562
FXUS63 KLMK 020745
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
345 AM EDT Thu May 2 2024

.KEY MESSAGES...

*   Very warm today with highs in the mid-to-upper 80s, with a few
    90 degree readings possible.

*   Widespread showers and scattered thunderstorms Friday, mainly in
    the afternoon and evening.  Brief heavy rain and lightning.

*   Rain/storm chances decrease for Saturday, but forecast
    confidence remains low at this time.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 342 AM EDT Thu May 2 2024

Quiet conditions are present across central KY and southern IN this
morning as earlier convection to our west has subsided, leaving
residual scattered high clouds over the area. Temperatures as of 07Z
are primarily in the 60s, with a few cooler locations cracking the
upper 50s within the last hour or two. Between now and sunrise, no
significant weather is expected with calm or light winds continuing
and temperatures expected to fall into the upper 50s and low-to-mid
60s.

Unseasonably warm temperatures will be the main feature in today`s
forecast with highs expected to be about 15 degrees above normal for
this time of year. A frontal boundary which moved into southern and
central IN on Wednesday is expected to lift north during the morning
today as a warm front as mid-level ridging over the eastern one-
third of the CONUS amplifies. Increasing heights aloft, light
southerly flow, and limited low level cloud cover will allow
temperatures to go several degrees higher this afternoon than on
Wednesday. High temperatures this afternoon should top out in the
mid-to-upper 80s in most locations, with a few spots potentially
reaching 90 degrees. NBM probabilities of reaching 90 degrees
approach 60-70% within the Louisville urban heat island, as well as
within some of the deeper river valleys. Heat index values aren`t
particularly concerning, mainly due to the fact that dewpoints are
expected to mix out into the upper 50s and lower 60s during the
afternoon hours.

Outside of the warm temperatures today, winds should remain fairly
light as the approaching sfc low from the west is not particularly
deep, with the pressure gradient only supporting 5-10 mph southerly
winds. 00Z high resolution model guidance (most notably, the HRRR)
does try to develop a few showers and thunderstorms late this
afternoon, mainly along and north of I-64. Model sounding data does
show greater than 1000 J/kg SBCAPE across much of the area; however,
there is not much of a triggering mechanism present across the
region, and the HRRR does have a tendency to be quite aggressive
with convective initiation in steep lapse rate environments. As a
result, will continue with silent PoPs through the evening hours
tonight, though one or two brief showers or a storm cannot be ruled
out.

Tonight, a weak perturbation in the mid-level flow will swing
northeast across the mid-Mississippi Valley and into the lower
Ohio Valley. This will help to nudge an elongated cold front
close to the region by Friday morning. Increasing moisture,
especially below 700 mb, will help to increase PW values from
around 1" this afternoon to 1.3-1.5" by sunrise Friday. Within
this moisture advection regime, scattered rain showers are
expected to push into the region late tonight, with the onset of
widespread rain not expected until after midnight. The
probability of thunder should remain low (20% or less) tonight,
as soundings show that the moisture advection in the mid- levels
will greatly reduce instability. Temperatures should remain
mild tonight, with lows only expected to fall into the 60s.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 342 AM EDT Thu May 2 2024

Quasi-zonal pattern with flat ridging over the southeast CONUS will
yield a period of warm but at times muggy and unsettled weather.
High confidence in rain on Friday, and moderate confidence in rain
on Tuesday. Notably low confidence in between, with most of the
uncertainty having to do with timing.

Friday and Friday Night...Approaching cold front will interact with
a moist air mass and a few disturbances in deep SW flow. Look for
widespread showers to expand west to east across the Ohio Valley
during the morning and continue through the evening. It`s
important to note that there will be breaks in the rain, but any
heavier shower or embedded thunderstorm will produce brief
moderate to heavy rainfall. Weak mid-level flow and modest lapse
rates will limit any severe potential.

Saturday and Saturday Night...Low-confidence forecast as it depends
greatly on the progression of the front on Friday night. Still looks
like the front lays out somewhere across Kentucky, and there`s
enough post-frontal subsidence for at least few dry hours. However,
model agreement is not good with roughly half the NBM ensemble
members showing measurable precip, and the 00Z NAM12 lifting an
upper shortwave out of the Deep South along the slow-moving front.
Our official forecast will include a 40-50% chance for showers, and
at least a slight chance for thunderstorms at anytime during the
day. However, do not expect rain or storms to last that long in any
given location. Another, possibly better, shot at precip comes Sat
night as another weak cold front moves in from the NW.

Sunday into Next Week...Daily rain chances continue through the
forecast period as a parade of disturbances continues but remains
difficult to time. Best potential for organized storms appears to be
Tuesday, as a deep occluding cyclone over the Dakotas takes on quite
a negative tilt, with a strong secondary low over the mid-
Mississippi Valley driving a cold front into the Ohio Valley. Still
fairly low confidence in severe wx at this point, but we still have
several days to sort out the details.

&&

.AVIATION /06Z TAFS THROUGH 12Z FRIDAY/...
Issued at 121 AM EDT Thu May 2 2024

VFR conditions are expected through the current forecast period.
Thunderstorms to the west of the region from earlier this evening
have dissipated, with lingering high clouds left over from those
storms drifting across the region at this hour. Light and variable
winds are expected from now through late morning, with southerly
winds expected to pick up to 5-10 knots during the afternoon hours.
Tonight, moisture will begin to increase from the southwest, leading
to a gradual drop in ceilings and an increasing chance for rain
showers. However, at this time, it looks like any impacts to
CIGs/VIS should hold off until after the end of the current forecast
period Friday morning.

&&

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

&&

$$

SHORT TERM...CSG
LONG TERM...RAS
AVIATION...CSG