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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 210513
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
113 AM EDT Wed Apr 21 2021

.SYNOPSIS...
Low pressure developing along the Ohio River will bring a band of
rain, changing to snow tonight. Chilly temperatures and a chance of
rain showers will follow for Wednesday. After freezing temperatures
are observed Wednesday night, a modest warmup is forecast for
Thursday as high pressure reaches Kentucky.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
LATE EVENING UPDATE: expanded the Winter Weather Advisory to
include most areas north of I-70 from west-central Ohio through
central Ohio (Wayne Co IN through Delaware Co OH).

Our rare mid/late April snow event has already begun in parts
of the ILN CWA, with snow reported in Mercer and Auglaize
counties already this evening. Pcpn will continue to overspread
the local area through the late evening/early overnight period,
with a rapid wet-bulbing of the column and CAA aloft allowing
for rain to eventually mix with and change to snow as the pcpn
becomes a bit steadier/heavier around/past midnight. Do think
that the coverage of snow may be a bit more widespread than
originally thought, especially with many fcst soundings showing
the cooling of the column in such a quick manner once the
steadier pcpn begins. This is being corroborated well with
numerous upstream obs over central/south-central showing snow as
the predominant ptype, even with sfc temps of 33F-34F.

As the frontogenetically-driven band pivots into the ILN FA this
evening, will see that rain change to snow progressively from
west to east. There are several things that will work in favor
of better/more efficient accumulation than many spots upstream
have seen through the late afternoon and early evening. Most
notably will be the fact that it will be, of course, nighttime.
The lack of solar insolation this time of year is significant
from an accumulation efficiency standpoint. This makes the light
accumulations in central IN during the daytime hours earlier
today all the more impressive. In fact, this points to the
fairly robust /rates/ of snow that were occurring for
accumulation to occur during the late afternoon in mid April to
our west. Therefore, presuming the snowfall rates stay the same
(and there is nothing to suggest anything about the ingredients
or forcing or lift being less favorable for the local area) or
approximately the same, this setup occurring over the local
area during the nighttime means accumulation will be much more
efficient. We will, of course, still have the warm ground to
overcome which is why most of the accumulation is still expected
on grassy and elevated surfaces. However, with this in mind,
did decide to expand the Winter Weather Advisory a bit further
south to include a greater portion of west-central OH and even a
part of east-central IN. Do think accumulations will be 2 to 4
inches in many spots in the advisory area, with 1-2 inches
favored between the I-70 corridor and the Ohio River, with
generally less than an inch south of the Ohio River. The good
news -- the snow will be tapering off area-wide for the start of
the AM commute, even in central Ohio. Any snow-covered roads
(favored in west-central Ohio) will be short-lived as the April
sun will be quick to melt the snow in the pre-noon hours.

Low temperatures dropping to the low and mid 30s will require
continuation of the Freeze Warning in effect for much of the
area.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 AM THURSDAY/...
Low pressure and wintry precip will be moving quickly east
Wednesday morning. Rain showers may develop for a few hours
Wednesday afternoon under a short wave rounding the west side of
an upper trough. Otherwise, we can expect mostly cloudy skies
and chilly temperatures with highs in the 40s.

For Wednesday night, surface high pressure will be moving toward
Kentucky behind the axis of the upper trough. Under reduced sky
cover and winds, temperatures are likely to plummet to the mid 20s
to low 30s, and a freeze watch remains in effect for the entire
area.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Northwest flow with surface high pressure offering dry and cool
temperatures to start the long term forecast period. After sub-
freezing temperatures Thursday morning -- expect cold highs in the
upper 40s to lower 50s.

Broad mid level ridging and associated height rises will result in a
warming trend Friday. Although temperatures warm, they still will be
a little below normal with highs on Friday around 60.

Progressive mid level shortwave to track from the Plains across the
the area -- with surface low pressure tracking across the Tennessee
Valley. Moisture will spread into the region with rain developing
Friday night and then becoming widespread on Saturday. As the mid
level trof shifts east the rain will end late Saturday night.

Clouds and precipitation will keep temperatures down with highs on
Saturday from the upper 50s to lower 60s.

Northwest flow aloft with surface ridging building into the area
Sunday providing dry weather and cool temperatures. Forecast highs
on Sunday to range from the upper 50s to the lower 60s.

Model solutions consistent with mid level riding building into the
area early next week. This will pattern will bring dry weather with
a warming trend. Expect highs Monday of 65 to 70 and in the mid and
upper 70s on Tuesday.

&&

.AVIATION /05Z WEDNESDAY THROUGH SUNDAY/...
An area of snow will continue to push eastward across the TAF sites
early in the TAF period. IFR ceilings along with IFR visibilities
are being observed in the snow band and are forecast to persist
until the snow ends between approximately 0800Z and 1000Z. After the
snow moves east, visibilities rapidly improve to VFR. IFR ceilings
will start to lift not too long after and VFR conditions are
expected to return areawide between 1200Z and 1500Z. Northwesterly
winds from 10-15 knots continue through 1500Z.

After 1500Z, VFR conditions are likely to persist as diurnal cumulus
develops. Cumulus is expected to grow into isolated showers by the
afternoon with the chance of a few showers producing lightning in
the unstable environment that will exist. Cumulus starts to die off
around 0000Z. Northwesterly/westerly winds from 10-15 knots persist.

Continued VFR conditions and weakening westerly winds are then
expected after 0000Z.

OUTLOOK... MVFR conditions possible Friday night into Saturday.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...Freeze Watch from late tonight through Thursday morning for
     OHZ026-034-035-042>046-051>056-060>065-070>074-077>082-
     088.
     Freeze Warning until 10 AM EDT this morning for OHZ026-034-035-
     042>045-051>054-060>063-070>072.
     Winter Weather Advisory until 7 AM EDT this morning for OHZ026-
     034-035-042>046-051-052.
KY...Freeze Watch from late tonight through Thursday morning for
     KYZ089>100.
     Freeze Warning until 10 AM EDT this morning for KYZ089.
IN...Freeze Watch from late tonight through Thursday morning for
     INZ050-058-059-066-073>075-080.
     Freeze Warning until 10 AM EDT this morning for INZ050-058-059-
     066-073>075-080.
     Winter Weather Advisory until 7 AM EDT this morning for INZ050.

&&

$$
SYNOPSIS...Coniglio
NEAR TERM...KC
SHORT TERM...Coniglio
LONG TERM...AR
AVIATION...Campbell