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FXUS61 KILN 230542
AFDILN

AREA FORECAST DISCUSSION
National Weather Service Wilmington OH
1242 AM EST Wed Jan 23 2019

.SYNOPSIS...
An area of low pressure will move into the Great Lakes tonight
into tomorrow, with rain and warmer air spreading northward into
the Ohio Valley. A cold front will move through the area
Wednesday afternoon and evening, with much cooler temperatures
expected through the end of the week and into the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
The low level jet will continue to strengthen tonight as a
developing low pressure system lifts northeast out of the mid
Mississippi Valley. WAA is well underway across our area with
southerly winds gusting to 20 to 25 knots across western
portions of our fa. This has helped temperatures continue to
rise with readings currently ranging from the low 30s in the
northeast to the mid 40s across the southwest.

Some spotty showers have developed across northwest portions of
our area. While air temperatures at the surface have risen
above freezing, road sensors are still indicating road surface
temperatures a couple of degrees below freezing across our far
northwest. This is also backed up by the METRo road model which
is keeping road temperatures at or just below freezing this
evening up across that area. As a result, am a little concerned
that there could be some re-freezing on untreated surfaces
across our far northwest this evening so will continue to
mention some spotty freezing rain for the next few hours. Have
made some calls to our far northwest counties and so far they
are not reporting any issues with ice, but interestingly in
talking to Hardin County, the increasing southerly winds are
causing some blowing/drifting snow issues up that way this
evening.

Otherwise, the rain will continue to fill in from the west
overnight as the better low level dynamics work their way into
our area. Temperatures should also continue to rise as we
progress through the night.

&&

.SHORT TERM /WEDNESDAY NIGHT/...
Coverage and intensity of rain will continue to gradually
increase through the first half of Wednesday, as surface low
pressure tracks northeast from northern Illinois into southern
Michigan. The WRF-ARW is perhaps the first model of this
forecast cycle to properly resolve the likely pre-frontal
trough, which will likely come with an enhancement to rainfall
rates, but with just a slight wind shift to the SSW. The cold
front will trail a couple hours behind, marked by a more
pronounced shift to westerly flow. The precipitation is almost
exclusively expected to be concentrated ahead of the cold front,
with the heaviest rain expected to affect the ILN CWA between
09Z-18Z. With only around an inch of rain in most locations, the
flooding threat does not appear especially large, but snow melt
adds another element to the equation.

There had been some previous indications of mixed precipitation
at the tail end of this event, but as of now it is looking like
there will be more of a straight transition from rain to snow,
and even that transition may only affect the eastern half of the
forecast area. Because there are still some model differences
regarding timing of the falling temperatures and the end of the
precipitation, a blend could erroneously suggest an overlap of
cold surface temperatures and low-end precipitation chances.
Looking at individual models via plan views and BUFKIT
soundings, it does not appear that any models suggest enough of
an inversion to lead to mixed precip, and in fact the transition
to snow appears fairly brief as well (before precipitation cuts
off). This forecast update will allow for up to a half inch of
snow in just the final couple hours of precipitation, and mainly
focused in the eastern half of the CWA -- generally east of a
line from Pendleton County KY to Delaware County OH.

With influence from several factors -- warm advection,
precipitation, the advancing front -- there should be a sharp
gradient in max temps across the forecast area on Wednesday. The
far northwestern CWA may only reach around 40 degrees before
temperatures begin to drop after 18Z. Where advection will be
strongest, and the front latest to arrive, the southeastern
section of the CWA should get well into the 50s. Cold advection
for everybody will bring temperatures into the lower to middle
20s on Wednesday night.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
The extended period begins with the region on the backside of
an exiting storm system. Surface flow will become northwest off
of the Great Lakes, which will combine with H8 cold advection to
bring scattered flurries to the region Thursday afternoon.
Highs on Thursday will range from the upper 20s in the north to
the lower 30s in the south. Flurries could linger into Thursday
night, especially in the north.

High pressure at the surface will bring dry and cold conditions
for Friday. Highs will be about 20 degrees below normal ranging
from the lower teens across the north to the lower 20s south.

GFS and ECMWF have sped up the precipitation that was supposed
to affect the region Saturday into Saturday night. They now
bring the quick shot of snow Friday night into early Saturday
morning. Have slight chance to low chance PoPs due to the speed
and timing uncertainty. Overall expect less than an inch of snow
with the system.

Another system is expected Sunday, followed by a better
organized sfc low Monday night into Tuesday. For Sunday another
embedded s/w swings through the region bringing some light snow.
The counties around the Ohio River could see a rain snow mix.

For the bigger system Monday night into Tuesday, low pressure
swings through the Ohio Valley or Great Lakes. As expected
models are showing varied tracks and timing of the low. Southern
sections could again see rain mix with the snow on Monday, or
rain could be the dominant ptype.

Behind this system, another shot of arctic air will affect the
region for the middle of next week.

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As expected, TAF sites will be affected by low pressure and a
cold front. Rain developing in moist ascent on a southerly flow
ahead of the low will move to TAF sites tonight and then
continue through much of the forecast period. Ceilings and
visibilities will fall to MVFR and IFR starting around 13z as
the boundary layer approaches saturation, with IFR ceilings
probably lingering as precip changes to snow while diminishing
toward the end of the forecast as winds shift to west in the
vicinity of the cold front.

This weather system will also feature surface wind gusts over 20
knots out of the south to southwest, and wind shear up to 55
knots coinciding with periods of moderate rain.

OUTLOOK...MVFR ceilings may continue through Friday. MVFR
conditions are possible again on Saturday and Sunday.

&&

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

&&

$$
SYNOPSIS...Hatzos
NEAR TERM...JGL
SHORT TERM...Hatzos
LONG TERM...Sites
AVIATION...Coniglio
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