Area Forecast Discussion
Issued by NWS Louisville, KY

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184
FXUS63 KLMK 180543
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
1243 AM EST Sat Nov 18 2017

.Forecast Update...
Issued at 1159 PM EST Fri Nov 17 2017

Some light showers continue to move across southern IN and north
central KY this evening, but winds have not begun to pick up much
yet. Taking a look at soundings for tomorrow evening behind the
front, they show the potential for gusts to around 40 mph to
continue through the evening hours. Therefore, decided to extend the
expiration time for the Wind Advisory for the entire area to 06Z.

Issued at 927 PM EST Fri Nov 17 2017

Starting to see some light showers show up on regional radars at
this hour in western portions of the CWA. These showers are
developing in response to isentropic lift and a strengthening low
level jet which is aiding to enhance a theta-e ridge over western
KY/southern IL. Coverage of showers should increase over the next
few hours.

Additionally, surface temperatures have been steadily going up over
the past few hours thanks to strong warm air advection, and think we
can safely assume we`ve hit our "low" temperatures for the evening
as temperatures steadily climb into tomorrow morning.

Only major update to the forecast was to start precipitation for
parts of central KY a few hours sooner given radar trends.
Otherwise, rest of forecast looks on track.

&&

.Short Term...(Today through Sunday)
Issued at 235 PM EST Fri Nov 17 2017

...Gusty Winds Saturday and Saturday Evening...

Low pressure now is over Kansas with a High pressure center to our
east. The gradient in between will tighten tonight, starting to
bring in some warmer and more moist air. It will be one of those
fall nights where the lowest temperature will be early this evening
and then steadily rise under those southerly winds. NAM is pulling
up a strong low-level jet of 60-70 knots over southern IN in the 06-
09Z time frame. GFS is weaker, with the RAP in between...around 60
knots. Would not be surprised to see some of those winds mix down
early in the morning...so the current advisory starting at 12Z looks
good.

That low-level jet should kick off some rains and perhaps isolated
storms along/north of the Ohio River before daybreak. After
daybreak, we should get more showery before a ling of storms.
Precipitable water values come up to around 1.4 inches...which is
pretty high for this time of year. A more solid line of showers
should come through just ahead of the cold front in the mid to late
afternoon hours. Soundings indicate some limited instability that
should produce scattered thunder along that line. Stronger winds are
expected just behind the front, with gusts likely to around 45 mph
from the west and northwest. The gradient across our area should
relax pretty quickly behind this surge, so the timing of the end of
the advisory looks good for our region.

As for cloud cover behind the front, model RH fields in the 900-950
mb layer hold back moisture and keep that thin layer saturated
through daybreak Sunday. Previous forecast hung on to this cloud
layer through that time period and see no reason to deviate from
that at this point. Model statistical guidance has not been handling
this trapped moisture very well thanks to how thin the layer is.

&&

.Long Term...(Sunday night through Friday)
Issued at 235 PM EST Fri Nov 17 2017

After a couple days earlier in the week advertising a headache for
next week, the models have stabilized around a quiet solution for
the midweek. It looks like we`ll have a quasi-zonal flow, so
temperatures should moderate closer to normal and, at least for now,
Thanksgiving looks good. The only potential break in that zonal flow
comes Wednesday, but again this looks dry for now.

&&

.Aviation...(06Z TAF Issuance)
Issued at 1242 AM EST Sat Nov 18 2017

Challenging flying conditions...and forecasting...throughout this
TAF period.

A strong cold front will approach from the west today and cross the
terminals between mid afternoon and early evening. Ahead of the
front low level moisture will increase and create MVFR ceilings,
with some high end IFR ceilings possible, and scattered showers. The
best chance for thunder will be just ahead of the front this
afternoon. Behind the front this evening showers will taper off but
low ceilings will persist.

LLWS will be an issue during the pre-dawn hours, with AMDAR
soundings and VWP data already verifying 50kt winds at 2000 feet.
Surface winds will also increase, with gusts over 30kt out of the
south expected for much of the day, especially this afternoon ahead
of the front. Even higher gusts will be possible with any
thunderstorms. The FROPA this afternoon will be sharp and will
switch winds to the west. Speeds will remain very high for several
hours behind the front before gradually starting to slacken
overnight.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Wind Advisory from 7 AM EST /6 AM CST/ this morning to 1 AM EST
     /midnight CST/ Sunday for INZ076>079-083-084-089>092.

KY...Wind Advisory from 7 AM EST /6 AM CST/ this morning to 1 AM EST
     /midnight CST/ Sunday for KYZ023>043-045>049-053>057-
     061>067-070>078-081-082.

&&

$$

Update...EER/DM
Short Term...RJS
Long Term...RJS
Aviation...13



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