Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 011922
AFDLMK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
322 PM EDT Wed Apr 1 2015

.SHORT TERM (Now through Thursday Night)...
Issued at 320 PM EDT Wed Apr 1 2015

...Strong to Severe Storms and Flash Flooding Possible
Thursday/Thursday Night...

Sfc high pressure and upper level ridging will remain in place for
much of tonight providing dry conditions.  With mostly clear skies
for the first half of tonight, temps should drop into the mid 40s to
lower 50s.  A weak warm front will lift north through the area just
after midnight turning the temp trend around to a slow warming
during the pre-dawn hours.

For Thursday, expect on and off rounds of showers and storms
throughout the day.  The first round will arrive around sunrise
bringing mainly elevated clusters of multi-cells through the
morning.  As we get closer to the late morning and afternoon hours,
convection may become more sfc based with strong winds and some hail
possible.  Another shortwave is progged to push through Thurs mid
afternoon/evening sparking more storms.  Although we`ll be in a
moisture rich environment with improving wind profiles throughout
the day on Thursday, morning convection and resultant cloud cover
may hinder storm strength Thurs afternoon/evening.  Right now the
best area for strong to potentially severe storms would be areas
along and west of I-65 near the better wind fields and theta-e axis.

Thursday night a frontal boundary will settle over the Ohio Valley
and slow as flow aloft becomes parallel to the boundary.  This will
result in multiple rounds of showers/storms Thurs night with the
potential of training storms along the boundary.  With precipitable
water (PWATS) amounts rising to 1.4-1.5 (near the upper end of
climatologically PWATS for early April), storms will become very
efficient rain producers.  The combination of these factors could
lead to some flash flooding where repeated thunderstorms occur.
Considered hoisting a flash flood watch this afternoon, but much
model spread still exists on if/where an axis of very heavy rain
will set up.  Stay tuned!

.LONG TERM (Friday through Wednesday)...
Issued at 145 PM EDT Wed Apr 1 2015

...Strong to Severe Storms Possible Friday Afternoon...

Focus in the long term period is on Friday and the potential for
strong to severe storms across parts of the area. The upper level
pattern Friday morning is expected to feature southwesterly flow
with an approaching shortwave trough during the course of the day.
At the surface, a messy pattern is likely, characterized by ongoing
showers and storms associated with a slow moving boundary draped
across parts of the area. A developing surface low to the west will
eventually drag a cold front through during the afternoon and
evening hours.

There remains some timing and placement differences between the
01.12z guidance as to where the surface boundary lies up Friday
morning and how fast the surface low works through the area. The
slower solutions would allow more destabilization/recovery from
morning showers, putting more of the area under a severe threat
later in the day. This idea is supported by the ECMWF/GEM while the
GFS/NAM are more progressive, which would bring a narrower window of
opportunity for stronger storms for a smaller portion of the area.
What happens Thursday night / Friday morning will dictate the
overall threat for Friday.

During the day, increasing moisture characterized by dewpoints in
the 60s will be advected northward into Tennessee and Kentucky. By
afternoon, MLCAPE values of 500 to 1000 J/kg is forecast to develop
while 0-6km bulk shear values increase to 30 to 50 kts. Soundings
show some low level curvature in the wind profile but most is speed
shear. If the air mass destablizes and as the cold front approaches,
discrete storms would be the primary storm mode. Main hazard would
be damaging winds and large hail and at this time, south central
Kentucky is the higher threat area. Main timing is early/mid
afternoon to mid evening. As the cold front moves through, the storm
threat would end northwest to southeast during the evening hours.

Saturday into Sunday will feature drying conditions as surface high
pressure builds into the Ohio Valley. Look for seasonably cool but
mostly sunny conditions Saturday with highs mainly in the upper 50s
to near 60. Sunday will be about the same but tack on several
degrees. Readings look to top out in the mid/upper 60s. Should be a
pleasant spring weekend.

Heading into next week, the upper levels turn more southwesterly
ahead of a digging trough across the Rockies. Southerly return flow
will pull warmer and eventually more moist air into the region by
Monday. A series of disturbances look to rotate through so rain
chances will increase early next week. Too far out to pin down
details but another unsettled pattern looks possible Monday into
Tuesday.

&&

.AVIATION (18Z TAF Update)...
Issued at 135 PM EDT Wed Apr 1 2015

VFR conditions are expected for the rest of the day and most of
tonight.  SE winds between 6-10 kts will prevail through tonight.
Late tonight a weak warm front will lift north through the area
shifting winds to the SSE.  An upper level shortwave will spark a
round of showers and storms tomorrow morning.  Although MVFR
conditions will be possible in a t-storm, it`s unclear if/when MVFR
will occur at individual TAF sites so will keep VFR through tomorrow
afternoon for now.  South winds will become gusty by late morning or
early afternoon with t-storm chances continuing throughout the day
as a frontal boundary approaches.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

$$

Short Term........AMS
Long Term.........ZT
Aviation..........AMS




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