ILN issues Area Forecast Discussion (AFD) at Dec 11, 12:46 PM EST122
FXUS61 KILN 111746
AFDILN
Area Forecast Discussion
National Weather Service Wilmington OH
1246 PM EST Wed Dec 11 2024
.SYNOPSIS...
A large mid-level trough will move east through the region
today, bringing some light snow this morning. As a cold front
moves into the area this afternoon and evening, snow showers are
expected, along with much cooler temperatures. A warming trend
is expected going into the weekend, as an area of low pressure
brings the next chance of rain.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Morning update...
Light snow accumulations, in combination with more vulnerable
roadways like overpasses, have resulted in traffic impacts this
morning, especially in eastern Dayton and portions of Cincinnati.
The majority of roadways remain wet, but with road temperatures
near freezing, overpasses have become slick even after the snow
ends. An SPS was issued as a result of these conditions
lingering through the morning. As snow continues in the
Columbus and US-23 corridor, can't rule out developing slick
spots even though solar insolation is increasing.
Minor adjustments were made with accumulation amounts across the
US-23/Scioto Valley areas with forecasted amounts focused on
grassy surfaces.
Previous discussion...
The main concern for this morning is a developing band of snow.
The Ohio Valley is currently underneath a very strong upper
jet. The 00Z KILN sounding recorded 300mb flow of 135kts, with
even higher values (150kt+) at 200mb. Models indicate this jet
may still be strengthening. As a result of upper forcing
associated with this jet, and ascent from the overall shortwave
moving closer to the region, a SSW-to-NNE band of snow has begun
to develop. Most of the echoes on radar right now are failing
to reach the ground, with just a few ASOS/AWOS observations of
snow as of 2AM. However, this feature will continue to gradually
strengthen as it moves east, eventually producing light snow
over a solid portion of the forecast area from 08Z-14Z. It will
take some time for this feature to be able to produce measurable
snow, but some very light amounts (one or two tenths) could
occur along and east of a line from Owenton KY to Marysville OH.
Some slightly more steady snow will be possible in the Columbus
metro area, with accumulations of up to a half inch in the
12Z-14Z time frame. Road temperatures do not suggest that
accumulations on roadways will be a significant concern, but
given the morning weekday timing, will keep an eye on things in
the Columbus metro and south-central Ohio to see how this band
of snow develops.
Once this snow has moved out, a period of dry weather -- perhaps
with some breaks in the clouds -- will occur through early to
mid afternoon. Highs today are expected to reach the lower to
upper 30s. An increasing pressure gradient will mean that some
20-25 MPH wind gusts will occur during the afternoon hours.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
After a dry period of weather early this afternoon, attention
will turn to the potential for snow showers from late afternoon
through the evening. There will be a cold front approaching the
area at around this time, but the main feature driving the snow
showers will be a mid-level wave with a Potential Vorticity (PV)
anomaly, which will lead to a quick cooling of the 850mb-650mb
layer after 21Z. This will lead to steepening lapse rates and
small amounts of convective instability, which will combine with
the forcing to produce scattered snow showers. The surface cold
front actually lags behind the cooling aloft by several hours,
and is not fairly well-defined. This means that forcing will be
somewhat broad and unfocused, limiting the potential for banded
or stronger snow showers. Nonetheless, these snow showers could
be briefly moderate to heavy, capable of reduced visibilities
and some small accumulations (generally under a half inch).
Particularly for areas ahead of the cold front, surface
temperatures will be within a couple degrees of freezing,
suggesting the potential for accumulations will (at least
initially) be limited.
By evening, wind gusts will be increasing, with some 30-40 MPH
gusts possible. Winds will probably be strongest in the northern
ILN CWA, generally near and north of Interstate 70.
Dry weather is expected from late Wednesday night through
Thursday, but with some cold air moving into the area. With
Thursday morning low temps in the teens to lower 20s, and winds
still above 10 knots, wind chills on Thursday morning will
likely get below zero for the northern half of the forecast
area. Single digits above zero are likely for the southern half.
&&
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Warm air advection and the passage of a sheared out short wave
will result in a fair bit of cloud cover across northern
counties to start the period. There could even be some light
snow in west central Ohio Thursday evening, although it may
evaporate before reaching the surface. Surface warm front will
extend across Kentucky Thursday night and only make very slow
northward progress on Friday, perhaps getting into southern
counties late in the day allowing temperatures to jump up into
the mid to upper 40s there. But north of the boundary
temperatures will top out generally in the mid to upper 30s. The
front will then lift across the entire region Friday night.
Guidance is coming into much better agreement with the speed of
a closed mid level low which is forecast to move out of the
central Plains on Friday night, pass through the mid Mississippi
Valley on Saturday, and then cross the lower Great Lakes
Saturday night into Sunday. Given this track, not expecting any
chance of rain until late Saturday near and west of the Indiana-
Ohio border. But then rain will overspread the entire region
Saturday night and move off to the east on Sunday. Temperatures
will have risen back above normal by Saturday and will warm
further after this system passes.
There is quite a bit of timing uncertainty with the subsequent
system which could come through as early as Monday evening or as
late as Tuesday afternoon. Thus have broadbrushed chance PoPs
for this entire period with temperatures cooling a bit on
Tuesday, leaning towards a bit faster solution.
&&
.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
The expected period of dry conditions has settled in over the
area and will continue for another few hours. Snow shower
activity observed across Indiana/Illinois is moving eastward
with no changes made to timing from the previous forecast.
Snow showers will be capable of producing MVFR conditions for
sure, with IFR visibilities possible in some of the heavier
showers. Increasing winds are beginning to be observed, with
gusts in the 25-30 knot range expected after 02Z. Some slightly
stronger gusts (30-35 knots) are possible for Dayton and
Columbus.
Wind gusts linger Thursday morning with prevailing VFR
restrictions.
OUTLOOK...MVFR conditions for DAY/CMH/LCK possible Thursday
evening due to snow. MVFR to IFR conditions are possible
Saturday night into Sunday.
&&
.ILN WATCHES/WARNINGS/ADVISORIES...
OH...None.
KY...None.
IN...None.
&&
$$
SYNOPSIS...Hatzos
NEAR TERM...Hatzos/McGinnis
SHORT TERM...Hatzos
LONG TERM...
AVIATION...McGinnis
Source:
ILN issues Area Forecast Discussion (AFD) at Dec 11, 12:46 PM EST---------------
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