Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 271738

Area Forecast Discussion
National Weather Service Louisville KY
138 PM EDT WED APR 27 2016

...Updated Aviation Discussion...

...Forecast Update...
Issued at 1145 AM EDT Wed Apr 27 2016

A warm front is still draped along the I-64 corridor, and will
likely move little this afternoon. Showers and thunderstorms have
been common along and south of this boundary this morning, and will
continue into the afternoon.

Meanwhile, a 5H low is advancing from Kansas into Nebraska. A speed
max rounding the base of the low will help to spark storms over the
mid-Mississippi Valley this afternoon as lapse rates steepen and the
surface destabilizes. Those storms are then expected to head
northeast into southern Indiana and central Kentucky this evening.
The best chance of severe storms will be west of I-65 where there
will be the greatest instability. With WBZ heights around 10k feet
and a possible layer of slightly more stable air at the surface from
the ongoing showers/storms INVOF the warm front, hail will be the
main threat from the strongest storms with gusty winds a secondary

Issued at 625 AM EDT Wed Apr 27 2016

Issued a grid update for some patches of fog in our northwest and
west and also to narrow the focus for precip the next couple of
hours. Had one cell pop up and likely become severe, but have not
had any reports from that sparsely populated area.  No other changes
planned beyond those first few hours, and a zone update is not

.SHORT TERM (Now through Thursday)...
Issued at 300 AM EDT Wed Apr 27 2016

Stalled frontal boundary resides just north of the region, whereas a
second boundary is just south of the region, the remnant from the
line of storms that moved through the region last evening. In
between we are seeing some weak isentropic lift that is resulting in
some new shower development across central Kentucky. Model QPF
fields seem overdone in areal coverage of this precip, based on
latest radar, but for the daylight morning hours, the higher-res
versions try and provide more focus on a northwest/southeast-
oriented line. Have gone in line with this thinking and placed a
narrow band of high-likely pops from HNB to AAS with pops tapering
off north and south of that line.

Beyond the morning hours, expect a brief lull in coverage, with the
airmass just juicy enough to squeeze out some scattered showers
perhaps thunder. A PV anomaly will then rotate around a larger upper
low centered over southeast Nebraska. Timing this feature with peak
daytime heating, expect a line of storms to develop across western
TN/KY and head northeastward. The main threat with these storms
again will be damaging winds, with this threat mainly limited to
points west of the I-65 corridor. The storms should weaken with loss
of heating as they continue into the rest of the forecast area.

We dry out some for Thursday, with precipitable waters dropping down
to around an inch. The upper low over the Central Plains this
afternoon should be over the upper Midwest Thursday. The distance
from this feature and lack of a trigger should limit coverage of any
storms to isolated to scattered.

As for temperatures, our string of above normal days will continue,
with highs ranging from the mid 70s to low 80s and lows around 60.

.LONG TERM (Thursday night through Tuesday)...
Issued at 300 AM EDT Wed Apr 27 2016

The drying trend should continue at least through Friday, as ridging
moves over the region. Then Friday night, that ridging will start to
push east of us as another storm system comes out of the Plains.
This system should lift a warm front toward the region, which could
bring some light rain showers west of I-65 by daybreak Saturday.
Deterministic model guidance shows this boundary stalling over our
region for the weekend, meaning another couple of days with good
rain chances. A surface low crossing the region during the day
Sunday could mean some stronger storms, and will be something to
watch for, to see if we can get some instability to go along with
the dynamics of this system.

Latest deterministic models pull this low out of the region by
Monday morning, whereas the GEFS mean has it a little slower, a sign
of timing differences within the ensemble members, as spread also is
high. Thus will keep in a lower-end chance for rain into Monday.
After that Tuesday should have even less chance for rain, as a
narrow shortwave ridge moves into the region. Given how small this
feature is and another wave potentially dropping into the Midwest,
cannot pull rain chances altogether.

As for temperatures in this period, Friday should be one more above
normal day, then we should be closer to normal for the weekend and
possibly below for the start of the next work week.


.AVIATION (18Z TAF Update)...
Updated at 137 PM EDT Wed Apr 27 2016

A challenging forecast cycle as the TAF sites deal with several
rounds of showers and thunderstorms through late this evening. SDF
and LEX are currently being impacted by showers and storms lifting
over a warm front. This boundary will only very slowly lift north
through the afternoon, which may help to keep the MVFR ceilings in
place at times. Additionally, visibilities will drop into IFR/low
MVFR in the heavier showers and storms.

Best chances for a lull in storm activity at SDF will be mid
afternoon to early evening. Then another round of storms is expected
between sunset and Midnight. Some gusty winds along with heavy
rainfall and CG lightning are expected. Some trailing stratiform
rain may follow into the pre-dawn hours along with ceilings dropping
below fuel alteranate toward dawn. Cold front approaches Thursday
morning with gustsy WSW winds, but dry.

Expecting LEX/BWG to see showers and storms most of the afternoon
with a brief break around and just after sunset. Then, another round
of showers and storms just before Midnight. LEX will then follow the
same pattern as SDF with trailing stratiform rain and ceilings
dropping into low IFR through the pre-dawn hours.


.LMK Watches/Warnings/Advisories...


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