191  
FXUS63 KLOT 202328  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
528 PM CST WED FEB 20 2019  
   
SHORT TERM
 
 
153 PM CST  
 
THROUGH THURSDAY NIGHT...  
 
WITH THE FREEZING PRECIPITATION THREAT COMING TO AN END ACROSS  
THE REGION, THE MAIN FORECAST FOCUS IS WITH THE GUSTY WEST-  
SOUTHWESTERLY WINDS EXPECTED TO DEVELOP ACROSS THE AREA THIS  
EVENING. GIVEN THE CURRENT OBSERVATION TRENDS, WE SHOULD BE ABLE  
TO DROP THE REST OF THE WINTER WEATHER ADVISORY EARLY THIS  
AFTERNOON.  
 
SURFACE LOW PRESSURE OVER SOUTHERN MN WILL SHIFT EAST-  
NORTHEASTWARD OVER NORTHERN LAKE MICHIGAN THIS EVENING. AS IT DOES  
SO, OUR SURFACE WINDS WILL SHIFT FROM THE SOUTH TO THE WEST-  
SOUTHWEST AND BECOME GUSTY UP TO 35 MPH THIS EVENING FOLLOWING A  
FRONTAL PASSAGE. THESE WIND SPEEDS WILL ABATE LATE TONIGHT INTO  
THURSDAY. THE ARRIVAL OF THE FRONTAL BOUNDARY EARLY THIS EVENING WILL  
ALSO BRING AN END TO MUCH OF THE DRIZZLE AND FOG THAT IS  
CURRENTLY IN PLACE ACROSS THE AREA.  
 
QUIET WEATHER WITH SEASONAL TEMPERATURES IN THE 30S IS EXPECTED ON  
THURSDAY AS SURFACE HIGH PRESSURE SETS UP OVER THE AREA. WHILE WE  
SHOULD LOSS THE LOW-LEVEL CLOUD COVER TONIGHT, HIGHER LEVEL CLOUDS  
LOOK TO RESULT IN PARTLY CLOUDY TO PARTLY SUNNY SKIES DURING THE  
DAY THURSDAY.  
 
KJB  
 

 
   
LONG TERM
 
 
309 PM CST  
 
THURSDAY NIGHT THROUGH WEDNESDAY...  
 
ACTIVE WEATHER WILL CONTINUE FOR THE LONG TERM FORECAST PERIOD. MAIN  
CONCERNS WILL FOCUS ON POTENTIAL ICE ACCUMULATION IN FREEZING RAIN  
LATE FRIDAY NIGHT INTO SATURDAY MORNING AND THEN STRONG, GUSTY WINDS  
LATE SATURDAY NIGHT INTO SUNDAY NIGHT.  
 
QUIET WEATHER WILL CONTINUE INTO THE BEGINNING OF THE LONG TERM  
FORECAST PERIOD AS BROAD UPPER RIDING COVERS THE ERN 2/3 OF THE  
CONUS. THE NEXT SYSTEM TO IMPACT THE REGION WILL BE A PACIFIC  
SHORTWAVE DROPPING SOUTH INTO THE DESERT SOUTHWEST FRIDAY AND THEN  
QUICKLY LIFTING OUT OVER THE CENTRAL PLAINS. THE LONG RANGE  
GUIDANCE IS IN GOOD AGREEMENT ON THE 500MB PATTERN WITH THIS SYSTEM,  
WITH ONLY MINOR DIFFERENCES IN THE TIMING/INTENSITY OF THE UPPER LOW  
AS IT LIFTS ACROSS MISSOURI SATURDAY EVENING. UNFORTUNATELY, THE  
SAME CANNOT BE SAID FOR THE ASSOCIATED SFC LOW, WITH THE MODELS  
SHOWING A FAIR SPREAD, ESPECIALLY FOR THE TRACK OF THE LOW CENTER.  
SO, HAVE BASED THE SENSIBLE WEATHER FEATURES AND IMPACTS FROM THIS  
SYSTEM ON THE BLENDED SOLUTION, WHICH WILL NEED TO BE REFINED IN  
LATER UPDATES. HOWEVER, THE MAIN IDEA IS THAT AS THE SFC LOW LIFTS  
NEWD, A WARM FRONT SETTING UP ACROSS THE LOWER OHIO VALLEY FRIDAY  
NIGHT WILL EVENTUALLY SURGE NORTH THROUGH THE DAY ON FRIDAY. A RIDGE  
OF HIGH PRESSURE WILL REMAIN ACROSS THE UPPER GREAT LAKES, LIMITING  
THE NORTHWARD PROGRESSION OF THE SFC BOUNDARY, BUT ABOVE THE  
BOUNDARY LAYER, THE MODELS ARE IN GOOD AGREEMENT DEPICTING STRONG  
WARM, MOIST ADVECTION. LATEST THOUGHTS ARE THAT A SHALLOW LAYER OF  
COLDER, SUB-FREEZING AIR WILL REMAIN IN PLACE ACROSS THE NORTHERN,  
PORTIONS OF THE CWA, WHILE WARMER SFC AIR MAY REACH UP TO, ROUGHLY,  
THE I-80 CORRIDOR. PCPN SHOULD SPREAD ACROSS THE AREA LATE FRIDAY  
NIGHT, WITH THE FREEZING RAIN LIKELY NORTH OF THE I-80 CORRIDOR AND  
ALL RAIN TO THE SOUTH. THE SURFACE FREEZING LINE IS THE MAIN  
QUESTION MARK AT THIS TIME, AND WILL BE HIGHLY DEFENDANT ON THE  
EXACT TRACK AND SPEED OF THE MAIN SFC LOW. CONSEQUENTLY, THERE IS  
SOME UNCERTAINTY ON THE COVERAGE AND DURATION OF ICE ACCUMULATION  
WITH THE FREEZING RAIN. THIS SITUATION CERTAINLY BEARS WATCHING.  
BASED ON THE LATEST GUIDANCE, EXPECT SOMEWHAT OF A NON-DIURNAL  
SURFACE TEMPERATURE TREND, WITH SFC TEMPS RISING THROUGH THE LATE  
NIGHT HOURS, AND THEN RISING ABOVE FREEZING DURING THE MORNING HOURS  
ALLOWING THE PCPN TO TRANSITION OVER TO ALL RAIN.  
 
THE NEXT AREA OF CONCERN WILL BE STRONG, GUSTY WINDS FOLLOWING THE  
PASSAGE OF THE ASSOCIATED COLD FRONT. WHILE THERE ARE SOME  
DIFFERENCES AMONG THE MODELS IN THE EXACT TRACK OF THE SURFACE LOW,  
THERE ARE SOME STRONG SIGNALS THAT THE SFC LOW WILL CONTINUE TO  
DEEPEN AS IT LIFTS NORTHEAST THROUGH THE CENTRAL GREAT LAKES EARLY  
SUNDAY. A STRONG PRESSURE RISE/FALL COUPLET WILL ACCOMPANY THE  
FRONTAL PASSAGE WITH +/ 20 MB PER 6 HR AND +/- 12 MB PER 3 HR  
PRESSURE TENDENCIES INDICTED IN THE LONGER RANGE GUIDANCE. ALSO,  
MODEL SOUNDINGS SHOW 50 TO 60 KT WEST-NORTHWEST WINDS AT THE TOP OF  
THE MIXED LAYER ON SUNDAY. DEPENDING ON HOW DEEP MIXING MAY OCCUR,  
THERE WILL BE A CHANCE FOR WIND GUSTS IN EXCESS OF 45 MPH POSSIBLE  
AND A WIND ADVISORY OR HIGH WIND WARNING MAY BE NEEDED. A LARGE  
TEMPERATURE SWING IS LIKELY WITH THE PASSAGE OF THIS SYSTEM. AHEAD  
OF THE FRONT, TEMPERATURES ARE EXPECTED TO REACH HIGHS RANGING FROM  
AROUND 40 F ALONG THE IL/WI BORDER TO THE LOW 50S FOR THE SOUTHERN  
PORTIONS OF THE CWA. HIGHS ON SUNDAY SHOULD ONLY BE IN THE LOWER TO  
MIDDLE 30S.  
 
YET ANOTHER SYSTEM IS FORECAST TO MOVE ACROSS THE REGION EARLY NEXT  
WEEK. AT THIS DISTANCE, THERE ARE STILL LARGE DIFFERENCES IN THE  
STRENGTH AND TRACK OF THIS NEXT SYSTEM. WHILE THERE ARE SOME  
INDICATIONS THAT ANOTHER ROUND OF SNOW IS POSSIBLE, BUT MODEL SPREAD  
IN THE LONG RANGE GUIDANCE IS TOO LARGE TO HAVE ANY CONFIDENCE IN  
ANY SPECIFICS.  
 

 
   
AVIATION
 
 
FOR THE 00Z TAFS...  
 
528 PM...PRIMARY FORECAST CONCERNS ARE GUSTY SOUTHWEST WINDS AND  
CIGS THROUGH DAYBREAK THURSDAY.  
 
SOUTHWEST WINDS WILL REMAIN GUSTY THROUGH EARLY THURSDAY MORNING  
IN THE 20-25KT RANGE. SPEEDS/GUSTS WILL SLOWLY DIMINISH OVERNIGHT  
WITH GUSTS LARGELY OVER BY DAYBREAK. WESTERLY WINDS 10-15KTS WILL  
CONTINUE THURSDAY. CIGS ARE SLOWLY LIFTING TO LOW MVFR EARLY THIS  
EVENING WITH SOME IFR CIGS BUT THE TREND WILL BE FOR CIGS TO LIFT  
THROUGH MVFR THIS EVENING AND BEGIN TO SCATTER OUT OVERNIGHT FROM  
WEST TO EAST. FEW/SCT LOW CLOUDS ARE POSSIBLE MAINLY THURSDAY  
MORNING ALONG WITH HIGH CLOUDS THURSDAY. CMS  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS UNTIL 9 AM THURSDAY.  
 

 
 

 
 
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