Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 280514

Area Forecast Discussion
National Weather Service Louisville KY
1214 AM EST Tue Feb 28 2017

...Updated Aviation Discussion...

...Forecast Update...
Issued at 748 PM EST Monday Feb 27 2017

Skies have mostly cleared out this evening, and with large T/Td
depressions and still relatively light winds, temps are dropping
faster than expected. Still expect an increase toward dawn as the
warm front passes, sky cover thickens, and surface winds increase,
but will probably start from most spots in the upper 40s rather than
low 50s. Adjusted min T`s down, and lowered sky cover over the next
several hours.

Otherwise, forecast looks on track with numerous showers and
thunderstorms overspreading the area around sunrise as the warm
front and deeper moisture take over.

.Short Term (Now through Wednesday)...
Issued at 304 PM EST Mon Feb 27 2017


Low level moisture return off the Gulf of Mexico ahead of surface
low pressure over the central Plains will interact with isentropic
lift ahead of a broad upper trof over the Rockies tonight. This will
result in showers returning to the region from the west after
midnight. Soundings show some weak elevated instability suggesting
isolated elevated thunder, especially west of I-65 and in southern

Scattered showers and isolated thunderstorms will continue through
the day Tuesday. By afternoon general ascent will decrease and some
dry air will work into the mid levels, causing convective coverage
to decrease. However, this may also lead to an increase in
instability so thunderstorms will still be possible. Though there
will be some low level capping, it`s actually not out of the
question that we could see some gusty thunderstorm winds in
southeastern portions of central Kentucky given the dry layer aloft,
DCAPEs increasing to 500-1000J/kg, and 850hPa winds increasing
throughout the day.

Tuesday night a complex area of surface low pressure will advance
from the mid-Missouri Valley to the eastern Great Lakes, with its
trailing cold front just arriving in the Wabash and mid-MS valleys
by sunrise Wednesday. The low level jet will increase significantly
out ahead of the system from the mid-MS Valley into the Ohio Valley
underneath a 130kt upper jet. Storms will develop in this atmosphere
out ahead of the cold front as a 500hPa speed max moves from
southern Illinois to Ohio after midnight.

Late night is not normally a favored time of day for severe weather
here, however this time we have a very dynamic system and we retain
surface based instability through the night. LI will remain well
negative (still around -5C at 12Z Wednesday), with DCAPEs around
1000J/kg, especially west of I-65 where capping will be weakest.

SPC calibrated severe thunderstorm parameter values actually
increase after midnight over southern Indiana and western central
Kentucky. Supercell composite parameter climbs above 6, 0-6km bulk
shear looks to be on the order of 70kt, with 0-1km helicity possibly
reaching 300-400m2/s2.

Mid-level lapse rates remain steep Tuesday into Tuesday night. Also,
wet bulb zero heights suggest large hail will be possible from
Tuesday afternoon through Tuesday night.

Storms will continue to roll across the area Wednesday morning ahead
of the front, which will cross southern IN/central KY during the
day. Still plenty of wind energy aloft and some weak surface-based
instability ahead of the front Wednesday morning for continued storm
chances, especially east of I-65.

Though the Kentucky statewide tornado drill has been postponed to
Friday because of this threat of severe weather, we still strongly
encourage residents of southern Indiana and central Kentucky to take
a moment to review their severe weather plans tonight or Tuesday
ahead of this strong storm system. Make sure your NOAA Weather Radio
has fresh batteries and is ready to go. Keep in mind that the worst
of the weather may occur after midnight Tuesday night, so you`ll
need a way to be alerted in case a warning is issued for your locale
while you`re asleep.

Behind the front Wednesday afternoon west winds will bring colder
air in, with a fall in temperatures likely. Winds will be quite
gusty, possibly approaching advisory criteria.

.Long Term (Wednesday Night through Monday)...
Issued at 310 PM EST Mon Feb 27 2017

Wednesday night will be quiet as surface ridging builds in behind
the departing cold front.

Thursday afternoon and evening a clipper system will swing by just
to our north. While the main area of precipitation associated with
this quick-hitter will remain to our north, we could still see some
precipitation along and north of I-64. Depending on timing, if the
precipitation hangs around late enough into the night we could see
some light snow, possibly even dropping a slushy tenth or two of an
inch on grassy areas in southern Indiana Thursday night.

High pressure will then move slowly across the region with dry
weather Friday through Sunday.

Sunday night-Monday another large system will approach from the
Plains. Significant model differences abound with this system both
in timing and placement.


.Aviation (06Z TAF Update)...
Issued at 1205 AM EST Tue Feb 28 2017

Main challenge will be timing and impact of the warm frontal precip
arriving during the morning. Mid-level cloud deck in place now will
lower and thicken overnight, with ceilings coming in just barely VFR
just before daybreak. Low-level jetting picks up as well, and will
bring us close to LLWS thresholds, but it`s marginal and lacking a
sharp low-level inversion to focus that shear.

Showers will increase in coverage by mid-morning with visibilities
dropping into MVFR and ceilings into fuel-alternate. Elevated
instability supports a few rumbles of thunder, just enough for VCTS
at SDF and LEX. Precip tapers off late in the afternoon, but
ceilings will stay in fuel-alternate. Southerly winds will gust to
20-25 kt starting around midday and continuing into the evening.

After a lull in the late afternoon and evening, expect precip
chances to increase with even stronger low-level jetting. Later
shifts will need to look at LLWS potential again, with winds over 40
kt just 1000 feet off the deck. Precip coverage, even in the
planning period at SDF, could remain fairly spotty, so will limit
the mention to VCSH for now.




Short Term.....13
Long Term......13
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