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Area Forecast Discussion (AFD)

Issued by Wilmington, OH (ILN)

FXUS61 KILN 170153

National Weather Service Wilmington OH
853 PM EST Sun Dec 16 2018

High pressure will briefly push into the area tonight. A dry 
cold front will cross the region on Monday. High pressure will 
then build in through mid week.


Clearing has slowed across the area with low clouds still across
about the southeast half of our area. Along and just behind the
clearing line, we have seen areas of fog develop with some of 
it locally dense. There is a lot of uncertainty with the 
overnight forecast at this point as the nighttime cooling going
on now, may very well continue to slow the low cloud clearing. 
Meanwhile, some drier dewpoints are forecast to advect in from 
the northwest overnight, so also not sure how long these lower 
visibilities along the I-71 corridor will persist. Checking 
local web cams across the area, the dense fog does not appear to
be too widespread at this time. Given the uncertainties, think 
the best way to handle it at the moment is with an SPS but will
continue to monitor for a possible dense fog advisory if 
conditions become more widespread and/or persist.


A cold front will cross the region Monday morning. Little to no
moisture for this to work with. However in its wake, cold air
advection and flow off the lakes will lead to development of
stratocumulus. This will be more extensive across the northeast
part of the forecast area. Clouds will diminish in the evening
as high pressure builds in Monday night. Temperatures will be
near normal.


The long term period will begin with rather benign weather 
locally as surface high pressure builds into the Ohio Valley by 
Tuesday and slowly drifts east of the region towards midweek. 
This setup should support plentiful sunshine Tuesday through the
first part of the day on Wednesday before clouds begin to 
increase from the southwest ahead of the next system poised to 
impact the area for the second part of the workweek. 

Temperatures on Tuesday should be fairly close to seasonal norms -- 
with highs ranging from the upper 30s (north) to the lower 40s 
(south). Slightly warmer air will begin to filter into the area by 
Wednesday as southerly surface flow becomes established. Anticipate 
the highs will top out several degrees either side of the 50 degree 
mark for Wednesday. 

The primary weather-maker for the local area this week will begin to 
move into the region by late Wednesday night into Thursday. Even by 
early Wednesday, an upper level S/W within the southern stream 
jet will be organizing/deepening across the south-central 
plains. Models remain in fairly good agreement regarding the 
track and even amplitude of this system -- especially as it 
undergoes a fairly rapid deepening/strengthening cycle by 
Thursday as energy from the northern stream begins to phase with
the southern stream disturbance. This will allow for troughing 
to transition to a potent upper level system, with surface 
cyclogenesis being induced on Thursday in the Tennessee Valley. 

As of right now, confidence continues to increase in the potential 
for rain/showers to overspread the area on Thursday before better 
forcing/dynamics arrive Thursday night into early Friday. Widespread 
rain will be possible, even as the surface low is fcst to track 
approximately parallel to the spine of the Appalachians (from near 
Knoxville to Buffalo in the Thursday night into Saturday morning 
time frame). While a track of the surface features (and the 
corresponding alignment of favorable airmass thermal 
characteristics) such as the one being fcst may typically suggest a 
greater potential for wintry precipitation in the local area, model 
guidance has remained remarkably consistent in its depiction of low 
level thicknesses and thermal profiles that simply would be too warm 
for any extended period of snow or even a rain/snow mix. Although it 
is a bit premature to be discussing details such as these this far 
out, the overwhelming majority of data would suggest that despite 
deep wrap-around moisture (on the back/western side of the surface 
low Friday/Friday night) and relatively good focused forcing to 
promote widespread banded precipitation, that there may not be 
enough deep cold air to promote any changeover or even much mixing 
of the pcpn late Friday into Friday night. While certainly there may 
be some mixing of rain with a few snowflakes Friday evening as the 
low pulls a bit further east, this system should be primarily a 
rainmaker for the ILN FA. 

With all of this being said, with the prospect of a sub-990mb-
surface low tracking just east of the area, breezy to potentially 
windy conditions will be possible Friday afternoon into Friday 
night, with gusts in excess of 35 MPH possible at times. 

Colder air (although not tremendously cold -- especially considering 
the time of the year) will filter in Friday night into Saturday 
morning. Despite this, temps aren't expected to stray too far from 
the freezing mark even during the diurnal min early Saturday. 

Although some flurries from time-to-time will be possible this 
weekend, mainly dry conditions look likely to develop after the 
banded precipitation of Friday night exits the region to the east. 

Near normal temperatures are anticipated both Saturday and


Clearing line is pushing east across the area early this 
evening, currently to around the I-71 corridor. This clearing 
line should continue to work its way east through mid evening 
with skies going mostly clear at all the TAF sites within the 
next hour or so. 

The main concern heading into tonight will be the possibility 
of br/fog development. With a fair amount of low level moisture 
being trapped below the low clouds through much of the day, some
uncertainty exists as to how fast/if vsbys will improve heading
into tonight. It's a mixed bag with the guidance, with some of 
the higher res models suggesting some dense fog possible and 
others, little if any fog. Meanwhile the NAM MOS is clearing 
vsbys early and then trying to develop fog later tonight while 
the GFS MOS is hitting the fog harder early this evening and 
then improving vsbys later tonight. Winds will likely stay up a 
bit tonight, at least in non sheltered areas, and some lower 
dewpoints should try to work in from the northwest and this 
could help counter fog persistence/redevelopment. Given the 
uncertainty, will go ahead and allow for at least some MVFR 
vsbys restrictions tonight and will monitor obs closely over the
next few hours to see if any trends develop. 

A cold front will push through the area during the day on 
Monday. Increasing lower level moisture behind the front could 
lead to some MVFR stratocumulus development as we progress 
through the day. The best chance for this appears to be at the 
central Ohio TAF sites where will allow for some MVFR cigs to 
develop heading into the afternoon.

OUTLOOK...MVFR to IFR ceilings and visibilities possible 
Thursday night and Friday.