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-- Discussion containing changed information from previous version are highlighted. --
209
FXUS61 KILN 152358
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
658 PM EST Thu Nov 15 2018

.SYNOPSIS...
Low pressure will move through the area tonight, bringing snow
as it moves to the east. An area of high pressure will then
develop over the region for Friday and into the weekend,
providing cooler and drier conditions. Temperatures will remain
cooler than normal through much of next week.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Current forecast is well in hand and no changes were made this
evening beyond the first hour or two in temperatures. 100% snow
moving east fairly quickly this evening is captured nicely and
any change to the forecast would be ill-advised at this moment
in time. Previous discussion:

Surface observations are proof that the inversion has totally
mixed out over the ILN CWA, as temperatures at the surface are
now solidly above freezing, but rain has already begun to
transition to snow. Most of this snow has been generally light
so far, with radar echoes becoming more scattered over the ILN
CWA, but there will be one feature to watch as the evening
progresses. Water vapor satellite shows that the center of the
compact mid-level low is currently located over far southern
Indiana. A curved band of snow has developed in a favorable
region for ascent just ahead of this low, which will continue to
develop as it moves ENE into the ILN forecast area this
evening. Earlier model runs had trended toward cooler boundary
layer conditions, and this expectation continues -- most, if not
all, of this precipitation will fall as snow. Snowfall forecast
amounts have been increased from the previous forecast, with
around an inch in the Cincinnati area, lesser amounts to the
north and south, and greater amounts in the eastern half of the
CWA. Where snow may persist the longest, over central Ohio, some
amounts approaching two inches appear possible. In addition, if
moisture becomes shallow while there is still lift ahead of the
center of the low, a brief period of freezing drizzle may also
occur. Right now, the freezing drizzle scenario looks like a
lower-probability possibility, given that more of the model
soundings suggest moisture will remain deep enough for ice
crystal introduction. In collaboration with JKL/RLX/CLE and
others, an SPS was issued for tonight, mainly to highlight the
potential for a brief period of snow accumulations. With the
recent colder model solutions, it is unsurprising that min temps
also needed to be adjusted slightly downward, now in the upper
20s to around 30.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Though a trough moving across the Great Lakes on Friday will be
a close call for the ILN CWA, it looks like precipitation (light
snow) associated with this feature should remain north of the
forecast area. At most, perhaps some flurries may affect the
northern tier or two of counties. This means that Friday and
Friday night should be dry, as high pressure begins to build
into the southern tier of states. One thing the passing trough
will do is briefly pick up the winds, which will gust to the
20-25 knot range out of the WSW on Friday -- primarily in the
first half of the day. The wind direction in the boundary layer
suggests perhaps a little bit of warm advection on the west side
of the Appalachians, but barely getting into the southeastern ILN
CWA if at all, leading to another day of well below normal
temperatures -- especially since skies should be cloudy to
mostly cloudy. Max temps are forecast to range from the upper
30s to lower 40s, with min temps in the upper 20s on Friday
night.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
The extended period begins with a cold front located in the
southern Great Lakes. The models bring this front into northern
sections Saturday and then work it farther south, while
weakening it. Much of the pcpn is post frontal, which brings on
a slight chance of pcpn into the extreme nwrn counties on
Saturday afternoon. As the front sags south Saturday night into
Sunday, the precipitation chances increase and move southeast
through the forecast area. Right now the best precipitation
chances appear to be Sunday afternoon into Sunday night when
some upper level support swings through. Precipitation type will
be a mix of rain and snow, based mainly on the diurnal cycle.
Highs Saturday and Sunday will range from the upper 30s in the
northwest to the upper 40s in southeast.

By Monday, northwest flow aloft develops, and high pressure
begins to build in at the surface. The GFS continues to try and
bring a disturbance down in the northwest flow on Tuesday, but
this is not currently supported by the other models. So, will
keep next week dry. The first part of next week will be on the
cool side with highs Monday from the mid 30s northwest to the
lower 40s in the southeast.

On the back side of the high there will be a gradual warm up,
with highs by Wednesday ranging from 40 northwest to the upper
40s south, and the mid 40s to the lower 50s on Thanksgiving day.

&&

.AVIATION /0Z FRIDAY THROUGH TUESDAY/...
IFR to LIFR cigs and mvfr vsbys occasionally dropping to IFR
will be the rule for the next several hours. Snow will move
east but increase in coverage in the Scioto Valley as the
surface circulation tracks towards eastern Kentucky.

Low cigs will persist through the forecast with abundant low
level moisture trapped under an inversion between 1500-2kft. The
gradient will tighten during the morning and gusts to 20kt will
be possible across the area, calming down in the afternoon.
Dewpoints in the upper 20s will maintain a healthy dewpoint
depression from the temperature and not be supportive of any fog
development. However, the amount of moisture trapped at the
surface under a relatively low ceiling may necessitate a vsby
reduction at times when the winds calm down tomorrow night.

OUTLOOK...MVFR/IFR ceilings will continue into Friday night.
MVFR conditions are possible again from Saturday night through
Sunday night.

&&

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

&&

$$
SYNOPSIS...Hatzos
NEAR TERM...Franks/Hatzos
SHORT TERM...Hatzos
LONG TERM...Sites
AVIATION...Franks