Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 231117

617 AM EST Fri Jan 23 2015

...Updated Aviation Discussion...

.SHORT TERM (Now through Saturday)...
Issued at 310 AM EST Fri Jan 23 2015

...Minor Snow Accumulations Possible Today and Tonight...

Model Discussion/QPF Analysis:
The trend in the 23/00Z models is for the precip shield to spread
farther north across Kentucky, and faster than previously
advertised. This will bring solid chance POPs into south-central KY
mid to late morning, with precip chances reaching as far north as
the Ohio River by nightfall. Still looking at a slight chance at
best over southern Indiana, with POPs in the likely range along and
south of the Western Kentucky and Bluegrass Parkways.

On the back end, there is a slight divergence in solutions but
generally a faster trend with the exit of precip as the 500mb trof
pushes to our east. ECMWF depicts the slowest exit while the NAM and
GFS pull this feature through more quickly. Will taper down into the
chance range by late evening, with even slight chances limited to
the Cumberland Escarpment by daybreak Sat.

Thermal Profiles/P-Type:
Thermal profiles remain quite marginal, with the surface-based warm
layer as the limiting factor in precip type. The earlier arrival of
precip further opens the door for two bouts of snow, one at the
onset of precip this morning, and the second this evening. Best
chance for accumulations will be across south central KY, generally
south of a line from Bowling Green to Stanford. This is especially
true of the early round of precip, as it will arrive earlier while
temps are still near or below freezing.

Afternoon temps in the upper 30s to lower 40s, which is on the low
end of guidance given clouds, precip, and NE winds, will keep precip
all rain until around nightfall. With the sunset surface temps will
cool enough to switch over to all snow by mid to late evening. QPF
is not as robust as in previous runs, but still could see a half
inch especially where the precip rates are enough to overcome warm
surfaces. Storm totals range from a half to 1 inch generally east of
a Bowling Green to Frankfort line, with highest confidence from Lake
Cumberland into the southern Bluegrass region.

The cold air on the back side of this system will cause low temps to
fall into the upper 20s and lower 30s late Fri night into Sat
morning.  A few slick spots may be possible in areas that reach the
upper 20s toward Sat morning as leftover moisture on road surfaces
refreezes. Any impacts Saturday morning will be brief as temps
quickly recover well into the 40s.

.LONG TERM (Saturday Night through Thursday)...
Issued at 250 AM EST Fri Jan 23 2015

The synoptic pattern at the start of the long term period will
feature a general trough across the eastern CONUS, with an upstream
ridge over the West.  This trough will amplify through the first
part of next week, but will then break down by the middle of the
week as upper-level ridging briefly builds into the Ohio Valley.
This regime will make for a generally benign long term forecast,
with only a couple weak systems to contend with.

Saturday night through the first part of Sunday will be rather
tranquil.  However, forecast soundings do depict saturation in the
low-levels over the Bluegrass, which may be just enough for some
light drizzle/flurries early Sunday.  Will leave out of the forecast
for now as low-level lift looks to be lacking, but cannot rule out
some very light precip early Sunday morning.

Otherwise, attention will turn to the northwest as a pretty strong
clipper dives southeast through the trough aloft.  The surface
reflection associated with this system will remain off to the north,
putting the Ohio Valley within southwesterly surface winds which
will advect in warmer air.  Therefore, most of the precipitation
will fall as plain rain.  The 12Z guidance suite has trended a bit
quicker with this system, so have brought in precip a bit quicker
and have also lowered high temperatures across the northern CWA
where clouds/rain should hold them down. Still, think highs will
range from the 50s over southern KY, to the low and mid 40s across
southern IN.  Cooler air will spill in behind the associated cold
front Sunday night.  Forecast soundings still suggest there may be
just enough moisture lingering as the profile turns cold to support
a few flakes.  Certainly doesn`t look like a big deal and no
accumulations are expected (especially given wet grounds from
earlier rain).

The 00Z guidance suite suggests there may be another very weak
clipper to contend with on Tuesday, but timing and placement are
still uncertain so will continue with a dry forecast for now.
Otherwise, troughing will break down Wednesday into Thursday,
allowing for a warmup.  After highs Monday-Wednesday in the
30s/lower 40s, Thursday should warm well into the upper 40s/lower
50s.  Another weak system may bring some light rain on Thursday out
ahead of yet another cold front that will slide through the Ohio


.AVIATION (12Z TAF Update)...
Issued at 610 AM EST Fri Jan 23 2015

Ceiling forecast will be a bit more optimistic this time around
given that the precip shield over Tennessee is largely falling out
of a mid-level deck, and the stratus deck over north central
Kentucky is showing some decent breaks. Will keep the low stratus
deck in SDF and LEX scattered to initialize this TAF set, with a
cirrus ceiling at SDF and mid-level ceilings at LEX and BWG.

Precip shield advancing northward through middle Tennessee should
produce lowering cloud bases and light precip at BWG by mid-morning.
Will initially bring in a high-end MVFR ceiling with mixed precip.
Can`t even rule out a brief period of sleet given the upstream
observations carrying UP, but the probabilities remain quite low and
hinge on getting under a heavier pocket of precip.

By early afternoon expect the precip to spread into SDF and LEX,
while BWG drops into fuel-alternate ceilings. Will keep it plain
rain for most of the afternoon, with mixed precip or a changeover to
snow this evening, especially at LEX. Most likely IFR conditions are
now in LEX late this evening as there could be a brief period of
snow with minor accumulations. Snow will be much more limited at SDF
and BWG, with stratus scattering out around midnight and light NW




Short Term........RAS
Long Term.........KJD
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