525
FXUS63 KLMK 020137
AFDLMK

Area Forecast Discussion
National Weather Service Louisville KY
937 PM EDT Wed May 1 2024

.KEY MESSAGES...

*   Thursday will be warm with highs in the upper 80s to near 90.

*   Widespread showers and scattered thunderstorms on Friday, with
    brief heavy rain and lightning.

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

&&

.UPDATE...
Issued at 936 PM EDT Wed May 1 2024

Isolated thunderstorms developed earlier this evening along and
either side of the Ohio River in southwest Indiana and northwest
Kentucky. These storms went up in a corridor of 1.3" precipitable
water, theta-e ridging, and moderate lapse rates ahead of a surface
cold front just north of the I-70 corridor. Isolated storms did
manage to get a little rambunctious and produce some hail and gusty
winds. New cells occasionally developed on the outflow of collapsing
towers. However, shear is extremely weak this evening and the storms
have completely fallen apart with the setting of the sun. The
activity currently south of St Louis is expected to weaken as it
moves northeast and its upper support wanes, and should be of little
threat to southern Indiana other than perhaps a shower or two
grazing the northwest edge of the region. So, the overnight hours
will be generally quiet outside of the possibility of a very
isolated shower or storm in southern Indiana. No significant changes
to the forecast.

&&

.SHORT TERM /THROUGH THURSDAY/...
Issued at 338 PM EDT Wed May 1 2024

High pressure to the south is keeping skies over central
Kentucky mostly clear, but as you approach the Ohio River a few
cumulus and cirrus are streaming overhead. Overall, it`s been a nice
warm day with temperatures reaching into the 80s, but as we head
into the evening and early overnight hours, a southwest to northeast
oriented cold front stretching across northern Indiana will continue
its southern trek.

Later this evening, the cold front will lie west to east over
southern Indiana as moisture rich southwest winds flow up the Ohio
River Valley. This is expected to cause isolated thunderstorms to
develop along the front over southwest Indiana. Any developed
precipitation is expected to continue eastward and could make it as
far as Louisville later tonight. Not expecting widespread coverage,
and whatever does develop will be elevated, so severe weather isn`t
expected. As instability weakens into the night, thunderstorms will
likely become showers. The surface high will help winds go near
calm, and besides any convection and some scattered cirrus, skies
should see some clearings. Temperatures will fall into the upper 50s
to low 60s which is still 8 to 10 degrees above normal.

Tomorrow, upper ridging and surface high pressure to the southeast
will keep south winds around 5-10 mph and warm air advection in
place. Sunshine will help to lift highs into the upper 80s nearing
90, and that`s about 15 degrees above normal.

&&

.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
Issued at 338 PM EDT Wed May 1 2024

Synopsis...Upper-level height anomaly pattern during the medium-
range period will generally consist of ridging/positive anomalies
over the eastern half of the CONUS while a couple of northern-stream
troughs/negative anomalies training over the western half.
Meanwhile, southern-stream shortwave energy will advect across or
close to the lower Ohio Valley keeping daily rain chances in the
forecast this weekend into next week. Last but not least, there
might be a non-zero chance of strong to severe storms early next
week given the proximity and strength of the mid-level flow
associated with the second trough.

Model Evaluation/Confidence...Forecast confidence remains high for
Friday precipitation and thunder chances as models converge on
increasing storm coverage throughout the day with several runs of
SREF hinting at 30-40 percent chance of thunder in the afternoon
and/or evening timeframe. As mentioned in the previous discussion,
confidence in Saturday rain/thunder decreases, but overall consulted
reflectivity model output and soundings indicate much lower
probabilities compared to Friday. Lastly, WPC Cluster Analysis
depicts a fair amount of variability regarding the second, stronger
northern-stream trough evolution across the Central US and the
amplitude of the downstream East Coast ridge. That being said, ML-
based severe probability guidance from CSU and NCAR show a low
chance of strong to severe storms during Tuesday/Wednesday

Friday...First northern-stream trough will be lifting from the
northern Plains to Canada as southern-stream shortwave energy gets
advected across the forecast area. The associated mid-level forcing
combined with sufficient instability and some mid-level cooling will
provide scattered shower coverage with embedded storms. Organized,
strong or severe weather is not expected at the moment based on
weak mid-level flow, high freezing levels, and lack of strong
forcing. Anticipate cloud-to-ground lightning and moderate-to-heavy
rainfall to be the main impacts with this activity.

Saturday...Diffuse frontal boundary will move through the area late
Friday night into Saturday morning, pushing most of the showers to
the east and south of the boundary. GFS and ECMWF forecast soundings
show mid-level dry air and subsidence rushing in behind the frontal
boundary with no apparent forcing mechanism the rest of the day.
Therefore, highlighted decreasing rain chances through the morning
and into the afternoon. Thoughts for the afternoon are that enough
BL moisture and convective temperatures will force a shallow cu
field with isolated coverage of rain/thunder, especially late
afternoon and early evening as another weak frontal boundary
approaches from the NW.

Sunday - Next Week...Kept daily rain chances during the rest of the
forecast period following model consensus, the presence of a frontal
boundary over the area, and moistening of the profile. Enhanced
forcing and stronger wind field might support a low chance of
organized, strong convection early next week (see section above).

&&

.AVIATION /00Z TAFS THROUGH 06Z SATURDAY/...
Issued at 720 PM EDT Wed May 1 2024

A weak cold front will drop south to around the Ohio River tonight,
then rebound northward as a warm front tomorrow ahead of low
pressure crossing the Midwest. While an isolated thunderstorm can`t
be entirely ruled out with this front, and a few storms have popped
up this evening in the EVV region, any activity should be very
isolated. The confidence and expected spatiotemporal coverage of any
storms don`t rise to the definition of VCTS, so will keep out of the
SDF TAF for now.

Tomorrow will be a very warm day with scattered cirrus and perhaps
just a few cu. Winds in the warm sector will come in from the south
around 5 to 10 knots.

&&

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

&&

$$

UPDATE...13
SHORT TERM...KDW
LONG TERM...ALL
AVIATION...13