Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 231722

Area Forecast Discussion
National Weather Service Louisville KY
1222 PM EST Thu Feb 23 2017

...Updated Aviation Discussion...

.Short Term (Now through Friday)...
Issued at 315 AM EST Thu Feb 23 2017

Temps are running in the upper 50s and low 60s this morning, and
with small T/Td spreads patchy fog is a possibility. The limiting
factor at this points should be steady low level winds, so won`t
mention it too much unless we start to observe more development.

Currently, a cold front stretches from a surface low over the Great
Lakes, down through the mid Mississippi River Valley and into the
southern Plains. This feature will progress a bit further east this
morning, before stalling near the Wabash River Valley and then
lifting back north as a warm front. Will keep mention of an isolated
rain shower across the northern half of our CWA today as isentropic
lift occurs near this boundary. Sounding depict a rather strong
inversion around 700 mb, so this should keep any thunder potential

The other big focus for today will be near-record high temperatures.
Think upper sky cover should keep us from reaching the records (see
climate section below), however will could make a good run at them
with highs peaking in the low to mid 70s on steady southerly flow
and good mixing.

Tonight, shortwave energy begins to eject across the central CONUS
with strong surface low moving from the central Plains to the mid
Mississippi River Valley. Continued steady S flow and increasing
Td`s will keep overnight lows very mild in the upper 50s to around
60. Record warm mins will likely fall (see climate section again).


Strong shortwave and it`s surface low move into the upper Midwest on
Friday, with deep SW flow over the Ohio Valley ahead of it. The
strong pressure gradient will allow for surface winds between 15 and
25 mph, gusting around 35 mph. Can`t rule out that a Wind Advisory
may be needed for Friday if we can tap a bit deeper into the 40-50
knot low level jet.

Soundings show good mixing up through H85, and with a steady warm
advective component and peaks at the sun temps should surge into the
upper 70s in most spots. Right now, am forecasting the all time
February High Temp for Louisville to be tied at 78 (see climate
section). At this point, it appears the records at the other major
climate sites will stand.

Soundings continue to indicate a strong cap between 800-700 mb, and
this should keep showers and storms at bay through the afternoon.
Mid level lapse rates begin to crash late afternoon with the arrival
of the better forcing, and will mention isolated to scattered
coverage mainly across our west by this time. It appears we`ll pay
the price for our record/near-record warmth with potential for
severe storms Friday evening. See analysis in the long term

.Long Term (Friday Night through Wednesday)...
Issued at 315 AM EST Thu Feb 23 2017


A potent neutral-tilt shortwave will move across the upper Midwest
through Friday night, taking on a slightly negative tilt as it does
so. Meanwhile, a strong surface low (~995 mb) will move into the
Great Lakes, and drag a pre-frontal trough and cold front through
the Ohio Valley Friday evening. Ahead of these features, an
unseasonably warm and relatively moist airmass (T 70s/Td`s 55-59)
will develop with the aid of deep SW flow. This should yield ML CAPE
values between 500-1000 J/KG, especially along and west of I-65
Friday evening. In addition, 0-6 km shear values will range between
40-60 knots as exit region of a mid and upper level speed max nose
into the area, and 40-50 knot LLJ responds beneath.

Forecast soundings continue to show a fairly strong cap between 800-
700 mb holding for much of the afternoon, before finally breaking in
the evening with the arrival of stronger forcing beneath the exit
region of the mid and upper level impulse. A look at forecast
soundings shows rapid steepening of mid level lapse rates between
21z-03z, along with hi-res model depiction of broken convective
segments along the pre-frontal trough and frontal boundary. Initial
development is expected to be along the Wabash River Valley, then
growing upscale as it moves east into the late evening hours.

Overall low level wind profiles should exhibit enough of a veering
profile in the early evening that a few storms could rotate. Cannot
rule out a brief hail threat with initial storm development, along
with a non-zero, but not overly high tornado threat. Convective mode
should quickly congeal into a more solid line as better forcing
arrives with the main threat being damaging winds for the rest of
the event. Vertical wind profile becomes more unidirectional the
deeper into the evening we go. Still thinking that areas west of I-
65 have the best threat early evening, with a continued threat
heading toward the Midnight EST hour across the rest of our CWA.
Overall, like the southward expansion of 30% probabilities with the
Day 2 Outlook.

Saturday - Sunday...

Cold front is through our area before dawn on Saturday with much
cooler air crashing in behind. Temps should range from the mid 30s
West to the mid 40s East by dawn on Saturday. Deep moisture be
mostly gone by this time, but may hold onto a slight chance of a
measurable shower east of I-65. Otherwise, expect a dry and blustery
day as strong high pressure begins to build in. Highs will only be
in the mid to upper 40s. Surface high settles nearly directly over
us Saturday night with lows dropping into the mid 20s under good
radiational cooling. Light southerly flow returns by later Sunday
with highs mostly in the upper 40s to around 50.

Sunday Night - Wednesday...

Fast SW flow aloft will dominate through the middle of next week,
with a series of embedded disturbances passing through. The first
will be later Sunday night into Monday. It`s possible that p-type
could be an issue at onset across our NE, but will not get too fancy
with details at this point. As we move into the day on Monday, p-
type would change to all rain. More disturbances are possible
Tuesday and Wednesday, with temps back above normal as surface low
passes to our north. Overall, a couple rounds of widespread rainfall
look likely, along with a chance at some thunder by mid week. Highs
Tuesday and Wednesday are back in the 60s.


.Aviation (18Z TAF Update)...
Issued at 1215 PM EST Thu Feb 23 2017

Moist low-level air mass and modest warm advection have helped keep
stratus in place over the terminals this morning. The stratus will
be extensive enough at times for a MVFR ceiling this afternoon, but
will remain above fuel-alternate.

This evening, south winds will diminish and we`ll see mid-level
ceilings as the low clouds scatter out. It`s worth noting that SDF
winds will initially lay down to 6 kt or less, but will increase
again before midnight EST, during the late-evening peak in traffic.

Winds continue to increase through the night and even more so on
Friday, with gusts kicking up to around 25 kt by mid-morning as the
gradient tightens ahead of the approaching front. Stratus ceilings
will also come back in, and it`s a close call between MVFR and VFR,
but still above fuel-alternate regardless. A line of strong T-storms
is likely to develop in Indiana late Friday afternoon, and push into
Kentucky with gusty winds. However, the timing is too close to the
end of the planning period at SDF, and solidly beyond the scope of
this TAF issuance, so will not mention it at this time.




Short Term........BJS
Long Term.........BJS
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