Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 172030

Area Forecast Discussion
National Weather Service Wilmington OH
Issued by National Weather Service JACKSON KY
430 PM EDT Tue Apr 17 2018

Surface high pressure will continue to build into the region
this this evening and overnight. As clouds clear, expect many
locations to drop below freezing across the CWA overnight.
Clouds will also be on the increase late tonight and into the
day Wednesday as a low pressure system tracks towards the area.
This system will bring a rain showers to much of Ohio Wednesday
and Thursday. A large area of high pressure will then build
into the Great Lakes for the end of the week into next weekend
providing dry weather conditions.


A brief area of high pressure will move across the CWA overnight as
Ohio finds itself between an exiting surface low pressure system
just north of New England and an approaching surface low moving
across the central Plains this afternoon. As high pressure continues
to settle in, dry air advection will erode away at the cloud deck
that has plagued the CWA throughout the day, giving way to mostly
clear skies by midnight. Winds at the surface will become light and
variable, but the flow aloft will be quite strong out of the NW,
pulling a colder northerly airmass into the region. This combination
of light winds, clearing, and a colder airmass advecting into the
region will allow temperatures to fall quite rapidly overnight.
Furthermore, the ongoing cloud cover across the region today has
resulted in temps that were quite a bit cooler than originally
expected, with many places across the central and NE portion of the
CWA still only in the upper 30s and low 40s. Meanwhile for points
along and just south of the Ohio River where clearing has already
taken place throughout the day, temperatures have risen into the
upper 40s and low 50s.


A warm front will push northward through Kentucky overnight,
extending from the low pressure system approaching from the Plains.
This will result in an influx of moisture in the form of clouds that
will begin to impact the Ohio River by around midnight and then
continue to extend northward across ILN into the second half of
overnight. Expect that the influx of clouds will be slow enough
across much of central and northern tiers of ILN that it shouldn`t
play much of a factor into temps dropping below freezing. However
for locations along and south of the Ohio River, warmer temps this
afternoon (due to clearing that took place through the day), and the
earlier influx of clouds overnight will prevent locations here from
dropping below freezing.

A freeze warning was issued for portions of the CWA from 3Z
through 13Z. The far southern portion of the CWA was left out
given borderline or above freezing temperatures forecast for
overnight, while the northern half of the CWA is not currently
within its frost/freeze program. The tier of counties just south
of the warning could see borderline freezing temperatures, so
will need to continue to monitor in case the warning needs to be
extended further south.

As we head into the day tomorrow, the center of low pressure is
expected to shift eastward and traverse the ILN CWA during the late
afternoon and evening. Winds will become more southerly and
intensify throughout the afternoon ahead of this approaching system.
This will also result in an influx of moisture and rain chances
across the CWA throughout the afternoon as well. Rain should
continue through the overnight Wednesday night, with northerly flow
behind the exiting low taking hold and quickly dropping temperatures
throughout the night. Overnight temps could fall to or just above
freezing, especially in the northern portion of the CWA. Would not
be surprised that lingering rainfall could mix with snow across the
northern CWA during the late night (after 6Z). However, given the
warm temps leading into this event, do not expect much impacts from
this snowfall, unless we start to trend colder with the next model

The extended begins with a fairly sharp trough axis swinging east
across the Ohio Valley, with scattered rain showers diminishing
from west to east across the area through the day. Another cool day
will be on tap, with readings running 10 to 15 degrees below normal.
Clouds will clear out Thursday night, with temperatures likely near
or below the freezing mark by early Friday morning.

A nice stretch of dry weather will continue into early next week as
ridging maintains control across the region. Surface high pressure
will gradually move from the Great Lakes region to just off the New
England coast by Tuesday. North to northeast winds will keep
temperatures averaging below normal through the first half of the
weekend, before moderating to near or slightly above normal by early
next week.


An elongated low pressure system continues to slowly shift NE
across southern Quebec and New England. As it pulls away from
the Ohio Valley, high pressure is beginning to move in from the
west. This is advecting drier air into the region, which is
cutting off the llvl cloud deck which has plagued Ohio for much
of the day. That being said, this clearing trend is quite slow,
with MVFR clouds likely linger in the NE TAF sites (KCMH and
KLCK) into the evening. As clouds clear (which is already taking
place at KCVG and KLUK), conditions are improving to VFR which
they should remain through much of the night.

Another low pressure system will shift into the Ohio Valley by
tomorrow afternoon, bringing with it the return of southerly
winds and moisture. Cloud cover will begin to overtake Ohio,
starting from the south, before daybreak tomorrow (Wednesday)
morning, lowering to MVFR at the southern most TAF sites through
the first half of the day Wednesday. CIGS will continue to
deteriorate with rain moving back into the region after the end
of the TAF period late Wednesday afternoon and Wednesday night.

West winds will continue to gust close to 30 kts at times
through this afternoon. Winds will drop off tonight as the
surface high builds into the area, but could increase again from
the S (gusts 15 to 25 knots) during the afternoon Wednesday
ahead of the approaching system.


OH...Freeze Warning from 11 PM this evening to 9 AM EDT Wednesday
     for OHZ060>065-070>074-080-082.
IN...Freeze Warning from 11 PM this evening to 9 AM EDT Wednesday
     for INZ050-058-059-066.


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