Severe Thunderstorm Warning 129, NWS Jackson, KY

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
408 PM EDT Fri May 2 2025

.KEY MESSAGES...

- Strong to severe storms are expected late this afternoon and
  evening. Damaging wind gusts will be the primary threat, but a
  few instances of large hail or a brief, spin-up tornado cannot
  be ruled out.

- The periodic potential for showers and thunderstorms continues
  at times into Sunday.

- Below normal temperatures will envelop eastern Kentucky from
  Saturday into early next week.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 346 PM EDT FRI MAY 2 2025

Scattered pop-up showers, some with thunder and small hail, have
developed over eastern Kentucky this afternoon. Temperatures are
warm ranging from the upper 70s to lower 80s outside of any
localities recently affected by showers. Meanwhile, dew points
range from the upper 50s in the northeast to lower/middle 60s
further south and west. The regional radar mosaic shows two lines
of thunderstorms lifting east northeast toward the Coalfields. The
first line of thunderstorms, several of which are severe-warned,
extends from roughly Louisville, KY-to-Tompkinsville, KY-to-
McMinnville, TN. The second line which extends from roughly Land-of
the-Lakes down into western Middle Tennessee is associated with
the stronger forcing aloft, and appears to be moving faster than
the surface-based convective line ahead of it. The supporting
energy is ejecting northeast out of a 500H large-scale parent
trough lingering back over the Central CONUS.

The leading line of the mesoscale convective system (MCS) is riding
into a moderately high instability axis (1,500 to 2,000 J/kg of
MLCAPE) extending from northern Alabama northward through Central
Kentucky and into Southern Ohio. Lesser instability is noted over
far eastern Kentucky (closer to 1,000 J/kg MLCAPE). While
instability is ample, the effective bulk shear is rather weak (~25
to 30 kts), favoring multicells. Given the rapid east
northeastward movement of the 500H vort max relative to
tropospheric steering flow, an amalgamation of the two lines into
a single line over the next few hours seems likely as the forced
line of convection overtakes the surface-based cold pool driven
line. In the unstable environment ahead of the line, the 0-3 km
lapse rates are also analyzed as being quite steep, generally from
7.5 to 8.5C/km and DCAPE values are around 800 J/kg. While the
latter is not ideal for severe wind gusts, an isolated severe wind
gust or two cannot be ruled out from a pop up storm ahead of the
line. The main line is likely to produce widespread strong severe
wind gusts, especially along any line segments that become more
northwest-to-southeast-oriented (and thus perpendicular to a
strengthening 850 mb jet). The greatest severe wind threat is
outlined in the Enhanced Risk from the SPC, generally northwest of
a line from Williamsburg-to-Jackson-to-Morehead. As for the hail
threat, shear is not supportive of more than transient weak
supercell structures. However, with relatively straight
hodographs, it is conceivable for even some of the stronger multi-
cell storms to produce large hail. Additionally, as the low-
level jet ramps up this evening, a little more directional shear
in the low-levels could aid in the formation of a brief spinup
tornado, though the chances of one occurring are very low.

The leading edge of the organized thunderstorm activity is
expected to reach our Lake Cumberland counties shortly after 4 PM
EDT and progress east northeast through mid-evening, reaching the
Tug Fork Valley counties by around 8-9 PM EDT. The line is likely
to weaken as it moves into far eastern Kentucky as instability
will be waning. Anticipate most of the shower and thunderstorm
activity to be east of our area by midnight with just some
scattered showers and perhaps an isolated rumble of thunder around
through the remainder of the night. Surface low pressure will
lift northeast along the Ohio River on Saturday while the 500H
trough to our west pinches off into a closed low and drifts over
Kentucky. This will sweep a surface cold front across the
forecast area during the day on Saturday. While shear will be
stronger on Saturday, abundant cloud cover and showers lingering
from the overnight will likely inhibit substantial
destabilization. Given the forcing, cannot rule out a stray strong
thunderstorm, but the overall threat is much lower than today,
only warranting a Marginal Risk from SPC. Leftover showers taper
off as cooler and somewhat drier air filters in Saturday night
with an incoming dry slot. Temperature-wise, look for lows in the
upper 50s to lower 60s tonight, highs in the mid 60s to lower
70s, west to east, on Saturday, and lows in the upper 40s to mid
50s on Saturday night.

.LONG TERM...(Sunday through Friday)
Issued at 408 PM EDT FRI MAY 2 2025

The long-term will open with an ~552 dam closed low over Kentucky
on Sunday morning while a high amplitude ridge axis extends from
Texas northward through Manitoba. The blocky pattern will linger
through the first half of the period. The upper level low will
gradually weaken on Sunday and Monday all the while wobbling over
the Lower Ohio Valley. The pattern finally breaks down and allows
the low to be recaptured by the increasing flow aloft and swept
away to the northeast on Tuesday and Wednesday. However another
upper level trough sinks south from Canada later in the week,
likely dropping a new cold front through the forecast area.
Specifics remain uncertain due to substantial model spread by late
week.

In sensible terms, below normal temperatures are likely on Sunday
and Monday with abundant cloud cover during the diurnal heating
periods while partial clearing occurs each night. A few showers are
possible as well (perhaps a thunderstorm on Sunday in the far east),
but much of the time is likely to be dry. Look for high temperatures
in the mid 60s to lower 70s on Sunday and mainly in the 60s on
Monday. Meanwhile, nighttime minimums will be cooler, mainly in the
40s. Temperatures rebound back into the 70s for highs in most
locations for Wednesday and Thursday before the next cold front
arrives. Low-end shower chances remain in the forecast each day next
week, though either Tuesday or Wednesday could trend dry, depending
upon when the next frontal system arrives.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
ISSUED AT 155 PM EDT FRI MAY 2 2025

VFR conditions prevail at TAF sites at forecast issuance.
Multiple rounds of showers and thunderstorms will move across most
of eastern Kentucky late this afternoon and evening, mainly after
20z, though a few showers and storms are already ongoing over
northern Kentucky in the vicinity of SYM. Stronger thunderstorms
could create brief reductions in flight categories to IFR or worse
and strong to damaging winds. The storms will diminish and
largely exit to the east by 3z. Low ceilings are likely to settle
in overnight with a lull in the rainfall before additional showers
move in late tonight and on Saturday morning. Thunderstorms will
also be possible heading into Saturday but forecaster confidence
in timing was too low to mention in the TAFs at this time.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
None.

&&

SHORT TERM...GEERTSON
LONG TERM...GEERTSON
AVIATION...GEERTSON

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