Area Forecast Discussion
Issued by NWS Paducah, KY

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FXUS63 KPAH 111730
AFDPAH

Area Forecast Discussion
National Weather Service Paducah KY
1130 AM CST Wed Jan 11 2017

.UPDATE...
Updated for 18Z aviation forecast discussion.

&&

.SHORT TERM...(Today through Friday night)
Issued at 303 AM CST Wed Jan 11 2017

Vsbys have improved as winds have picked up so may need to cancel
the fog advy early. Moisture associated with a frontal boundary that
passed through the area earlier is now heading back north at us.
Line of showers just south of the border will move into the area
this morning. Shower chances should wane later this afternoon as the
front pushes north. Instability parameters suggest isolated thunder
threat as well. Breezy conditions will also return today with strong
winds aloft so a wind advisory may be needed especially by the
afternoon hours.

Meanwhile, a frontal boundary will be developing to our northwest
during day today and be set up from about St. Louis to Chicago by
00Z Thursday. This boundary will slowly sag south tonight toward the
area and showers are expected to develop along it. While the better
location for precipitation will be off to our north tonight, we will
maintain chance type POPs due to southwest flow aloft and abundant
moisture. However, best chances and therefore the higher POPs will
be across our northern counties closer to the boundary.

During the day on Thursday, the front will slide south into the
region and hence, our chances for showers and isolated thunderstorms
will increase. By Thursday afternoon, the front should have cleared
the northwestern tier counties, leaving the better chances across
the southeastern half.

Things get more and more interesting (challenging) Thursday night
through Friday night. By 00Z Friday, the frontal boundary will be
sitting across the extreme southeastern counties (southern Pennyrile
region of west KY). The boundary sags further south into TN as the
evening progresses.

Southwesterly flow aloft increases Thursday night into Friday as a
strong upper level low pressure system moves from southern CA into
the Baja and a strong upper high builds north from the Gulf. The
problem lies in how quickly the moisture returns and what areas have
the better chances for precipitation and also the degree of cold air
that will infiltrate the area.

By 12Z Friday, the ECMWF/Canadian indicate our northern areas should
be fairly dry, and those are the areas that would have the best
chances to drop below freezing. The GFS develops more precipitation
by that time but continues to indicate warmer sfc temps, with the
freezing line flirting with our northern CWA border. For a third
option, the NAM is the most robust with QPF and does indicate a good
part of our northern tier counties will be at or below freezing. So
Thursday night`s forecast (thru 12Z Friday) continues to be in
limbo. Will continue to indicate the freezing rain potential in our
far northern areas.

The temperatures off the ECMWF have been a bit back and forth the
past few days while the GFS has maintained its warmer solution.
Therefore, the challenge for what to do with the forecast for during
the day Friday continues. If we discount the warmer GFS, the best
chance for fzra on Friday will be over parts of SEMO and southern
IL, lesser chances across SWIN. Right now, the greatest ice
accumulation potential will be along and north of a line from Van
Buren MO to Carbondale and Carmi IL. As we go through the day on
Friday, temperatures will eventually warm up. All liquid is expected
across almost the entire CWA by Friday night.

.LONG TERM...(Saturday through Tuesday)
Issued at 303 AM CST Wed Jan 11 2017

Average confidence in the extended period. Leaned toward
deterministic Euro/GFS runs. These were in agreement for the general
synoptic pattern over the weekend and through the beginning of next
week, but locations/details regarding pops still need to be worked
out, especially next week. Trended toward deterministic guidance as
GEFS mean blended sfc boundary features a bit too much.

Over the weekend, a closed upper low meanders slowly from northern
Old Mexico into the Southwest. This puts us in southwest flow aloft,
with most of our forecast area still having a northerly component to
the surface winds for much of the weekend. With the models currently
expecting the sfc front to be in our forecast area or just to its
south Saturday, northerly component to sfc winds has a solid impact
on our weekend temps and pops. Collaboratively adjusted temps down a
bit to reflect this. Expect the better chances of greater QPF
Saturday (rather than Sunday) with Pwats just over an inch, with
chance to likely pops Sat through Sun. Concur with previous shifts
concerning lack of flash flood potential during this period with
limited, if any, instability and not much additional forcing besides
the sfc front.

Looking into Sunday night and early Monday, parts of west KY may see
slight chance pops, if any, as forcing from the front lifts north
and moisture wanes a bit. On Monday, a southerly component to the
flow at lower levels settles in and the sfc low begins its approach.
This pattern feeds warmer air and better moisture back into the Mid
South and lower Ohio River valley Monday through Tuesday night.
Better chance of heavier rain concerns are beginning to show Monday
night into Tuesday with combination of Pwats of 1-1.5" and better
forcing with strong 850hPa jet and sfc low center passage.
Significant or flash type flooding not much of a concern
necessarily, but will monitor as it is still relatively far out.

Temperature forecasts still have greater than usual uncertainty due
to setup of sfc front, timing of precip, and strength of temp
advection over the weekend. Generally stuck with model blends except
for aforementioned adjustments.

&&

.AVIATION...
Issued at 1130 AM CST Wed Jan 11 2017

MVFR cigs are forecast to prevail through this taf period.
Widespread IFR conditions this morning will improve to MVFR early
this afternoon. South winds will strengthen this afternoon, with
gusts around 30 knots likely. The winds will remain rather gusty
much of tonight. A cold front will approach from the northwest on
Thursday morning. In advance of the front, winds will veer into the
southwest. Cigs will lower as the front approaches after 12z,
probably into the IFR category. Some showers are possible at almost
any time, but no widespread prolonged precip is expected.

&&

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

$$

AVIATION...MY



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