Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270501
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
1201 AM EST Thu Nov 27 2014

...Updated Aviation Discussion...

...Forecast Update...
Issued at 845 PM EST Wed Nov 26 2014

Overall the forecast is in good shape.  Only significant change
made at this time is to ramp PoPs up to 100% where precipitation is
currently falling or is imminent.  Did increase PoPs just a bit
along the northern edge of the band as well. PoP changes were based
off of mesoscale model data and current radar information.

Clipper low at 01Z was centered between Paducah and Evansville, with
a surface trof reaching northwestward into Illinois.  This system
will move quickly eastward across the region tonight.  Light rain
has been falling ahead of the clipper, with light snow behind it in
the colder air.

The rain/snow line has been creeping slowly but steadily
southeastward, and the freezing level aloft has been lowering very
slowly over the past few hours as indicated by radar.  So, some
light snow is still expected after midnight across portions of
central and south central Kentucky.  There still appears to be only
minor impact, though, with warm surface temperatures, warm boundary
layer temperatures, and the fact that the snow will be falling
during the late night/pre-dawn hours.  Nevertheless, something to
keep an eye on for anyone out traveling overnight in central
Kentucky.

.SHORT TERM (Now through Thursday Night)...
Issued at 300 PM EST Wed Nov 26 2014

...Minor Snow Accumulations Possible Overnight...

Warm advection precip shield is fairly well established along the
Mississippi River, as a Clipper low dives SE across Iowa. Clouds are
already on the increase west of I-65, and temps have climbed solidly
into the 40s. Main challenge in this forecast will be the impacts of
any snow produced by this Clipper as it swings through the Ohio
Valley.

Expect precip to reach our far southwest counties, including the
Bowling Green area and the Natcher Parkway, around sunset or shortly
thereafter. May take some time to overcome dry low-level air, but we
are warm enough that it will start off primarily as rain.

Precip will continue to spread east as the evening wears on, with
the better chances south of a line from Jasper to Elizabethtown to
Jamestown. Temps aloft are cool enough that the changeover to snow
will occur with surface air temps above freezing. Good model
agreement on decent QPF with this system, perhaps even pushing a
quarter inch of liquid along the TN border. However, warm temps will
limit accumulation, and impacts will be further mitigated by ground
and pavement temps in the 40s and 50s. The sweet spot for snow
accumulation actually appears to be near the Cumberland Parkway,
where we could approach 1 inch before it melts away quickly after
the precip shuts off. Will detail this in a Special Weather
Statement, and reserve the right to hoist a Winter Weather Advisory
if the snowfall rates upstream suggest there will be a greater
impact.

Temps will remain just above freezing even where it snows, albeit
with minimal daytime recovery on Thanksgiving Day. Afternoon highs
still unseasonably chilly, as well as the Thursday night lows as we
get into favorable radiational cooling conditions.

.LONG TERM (Friday through Wednesday)...
Issued at 255 PM EST Wed Nov 26 2014

Friday - Friday Night...

A surface high pressure will slide off the to our east on Friday
with light southerly flow returning on the back side. Meanwhile,
benign NW flow aloft will hold. This will yield a dry forecast with
milder temperatures in the low and mid 40s. A few upper 40s are
possible SW. Southerly flow will increase on Friday night as a
surface low moves into the upper Midwest, resulting in lows a full
10-15 degrees milder than Thursday night. Look for low 30s NE to
upper 30s SW.

Saturday - Monday...

Upper level flow will flatten out as we progress through the
weekend, even taking on a slight SW flow by Sunday. Will include
mention of a chance of sprinkles on Saturday as moisture in the
1000-850 mb layer pools into the area on steady SW flow. This
moisture combined with a weak isentropic component may be able to
squeeze out a few drops. Otherwise, expect continued warming
temperatures mainly on the advective component. Saturdays highs
should be in the 50s.

Slightly deeper moisture arrives Saturday night and Sunday, pooling
just ahead of a passing cold front that extends from a system moving
into eastern Canada. Will continue mention of some isolated to
scattered measurable rain chances during this time, however not
enough deep moisture to go much higher with Pops. Temps continue to
trend milder during this time with lows Saturday night in the 47-52
range and highs on Sunday in the 60 to 65 range. Again, this will
purely be on an advective component as cloud cover should be pretty
extensive.

Will continue to mention the best chances for rain on Sunday night
Monday as the front (nearly parallel to the upper flow) slowly
passes. Temperatures will be tricky during this time, and obviously
still mild south and east of the boundary versus much cooler north
and west of the boundary.

Monday Night - Wednesday...

Model solutions diverge as we head into the new work week. However,
most solutions indicate we will have a drying period as the front
tries to push east and surface high of Canadian origin slides across
our north. Can`t rule out some lingering light showers on Tuesday as
low level moisture lingers around the stalled front just to our SE.
Have tried to indicate some cold nights across our north with Monday
night dipping just below freezing north of the I-64 corridor. Will
stay in the mid and upper 30s south. High temperatures will be
dependent on how much progress SE the front makes it.

&&

.AVIATION (06Z TAF Update)...
Updated at 1200 AM EST Thu Nov 27 2014

A clipper system will continue to slide across southern Kentucky
tonight bringing precipitation and low ceilings to mainly the KBWG
terminal overnight.  Some light rain/snow may impact the KSDF
terminal later this morning...between 27/05-11Z...while KLEX looks
to remain pretty much dry.  Northeasterly surface winds will
continue at KSDF and KLEX in the near term and then shift to the
northwest/west as the clipper moves on off to the east.

Main aviation impacts will be further south at KBWG where ceilings
will likely oscillate between MVFR and IFR throughout the night
while visibilities generally remain MVFR due to light rain and
snow.  The precipitation looks to remain a mix in the near term but
will become all snow after 27/07Z.  Low ceilings are likely to
continue at KBWG through sunrise.

It appears that quite a bit of cloudiness will linger during the
daytime hours in the wake of the passing clipper system. KBWG should
see a return to VFR conditions after 27/14Z with continued improving
conditions at KSDF/KLEX throughout the day.  Surface winds will
remain out of the NW at 8-10kts and then start to slacken by evening.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Update.........13
Short Term.....RAS
Long Term......BJS
Aviation.......MJ





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