208
FXUS63 KLMK 191038
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
638 AM EDT Sun May 19 2024

...Updated Aviation Discussion...

.KEY MESSAGES...

*   Patchy dense fog east of I-65 this morning.

*   Dry and unseasonably warm weather through Tuesday.

*   Unsettled weather returns by Wednesday, with rounds of showers
    and thunderstorms possible through the end of the week. Severe
    storm potential remains uncertain, with somewhat higher
    confidence in the potential for localized flooding.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 325 AM EDT Sun May 19 2024

Synopsis...Upper-level pattern will consist of high pressure ridge
building across the southern and eastern portion of the country as
trough amplifies to the west. At the surface, broad area of high
pressure will slowly move from the Mississippi Valley towards the
Mid Atlantic and Northeast US while a weak cold front stalls over the
Upper Ohio Valley.

This morning...NT RGB satellite imagery and webcam pictures confirm
fog developing over the Bluegrass and Cumberland regions this
morning with more isolated coverage to the west. Surface
observations indicate visibilities anywhere between 4-7 SM, which
agrees fairly well with previous runs of the HRRR and RAP models. On
the other hand, another widespread dense fog event is not
anticipated at the moment based on the shallow moisture depth
depicted in the LEX ACARS and subsaturated conditions in the near-
surface layer reported by the KY Mesonet relative humidity inversion
profiles. That being said, patchy dense fog will be likely in the
valleys and protected areas east of I-65. Any instance of radiation
fog will dissipate by midmorning.

Rest of Today and Tonight...Mid-level subsidence along with a dry
airmass will yield mostly sunny conditions with highs in the mid to
upper 80s. Winds will remain light and from the northeast as primary
surface pressure center located north of the forecast area drifts
eastward. Daytime heating will promote a high-based cumulus layer,
but no precipitation is expected as weak updrafts remain capped
below 700-mb and any mesoscale triggering mechanism stays well to
north. For tonight, winds will remain light while slowly shifting to
the east-southeast and although fog may once again form, it will be
more isolated and mainly confined to the valleys thanks to moisture
depletion via evapotranspiration.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 325 AM EDT Sun May 19 2024

Monday through Tuesday Night...

Deterministic and ensemble guidance is in general agreement with an
upper level ridge axis being oriented from the southern Plains into
the Ohio Valley during this time frame.  Model soundings through the
period show warm temperatures aloft as well a plenty of subsidence
which will keep convection at a minimum for Monday and Tuesday.
Winds will be out of the south to southwest during the period and
above normal temperatures are expected across the region.  The
question of how high temperatures will go is in question.  Recent
rainfall events have led to saturated soils across the region and
vegetation is quite green.  So while the models suggest upper 80s to
near 90 for Monday and Tuesday, we`ll probably end up a bit cooler
than that.  For now, current thinking is that we`ll end up in the 82-
87 degree range for daily highs with overnight lows in the 60s.
Toward the end of the period (Tuesday night), we may see our first
chances at rainfall as weakening convection along a cold front push
in from the west toward sunrise Wednesday.

Wednesday through Saturday...

As we move into the mid-week time frame, cold frontal boundary will
push toward the region from the west.  Weakening convection is
likely to be in progress Wednesday morning and this activity should
continue to weaken as it pushes eastward.  The surface cold front
looks to stall out to our west, while stronger synoptic scale
forcing moves northeast from the Midwest into the Great Lakes.
Latest machine learning guidance has trended a bit more
west/northwest with the severe threats on Wednesday.  Model
soundings across our region do show instability being present
Wednesday afternoon.  However, with warmer temperatures aloft,
rather weak shear across the area, and the stronger forcing well to
our west/northwest, the threat of organized severe looks marginal at
this time.  Given anticipated atmospheric recovery, scattered
showers and storms are likely Wednesday afternoon with gusty winds
and marginally severe hail as the main threats.  Highs Wednesday
will be in the low-mid 80s with overnight lows in the low-mid 60s.

For Thursday through Saturday, model agreement continues to diverge
here as the GFS and its ensembles are more aggressive in pushing a
cold front through the region on Thursday.  However, the Euro and
its ensembles disagree and keep the frontal boundary across the Ohio
Valley during the period.  Small perturbations moving through in the
southwest flow aloft would be responsible for episodic bouts of
convection moving through the region.  Model soundings do show
instability available for convection, but the main belt of
westerlies will be confined well north of our area, so our
environmental shear remains quite low.  Overall threat of severe
weather looks pretty marginal given the forecast shear values.  The
stalled out boundary though may be a sign that heavy rainfall and
possible hydrologic issues may be the main threat during this period.

Highs during the period will likely be near normal with upper 70s
and lower 80s for highs with overnight lows in the low-mid 60s.

&&

.AVIATION /06Z TAFS THROUGH 12Z MONDAY/...
Issued at 638 AM EDT Sun May 19 2024

Discussion...Intermittent dense fog was observed at LEX and RGA
earlier this morning, but recent observations indicate some
visibility improvements at those terminals. Expect fog to completely
dissipate by 13 or 14Z with prevailing VFR conditions the rest of
the day and also tonight as stable and dry airmass settles in.
Additionally, surface high pressure will keep light northeast winds
today turning calm or variable overnight.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.

&&

$$

SHORT TERM...ALL
LONG TERM...MJ
AVIATION...ALL