Area Forecast Discussion
Issued by NWS Wilmington, OH

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FXUS61 KILN 210610
AFDILN

Area Forecast Discussion
National Weather Service Wilmington OH
110 AM EST Sun Jan 21 2018

.SYNOPSIS...
Southerly flow will lead to a continued warming trend through
the weekend, along with a chance of rain. A better chance of
rain showers will overspread the region through the day on
Monday as a cold front approaches from the west. Showers will
change to snow prior to ending Tuesday. High pressure will then
offer dry conditions and near normal temperatures for the middle
of the week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
A southerly low level flow will continue to advect warmer air
and low level moisture into the region overnight. Moisture will
be shallow at first along with weak forcing, which may allow
for some patchy drizzle this evening. Isentropic lift becomes a
little more favorable after midnight, especially across east
central Indiana and the Miami Valley. Therefore, will start pops
as slight chance and increase pops into the high chance
category across east central Indiana and the Miami Valley
overnight. With warm temperatures, snow pack will continue to
melt. It is unclear how low visibilities will drop overnight
giving the variability among the the models, but at least MVFR
conditions are expected. Will still have to monitor the
potential for fog development given moist and/or snow covered
ground. Temperatures will not drop off much from current
readings in the upper 30s to the mid 40s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Surface low pressure develops in the central Plains Sunday and
begins to eject northeast into the upper MS VLY Sunday night.
Isentropic lift becomes more favorable Sunday morning and then
shifts north over the Great Lakes Sunday night.

Will continue chance pops with the best chance shifting north
during the day light hours. On the warm side of the system,
temperatures will be 10 to 13 degrees above normal Sunday with
highs from the mid 40s northwest to the lower 50s southeast.

With best lift and pressure condensation deficits shifting
north Sunday night will allow the southeast counties to dry out
while keeping chance pops over the northwest. Do not expect too
much of a drop Sunday night with mild lows from near 40
northeast to the mid 40s southeast.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
On Monday morning, stacked low pressure is expected to be centered
somewhere in the vicinity of St Joseph MO, moving on an ENE track
from there into the southern Great Lakes. In an amplified pattern,
deep-layer meridional flow will extend from the Gulf of Mexico into
the Ohio Valley, providing continued warm advection through the day.
Precipitation is expected to spread into the CWA from west to east
during the day, starting as early as the morning hours. This appears
tied to a pre-frontal trough rather than the actual cold front,
which seems to not reach the area until later in the evening or
overnight. Model soundings do not indicate that the boundary layer
ever becomes truly mixed, which will limit wind gust potential to
the 20-25 knot range, despite the stronger 850mb SSW winds (at least
50 knots). PoPs have been held at about 80 percent for this forecast
update owing to some slight timing differences in the models, but
this should eventually be bumped up to 100 percent as soon as this
is pinned down. With temperatures running non-diurnally coming out
of Sunday night, continued warming on Monday will bring max temps
into the 50s (possibly lower 60s in the southeastern ILN CWA).

With the low center lagging westerly compared to the position of the
Monday night cold front, flow behind the front will exhibit a wind
shift, but only veering to the WSW. The cold advection will lead to
temperatures struggling to warm on Tuesday, but still a far cry from
the cold fronts that have passed through in previous weeks. Max
temps will actually be very close to normal (middle 30s to around
40) for both Tuesday and Wednesday. In terms of precipitation, after
a break behind the cold front, some forcing and enhanced low-level
RH will combine with some deeper mixing to allow for showers to
develop across the southern Great Lakes and northern Ohio Valley.
Have made some increases to PoPs on Tuesday for this, with an
expectation that there will eventually be some snow mixing in as
temperatures cool. Finally, but far from least important, is the
issue of wind on Tuesday. The pressure gradient associated with the
low will be relatively strong, and mixing will allow some higher
winds to be tapped -- as opposed to the more isothermal sounding
profiles expected for Monday. Gusts have been increased into the 25-
30 knot range and there is some room that this could increase,
particularly in the northern ILN CWA.

Broad surface high pressure will move east into the area during the
second half of the week, as the upper pattern gradually switches
from troughing to ridging over the eastern half of the CONUS. This
will bring dry conditions and gradually warming temperatures through
Friday.

Behind the departing surface high, and with troughing developing
over the plains, moist flow from the Gulf is expected to move into
the Ohio Valley again over the weekend -- especially later Saturday
into Sunday. Overall model agreement in this pattern remains strong
across several GFS/ECMWF runs -- and without getting into specifics
that far out, conditions appear warmer than normal with rain
expected.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
IFR to LIFR cigs will affect KDAY over the next several hours,
as well as KLCK and KCMH for the next few hours as upglide and a
moist convergent lower layer wrings out drizzle, fog, and low
clouds in these regions early this morning. Remaining TAF sites
will see MVFR cigs/vsbys to occasionally VFR conditions as a
more well-mixed layer noses in from the south. Ceilings will
improve for a while this morning and then come back down after
about 18-20z as moisture continues to pool in the warm sector
this afternoon. Scattered light rain and drizzle will once again
be a possibility as the warm front becomes active north of the
region late today. Focus for light showers will be along and
north of the I-70 corridor and corresponding northern TAF
sites. Conditions will improve to VFR after 6z for all sites as
the warm front lifts north of the region and the warm sector
becomes more mixed.

OUTLOOK...MVFR ceilings and visbilities in rain likely late
Monday into Monday evening. MVFR ceilings likely Tuesday with
possible MVFR visbilities.

&&

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

&&

$$
SYNOPSIS...AR
NEAR TERM...Hickman/AR
SHORT TERM...AR
LONG TERM...Hatzos
AVIATION...Franks



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