147  
FXUS63 KLOT 230231  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
931 PM CDT MON OCT 22 2018  
   
UPDATE
 
 
924 PM CDT  
 
AFTER ABOVE NORMAL TEMPERATURES FOR A CHANGE, A COLD FRONT IS  
NEARING THE AREA THIS EVENING. NO PRECIP IS COMING WITH THIS  
FRONT, BUT THE SHIFT TO NORTHERLY WINDS WILL SIGNAL THE RETURN TO  
A BIT COOLER WEATHER FOR A FEW DAYS. WE WILL JUST SEE SOME  
SCATTERED STRATOCUMULUS CLOUDS, POSSIBLY SLIGHTLY HIGHER COVERAGE  
NEAR THE LAKE.  
 
KMD  
 

 
   
SHORT TERM
 
 
148 PM CDT  
 
THROUGH TUESDAY...  
 
FOR THE REMAINDER OF THE AFTERNOON AND THROUGH THE NIGHT TONIGHT,  
SKIES WILL BE MOSTLY CLEAR WITH ONLY A LITTLE CIRRUS FOR CLOUD  
COVER. WINDS SHOULD BE AROUND 10 KT FOR THE EVENING AND  
OVERNIGHT, GRADUALLY VEERING FROM WLY TO NWLY AS LOW PRESSURE  
MOVES ACROSS THE UPPER GREAT LAKES AND HIGH PRESSURE BUILDS INTO  
THE NORTHERN PLAINS. A WEAK SECONDARY COLD FRONT WILL PUSH SOUTH  
ACROSS THE LOCAL AREA DURG THE EARLY MORNING HOURS, SHIFTING WINDS  
TO NORTHERLY, AND BECOMING MORE BREEZY FOR THE MORNING HOURS  
TOMORROW. THIS SECONDARY COLD FRONT OR SURGE OF COOLER AIR WILL  
OCCUR EARLY ENOUGH IN THE DAY THAT THERE WILL STILL BE SOME  
OPPORTUNITY FOR DIURNAL WARMING AS SKIES REMAIN MOSTLY CLEAR  
THROUGH THE DAY. THE MORNING SHOULD START OUT A BIT CHILLY WITH  
MORNING LOWS IN THE 30S. WHILE THERE SHOULD BE DEEP LAYER COLD  
ADVECTION THROUGH THE DAY UNDER NWLY FLOW ALOFT, HEIGHT RISES  
FROM UPPER RIDGING BUILDING OVER THE PLAINS WILL HELP KEEP  
CONDITIONS DRY WITH HIGHS IN THE LOW 50S.  
 

 
   
LONG TERM
 
 
201 PM CDT  
 
TUESDAY NIGHT THROUGH MONDAY...  
 
UPPER TROUGH WILL BE IN THE PROCESS OF MOVING EAST OF THE GREAT  
LAKES REGION MIDWEEK. HIGH PRESSURE WILL MOVE EAST OF THE REGION  
AS WELL AND ALLOW FOR A BRIEF PERIOD OF RETURN SOUTHERLY FLOW, BUT  
NOT LOOKING FOR ANY BIG MODERATION IN TEMPERATURES BEFORE NEXT  
SHORTWAVE TROUGH MOVES ACROSS THE REGION FRIDAY WITH SOME SHOWER  
POTENTIAL.  
 
HEADING INTO THE WEEKEND, FORECAST CONFIDENCE IN THE OVERALL LARGE  
SCALE PATTERN IS INCREASING WITH MEDIUM RANGE MODELS IN GOOD  
AGREEMENT ON DEVELOPING A SIGNIFICANT CYCLONE THAT TRACKS NORTH  
UP THE EASTERN SEABOARD. CONCURRENTLY, A SERIES OF POTENTIALLY  
FAIRLY VIGOROUS CLIPPER-LIKE NORTHWEST FLOW SHORTWAVE TROUGHS ARE  
PROGGED TO DIG SOUTHEAST INTO THE GREAT LAKES REGION, EVENTUALLY  
PHASING WITH STRONG SOUTHERN STREAM TROUGH RESPONSIBLE FOR THE  
EAST COAST CYCLONE. PRECISE DETAILS IN THE INDIVIDUAL CLIPPER  
SYSTEM TRACKS AND IMPACTS AS WELL AS THE TRACK/INTENSITY OF THE  
EAST COAST STORM COULD CHANGE SOME IN TIME, BUT THE OVERALL LARGE  
SCALE PATTERN MODELS SEEMED TO HAVE LOCKED IN TO.  
 
THE RESULT WILL BE A CONTINUATION OF UNSEASONABLY COLD  
TEMPERATURES THIS WEEKEND INTO EARLY NEXT WEEK. GOING FORECAST  
TEMPS NEAR 50 WILL LIKELY NEED TO BE LOWERED IN LATER FORECASTS IF  
MODELS REMAIN CONSISTENT AS CURRENT FORECAST TEMPS ARE BEING  
WEIGHTED UP SOMEWHAT BY MOS AND CLIMO. THERE WILL LIKELY BE SOME  
PERIODIC BOUTS OF SHOWERS AS THE INDIVIDUAL CLIPPERS MOVE ACROSS  
THE AREA AS THEY HELP CARVE OUT THE DEEP LONG WAVE TROUGH OVER  
EASTERN NOAM AND GIVEN THE DEPTH OF THE TROUGH AND MAGNITUDE OF  
THE INCOMING COLD AIR, SOME MIXED PRECIP OR SNOW SHOWERS CANNOT BE  
RULED OUT AS WELL.  
 
- IZZI  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
THERE ARE AGAIN NO SIGNIFICANT AVIATION IMPACTS EXPECTED FOR THE  
NEXT 24 TO 30 HOURS. THE MAIN CONCERN IS WINDS LATER TONIGHT  
THROUGH TUESDAY. A COLD FRONT PASSAGE WILL SHIFT WINDS TO  
NORTHWEST (300-330) BY 05-07Z TONIGHT. WINDS WILL THEN BECOME  
NORTH-NORTHWEST TO NORTH AT TIMES (340-350) BY MID TUESDAY MORNING  
THROUGH EARLY TO MID AFTERNOON. HAVE MEDIUM-HIGH CONFIDENCE THAT  
PREVAILING DIRECTION WILL PRIMARILY BE WEST OF NORTH. SPEEDS  
SHOULD BE IN THE 10-13 KT RANGE. THERE COULD BE SOME GUSTINESS IN  
15-20 KT RANGE AT ALL SITES BEHIND THE FRONTAL PASSAGE TONIGHT AND  
DURING THE DAY ON TUESDAY. HOWEVER, FORECAST SOUNDINGS ARE A  
MIXED BAG AS TO THE MAGNITUDE AND FREQUENCY OF GUST POTENTIAL.  
HAVE HIGHEST CONFIDENCE IN PREVAILING GUSTS AT GYY DUE TO  
PROXIMITY OF UNSTABLE AIR MASS OVER LAKE MICHIGAN AND NW TO NNW  
WIND DIRECTION.  
 
FINALLY, AS GRADIENT RELAXES TUESDAY AFTERNOON WITH HIGH PRESSURE  
ESTABLISHING ITSELF OVER THE AREA, EXPECTING WINDS TO FLOP OVER  
TO NORTH-NORTHEAST. THERE COULD BE A FEW HOURS OF SPEEDS  
NEAR/AROUND 10 KT AT ORD/MDW AFTER WIND SHIFT TO 020-030 BEFORE  
SPEEDS DIMINISH TO 5 KT OR LESS TUESDAY EVENING. EXPECTING  
CONDITIONS TO REMAIN VFR THROUGH THE PERIOD AT MOST SITES, WITH  
VFR CLOUDS AROUND 3500-4000 FT ON TUESDAY THAT MAY GO BKN AT TIMES  
FOR CHICAGO AREA TERMINALS. THERE'S A CHANCE THAT GYY COULD HAVE  
A PERIOD OF LAKE INDUCED MVFR CIGS AROUND 1500-2500 FT FROM MID  
MORNING THROUGH EARLY-MID AFTERNOON.  
 
CASTRO  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY...LMZ744-LMZ745...1 AM TUESDAY TO 10 PM  
TUESDAY.  
 

 
 

 
 
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