Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 121649
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1049 AM CST Thu Jan 12 2017

.UPDATE...
Issued at 1049 AM CST Thu Jan 12 2017

Monitoring model QPF for the freezing rain event late tonight /
Friday. The trends in the models are trying to even out. The 24 hr
QPF was higher back in Monday`s model runs, then backed off
significantly. The latest runs show a slight uptick again in QPF,
especially extending east across southern IL. The NAM 2m temps
seem to be doing as good as any model and will likely be followed
through this latest forecast package.

After we run the local scripts and incorporate the latest QPF
trends early this afternoon, we will make a call on no less than
an Advisory for the NNW 1/2 of the area, but possibly a warning as
well. We will likely issue the headline with the afternoon
package. Still ironing out the details. Even if there is an uptick
in QPF and we meet the 1/4" ice thresholds for a warning, the
difference in impacts should be minimal and not really any
different than what we have been advertising since the beginning
of the week. Still a very tough forecast. But I think the message
is right and getting us where we need to be prior to the event.

In the meantime, we actually have surface based instability and
decent wind fields with this front coming through. Shouldn`t be a
big deal overall, but the SE 1/3 to 1/2 of the area may see a
strong storm or two before the front clears the area. Low
confidence call at this point.

Noles

&&

.SHORT TERM...(Today through Saturday night)
Issued at 308 AM CST Thu Jan 12 2017

Let`s get near term issues out of the way first: Sfc low which was
over Kansas City yesterday has moved into the eastern Great Lakes at
this hour. The trailing cold front has been slowly sagging southward
during the evening and overnight. A narrow band of forced showers
has developed along it and other development further south in our
area. Expect to see scattered showers and some thunderstorms
today ahead of the front. Windy and warm conditions will
continue early today. However, an abrupt end to the warmth will
occur when temperatures drop 20 degrees or more as that front
plunges into the area. The front will be exiting the area by
around 00Z Friday.

By 06Z Friday, we start to see the freezing line moving into the
northwestern/northern parts of the area as CAA continues behind
the front. The NAM/SREF/Canadian continue to be the farthest
southeast with the cold air. Given a consensus of model QPF for
06Z-12Z Fri, the most likely place for any freezing rain will be
over parts of SEMO and maybe southwest IL. The I-64 corridor just
looks too dry right now to worry about much.

After 12Z, the band of moisture and QPF slowly moves northward while
the cold air pretty much stays over sections of SEMO, S. IL and
SWIN, at least during the morning. However, there are still
discrepancies as far as where and when the precip will set up and of
course, exactly where the freezing line may be and how it may change
during the course of the morning. Locations along and northwest of a
line from Greenville MO to DuQuoin IL to Mount Vernon IL, are where
the greatest amounts could occur, keeping in mind the threat for
freezing rain will still exist across a good part of SEMO and
southern IL, with lesser chances across SWIN.

It looks like we will start to get dry slotted Friday afternoon
sometime from the south, and the main band of moisture/QPF should
keep moving northward. With that said, our far northern counties
may still have to deal with some freezing rain in the afternoon.
In addition, we should see temperatures warming throughout the
afternoon as well, which should help matters. But, temps may stay
near freezing or below in the northwestern counties even into the
early evening, which is another reason our ice totals will be
higher there, longer time duration in fzra. We will need to watch
the retreat of the cold air closely because by Friday night, more
precipitation looks to move in, especially after midnight Friday.
Rain chances continue into Saturday/Saturday night with a bit
warmer conditions.

Hard to say exactly what the impacts of this event will be. But past
history has shown that it does not take much ice accumulation on the
roads to be problematic. Accumulations on elevated surfaces
(bridges, power lines etc) are likely though. The impact on the
main roadways is not as certain for a number of reasons. At this
point, we are leaning toward an advisory but going to let day
shift take one more look at 12Z data. Surrounding offices are
staying at the watch stage at the moment...so decisions made on
any warning/advisories will be made on the day shift region-
wide.

.LONG TERM...(Sunday through Wednesday)
Issued at 308 AM CST Thu Jan 12 2017

Average confidence in the long term due to subtle model differences
and multiple chances for precipitation. It`s going to be a soggy
period for the most part but at least temperatures will remain well
above normal through the period.

The long term period starts out with an E-W oriented quasi-
stationary frontal boundary just to the south of our CWA. As a
result, precipitation chances will be decent Sunday morning,
especially across the northern sections of our CWA. Precipitation
chances diminish from south to north Sunday afternoon as the
boundary begins to lift northward across the area in response to a
storm system lifting northeast out of the four corners region.

The boundary is forecast to be just north of our CWA by 12Z Monday
thus putting us in the warm sector Sunday night. Therefore
precipitation chances should be somewhat limited and mainly confined
to the western and northwestern sections where moisture will be
deepest.

On Monday the aforementioned system pushes a cold front toward our
region as it lifts northeast across the central plains.
Precipitation chances increase from the west Monday with the
approach of the front and continue to increase Monday night as the
boundary moves into our CWA. Instability never becomes impressive in
these two periods, but where there is surface based instability,
there is no elevated instability, and vice versa. Added thunder in
areas where instability seemed most likely.

Unfortunately due to parallel flow aloft the boundary will become
quasi-stationary across our area from NE-SW Tuesday morning.
Precipitation chances will decrease slightly on Tuesday mainly due
to a lack of upper support, but Tuesday night begin to ramp up
considerably as a surface low develops on the boundary in response
to a short wave lifting northeast out of the southern plains.
Instability begins to work its way back into the far western
sections of the CWA late Tuesday night, so added thunder there.

On Wednesday the surface low tracks northeast across our CWA and
pulls a cold front across the area with it, so precipitation chances
remain high, especially in the morning. There should be enough
instability to warrant the mention of thunder over the southeast
half of the CWA Wednesday morning. With the passage of the front,
precipitation chances begin to diminish from the west Wednesday
afternoon.

&&

.AVIATION...
Issued at 525 AM CST Thu Jan 12 2017

Gusty south to southwest winds will continue through much of today
ahead of a cold front. The front is expected to pass through the
TAF sites in the early afternoon. Scattered showers will be
possible ahead of the front and continue until more steady rains
arrive near and behind the front. Any substantial rainfall should
be out of the picture this evening. Hard to say whether cigs will
rise to VFR or settle down into the MVFR category for the rest of
the evening hours so opted keep at the threshold.


&&

.PAH WATCHES/WARNINGS/ADVISORIES...
IL...None.
MO...None.
IN...None.
KY...None.
&&

$$



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