011  
FXUS61 KILN 261127  
AFDILN  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE WILMINGTON OH  
627 AM EST TUE JAN 26 2021  
   
SYNOPSIS
 
 
LOW PRESSURE WILL MOVE NORTHEAST THROUGH THE OHIO VALLEY TODAY,  
WITH RAIN AND FOG EXPECTED THIS MORNING, AND SOME CHANCES FOR  
RAIN CONTINUING INTO THE DAY. ANOTHER LOW PRESSURE SYSTEM WILL  
PASS SOUTH OF THE AREA WEDNESDAY AFTERNOON AND EVENING, BRINGING  
SOME SNOW TO THE REGION. HIGH PRESSURE WILL BRING DRIER  
CONDITIONS ON THURSDAY AND FRIDAY.  
 

 
   
NEAR TERM /UNTIL 6 PM THIS EVENING/
 
 
QUICK UPDATE TO MAKE A FEW ADJUSTMENTS TO PRECIPITATION CHANCES  
(PRIMARILY TO FOCUS ON DRIZZLE) AND FOG.  
 
IN ADDITION, THE WINTER WEATHER ADVISORY HAS EXPIRED AS PLANNED  
AT 6 AM.  
 
TO UPDATE THE SITUATION WITH THE FOG, WIDESPREAD VISIBILITIES OF  
1/2SM TO 1 1/2SM HAVE OVERSPREAD MUCH OF THE ILN FORECAST AREA.  
SO FAR, HOWEVER, VISIBILITIES HAVE NOT DROPPED TO 1/4SM, WHICH  
IS PRECLUDING THE NEED FOR A DENSE FOG ADVISORY AS OF THIS  
WRITING. HRRR VISIBILITY FORECASTS CONTINUE TO SUGGEST THAT THIS  
FOG MAY CONTINUE TO WORSEN OVER THE NEXT FEW HOURS, AS THE WIDE  
SWATH OF LOWEST VISIBILITIES GRADUALLY SHIFTS NORTHWARD.  
HOWEVER, IT MAY BE A SCENARIO IN WHICH THE WORST OF THE ISSUE IS  
SIMPLY THE PRESENCE OF THE VERY LOW STRATUS DECK, WHILE SURFACE  
VISIBILITIES REMAIN JUST ABOVE DENSE FOG CRITERIA. IT IS ALSO  
WORTH NOTING WHAT HAS OCCURRED UPSTREAM IN THE NWS LMK FORECAST  
AREA -- ONCE THE WSW WINDS REALLY KICKED IN, VISIBILITIES  
IMPROVED QUICKLY. SO, FOR NOW, THE SPECIAL WEATHER STATEMENT  
APPROACH WILL BE MAINTAINED FOR THE ILN CWA.  
 
PREVIOUS DISCUSSION (402 AM) >  
ALTHOUGH HEAVIER PRECIPITATION HAS ENDED ACROSS THE ILN  
FORECAST AREA, THIS FORECAST REMAINS SOMEWHAT COMPLICATED, WITH  
SEVERAL ELEMENTS TO DISCUSS.  
 
ONE ELEMENT TO THE FORECAST THAT SEEMS TO BE A DIMINISHING  
THREAT IS THE POTENTIAL FOR HAZARDOUS WINTRY PRECIPITATION. A  
WINTER WEATHER ADVISORY REMAINS IN EFFECT FOR EIGHT ILN COUNTIES  
IN THE NORTHERN PART OF THE FORECAST AREA, WHERE AIR  
TEMPERATURES REMAIN RIGHT AROUND FREEZING, AND ROAD SURFACE  
TEMPERATURES ARE PERHAPS A DEGREE OR TWO ABOVE FREEZING.  
ALTHOUGH TEMPERATURES HAVE BEEN STUBBORNLY STEADY FOR THE PAST  
FEW HOURS, A SLOW WARMING TREND SHOULD BEGIN SOON. AS IT IS, ICE  
ACCUMULATIONS WILL LIKELY BE LIMITED TO ELEVATED SURFACES -- AND  
PRECIPITATION HAS BECOME QUITE LIGHT ACROSS THE AREA. IT SEEMS  
THE RIGHT IDEA TO KEEP THE ADVISORY IN EFFECT FOR A LITTLE  
LONGER, BUT UNLESS THERE ARE SIGNS OF THINGS GOING AWRY, IT WILL  
LIKELY MEET ITS PLANNED EXPIRATION AT 6 AM.  
 
FOG, HOWEVER, IS EXPECTED TO BECOME A BIGGER ISSUE OVER THE NEXT  
FEW HOURS. CURRENT OBSERVATIONS SHOW WIDESPREAD VISIBILITIES  
BELOW 1SM (WITH SOME 1/4SM OBS) IN SOUTHEAST ILLINOIS, SOUTHERN  
INDIANA, AND AREAS OF KENTUCKY NEAR AND WEST OF LOUISVILLE. THIS  
THICK LOW-LEVEL MOISTURE IS GRADUALLY ADVECTING TO THE  
NORTHEAST, AND WILL OVERSPREAD THE ILN CWA BETWEEN 5AM AND 8AM.  
THE SIGNAL FOR THIS FOG ON THE HRRR HAS BEEN QUITE CONSISTENT  
ALL NIGHT, WITH AN EXPECTATION THAT DENSE FOG WILL BE A  
POSSIBILITY. ALTHOUGH FOG IS NOT ALWAYS EASY TO FORECAST (OR  
ISSUE PRODUCTS FOR) IN ADVANCE, THE OBS/MODELS/METEOROLOGY  
PROVIDE A REASONABLE AMOUNT OF CONFIDENCE THAT THIS WILL BECOME  
AN ISSUE IN THE ILN CWA WITHIN A FEW HOURS, AFFECTING THE  
MORNING COMMUTE. A SPECIAL WEATHER STATEMENT WAS ISSUED FOR THE  
AREA OF THE CWA WHERE CONFIDENCE IS HIGHEST, AND IT WOULD NOT BE  
SURPRISING IF THIS STATEMENT NEEDS TO BE RE-ISSUED AND EXPANDED,  
OR EVEN IF A DENSE FOG ADVISORY MAY BECOME NECESSARY.  
 
THE PRECIPITATION FORECAST TODAY IS LARGELY BASED ON LOW-END  
DRIZZLE AND SHOWER POTENTIAL, WITHOUT MUCH IN THE WAY OF FORCING  
OR DEEP-LAYER MOISTURE. THE FRONTAL STRUCTURE OVER THE AREA  
RIGHT NOW IS SOMEWHAT CONVOLUTED. THERE IS A BROAD/WEAK SURFACE  
LOW SOMEWHERE IN THE CINCINNATI AREA RIGHT NOW, AND THIS LOW  
WILL BE MOVING NORTHEAST FROM HERE THROUGH THE MORNING. A MORE  
SIGNIFICANT POOL OF HIGHER THETA-E AIR WILL BE LARGELY MISSING  
THE ILN CWA TO THE SOUTHEAST, BUT FLOW ON THE BACK SIDE OF A  
FRONTAL BOUNDARY WILL SWITCH WINDS TO THE SOUTHWEST -- AMONG  
OTHER THINGS, HELPING TO ADVECT THE FOG INTO THE AREA THIS  
MORNING, AND THEN ALSO HELPING TO VERY SLIGHTLY MIX OUT SOME OF  
THE SURFACE MOISTURE LATER IN THE DAY. THERE IS ALSO EXPECTED  
TO BE AN OCCLUDED BOUNDARY EXTENDING WSW FROM THE LOW CENTER,  
AND THIS BOUNDARY WILL SET UP ACROSS THE NORTHERN SECTIONS OF  
THE FORECAST AREA LATER THIS MORNING. ALL IN ALL, THERE WILL BE  
COPIOUS LOW-LEVEL MOISTURE, BUT WEAK FORCING IN THE VICINITY OF  
THE FRONT, AND SOME GENTLE ASCENT IN THE SOUTHWESTERLY FLOW TO  
THE SOUTH OF THE FRONT. IT IS A SETUP THAT LOOKS MORE FAVORABLE  
FOR PATCHY DRIZZLE THAN ANYTHING ELSE, PERHAPS WITH A FEW  
LEGITIMATE SHOWERS DEVELOPING IN THE NORTHERN SECTIONS OF THE  
FORECAST AREA. THE GOOD NEWS IS THAT ALL SIGNS POINT TO THIS  
PRECIPITATION FALLING AS RAIN, MAYBE MIXING WITH SOME SNOW (WITH  
NO ACCUMULATIONS) LATE IN THE DAY NORTH OF INTERSTATE 70. WITH  
THE FRONT IN THE AREA, THE TEMPERATURE GRADIENT SHOULD BE FAIRLY  
STRONG -- WITH HIGHS RANGING FROM THE MID 30S (NW) TO LOWER 50S  
(SE). IN THE SOUTHERN AND SOUTHEASTERN SECTIONS OF THE FORECAST  
AREA, SOME WIND GUSTS TO AROUND 25 MPH WILL BE POSSIBLE THIS  
AFTERNOON.  
 

 
   
SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/
 
 
THERE MAY STILL BE SOME LIGHT PRECIPITATION IN THE CENTRAL OHIO  
AREA THIS EVENING, BUT DRY CONDITIONS ARE EXPECTED THEREAFTER,  
AS THE FRONT BEGINS TO MOVE SOUTHWEST AS A COLD FRONT -- AND  
DRIER AIR ADVECTS INTO THE AREA. THIS MAY NOT BE ENOUGH TO CLEAR  
UP THE THICK LOW CLOUDS, BUT IT SHOULD BRING AN END TO  
PRECIPITATION CHANCES.  
 
ATTENTION WILL THEN FOCUS ON A SHORTWAVE MOVING INTO THE AREA  
LATE ON WEDNESDAY. AFTER A BRIEF PERIOD OF HEIGHT RISES ON  
WEDNESDAY MORNING, THIS WAVE WILL MOVE EAST ACROSS MISSOURI AND  
KENTUCKY, SPREADING SOME PRECIPITATION INTO THE ILN FORECAST  
AREA AFTER 18Z. THIS SYSTEM WILL BE COVERED IN DETAIL IN THE  
LONG TERM SECTION, BUT IT IS WORTH NOTING HERE THAT SOME  
ACCUMULATING SNOW MAY ALREADY BE ONGOING IN THE SOUTHWESTERN ILN  
CWA BEFORE 00Z.  
 

 
   
LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/
 
 
A MID LEVEL SHORTWAVE TO TRACK FROM THE CENTRAL PLAINS THRU THE  
OHIO VALLEY WED/WED NIGHT. ASSOCIATED SURFACE LOW PRESSURE TO  
TRACK THRU THE TENNESSEE VALLEY. THIS PLACES ILN/S SOUTHERN  
COUNTIES ON THE NORTHERN PERIPHERY OF THE PRECIPITATION SHIELD.  
ALTHOUGH EXPECTED SOLUTION DIFFERENCES EXIST AT THIS TIME --  
MODEL SOLUTIONS ARE GENERALLY IN BETTER AGREEMENT. BOTH THE  
ECMWF AND GFS ENSEMBLE PROBABILITIES FOR AN INCH OF SNOW WED/WED  
NIGHT ALONG AND SOUTH OF THE OHIO RIVER IS AT 60 TO 70+  
PERCENT. GFS IS POSITIONED SLIGHTLY FURTHER SOUTH WITH THE NAM  
BEING THE FURTHEST SOUTH. STORM TOTAL SNOW OF 1 TO 2 INCHES  
LOOKS POSSIBLE FROM THIS EVENT THROUGH WEDNESDAY EVENING WITH  
SOME UNCERTAINTY EXISTING REGARDING EXACT PLACEMENT.  
 
THE SHORTWAVE AND LOW ARE PROGRESSIVE AND QUICKLY MOVE OFF TO  
THE EAST THURSDAY. NORTHWEST FLOW REGIME DEVELOPS WITH SURFACE  
HIGH PRESSURE BUILDING IN FOR THURSDAY AND FRIDAY OFFERING DRY  
WEATHER AND COLDER TEMPERATURES.  
 
TEMPERATURES LOOK TO BE A LITTLE BELOW NORMAL THURSDAY WITH  
HIGHS FROM THE MID 20S NORTH TO THE LOWER 30S SOUTH. READINGS A  
LITTLE CLOSER TO NORMAL FRIDAY WITH HIGHS RANGING FROM THE UPPER  
20S NORTH TO THE UPPER 30S SOUTH.  
 
FLOW BACKS WITH AN INCREASE IN MOISTURE AS NEXT SHORTWAVE AND  
SFC LOW TRACK FROM THE CENTRAL PLAINS INTO THE GREAT LAKES THIS  
WEEKEND. THIS IS A COMPLEX SYSTEM AND MODEL SOLUTION TIMING  
DIFFERENCES EXIST REGARDING THE ONSET AND PROGRESSION OF THE  
PRECIPITATION. WILL RAMP UP POPS SATURDAY NIGHT INTO SUNDAY WITH  
CATEGORICAL TO LIKELY POPS ACROSS THE AREA. A SIGNAL EXISTS  
POINTING FOR THE POTENTIAL FOR ACCUMULATING SNOW SATURDAY  
NIGHT/EARLY SUNDAY AS LOW LEVEL JET/ISENTROPIC LIFT COME INTO  
PLAY AND THERMAL PROFILES ARE COLD ENOUGH FOR SNOW -- ESPECIALLY  
ACROSS THE NORTHWEST/NORTH COUNTIES. TOO EARLY TO PINPOINT  
AMOUNTS OR PLACEMENT BUT WILL HAVE TO SEE HOW THIS SYSTEM  
EVOLVES. EVENTUALLY, UNDER THE INFLUENCE OF WAA PCPN CHANGES  
OVER TO RAIN IN MOST LOCATIONS SUNDAY. WITH THE UPPER TROF  
COMING ACROSS THE AREA CHANCE POPS CONTINUE MONDAY WITH A  
TRANSITION BACK TO LIGHT SNOW.  
 
TEMPERATURE WISE...HIGHS TO RANGE FROM THE LOWER 30S NORTHEAST  
TO LOWER 40S SOUTHWEST ON SATURDAY, AND THEN UPPER 30S TO NEAR  
50 SUNDAY, DROPPING BACK TO LOWER 30S TO UPPER 30S MONDAY.  
 

 
   
AVIATION /12Z TUESDAY THROUGH SATURDAY/
 
 
PATCHY DRIZZLE WILL CONTINUE TO IMPACT THE TAF SITES THROUGH  
THE MORNING HOURS. HOWEVER, IT APPEARS THAT FREEZING  
PRECIPITATION HAS ENDED AT THE AIRPORTS, SO ONLY -DZ IS  
EXPECTED FROM THIS POINT FORWARD.  
 
THE MAIN ISSUE WILL BE VERY LOW CEILINGS AND VISIBILITIES. THE  
POOR VISIBILITIES ARE EXPECTED TO CONTINUE FOR ANOTHER FEW  
HOURS, AND THE POOR CEILINGS WILL CONTINUE WELL INTO THE DAY  
TODAY. RIGHT NOW, CEILINGS ARE LIFR AT ALL TAF SITES.  
VISIBILITIES ARE GENERALLY IN THE 1/2SM TO 1 1/2SM RANGE, THOUGH  
SOME TOWER VISIBILITIES HAVE BEEN 1/4SM AT TIMES. THE TAFS ARE  
TIMED OUT TO SHOW A NORTHWARD PROGRESSION OF THE SLOW  
IMPROVEMENT -- FIRST TO VISIBILITIES, AND THEN TO CEILINGS.  
HOWEVER, CEILINGS WILL REMAIN NO BETTER THAN THE LOW END OF THE  
MVFR CATEGORY THIS AFTERNOON.  
 
SOME DRIZZLE OR LIGHT RAIN WILL BE POSSIBLE LATER TODAY,  
PARTICULARLY AT KCMH/KLCK, BUT WITH NO IMPACTS EXPECTED. WINDS  
WILL ALSO INCREASE SLIGHTLY OUT OF THE SOUTHWEST, WITH SOME  
GUSTS TO AROUND 20KTS POSSIBLE.  
 
OVERNIGHT TONIGHT, CEILINGS MAY LOWER TO THE IFR CATEGORY AGAIN,  
AS WINDS TURN FROM THE WEST TO THE NORTH AND EVENTUALLY TO THE  
NORTHEAST.  
 
OUTLOOK... MVFR/IFR CONDITIONS WILL PERSIST THROUGH WEDNESDAY  
NIGHT. SOME SNOW IS POSSIBLE ON WEDNESDAY NIGHT, PARTICULARLY  
FOR KCVG/KLUK.  
 

 
   
ILN WATCHES/WARNINGS/ADVISORIES
 
 
OH...NONE.  
KY...NONE.  
IN...NONE.  
 

 
 

 
SYNOPSIS...HATZOS  
NEAR TERM...HATZOS  
SHORT TERM...HATZOS  
LONG TERM...AR  
AVIATION...HATZOS  
 
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