Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 262358

Area Forecast Discussion
National Weather Service Louisville KY
758 PM EDT Wed Apr 26 2017

...Updated Aviation Discussion...

.Short Term...(This evening through Thursday night)
Issued at 230 PM EDT Wed Apr 26 2017

...Becoming Breezy Late Tonight...

Surface low pressure forming across Arkansas this afternoon, and
models prog that low to move to the Bootheel. As it does so, it
should force a line of showers and storms slowly eastward tonight.
The trough looks to become negative-tilt tonight, and as it does so
we will see an increase in winds above the surface, with the latest
hi-res guidance showing a 60- to 70-knot 850 mb jet by 6Z in a
narrow north/south axis across the region. So will have to watch as
the line of decaying showers/storms move through tonight to see if
any of these stronger winds can mix down late tonight.

Those showers should end during the morning hours as the front
pushes east of the region and a narrow bubble of high pressure
builds over the Ohio Valley by the end of the day Thursday. Clouds
should stick around most of the day and keep our temperatures down,
but not too far below normal for late April.

.Long Term...(Friday through Wednesday)
Issued at 230 PM EDT Wed Apr 26 2017

Winds will pick up out of the south Friday, as a dry warm front
lifts northward over the Ohio Valley region. Temperatures Friday
should end up ~10 degrees warmer than Thursday. That front should
serve as the focus for storm development just west and north of the
region, while capping in place over our part of the warm sector
should keep this area dry. There is some elevated instability above
this cap, so any good cold pool from the storms to our north that
can push into our region could be able to get to this level and
maintain themselves as they head eastward Friday night.

Models struggle a bit in how far north the front gets and stalls for
the weekend, but should it stall over one place for long, the amount
of moisture moving in along it will be well above normal for this
time of year, and could lead to some flood potential. Ensemble
guidance in this forecast suite tends to agree with the operational
NAM in keeping most of that moisture just north of the area, but we
will need to monitor the forecast over the next couple of days for
any southward push there, especially as we could get some severe
storms depending on that location and available instability later in
the day Saturday.

Saturday night and Sunday, a stronger upper low will move out of the
Central Plains and finally force this slug of moisture eastward.
Given extent of time out in the model world, there still is some
uncertainty factored in here to the exact timing, but a push that
comes through during the day Sunday would take advantage of good
heating that could cause severe weather. Again, something to watch
for over the several model runs.

Monday should turn breezy and cooler as that front pushes east. We
moderate a little on Tuesday before the GFS/Euro bring back a shot
at rains along a slowly lifting warm front.


.Aviation...(00Z TAF Issuance)
Issued at 750 PM EDT Wed Apr 26 2017

VFR weather is expected for much of the night until around dawn on
Thursday. A band of showers with some embedded thunder will likely
drop ceilings to MVFR from west to east after 09z. Also of aviation
concern, however, will be a strong low level jet that develops
shortly after 00z. Wind shear is expected to remain fairly
unidirectional, but south winds should increase to 45-55 kts at 2
kft AGL. Vertical wind shear will subside with the arrival of the
shower activity.

A line of strong convection is pushing into far western KY this
evening, and these thunderstorms are forecast to gradually diminish
in intensity after sunset. As these showers and isolated, decaying
storms move into the I-65 corridor after 06z, a brief stronger wind
gust will be possible if the stronger flow aloft can get mixed down
to the ground. Winds will remain breezy as they veer SW behind the
cold front on Thursday. Ceilings will gradually lift back to VFR
around 18z.




Short Term...RJS
Long Term...RJS
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