175  
FXUS63 KLOT 231953  
AFDLOT  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE, IL  
153 PM CST FRI FEB 23 2018  
   
SHORT TERM
 
 
157 AM CST  
 
THROUGH TONIGHT...  
 
SCATTERED SHOWERS ARE APPROACHING THE I-39 CORRIDOR AND MORE  
WIDESPREAD SHOWERS WILL SPREAD EAST ACROSS THE FORECAST AREA EARLY  
THIS MORNING. 0.1-0.2 INCHES OF RAIN ARE EXPECTED FROM THE SHOWERS,  
BUT THE ADDITIONAL RAINFALL SHOULD HAVE LITTLE TO NO IMPACT ON AREA  
RIVERS. AREAS OF FOG ARE ALSO BEING REPORTED AT MOST LOCATIONS, BUT  
DENSE FOG IS NOT EXPECTED.  
 
THE WEAK SURFACE LOW WILL SHIFT NORTH OVER THE NORTHERN GREAT LAKES  
WHILE THE LOW'S FRONT SHIFTS NORTHEAST. RAIN WILL SHIFT OUT OF THE  
FORECAST AREA LATE THIS MORNING, BUT CLOUDY CONDITIONS WILL  
CONTINUE. HIGH TEMPERATURES WILL BE IN THE MID 40S TO AROUND 50.  
 
HIGH PRESSURE SPREADS OVER THE UPPER MIDWEST TONIGHT AS A FRONTAL  
BOUNDARY AND WEAK UPPER LEVEL DISTURBANCE SHIFTS NORTH INTO CENTRAL  
IL. GUIDANCE DIFFERS ON HOW FAR NORTH THE PRECIP ASSOCIATED WITH  
THIS FRONT WILL GET, BUT I THINK PRECIP WILL BE ALONG AND SOUTH OF I-  
80 BY SUNRISE SATURDAY MORNING.  
 
A WINTRY MIX OF PRECIP INCLUDING FREEZING RAIN IS POSSIBLE. FORECAST  
SOUNDINGS FEATURE A DEEP WARM LAYER AND VERY LITTLE SATURATION IN  
THE DGZ. THEREFORE, ANY PRECIP THAT FALLS SHOULD BE LIQUID PRIOR TO  
HITTING THE GROUND. SURFACE TEMPERATURES WILL BE KEY, AND RIGHT NOW  
SURFACE TEMPS ARE FORECAST TO BE RIGHT AROUND FREEZING ALONG THE I-  
80 CORRIDOR AND POINTS NORTH. THEREFORE, THERE COULD BE SLICK SPOTS  
SATURDAY MORNING, ESPECIALLY ON COLDER, ELEVATED SURFACES.  
TEMPERATURES WILL WARM TO ABOVE FREEZING BY MID TO LATE SATURDAY  
MORNING, ENDING THE ICE THREAT.  
 
I'M NOT EXPECTING MUCH ICE ACCUMULATION SO I WILL NOT BE ISSUING ANY  
ICE RELATED HEADLINES.  
 
JEE  
 

 
   
LONG TERM
 
 
SUNDAY THROUGH FRIDAY...  
 
153 PM...PRIMARY FORECAST CONCERNS ARE THE POTENTIAL FOR MORE  
RAIN WEDNESDAY/THURSDAY AND THE CHANCE OF MIXED PRECIP/SNOW  
THURSDAY.  
 
AS LOW PRESSURE LIFTS NORTH ACROSS THE UPPER LAKES REGION  
SUNDAY...STRONG/GUSTY WESTERLY WINDS WILL DIMINISH ON SUNDAY BUT  
THERE COULD BE A PERIOD SUNDAY MORNING WHEN WIND GUSTS ARE STILL  
IN THE 35-40 MPH RANGE.  
 
HIGH PRESSURE WILL MOVE FROM THE CENTRAL PLAINS SUNDAY TO THE  
OHIO VALLEY MONDAY WITH DRY CONDITIONS EXPECTED THROUGH TUESDAY  
EVENING. WITH SOME SUNSHINE EXPECTED...TEMPS LIKELY TO MODERATE  
BACK NEAR 50 ON MONDAY AND INTO THE 50S ON TUESDAY. WITH NO SNOW  
PACK...ITS POSSIBLE THESE TEMPS COULD BE A BIT LOW BUT CAN TREND  
HIGHER AS THIS TIME PERIOD APPROACHES.  
 
LOW PRESSURE IS EXPECTED TO DEVELOP OVER THE PLAINS TUESDAY NIGHT  
INTO WEDNESDAY AND MOVE NEAR NORTHERN IL BY THURSDAY MORNING.  
STILL CONSIDERABLE DIFFERENCES WITH THE GFS SHOWING A RATHER  
STRONG LOW AT THAT TIME VS. A WEAKER ECMWF LOW. AHEAD OF THIS  
LOW...SHOWERS WILL BE POSSIBLE TUESDAY NIGHT INTO WEDNESDAY WITH  
A PERIOD OF HEAVIER PRECIP POSSIBLE WEDNESDAY NIGHT INTO THURSDAY  
MORNING. WHILE THE TIMING LOOKS SIMILAR...THE LARGE DIFFERENCES IN  
THE STRENGTH OF THE LOW MAKE FOR AN UNCERTAIN FORECAST. IN  
ADDITION...SMALL TRACK CHANGES COULD MAKE THE DIFFERENCE BETWEEN  
ALL RAIN OR A STRIPE OF ACCUMULATING SNOW...WHICH CURRENTLY WOULD  
BE MOST FAVORED ACROSS FAR NORTHERN IL INTO SOUTHERN WI. CURRENT  
QPF FORECASTS WOULD SUGGEST THE POTENTIAL FOR A HALF INCH TO AN  
INCH OF RAIN WITH THIS SYSTEM. HIGH PRESSURE WILL THEN BUILD  
ACROSS THE REGION FRIDAY. CMS  
 

 
   
AVIATION
 
 
FOR THE 18Z TAFS...  
 
CIGS/VIS GRADUALLY IMPROVING AT THE TERMINALS AS A SECONDARY COLD  
FRONT PUSHES ACROSS THE REGION. EXPECT THAT CONDITIONS SHOULD  
IMPROVE TO VFR BY ARND 00Z. WITH THE PASSAGE OF THIS BOUNDARY,  
WINDS ARE VEERING TO JUST NORTH OF WESTERLY AND GUSTING IN THE  
20-25 KT RANGE. EXPECT GUSTINESS TO PERSIST THROUGH THE AFTERNOON  
AS THE REGION REMAINS UNDER A CORE OF PRESSURE RISES WITH LOW  
PRESSURE LIFTING AWAY FROM THE UPPER GREAT LAKES AND HIGH PRESSURE  
SPREADS EAST ACROSS THE NORTHERN PLAINS.  
 
MAIN CONCERN FOR THE PERIOD WILL BE THE CHANCES OF A WINTRY MIX OF  
PCPN SPREADING FROM SOUTH TO NORTH TOMORROW MORNING AS A WARM  
FRONT SETS UP ALONG THE OHIO RIVER AND LOW PRESSURE LIFTS THROUGH  
THE CENTRAL PLAINS AND THE HIGH PRESSURE TRACKS ACROSS THE UPPER  
GREAT LAKES. WINDS WILL SHIFT TO EASTERLY OVERNIGHT TONIGHT AND  
TOMORROW AS THE WARM FRONT SETS UP TO THE SOUTH OF THE TERMINALS.  
AT THE TIME OF PCPN ONSET, SFC TEMPERATURES SHOULD BE BELOW  
FREEZING, WITH A WARM LAYER ALOFT. PCPN COULD INITIALLY START OUT  
AS FZRA OR FZRASN FOR A SHORT PERIOD TOMORROW BEFORE CHANGING OVER  
TO RAIN BY LATE MORNING AS WARMER GRADUALLY AIR SPREADS  
NORTHWARD. IN THE PCPN AND EASTERLY FLOW, CIGS MAY DROP TO IFR,  
ESPECIALLY LATER IN THE DAY.  
 

 
   
MARINE
 
 
153 PM...PRIMARY FORECAST CONCERN REMAINS HIGH END GALES AND THE  
POTENTIAL FOR STORM FORCE GUSTS SATURDAY NIGHT INTO SUNDAY.  
 
OVERALL...NO SIGNIFICANT CHANGES TO THE FORECAST OR REASONING. LOW  
PRESSURE WILL DEVELOP OVER THE SOUTHERN PLAINS SATURDAY AND THEN  
BEGIN TO RAPIDLY DEEPEN AS IT MOVES NORTH ACROSS WI SATURDAY NIGHT  
THEN CROSSING LAKE SUPERIOR SUNDAY MORNING. SOUTHEASTERLY GALES  
ARE EXPECTED TO DEVELOP OVER SOUTHERN LAKE MICHIGAN SATURDAY  
EVENING AS THE LOW APPROACHES WITH SOUTHERLY GALES ACROSS THE  
ENTIRE LAKE EARLY SUNDAY MORNING. AS THE LOW CONTINUES TO DEEPEN  
OVER LAKE SUPERIOR SUNDAY MORNING...WINDS WILL BEGIN TO SHIFT TO  
THE SOUTHWEST AND THEN WEST AS COLDER AIR SPREADS ACROSS THE  
REGION. ITS DURING THIS TIME PERIOD...SUNDAY MORNING...THAT HIGH  
END GALES ARE LIKELY AND AT LEAST SOME STORM FORCE GUSTS ARE  
POSSIBLE. IF ANY STORMS OCCUR...THEY LIKELY WOULD ONLY LAST A  
SHORT TIME...PERHAPS 3-6 HOURS. THE GALES WILL DIMINISH OVER THE  
SOUTHERN PART OF THE LAKE BY SUNDAY AFTERNOON BUT GALES MAY  
PERSIST ACROSS NORTH/CENTRAL PORTIONS OF THE LAKE WELL INTO  
SUNDAY EVENING. THE CURRENT GALE WATCH HAS THIS TIME PERIOD  
COVERED WELL AND NOT PLANNING ANY HEADLINE CHANGES THIS AFTERNOON.  
 
HIGH PRESSURE WILL MOVE ACROSS THE OHIO VALLEY SUNDAY NIGHT AND  
MONDAY AS WEAK LOW PRESSURE MOVES ACROSS ONTARIO...MAINTAINING A  
WEST/SOUTHWEST GRADIENT ACROSS THE LAKE. LOW PRESSURE MAY MOVE  
ACROSS THE SOUTHERN GREAT LAKES REGION NEXT WEDNESDAY NIGHT INTO  
THURSDAY. CMS  
 

 
   
LOT WATCHES/WARNINGS/ADVISORIES
 
 
IL...NONE.  
IN...NONE.  
LM...GALE WATCH...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-  
LMZ779...6 PM SATURDAY TO 3 AM MONDAY.  
 

 
 

 
 
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