754  
FXUS63 KLOT 190947  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
347 AM CST SUN JAN 19 2020  
   
SHORT TERM
 
 
347 AM CST  
 
THROUGH MONDAY...  
 
TODAY THROUGH MONDAY NIGHT...  
 
ARCTIC BLAST, WITH BLUSTERY WINDS AND BITTER COLD WIND CHILLS ARE  
THE MAIN FORECAST HIGHLIGHTS IN THE NEAR TERM, AS WELL AS THE  
POTENTIAL FOR SOME LAKE EFFECT SNOW SHOWERS LATER TODAY INTO  
MONDAY. SOME OF THESE LAKE EFFECT SNOW SHOWERS MAY AFFECT PORTIONS  
OF COOK COUNTY LATE THIS AFTERNOON AND TONIGHT.  
 
GUSTY WESTERLY WINDS CONTINUE TO PUSH ARCTIC AIR INTO THE REGION  
EARLY THIS MORNING, WITHIN A TIGHT SURFACE PRESSURE GRADIENT  
BETWEEN DEPARTING LOW PRESSURE TO THE NORTHEAST, AND 1040+ MB HIGH  
PRESSURE BUILDING SOUTHEAST ACROSS THE NORTHERN PLAINS. SURFACE  
OBSERVATIONS AS OF 3 AM CST INDICATE AIR TEMPERATURES HAVE FALLEN  
TO AROUND ZERO ACROSS OUR WESTERN CWA, AND THE LOWER SINGLE DIGITS  
ACROSS THE EAST. SUSTAINED WINDS NEAR 20 MPH, AND GUSTS OF 30-35  
MPH WERE PRODUCING WIND CHILLS IN THE -20 TO -22 RANGE FROM THE  
FOX VALLEY WESTWARD, WHERE CURRENT WIND CHILL ADVISORY REMAINS  
VALID THROUGH 10 AM THIS MORNING. WHILE SOME SLIGHT MODERATION OF  
THE AIR MASS IS EXPECTED TODAY, TEMPERATURES WILL STRUGGLE TO RISE  
FROM OUR MORNING LOWS INTO THE LOW-MID TEENS AT BEST BY THIS  
AFTERNOON. WINDS WILL SLOWLY DIMINISH, BUT WILL REMAIN BLUSTERY  
THROUGH THE DAY, KEEPING WIND CHILLS NEAR ZERO IN MANY AREAS EVEN  
INTO THE AFTERNOON. AREAS OF COLD ADVECTION STRATUS WILL MAKE FOR  
PARTLY TO MOSTLY CLOUDY SKIES, WITH THE RELATIVELY SHALLOW BUT  
COLD CLOUD LAYER AT IDEAL TEMPERATURES FOR PRODUCING FLURRIES AT  
TIMES.  
 
WITH WESTERLY LOW LEVEL WINDS THIS MORNING, LAKE EFFECT SNOW  
SHOWERS HAVE BEEN FOCUSED ACROSS THE LAKE, EAST OF THE FORECAST  
AREA. HOWEVER, A SUBTLE SURFACE TROUGH ACROSS NORTHERN LAKE  
MICHIGAN WILL PUSH SOUTHEAST TODAY IN ASSOCIATION WITH MID-LEVEL  
SHORT WAVE DIGGING AROUND THE TRAILING PERIPHERY OF THE DEPARTING  
STORM TO OUR EAST. WINDS, PARTICULARLY JUST ABOVE THE BOUNDARY  
LAYER, ARE PROGGED TO VEER MORE NORTHERLY WITH TIME LATE THIS  
AFTERNOON AND TONIGHT, WHICH IS EXPECTED TO ALLOW LAKE EFFECT SNOW  
SHOWERS TO EDGE BACK INTO OUR NORTHWEST INDIANA COUNTIES AND EVEN  
FAR EASTERN AND SOUTHEASTERN COOK COUNTY. THE DRY NATURE OF THE  
ARCTIC AIR, AND RELATIVELY SHALLOW INVERSION HEIGHTS (MAXING OUT  
AROUND 6 KFT TONIGHT) SHOULD PRECLUDE SIGNIFICANT MEASURABLE SNOW,  
THOUGH AMOUNTS OF PERHAPS 1-3" WILL BE POSSIBLE, ESPECIALLY  
ACROSS PORTER COUNTY WHERE THE LONGEST RESIDENCE TIME AND  
STRONGEST CONVERGENCE APPEARS LIKELY. MINOR ACCUMULATIONS OF LESS  
THAN AN INCH MAY OCCUR INTO THE COOK COUNTY SHORE AREAS,  
ESPECIALLY FROM DOWNTOWN CHICAGO SOUTHEASTWARD. BACKING/DECREASING  
LOW LEVEL WINDS SHOULD PUSH THE WEAKENING BAND BACK ACROSS LAKE  
AND PORTER COUNTIES MONDAY MORNING WHICH ALONG WITH A LOWERING  
SUBSIDENCE INVERSION SHOULD BRING LAKE SNOW TO AN END BY  
AFTERNOON.  
 
TEMPERATURE WISE, ONLY VERY SLOW MODERATION OF THE ARCTIC AIR  
MASS IS EXPECTED THROUGH MONDAY. LOWS SHOULD DIP INTO THE SINGLE  
DIGITS IN MANY AREAS TONIGHT DESPITE SOME CLOUD COVER, WITH  
RECOVERY INTO THE TEENS AND LOWER 20S MONDAY. CLEARING CLOUDS AND  
DIMINISHING WINDS MONDAY NIGHT WILL ALLOW FOR SIMILAR IF NOT  
SLIGHTLY COLDER MINS THAN TONIGHT.  
 
RATZER  
 

 
   
LONG TERM
 
 
347 AM CST  
 
TUESDAY THROUGH SATURDAY...  
 
UPPER RIDGING BUILDS ACROSS THE MISSOURI AND MISSISSIPPI VALLEYS  
AND WESTERN GREAT LAKES INTO MID-WEEK, WHILE SURFACE HIGH PRESSURE  
DRIFTS SOUTHEAST INTO THE OHIO AND TENNESSEE VALLEYS. THIS WILL  
MAKE FOR DRY AND SLOWLY MODERATING WEATHER TUESDAY AND WEDNESDAY.  
 
POTENTIALLY ACTIVE WEATHER LOOKS TO RETURN WEDNESDAY NIGHT  
THROUGH SATURDAY HOWEVER, WITH MEDIUM-RANGE MODELS DEPICTING THE  
DEVELOPMENT OF A CLOSED UPPER TROUGH ACROSS THE CENTRAL CONUS.  
WHILE DIFFERENCES IN THE DETAILS OF VARIOUS GUIDANCE REMAIN, THE  
GENERAL CONSENSUS IS FOR THE DEVELOPMENT OF BROAD SOUTHWESTERLY  
WARM/MOIST ADVECTION FLOW TO DEVELOP WEDNESDAY NIGHT AHEAD OF A  
BAROCLINIC FRONTAL ZONE WHICH LAYS OUT FROM ONTARIO BACK INTO THE  
CENTRAL PLAINS. WHILE THIS FOCUS IS INITIALLY WEST OF THE FORECAST  
AREA, THERE IS EVIDENCE OF A LEAD SHORT WAVE LIFTING NORTHEAST  
ALONG THE BAROCLINIC ZONE WEDNESDAY NIGHT, WHICH MAY SPREAD SOME  
VERY LIGHT SNOW INTO PARTS OF NORTHERN IL OVERNIGHT. WEAK BUT  
PERSISTENT WARM ADVECTION FLOW WILL PRESENT THE POTENTIAL FOR  
ADDITIONAL LIGHT PRECIP THURSDAY, THOUGH THE GREATER POTENTIAL FOR  
MORE ORGANIZED PRECIPITATION APPEARS TO COME LATE THURSDAY  
THROUGH FRIDAY NIGHT AS THE UPPER TROUGH CLOSES OFF AND A  
DEEPENING SURFACE LOW DEVELOPS AND LIFTS FROM THE LOWER  
MISSISSIPPI VALLEY TOWARD THE GREAT LAKES. THE GFS/CMC/ECMWF AND  
THEIR ENSEMBLES VARY WITH THE TRACK OF THE LOW AT THIS DISTANCE  
(GFS WARMER AND FARTHEST WEST, THE CMC FARTHEST EAST), SO  
CONFIDENCE IN DETAILS IS STILL LOW AT THIS DISTANCE. IT DOES  
APPEAR HOWEVER THAT THE POTENTIAL FOR A STORM SYSTEM TO PRODUCE  
SOME SORT OF MEASURABLE WINTRY PRECIPITATION EXISTS DURING THE  
LATE WEEK PERIOD.  
 
RATZER  
 

 
   
AVIATION
 
 
FOR THE 06Z TAFS...  
 
STRONG AND GUSTY WEST WINDS WILL CONTINUE THROUGH THE NIGHT WITH  
ONLY SOME SLIGHT EASING IN THE MAGNITUDE AS THE NIGHT WEARS ON.  
GENERALLY EXPECTING MVFR CIGS TO PERSIST WITH INTERMITTENT  
FLURRIES AND PERHAPS JUST A BRIEF VSBY REDUCTION OR TWO IN LIGHT  
SNOW, BUT NO ACCUMULATION EXPECTED. WINDS CONTINUE TO RELAX  
GRADUALLY SUNDAY WITH MVFR CIGS PROBABLY LINGERING. FLURRIES  
REMAIN POSSIBLE SUNDAY.  
 
- IZZI/KB  
 

 
 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...WIND CHILL ADVISORY...ILZ003-ILZ004-ILZ005-ILZ008-ILZ010-ILZ011-  
ILZ012-ILZ019-ILZ020-ILZ021-ILZ032 UNTIL 10 AM SUNDAY.  
 
IN...LAKESHORE FLOOD ADVISORY...INZ002 UNTIL NOON SUNDAY.  
 
LM...HEAVY FREEZING SPRAY WARNING...LMZ740-LMZ741-LMZ742-LMZ743-  
GARY TO MICHIGAN CITY IN UNTIL NOON SUNDAY.  
 
SMALL CRAFT ADVISORY...WINTHROP HARBOR TO GARY IN UNTIL 9 AM  
MONDAY.  
 
GALE WARNING...GARY TO MICHIGAN CITY IN UNTIL 6 AM SUNDAY.  
 

 
 

 
 
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