966  
FXUS63 KIWX 241744  
AFDIWX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE NORTHERN INDIANA  
1244 PM EST TUE JAN 24 2017  
   
SYNOPSIS
 
 
ISSUED AT 1221 PM EST TUE JAN 24 2017  
 
HIGH PRESSURE WILL CONTINUE TO KEEP THE REGION DRY TODAY WITH  
OVERCAST SKIES. FOR TONIGHT AND INTO WEDNESDAY, A LOW PRESSURE  
SYSTEM PASSES BY TO THE NORTH ALLOWING FOR A CHANCE FOR LIGHT RAIN  
ESPECIALLY WEST OF US-31 AND NORTH OF US-6. AS A COLD FRONT MOVES  
THROUGH WEDNESDAY NIGHT WITH MORE SEASONABLY COOL  
TEMPERATURES, ANY RAIN WILL BE ABLE TO CHANGE TO SNOW. HIGHS IN  
AND AROUND 40 DEGREES TODAY WILL BE ABLE TO DROP TO THE MID 30S  
TONIGHT BEFORE REACHING THE UPPER 30S TO LOW 40S ON WEDNESDAY.  
FOR THE LATTER PART OF THE WEEK AND INTO THE WEEKEND, HIGHS WILL  
MAINLY BE IN THE UPPER 20S TO LOW 30S ALLOWING FOR THE POSSIBILITY  
OF LAKE ENHANCED SNOW SHOWERS.  
 

 
   
SHORT TERM
 
(TODAY AND TONIGHT)  
ISSUED AT 345 AM EST TUE JAN 24 2017  
 
RELATIVELY BENIGN WEATHER ON TAP FOR TODAY AS STOUT MID/UPPER LEVEL  
RIDGE BUILDS OVER THE REGION DOWNSTREAM OF EJECTING WESTERN CONUS  
LONGWAVE TROUGH AND ASSOCIATED JET STREAK. LINGERING SHOWERS/DRIZZLE  
ASSOCIATED WITH RESIDUAL MIDLEVEL DEFORMATION AND INVERTED SURFACE  
TROUGH STILL IMPACTING OUR NE ZONES BUT THIS ACTIVITY WILL CONTINUE  
TO SHIFT EAST AND DISSIPATE THROUGH THE EARLY MORNING AS SHEAR VORT  
MAX PUSHES EAST AND SUBSIDENCE LAYER BUILDS OVERHEAD WITH SHARPLY  
RISING HEIGHTS AND STRONG AVA. ONLY DOWNSIDE TO THIS AGGRESSIVE PUSH  
OF SUBSIDENCE IS THAT LOW LEVEL DRY AIR ADVECTION WILL LIKELY BE  
INSUFFICIENT TO SCOUR OUT RESIDUAL MOISTURE THAT WILL BECOME TRAPPED  
UNDER SHARP 850MB SUBSIDENCE INVERSION. MAY GET LUCKY AND SEE A FEW  
BREAKS IN OUR SW HALF TOWARD THE END OF THE DAY BUT MORNING  
SATELLITE SHOWS AN EXPANSIVE AREA OF STRATUS THAT WILL BE TOUGH TO  
DISLODGE AND MAINTAINED MOSTLY CLOUDY FORECAST. THIS WILL KEEP  
DIURNAL RANGES IN CHECK WITH HIGHS ONLY IN THE LOW TO MID 40S.  
 
PRIMARILY DRY CONDITIONS ANTICIPATED OVERNIGHT. LEADING WING OF 290K  
ISENTROPIC ASCENT MAY TOUCH OFF AN ISOLATED SHOWER IN OUR FAR NW  
DURING THE EVENING BUT FORCING AND MOISTURE CONVERGENCE REMAIN QUITE  
WEAK WITH MORE FOCUSED LLJ NOT ARRIVING UNTIL EARLY WED MORNING.  
PRECIP CHANCES EVEN BY THEN NOT THAT GREAT OUTSIDE OF FAR NW ZONES  
GIVEN UNFAVORABLE UPPER JET PLACEMENT DIRECTLY OVERHEAD AND  
LACKLUSTER THETA-E PLUME INTERSECTING VERY DRY MIDLEVELS. MOST OF  
LATEST 00Z GUIDANCE HAS LOGICALLY BACKED OFF QPF. LOWERED POP'S  
ACROSS THE BOARD, SAVE FOR FAR NW ZONES THAT WILL LIKELY BE CLIPPED  
BY BETTER MIDLEVEL CVA/QG OMEGA 09-12Z WED. OVERNIGHT LOWS MAY DIP  
INTO THE MID 30S BUT MIXED PRECIP NOT A CONCERN GIVEN PRONOUNCED  
WARM NOSE JUST ABOVE THE SURFACE.  
 

 
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 345 AM EST TUE JAN 24 2017  
 
PRECIP CHANCES NOT GREAT DURING THE DAY WED EITHER. AS PREVIOUSLY  
MENTIONED, CORE OF 140+ KT UPPER JET PASSES DIRECTLY OVERHEAD,  
KEEPING BEST UPPER DIVERGENCE AND MIDLEVEL DEFORMATION/FGEN NORTH OF  
OUR CWA. BROAD/WEAK 290K ISENTROPIC ASCENT MAY BE ENOUGH TO TOUCH  
OFF A FEW ISOLATED SHOWERS/DRIZZLE GIVEN RELATIVELY MOIST LOW  
LEVELS. HOWEVER, DEEP LAYER MOISTURE IS SEVERELY LACKING WITH  
RESIDUAL WARM/DRY NOSE AROUND 800MB LIMITING DEEP ASCENT. LOWERED  
POP'S DURING THE DAY BUT DID KEEP SOME VERY LOW CHANCES IN PLACE  
WITH HIGHEST VALUES ACROSS MI WHERE BETTER FRONTAL FORCING/MOISTURE  
CONVERGENCE MAY CLIP THE AREA DURING THE MORNING. BETTER CHANCES FOR  
PRECIP FOR THE ENTIRE CWA ARRIVE WED NIGHT AS CORE OF HIGHLY  
ELONGATED/POSITIVELY TILTED TROUGH SWINGS THROUGH OUR AREA ALONG  
WITH ASSOCIATED UPTICK IN LOW/MIDLEVEL CONVERGENCE AND DECREASING  
STABILITY WITH COLDER AIR ALOFT. NOT EXPECTING A LOT OF QPF (A TENTH  
AT MOST) BUT MOST PLACES WILL LIKELY SEE A HUNDREDTH OR TWO SO HAVE  
INCREASED POP'S, ESPECIALLY IN NW HALF WHERE ADDED THETA-E  
CONTRIBUTION FROM LAKE MI AND CLOSER PROXIMITY TO PRIMARY VORT MAX  
WILL BOLSTER PRECIP A BIT. CAA WILL ALSO LEAD TO A GRADUAL  
CHANGEOVER TO SNOW BY LATE WED NIGHT. LIGHT QPF AND RELATIVELY WARM  
GROUND WILL LIMIT ACCUMULATION POTENTIAL BUT A FEW LOCATIONS IN OUR  
NW MAY PICK UP CLOSE TO AN INCH ON GRASSY SURFACES BY LATE THU  
MORNING. LITTLE TO NO ACCUMULATION ALONG AND SOUTH OF US-24.  
 
LITTLE CHANGE IN WEATHER STORY FOR THE END OF THE WEEK AND WEEKEND.  
LARGE NEGATIVE HEIGHT ANOMALY SETS UP SHOP OVER QUEBEC WITH MULTIPLE  
WEAK JET STREAKS AND SHORTWAVES ROTATING THROUGH THE GREAT LAKES IN  
PERTURBED NW FLOW. THIS LEADS TO AN EXTENDED PERIOD OF LIGHT, LAKE-  
ENHANCED SNOW SHOWERS, CLOUDY SKIES, AND TEMPS NEAR AVERAGE. STILL  
DIFFICULT TO PINPOINT BEST CHANCES FOR MORE MEANINGFUL SNOW ACCUMS  
BUT CURRENTLY APPEARS FRI MORNING AND SAT NIGHT/SUNDAY HAVE THE BEST  
CHANCES. THAT IS SUBJECT TO CHANGE OF COURSE, DEPENDING ON EXACT  
TIMING OF SUBTLE, EMBEDDED FEATURES AND WILL LIKELY GRIND OUT  
FLURRIES/LIGHT SNOW SHOWERS FOR MUCH OF THE PERIOD ANYWAY.  
ACCUMULATIONS IN ANY ONE PERIOD WILL BE LIGHT BUT MAY ADD UP TO  
SEVERAL INCHES BY MONDAY IN FAVORED WNW LAKE EFFECT SNOW BELTS.  
 

 
   
AVIATION
 
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY AFTERNOON)  
ISSUED AT 1221 PM EST TUE JAN 24 2017  
 
HIGH PRESSURE RIDGE MOVING IN ALLOWS SOME LOW LEVEL DRY AIR TO RAISE  
THE CIGS TO MVFR LEVEL. CIGS WILL DROP AGAIN TOWARDS MORNING HOURS  
WEDNESDAY WITH THE MOISTENING OF THE COLUMN AS A RESULT OF THE  
APPROACHING LOW PRESSURE SYSTEM FROM THE SOUTHWEST. ENOUGH DRY AIR  
NEARBY MAY KEEP FWA MOSTLY DRY WED, BUT CAN'T TOTALLY RULE OUT A  
SHOWER MIDMORNING. SBN HAS A BETTER CHANCE AT SHOWERS WITH THE  
LOW CLOSER AND THEREFORE A MORE MOIST COLUMN. WITH THE INCOMING  
LOW LEVEL JET, HAVE INDICATED THE BACKING WINDS OVERNIGHT AND  
ADDED A FEW HOURS OF SHEAR AT BOTH SITES.  
 

 
   
IWX WATCHES/WARNINGS/ADVISORIES
 
 
IN...NONE.  
MI...NONE.  
OH...NONE.  
LM...NONE.  

 
 

 
 
SYNOPSIS...ROLLER  
SHORT TERM...AGD  
LONG TERM...AGD  
AVIATION...ROLLER  
 
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