Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 270505

Area Forecast Discussion
National Weather Service Louisville KY
105 AM EDT Thu Apr 27 2017

...Updated Aviation Discussion...

.Forecast Update...
Issued at 900 PM EDT Wed Apr 26 2017

Unseasonably mild and quiet evening across southern Indiana and
central Kentucky, but an active cold front is just crossing the
Mississippi into western Kentucky and southern Illinois. The
convective line has featured a few bowing segments, the strongest of
which is producing near-severe wind gusts over far western Kentucky
within the last hour. These storms are taking advantage of the only
marginal instability that remains per SPC mesoanalysis pages, and
has plenty of effective shear to work with.

The environment ahead of the line is lacking in instability, and
only becoming less favorable as the evening goes on. The environment
just ahead of the front will remain quite sheared as it pushes east,
but without any instability, most of the storms will weaken well
below severe limits before approaching the I-65 corridor.

Still on track for showers and storms to move in as early as 04-05Z,
with the best chances from 06-10Z as weakening convection pushes
through from west to east. Still can`t rule out a rogue strong
storm, but it will be a struggle for any storms to remain surface-


.Short Term (Now 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...(06Z TAF Issuance)
Issued at 103 AM EDT Thu Apr 27 2017

An area of rain with some embedded thunderstorms continues to
approach the region early this morning. This rain will impact BWG
first, followed by SDF by around 09Z and LEX right around daybreak.
Lightning has been diminishing a bit in the rain, but has not
disappeared completely, so will continue to mention VCTS/TEMPO TS in
the forecast for a few hours.

Wind shear continues to be a concern. AMDAR soundings show winds
aloft are not quite as strong as models had depicted. However, they
could still strengthen over the next few hours, so will keep LLWS in
the TAFs. Surface gusts will then pick up and winds aloft diminish
somewhat closer to dawn. Surface winds will remain gusty through
much of the day. The wind direction will shift to more of a WSW
direction behind the cold front moving through this morning.




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