Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 142347
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
647 PM EST Tue Nov 14 2017

...Updated Aviation Discussion...

.Short Term...(This evening through Wednesday night)
Issued at 122 PM EST Tue Nov 14 2017

High pressure remains in control of weather in the lower Ohio
Valley. Most areas have broken out into sunshine this afternoon, but
stratus has lingered over the Bluegrass region. Latest visible
satellite shows stratus breaking up, and should see most of it
dissipate by late afternoon.

Mid to upper level clouds will gradually increase overnight ahead of
a northern stream shortwave and associated cold front in the Plains.
Overnight lows will be relatively cool with many places dropping
into the 30s.

Should start off tomorrow morning dry for nearly all locations.
Model consensus seems to bring the rain showers to areas west of I-
65 starting around mid-to-late morning, while areas east of I-65
shouldn`t see any rain showers until after noon. Most models keep
overall amounts under a quarter inch for Wednesday, with the
exception of the NAM which drops close to a 0.5"-0.75". A quick look
at NAM model soundings reveal a very saturated column with
impressive lift in the DGZ and mid levels of the atmosphere. Most
other model soundings aren`t nearly as aggressive with lift or
saturation within the column, which may explain the discrepancies in
QPF. Will side toward model consensus since the NAM is a bit of an
outlier, but will monitor future model input for any upward QPF
trends.

Showers will linger into tomorrow evening, but will gradually end
from west to east. Cooler, drier air will advect in from the
northwest behind the cold front.

.Long Term...(Thursday through Tuesday)
Issued at 129 PM EST Tue Nov 14 2017

High pressure builds in from the Midwest on Thursday and keeps the
region cool and dry. Surface high will slide to the east on Friday,
and a strong, dynamic storm system will begin developing in the
Plains. Flow will increase out of the south during the day Friday,
and temperatures will gradually warm into the 50s and even some low
60s in south-central KY by late afternoon as the area is enveloped
in the warm sector.

The latest (12z) GFS has come in a bit slower with the cold front
compared to its previous runs, placing it more in line with the
Canadian/ECMWF, though still about 6-12 hours slower than either of
those solutions. Even using the fastest (GFS) solution, it now looks
like fropa would begin occurring in southern IN around 12z Saturday.
This means overnight temperatures will be quite warm, with
temperatures remaining steady or even going up through the evening
hours just before fropa. Additionally, prefrontal winds will be
quite breezy out of the southwest, and if we`re able to even just
mix up 1000ft into the boundary layer, we could see +35kt winds
mixing down to the surface.

The severe weather potential continues to remain tricky with this
cold front. As earlier discussions have mentioned, the kinematics
associated with this system are very impressive, with a LLJ cranking
up to 60kts and upper level jets exceeding 130kts. So shear won`t be
an issue. What we will have to watch is for the development of an
instability corridor just ahead of the cold front where convection
could develop, even in meager amounts. Case studies in this area
have shown that as little as 200-300J/KG of mean CAPE have been
observed with severe weather events this time of year. Thankfully,
both the 12z GFS and ECMWF, even with their timing differences, are
not showing such an instability corridor along and ahead of the cold
front in our CWA, but keep it farther west into IL/MO/AR.
Additionally, some of the model soundings have a small cap/stable
layer in the lower levels of the atmosphere near the cold front,
which should prevent convection from becoming surface based. Still,
this system bears close watching given model discrepancies and that
we`re ~4 days out from it.

Forcing associated with this system/cold front will keep majority of
the precipitation along and behind the cold front. So most activity
Friday night should remain scattered in nature, and depending on the
timing of when the front, should see widespread rain showers
Saturday morning into Saturday night. Winds will be very breezy
behind the front as low level lapse rates steepen and pressure
rises.

Once the cold front and associated precipitation clear the region,
we should remain dry for the remainder of the long term period. Long
range guidance still in some disagreement in regards to pattern next
week, but the general consensus is that below normal temperatures
can be expected, with perhaps another shot of cold air late next
week.

&&

.Aviation...(00Z TAF Issuance)
Issued at 646 PM EST Tue Nov 14 2017

High pressure will be in control for much of this TAF cycle with VFR
conditions, although we will see deteriorating conditions as we move
into the afternoon hours of Wednesday as low ceilings, rainfall, and
reduced visibilities impact the region.

The rest of the evening and overnight will be quiet with light and
variable surface winds gradually veering to a S or SE component by
dawn. We`ll see some mid and upper clouds begin to stream into our
area overnight as well. A cold front approaches the area through the
afternoon with steady SW winds between 10 and 20 mph, with a few
gusts to 25 mph possible. Ceilings will gradually lower into the
MVFR and then IFR range the later into the afternoon and evening we
get, along with some reduced visibilities in rainfall.

&&

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

$$

Short Term...DM
Long Term...DM
Aviation...BJS



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