Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 162045

Area Forecast Discussion
National Weather Service Wilmington OH
345 PM EST Sat Dec 16 2017

An upper ridge will continue to bring dry conditions tonight.
Low pressure will lift northeast on Sunday, bringing a chance
of rain to the region. Lingering moisture may bring patchy
drizzle Sunday night into Monday.


Mid level ridge to build into the area ahead of a southern
plains shortwave. East-west stalled surface front across the
southern Great Lakes will lift north overnight in the low
level southerly flow. In the warm sector this evening to start
out mostly clear. Expect high level clouds to spill in from the
southwest and thicken overnight ahead of the next system.
Southerly winds and increasing clouds will keep temperatures a
little above normal tonight with lows from the mid/upper 20s
north to the lower 30s south.


Mid level shortwave over the southern plains to eject northeast
and deamplify as it encounters the mean ridge position Sunday.
Model solutions have trended slower and weaker with this feature.
This is reasonable considering mid level ridge position and dry
low levels at the onset of this event. Will slow down
precipitation, bringing a chance of rain into ILN/s southwest
counties toward midday and then spreading northeast across the
FA during the afternoon. Will continue to ramp pops up to likely
Sunday afternoon but qpf will be light with the maximum totals
of 1 to 2 tenths of an inch. Temperatures will be above normal
with highs from 40 north to the the mid 40s south.

As mid level shortwave and deeper moisture shifts east rain
showers will diminish Sunday evening. Low level moisture
increases with weak lift in the low levels. This signal points
to status and drizzle. Based on clouds, have low temperatures
from the lower/middle 30s north to the upper 30s south. With
temperatures above freezing have added a mention of patchy
drizzle after 06Z.


Monday morning will begin with copious low-level moisture remaining
in place in the ILN CWA. Although deep-layer moisture and ascent
will be moving off to the northeast, 925mb theta-e advection will
contribute enough lift to allow for stratus / low stratocumulus
development and reinforcement, with a strong signal for drizzle as
well. It may not be until afternoon that conditions begin to improve
(with clearing skies and an end to the drizzle). The temperature
forecast has two competing forces to mention -- warm advection and
low clouds -- which should roughly balance out and allow for
conditions to warm into the middle to upper 40s.

A split flow pattern will set up through the middle of the week,
with the ILN CWA largely remaining in between the two streams. A
shortwave moving through the Great Lakes on Tuesday will likely not
impact weather conditions over the Ohio Valley, though its
associated cold front on Tuesday night will switch winds to the
north and lead to cold advection. This front is also expected to
come through dry, with a lack of deep-layer moisture and large-scale
ascent. On Wednesday and into Wednesday night, a southern stream low
pressure system remains to be expected (by model consensus) to pass
south of the forecast area (the 00Z ECMWF had a more northerly
solution, unsupported by the last two GFS runs and only marginally
supported by the 12z CMC).

Forecast confidence begins getting lower by the end of the week,
though there is large-scale agreement on low pressure developing and
moving northeast into southern Michigan by Friday. This will lead to
non-diurnal (warming) temperatures on Thursday night, with increasing
chances for precipitation along and ahead of the associated cold
front. Timing differences are more significant with this system,
which will affect when an eventual change to snow (if any) on the
back side of the front may occur. For now, it appears that the best
chances for precipitation will be in the first half of the day on
Friday, but this is certainly subject to change.

By Saturday, differences in the modeled pattern become far too large
to even attempt to approximate or assimilate into a gridded
forecast. After the cold front passes on Friday, temperatures will
certainly cool back down, but any chances for precipitation are very
uncertain at this point in the forecast cycle.


VFR conditions to continue today and tonight. In warm sector expect
mostly sunny skies with only thin cirrus clouds. Southerly winds
will gust to around 25 kts through the afternoon.

This evening will start out mostly clear with high level clouds
thickening and lowering to 10,000-15,000 feet by sunrise Sunday.

Model solutions have trended slower with weak mid level s/w
moving across the Ohio Valley. Rain showers expected to
overspread the TAF sites from the southwest Sunday afternoon
with VFR cigs continuing.

OUTLOOK...MVFR ceilings and visibilities are likely from Sunday
night through Monday night with IFR conditions possible late
Sunday night into Monday.




LONG TERM...Hatzos
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