMULATION ARE POSSIBLE AND A WINTER STORM WATCH HAS BEEN ISSUED  
FOR AREAS HAVING THE GREATEST CHANCES OF SEEING MORE THAN 6 INCHES  
OF SNOW. STRONG NORTH NORTHWEST WINDS WILL CREATE BLOWING AND  
DRIFTING WHILE ALSO PUSHING THE LAKE EFFECT SNOW BANDS WELL  
INLAND ON TUESDAY. PORTIONS OF EASTERN INDIANA AND NORTHWEST OHIO  
WILL LIKELY SEE SOME ACCUMULATIONS.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 418 AM EST MON DEC 11 2017  
   
..WINTER STORM WATCH FOR HEAVY LAKE EFFECT SNOW
 
 
ACTIVE PATTERN CONTINUES WITH ANOTHER POTENTIALLY BIG LAKE EFFECT  
EVENT ON THE WAY BUT IMPACTING MORE COUNTIES FURTHER EAST AND  
SOUTHEAST. AREAS WELL INLAND AND NEAR OUR SOUTHERN BORDER MAY SEE  
ADVISORY LEVEL SNOWFALL IF BAND BECOMES STATIONARY.  
 
FIRST THINGS FIRST AND APPROACHING SHORT WAVE AND ASSOCIATED ARCTIC  
FRONT MUST BE DEALT WITH. WEAK ISENTROPIC LIFT BEGINNING EARLY THIS  
MORNING BUT BEST FOCUS LOOKS TO BE NEAR AND NORTH OF IN/MI BORDER.  
HIRES MODELS HAVE BEEN BACKING OFF ON QPF AMOUNTS AND FOCUSING BEST  
PCPN CHANCES IN EXTREME NORTH WITH THIS INITIAL WARM AIR ADVECTION  
LIGHT SNOW. SHORT WAVE IS IMPRESSIVE AND TIGHTLY WOUND ON WATER  
VAPOR IMAGERY DIVING OUT OF SOUTHERN CANADA AND INTO THE DAKOTAS  
THIS MORNING. REGIONAL RADAR MOSAIC AND SFC OBS SHOW LIGHT SNOW  
QUICKLY SPREADING SOUTHEAST AND EXPECT THIS TO CLIP THE FAR NORTH  
AFTER 12Z. HAVE USED THE CONSHORT HOURLY POPS FOR TIMING AS THIS  
HAS BEST SHORT TERM VERIFICATION AND LOOKS REASONABLE COMPARED TO  
TIMING AND PLACEMENT IN HIRES AND SPECTRAL MODELS. WITH THE QUICK  
MOVING NATURE AND WEAK LIFT NOW ONLY EXPECTING AROUND AN INCH IN  
FAR NORTH WITH POSSIBILITY OF UP TO 2 INCHES CLOSE TO OUR NORTHERN  
BORDER. HAVE ALSO TRIMMED SOUTHERN EDGE OF PCPN CHANCES WITH FEW  
IF ANY MODELS SHOWING PCPN IN THE DRIER REGIME OVER THE FAR SOUTH.  
BRIEF BREAK IN PCPN EXPECTED LATE MORNING INTO AFTERNOON WITH  
MODELS AGAIN SHIFTING BEST CHANCES AHEAD OF MAIN SHORT WAVE  
FURTHER NORTH. DID KEEP MID TO HIGH CHANCE POPS IN NORTH WHICH WAS  
HIGHER THAN MOST BLENDS AS HRRR AND RUC INDICATE SOME LIGHT PCPN  
CLIPPING THIS AREA AGAIN THIS AFTERNOON AND EVENING.  
 
SHORT WAVE TO PASS THIS EVENING WITH ARCTIC FRONT CROSSING THE AREA  
IN THE EVENING. EXPECT SOME SNOW SHOWERS TO MOVE IN ALONG AND BEHIND  
THIS FRONT WITH DEEPENING COLD AIR ADVECTION. WINDS WILL ALSO PICK  
UP AND BECOME QUITE STRONG AND GUSTY. DELTA TS TO QUICKLY INCREASE  
AFTER 03Z AND BECOME VERY FAVORABLE FOR THE LAKE EFFECT AFTER 06Z AS  
WINDS BECOME NORTHWEST. WOULD EXPECT SOME LAKE ENHANCED SNOW SHOWERS  
IMMEDIATELY BEHIND FRONT MID EVENING TRANSITIONING TO PURE LAKE  
EFFECT OVERNIGHT. ACCUMULATIONS OF 1 TO 3 INCHES EXPECTED BEFORE  
MORE INTENSE BANDS GET GOING TOWARD OR JUST AFTER 12Z TUE.  
 
 

 
   
LONG TERM
 
(TUESDAY THROUGH SUNDAY)  
ISSUED AT 418 AM EST MON DEC 11 2017  
 
VERY IMPRESSIVE LAKE PARAMETERS COMING TOGETHER ON TUESDAY AS  
EXTREME INSTABILITY IS PRESENT FOR THE ENTIRE DAY AS SFC-700MB  
DELTA TS ECLIPSE 30 SETTING STAGE FOR INTENSE SNOW BANDS. NAM12  
0-2KM THETAE LAPSE RATES REMAIN IMPRESSIVE AND NEARING -4 K/KM.  
FLOW WILL BE FROM A NORTH NORTHWEST DIRECTION WITH TAP INTO LAKE  
SUPERIOR MOISTURE FOR PRE-CONDITIONING BEFORE LONG NW FETCH OVER  
LAKE MICHIGAN. HIRES MODELS ALL IN GENERAL AGREEMENT WITH SEVERAL  
LONG AND INTENSE BANDS STREAMING WELL SOUTHEAST AND INTO OHIO AND  
BEYOND. THE DIFFERENCES AS EXPECTED ARE ON WHERE EACH OF THESE  
BANDS WILL SET UP AND HOW THEY WILL MIGRATE DURING THE PERIOD.  
 
AT THIS TIME STEP THERE IS ENOUGH CONFIDENCE FOR A WATCH AS  
SYNOPTIC AND MESOSCALE PARAMETERS WILL SUPPORT VERY INTENSE BANDS  
WITH SNOWFALL RATES LIKELY REACHING 2-3 INCHES PER HOUR ON  
TUESDAY. THE EXTREME INSTABILITY, LAKE INDUCED CAPE NEARING 1000  
J/KG ON NAM12 BUFKIT, WOULD ALSO SUGGEST RARE THUNDER SNOW A  
POSSIBILITY. STRONG FLOW OF 30 TO 40 KNOTS EXPECTED TO PUSH THESE  
BANDS WELL INLAND AND THEY SHOULD REMAIN QUITE STRONG THROUGH  
CENTRAL PORTIONS OF CWA. SEVERAL MODELS HAVE HIGH END ADVISORY OR  
LOW END WARNING CRITERIA AMOUNTS AS FAR SOUTH AS KOSCIUSKO AND  
NOBLE COUNTIES. WITH COMBINATION OF SNOW AND WIND HAVE OPTED TO  
INCLUDE THESE INLAND COUNTIES IN THE WATCH WITH SIGNIFICANT  
IMPACTS EXPECTED. ALSO THINKING ADVISORIES WILL BE NEEDED EVEN  
FURTHER SOUTH AND SOUTHEAST WHERE THE MOST DOMINANT BAND ENDS UP,  
POSSIBLY INTO FORT WAYNE AREA AND BEYOND ON TUESDAY.  
 
THE ONLY POSSIBLE NEGATIVE FOR THIS EVENT IS THE  
INVERSION HEIGHTS APPEAR TO REMAIN BETWEEN 7 AND 10KFT THROUGH  
ENTIRE EVENT. HOWEVER, STRONG LIFT IS COINCIDENT WITH SATURATED  
DGZ AND WITH UPSTREAM CONDITIONING THINK CONVECTION SHOULD BE  
SUFFICIENT TO OCCUR IN THE SATURATED LAYER. EXPECT EVENT TO BEGIN  
WANING LATE TUESDAY NIGHT AS LOW LEVEL FLOW BACKS AND DRIER AIR  
WORKS IN CRASHING INVERSION HEIGHTS OVERNIGHT.  
 
TOTAL ACCUMS RIGHT NOW EXPECTED IN THE 5 TO 9 INCH RANGE WITH  
LOCAL ACCUMS AROUND A FOOT POSSIBLE WHERE ONE OF THE BANDS REMAINS  
STATIONARY. QUESTION REMAINS ON WHICH OF THE MULTIPLE BANDS  
EXPECTED WILL BECOME MOST DOMINANT. ALSO MUST POINT OUT THAT THIS  
TYPE OF FLOW/EVENT OFTEN LEADS TO MERGING BANDS AND INCREASED  
SNOWFALL RATES. A FEW HIRES MODELS HINTING AT THIS BUT NO WAY TO  
ANTICIPATE WHEN OR WHERE IT WILL ACTUALLY HAPPEN.  
 
STILL LOOKS LIKE ANOTHER CLIPPER WEDNESDAY INTO THURSDAY FOLLOWED BY  
MORE LAKE EFFECT. ONLY ADJUSTMENT TO BLEND WAS TO INCREASE NW AREA  
POPS TO LIKELY FOR EXPECTED NEXT ROUND OF LAKE EFFECT. WARMING  
TREND FOR THE WEEKEND WITH HIGHS IN THE 40S POSSIBLE.  
 

 
   
AVIATION
 
(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)  
ISSUED AT 644 AM EST MON DEC 11 2017  
 
EXPECT LIGHT SNOW SHOWERS IN THE AREA TO HAVE LITTLE IF ANY LONGER  
TERM IMPACT AT KSBN TODAY, AND NO IMPACT AT KFWA. IT LOOKS AS IF  
THINGS WILL STAY VFR TODAY, THOUGH WITH THE WAY THINGS HAVE BEEN  
GOING THIS MORNING AND THE CLIPPER SYSTEM MOVING IN, CEILINGS COULD  
DIP TO HIGH END-MVFR BRIEFLY AGAIN, BUT DIDN'T FEEL CONFIDENT ENOUGH  
TO PUT IN THE TAF. OTHERWISE, EXPECT CONDITIONS TO DETERIORATE TO  
IFR TONIGHT INTO TUESDAY MORNING AS LAKE EFFECT SNOW DEVELOPS AT  
KSBN. WE COULD SEE SOME LIGHT SYSTEM SNOW AT KFWA, MAINLY THIS  
EVENING INTO TUESDAY MORNING. AFTER 12Z TUE, MODELS SUGGEST LAKE  
EFFECT SNOW BANDS REACHING AS FAR INLAND AS TO IMPACT KFWA. HAVE  
KEPT CONDITIONS MVFR AFTER 6Z AS PREVIOUSLY FORECASTED, WITH WINDS  
EXPECTED TO PICK UP TO 15 TO 25 KTS, WITH GUSTS UP TO 30 KTS  
POSSIBLE FURTHER INTO THE DAY TUE.  
 

 
   
IWX WATCHES/WARNINGS/ADVISORIES
 
 
IN...WINTER STORM WATCH FROM LATE TONIGHT THROUGH WEDNESDAY MORNING  
FOR INZ004>006-008-014-016.  
 
MI...WINTER STORM WATCH FROM LATE TONIGHT THROUGH WEDNESDAY MORNING  
FOR MIZ077>079.  
 
OH...NONE.  
LM...GALE WARNING FROM 10 PM THIS EVENING TO 7 PM EST TUESDAY FOR  
LMZ043-046.  
 

 
 

 
 
SYNOPSIS...LASHLEY  
SHORT TERM...LASHLEY  
LONG TERM...LASHLEY  
AVIATION...MCD  
 
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