Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 202340

Area Forecast Discussion
National Weather Service Wilmington OH
740 PM EDT Fri Apr 20 2018

An expansive area of high pressure will slowly drift east across
the Great Lakes and Ohio Valley through the weekend. This will
bring dry conditions and gradually warming temperatures.
Low pressure will bring a chance of rain on Monday night into
Tuesday, with rain remaining possible through the week as an
upper-level trough moves into the region.


A few cirrus clouds skirting western CWA this evening will see
them increase in coverage overnight, lowering slightly over
northern portions of the CWA early Saturday. An expansive area
of surface high pressure extending from the Great Lakes to the
Mid-Atlantic states will remain over northern Ohio and keep a
light and generally northeast wind over the CWA. As the light
winds and and generally clear skies prevail, a good setup for
radiational cooling conditions is expected overnight.

However, there may be some thickening of high clouds, and winds
may not go completely calm. A tiered approach has been taken to
the frost/freeze headlines, as the warmer starting point will
keep most of the areas from reaching lower than 32 degrees.
There are also some thoughts that frost may not be widespread in
the more marginal temperatures (32-36) due to a very dry airmass
and winds of around 5 knots.


On Saturday, surface high pressure will continue drifting east
across the Great Lakes, keeping light flow in place over the
Ohio Valley. There will be a continued increase in high and mid
level clouds, as the 500mb ridge flattens and isentropic ascent
aloft occurs. An area of low pressure in the southern plains is
on track to move south of the Ohio Valley, and as a result, the ILN
forecast area should remain on the north side of a surface
boundary -- with winds remaining generally easterly to
northeasterly through Sunday morning (and beyond).

Despite the unfavorable winds, another day of (filtered) sun
will allow for temperatures to warm into the upper 50s to lower
60s on Saturday. This remains below normal, but only by 4-8
degrees, which seems like a small departure compared to much of
the past month and a half. As clouds increase, min temps on
Sunday morning should range from the upper 30s to lower 40s --
likely with no significant chance for frost or freeze in the
current program area.


Models continue to be consistent in pushing an upper level low out
of southern plains and into the lower Mississippi Valley on Sunday.
Any precipitation with the system stays to the south for Sunday. 12Z
model rh fields are suggesting that the cloud cover on Sunday might
be a less than forecast yesterday. This will allow temperatures to
be a few degrees warmer, with highs ranging from around 60 in the
north to the mid 60 and possibly the upper 60s in the far south.

Upper low continues to shift eastward on Monday. While the
GFS/ECMWF/Canadian bring some pcpn into northern Kentucky late
Monday, the NAM is the outlier and pushes a band of QPF all the way
through the fa. Will lean towards the majority forecast and will
throw out the NAM solution. Kept slight PoPs in the south to cover
the uncertainty. Expect highs on Monday to be in the mid 60s.

Models left the upper low out of the Tennessee Valley beginning
Monday night. As this occurs scattered showers should lift into the
region. Kept chance PoPs through Tuesday night to cover the
situation. Temperatures will be slightly below normal Tuesday and
Wednesday with highs in the upper 50s.

For the last half of the week, the extended models continue to show
differences in the strength of H5 s/w dropping out the upper
Mississippi Valley. The GFS and Canadian are much stronger than the
ECMWF with this feature. Ran a blend to cover the uncertainty.
Another s/w enters the Ohio Valley on Friday keeping the unsettled
weather pattern across the region.


VFR conditions are expected through the TAF period. Skies will
see some high clouds moving in tonight, lowering somewhat tomorrow.
Winds will remain light, and generally out of the northeast
through the TAF period.

OUTLOOK...MVFR ceilings will be possible Monday night into


OH...Frost Advisory from 2 AM to 9 AM EDT Saturday for OHZ062-063-
     Freeze Warning from 2 AM to 9 AM EDT Saturday for OHZ064-065-
KY...Frost Advisory from 2 AM to 9 AM EDT Saturday for KYZ097>100.


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