LMK issues Area Forecast Discussion (AFD) at May 24, 9:58 PM EDT976
FXUS63 KLMK 250158
AFDLMK
Area Forecast Discussion
National Weather Service Louisville KY
958 PM EDT Fri May 24 2024
.KEY MESSAGES...
* Stormy pattern with risks of strong to severe storms and
localized flooding issues will continue into Monday.
* The greatest threat for severe weather will likely come Sunday
afternoon into Sunday night ahead of a cold front. Severe storms
will be capable of producing damaging winds, large hail, and
tornadoes.
&&
.UPDATE...
Issued at 958 PM EDT Fri May 24 2024
Current radar imagery shows fairly disorganized multicell clusters
moving across southern Illinois ahead of the cold front. Aside from
the mesoscale lifting provide by marked low-level frontogenesis, the
environment downstream of the front is characterized by moderate
elevated instability, improving mid-level lapse rates, and favorable
upper-level divergence. That being said, the surface layer is
steadily stabilizing north to south due to the lack of diabatic
heating and cooling effect from previous convection. As a result,
HRRR has been consistently showing an overall decreasing trend in
strongest convection over the Upper Ohio Valley, which is validated
by radar and lightning trends over the past hour. On the other hand,
the southern edge of the upstream cluster, currently over MO and IL,
will remain relatively active as it will tap into the elevated
instability gradient and convergence along the southward sagging
front. This will translate in higher chances of overnight rain and
lightning chances for the western third of the forecast area, with
the possibility of small hail and sub-severe wind gusts accompanying
the strongest updrafts. One tricky aspect of tonight storm coverage
will the eastward extension of the storm activity as individual
multicell elements are moving east-northeast while the overall
mesoscale system is heading to the south-southeast.
&&
.SHORT TERM /THROUGH SATURDAY/...
Issued at 326 PM EDT Fri May 24 2024
Currently, a cold front stretches from eastern Iowa south-southwest
back through Oklahoma City and continues on through Texas. Ahead of
the front, 5-10 mph southerly winds are keeping precipitable water
values mostly around 1.25" over the Lower Ohio Valley. Some pooling
in the area will cause pockets of 1.5" values, so we have plenty of
moisture in place with dew points ranging from the mid 60s to low
70s. Even after parts of southern Indiana and central Kentucky saw
clear skies earlier this morning, most areas now are seeing some
level of cloud cover debris from convection over western Kentucky
and Tennessee. This hasn't limited instability too much as SPC's
mesoanalysis currently shows 1,000 to 2,000 J/kg of MLCAPE over the
CWA, and over the next few hours, these values could grow 500 or so
more. With that being said, there is no shear. Deep layer, 0-6km
bulk shear, values are around 10 knots, so any thunderstorms today
would be limited in their development potential.
For the rest of this afternoon and evening, many areas will likely
remain dry, but a broken line of convection, that is currently
stretching northwest to southeast over the CWA, is expected to
continue to the east. Any development could produce lightning and
some gusty winds. Severe weather isn't expected, but a warning or
two is possible.
Tonight, as the earlier line of convection is ending in eastern
Kentucky, convection ahead of the front is expected to dive
southeast across southern Illinois and far southwest Indiana as it
travels towards the Lake Cumberland region. Being that the line is
expected to arrive after midnight, any storms should be elevated, so
winds will be less of a threat. Some hail could still be possible
before the line exits the region during the predawn hours. Believe
skies will remain cloudy for most of the night which will help limit
fog development. Some patchy fog will be possible, but not expecting
the widespread dense fog like we saw this morning. Lows are expected
to remain near normal in the low to mid 60s.
Tomorrow, the cold front should make it to near the Ohio River
between Indiana and Kentucky before it stalls. Precipitable water
values will remain slightly over an inch, and dew points will reach
the mid 60s. As high pressure tries to make it into the region,
winds throughout the day will begin veering towards the west and
northwest as skies become mostly sunny. This will help to begin to
dry the region. Can't rule out some low chances for precipitation,
but it should be a dry day after the early morning precipitation
exits southern Kentucky. Highs should reach into the low 80s.
&&
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
Issued at 326 PM EDT Fri May 24 2024
Some isolated showers and storms may linger into the early parts of
the overnight hours Saturday but should steadily taper off toward
midnight with a strengthening nocturnal inversion. The rest of the
overnight hours are shaping up to be fairly quiet.
By dawn Sunday morning, a strong LLJ will begin nosing in from the
west. Some scattered showers and storms could accompany the arrival
of the LLJ, but more notably, we'll gradually see an uptick in low
level moisture through the day as the LLJ overspreads the region and
the stalled frontal boundary across northern portions of the CWA
lifts northward as a warm front.
By the afternoon, we should see some clearing/drying within the warm
sector of an approaching low/cold front. Models predict very
unstable conditions as increasing low level moisture and steepening
low/mid level lapse rates result in MLCAPE surging into the 2,000 to
+3,000 J/KG range. Environmental low level and deep layer shear will
also increase due to the presence of the LLJ and an approaching
upper level trough. Forecast soundings from most models reveal a
fairly stout capping inversion near 750-700mb, which will serve to
limit convective development. Forecast models vary on afternoon
storm initiation, with some keeping the cap strong enough to hold off
convection, while others initiate isolated convection along weak
mesoscale boundaries. Should storms overcome the cap during the
afternoon in this environment, they would be capable of damaging
winds, very large hail (+2"), and tornadoes.
Better forcing for storms looks to arrive Sunday night as the
surface cold front approaches from the west. We could see one (or
multiple) waves of convection ahead of the front and the convection
could consolidate into one large squall line. Damaging winds, large
hail, and tornadoes would be possible with severe storms. Storm
severity will be somewhat dependent on a couple of factors,
including: (1), the strength of the capping inversion overnight, and
(2) if we end up in a scenario where we have multiple rounds of
storms, will we destabilize enough in the wake of the first round to
support severe weather for subsequent rounds?
The cold front should begin pushing into the region Monday morning
ending the severe threat. Isolated/Scattered showers and perhaps a
storm could develop during the daytime hours but drier air will
gradually filter in from the northwest so rain chances should
steadily decrease by Monday night. Much of next week will feature
cooler than normal temperatures with more comfortable dewpoints and
mostly dry conditions.
&&
.AVIATION /00Z TAFS THROUGH 06Z MONDAY/...
Issued at 734 PM EDT Fri May 24 2024
Impacts/Confidence:
- Low confidence in timing and coverage of overnight precipitation
- Medium confidence in MVFR ceilings Saturday morning
Discussion...Tonight VFR conditions will deteriorate tomorrow
morning as a cold front moves and eventually stalls over the
forecast area. Early evening radar highlights two areas of ongoing
storm activity: a recently develop set over the Bluegrass and fairly
disorganized cluster tracking across southern Illinois. Of the two,
the latter is the most concerning as it will continue moving east-
southeast and approach the TAF vicinity around midnight. Based on
current model guidance, BWG will be the most likely terminal to have
any impacts from the aforementioned cluster with low confidence in
any eastward extension. As a result, any storm-related impact at HNB
and SDF will be addressed with AMD if needed. Otherwise, expect
winds turning from the south (tonight) to the west-northwest
(tomorrow) as the actual cold front sinks in while ceilings fall to
MVFR thresholds. VFR conditions will return tomorrow afternoon.
Extended Outlook.. Advection fog/stratus cannot be ruled out
Saturday night as the front lifts to the north.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
KY...None.
IN...None.
&&
$$
UPDATE...ALL
SHORT TERM...KDW
LONG TERM...DM
AVIATION...ALL
Source:
LMK issues Area Forecast Discussion (AFD) at May 24, 9:58 PM EDT---------------
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