Area Forecast Discussion
Issued by NWS Louisville, KY

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FXUS63 KLMK 261005
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
605 AM EDT Tue Mar 26 2024

.KEY MESSAGES...

* Wind Advisory in effect until 6 PM EDT this evening. A few gusts
  over 40 mph expected, especially this afternoon.

* There is a small chance of a narrow line of thunderstorms this
  afternoon into early evening. A few of these storms could produce
  enhanced wind gusts and hail. The best chance at this time appears
  to be over southern Indiana and north central Kentucky.

* Dry and mild rest of the work week. Warmer temperatures and
  increasing shower and storm chances later this weekend.

&&

.UPDATE...
Issued at 604 AM EDT Tue Mar 26 2024

Seeing an uptick in the amount of 40+ mph wind reports over the past
30 minutes or so for areas along and west of I-65, including a 50
MPH report at the Meade County Mesonet. Looks like this is occurring
where precipitation has let up as temps have warmed around 5 degrees
in the post-saturated airmass. This also lines up with when
soundings showed the "less stable" look toward dawn. Dry slot is
starting to work into the area, so looks like we are going to build
on the potential to mix into the stronger winds aloft the deeper
into the day we get. Although, the strongest poriton of the low
level jet is already moving off to the east. No changes to the
forecast, and ongoing Wind Advisory headline looks better with the
renewed gustiness.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 337 AM EDT Tue Mar 26 2024

Widespread showers, and an occasional rumble of thunder, are ongoing
across the area at this time as an impressive low level jet is
peaking around 70-80 knots beneath strong mid and upper level jet
dynamics. We`ll remain under peak forcing/low to mid level moisture
transport over the next 2 to 3 hours before the low level jet core
pushes off to the east and weakens between 09z and 15z later this
morning. In fact, you can see the western edge of the low level jet
core in the reflectivity, defined by a N-S oriented thin line of
enhancement. This feature is beginning to enter our western CWA now.
So, have categorical rainfall chances over the next 2 to 3 hours,
that then diminish a bit from W to E between 09 and 15z. Models do
show redevelopment through mid to late morning as the exit region of
mid and upper level jetting remains favorable for good upper level
divergence. Adding confidence, seeing some hints of baroclinic
leafing in the HREF cloud cover product through the mid to late
morning hours. This westward thickening of the upper cloud band
could play a significant role in what happens later this afternoon,
particularly with the chance to destabilize in a narrow corridor
just ahead of the approaching cold front. More on this below.

Currently, the Wind Advisory isn`t working out all that well as the
low level stable layer evident on forecast soundings and verified by
AMDAR soundings is keeping the strongest low level jet core winds
off the surface. Forecast soundings have always showed this being
the case, however they also show us becoming a bit less stable
toward dawn. So, can`t rule out a few more gust over 40 mph through
the morning hours. We have seen a couple gusts reach the low 40 MPH
range, but they have been sporadic and far between. In the meantime,
most gusts should continue to range in the 25 to 35 mph range.

Given that we could still see some stronger gusts through the
morning, and that we still have a good shot to mix fairly deep into
a lingering 35 to 40 knot layer this afternoon as the dry slot
becomes established over the area, decided to keep the Wind Advisory
going in coordination with IND. Speaking of the dry slot, its
prominence will drive both the gradient wind gust potential as well
as the threat for any isolated strong to severe storm that
could develop just ahead of the front.

Tough call and still low confidence with respect to what will happen
this afternoon as there is only a brief window where we can get some
heating ahead of the front. Although, it won`t take a whole lot get
500 J/KG of ML CAPE either. Overall, some of the data has backed off
on us realizing CAPE values much over a couple hundred joules, and
forecast soundings are not as aggressive as they have been in other
runs. That being said, they look fairly conservative, and if we are
able to briefly reach highs up around 70, they will yield much
higher CAPE values than what is currently being shown. At this point
still think that a gusty S wind, a couple/few hours of insolation,
and our late March sun angle will be enough to help temps recover
quickly just ahead of the front. This would then keep an isolated
strong to severe threat on the table until fropa late afternoon
early evening. Shear profile is sufficient for organized convection,
and could even support some supercell and/or mini bowing segments if
robust convection does get going. By then, surface winds are
expected to be a little more veered, effectively shrinking the
hodograph and presenting a less favorable streamwise vorticity
ingestion scenario. Therefore, think the tor threat would be quite
low (although not completely zero). Instead, isolated damaging winds
and perhaps some hail given the lower freezing levels would be the
main threat. Like where SPC has drawn the Marginal Risk, and like
the Tor probs being mainly north of our area.

The other scenario for this afternoon is that we just don`t
destabilize enough as temps stay more solidly in the 60s. This would
yield little to no CAPE and only some isolated shower potential just
ahead of the front. Bottom line, the warmer we get this afternoon,
the better chance for a return of Wind Advisory gusts and potential
for a few strong to severe storms.

Cold front pushes through late afternoon and early evening, with
gusts diminishing somewhat and dry conditions returning. Cold
advection takes hold into tonight with low temperatures bottoming
out in the 35 to 40 degree range by dawn on Wednesday.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Issued at 337 AM EDT Tue Mar 26 2024

Synopsis...Medium-range forecast remains largely amplified with
quiet weather during the second half of the workweek while unsettled
conditions ramp up this weekend and potentially early next week.
Initially, mid/upper-level longwave trough over the Central US will
continue moving eastward to eventually reach the Atlantic by Friday.
At the same time, subtropical upper-level anticyclone will help
building an anomalous ridge from the Gulf of Mexico to the Upper
Midwest with surface high pressure relocating to the Southeast US.
Further amplification is expected this weekend as a strong upper low
digs across California and weaker shortwave energy ejects towards
the Ohio Valley ahead of the strengthening upper jet, allowing a
quasi-stationary front to extend across the forecast region most of
the weekend into next week. The aforementioned upper low will
probably progress eastward into the central US early next week and
although chances of showers and storms will increase, the exact
evolution is still uncertain so that several scenarios are still at
play.

Model Evaluation/Confidence...Confidence in the large-scale pattern
evolution through Sunday is generally high given deterministic and
ensemble model consensus. Moving into next week, model variance
increases considerably and forecast confidence is considered low at
the moment. Main sources of uncertainty appear to be related to the
strength of the upper subtropical ridge and degree of
amplification/interaction of Canadian energy. As for deterministic
model output, there has been large model-to-model and run-to-run
variance during the last 48 hours with CMC showing a more amplified
Canadian wave with stagnant upper low over California while the
ECMWF and GFS have depicted the idea of a more progressive upper low
with stronger upper ridging, which will favor active weather around
Tuesday or Wednesday of next week.

Wednesday - Friday...Presence of surface high pressure and slowly
rising upper heights will account for dry and slightly cooler
temperatures, especially Wednesday/Thursday as winds blow from the
north. Friday will continue to be dry but temperatures will
experience a gradual warm up as winds shift to the south and
slightly speed up based on southward track of the high pressure and
tightening of the pressure gradient.

Weekend...Notable changes for this weekend are the increasing
rain/storm chances and surface winds becoming a bit stronger. Low-
to mid-level vorticity waves riding along a frontal surface will
promote periods of showers and storms. There is still a fair amount
of uncertainty with actual frontal position and timing/strength of
the best storm coverage, but it seems that model consensus favors
two periods for strongest convection and/or precipitation coverage:
Friday night/Saturday morning and Sunday evening/night. Based on
current trends and potential mesoscale setup, it is worth keeping an
eye on a conditional risk of strong to severe weather chances on
Sunday as there will be higher instability and shear available.
Finally, the temperature forecast will greatly depend on timing of
precipitation and where the frontal boundary ends up settling.

Next Week...Although forecast confidence remains low, several
periods of showers and storms are still possible with a non-zero
chance of strong storms and/or localized flooding issues during the
Tuesday/Wednesday timeframe.

&&

.AVIATION /06Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 152 AM EDT Tue Mar 26 2024

Widespread rain is ongoing across the region at this time, and is
expected to hang around until sunrise or a little after before
becoming more sporadic. In addition, look for gusty winds mostly in
the 25 to 35 mph range out of the SE to SSE. Given the strong low
level jet, will keep LLWS mention going until the strongest low
level winds let go toward dawn. Ceilings are VFR at the moment, and
expect them to largely stay that way through this TAF cycle.
However, did continue to mention a brief MVFR TEMPO group possible
for lower ceilings and a brief period reduced vis in heavier rain.

Overall, look for a drier trend through the day on Tuesday, however
gusty winds will likely pick up again through the late morning and
afternoon. Surface winds veer to a SW and then W component later in
the afternoon as the cold front swings through. Could see some
shower or storm activity at SDF/LEX as the front passes, although
coverage and confidence are low at this time.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...Wind Advisory until 6 PM EDT /5 PM CDT/ this evening for
     KYZ023>032-034-038-045-046-053-054-061>065-070>078-081-
     082.
IN...Wind Advisory until 6 PM EDT /5 PM CDT/ this evening for
     INZ076>079-083-084-089>092.

&&

$$

UPDATE...BJS
SHORT TERM...BJS
LONG TERM...ALL
AVIATION...BJS


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