267
FXUS63 KJKL 050750
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
350 AM EDT Wed Jun 5 2024

.KEY MESSAGES...

- The threat of showers and thunderstorms will increase through
  mid-week.

- Relatively cooler and drier weather arrives behind a cold front
  which will pass through eastern Kentucky on Thursday.

&&

.UPDATE...
Issued at 1150 PM EDT TUE JUN 4 2024

The next in line upper wave is bringing a renewed threat of
showers and possible thunderstorms to the area late this evening.
Have updated the forecast mainly to add in the current radar and
CAMs` trends for the PoPs and thunder chances. Did also include
the current obs and tendencies for the T/Td/Sky grids with this
update. These minor adjustments have been sent to the NDFD and web
servers along with a freshening of the zones, SAFs, and HWO.

UPDATE Issued at 745 PM EDT TUE JUN 4 2024

23Z sfc analysis shows a very weak area of high pressure over the
central Appalachians while low pressure is noted to the west. This
high has been ineffectual at keeping the convection out of the
this part of the state this afternoon and evening. Plenty of
instability, but little shear resulted in mainly pulse storms,
though a few clusters were able to push several stout and
photogenic gust fronts and shelf clouds through the area. In
addition, moderately high PWS led to an incident of localized
high water from training storm cells. The worst of these are now
exiting stage right and using up the remaining instability for the
JKL CWA, though a few weaker storms will remain possible through
the night. Currently, temperatures vary from the mid and upper 60s
in the rain cooled areas to the upper 70s just ahead of some
storms in the far northeast. Meanwhile, dewpoints remain elevated
in the upper 60s to lower 70s most places - but mid 60s in the
rain. Did update the PoPs and thunder forecast through the night
per near term radar trends and the latest CAMs` guidance. Did also
include the latest obs and tendencies in the T/Td/Sky grids with
this update. These adjustments have been sent to the NDFD and web
servers along with a freshening of the zones and SAFs.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 407 PM EDT TUE JUN 4 2024

As of mid afternoon, the axis of a mid and upper level ridge
extended from off the southeast U.S. coast north through the
Carolinas and VA toward the eastern Great Lakes while an upper
level low was centered over Saskatchewan and an associated upper
level trough south through portions of the Plains. Upper ridging
extended into portions of the southwestern Conus while multiple
shortwaves were moving around it toward western Canada and the
northwest Conus. A couple of shortwaves/disturbances moving
through the flow ahead of the 500 mb through axis were nearing the
region at this point with the first moving across the western KY
to TN Valley area while another shortwave was nearing the mid MS
Valley. At the surface, a ridge of high pressure extended from the
southeast Conus into portions of the Atlantic with a frontal zone
extending from the Atlantic to VA/Mid Atlantic vicinity and then
west and northwest across the Central Appalachians to the Great
Lakes to the triple point of a sfc low in Alberta. A cold front
extended south from that system into the Northern to portions of
the Central Plains and then into the western Conus. Moisture has
been increasing across the region today, with PW analyzed in the
1.3 range east to nearly 1.75 inches near Lake Cumberland region.
Daytime heating of this airmass with temperatures rising into the
80s and dewpoints in the 60s to near 70 was yielding an analyzed
MLCAPE generally in the 500 to 1200 J/kg range with SBCAPE a bit
higher in the 1500 to 2500 J/kg range. Low level lapse rates are
generally 7C/km if not 8C/km,but mid level lapse rates are quite
meager about 5.5C/km at best. Winds aloft are weak and shear is
rather minimal at this time. Earlier activity was generally pulse
type with a bit greater coverage and longevity of the activity
nearer to the shortwave that is mainly just producing brief
downpours.

The initial shortwave trough nearing the area should continue
east and northeast across the region through the evening, while
the second shortwave upstream generally passes northeast. These
shift east overnight generally and this combined with the loss of
daytime heating should result in a lull in activity from the late
in the evening into the overnight. However, the 500 mb trough
axis will approach late tonight and on Wednesday downstream of the
upper low meandering into Manitoba. In addition, during this
time, sfc low pressure will track into northern Ontario with the
trailing cold front working across the western and into the
Central Great Lakes to mid MS and near the OH Valley before
becoming stationary in the Southern Plains. This trough is
expected to work across eastern KY late Wednesday and Wednesday
night with the weakening cold front also moving into eastern KY,
but likely not completely clearing the region before dawn on
Thursday.

The moist airmass will remain across the region through the near
term period, with PW rising to generally 1.6 or higher this
evening and then climbing to the 1.7 to 1.9 inch range on
Wednesday. There should be a breif drop off in between shortwaves
late this evening in PW back toward 1.5 inches briefly. PW will
remain generally 1.8 to 1.9 inches into Wednesday evening, before
decreasing as the next shortwave and cold front enter and move
into the region on Wednesday night at which point values drop
toward 0.8 northwest to about 1.5 inches late tonight along the
VA border.

Another uptick in coverage of convection should occur by the
diurnal cycle on Wednesday in advance of the next shortwave or
front and as the PW increase again after the overnight lull some
activity may develop in the moisture/PW gradient toward dawn or
shortly thereafter. The rather high PW values combined with 6 hour
HREF max QPF of about 2 to 2.5 inch range in the region on
Wednesday lead to some concern with torrential downpours and if a
location receives torrential downpours the threat of high water.
Storm motions should be a bit swifter on Wednesday with 0-6km mean
winds rising toward 20 to 25KT and at that point effective shear
should be near 20KT. During peak heating on Wednesday, MLCAPE is
forecast in the 850 to 1300 J/kg range and with this in mind
activity on Wednesday should be a bit more organized with a strong
storm or two with gusty winds a possibility with low level lapse
rates about 7C/km or higher.

Temperatures will remain mild through the near term ahead of the
front with highs on Wednesday averaging a couple of degrees above
normal while low will about 5 to 7 above normal for early June.

.LONG TERM...(Thursday night through Tuesday)
Issued at 350 AM EDT WED JUN 5 2024

The 05/00z model suite is generally in good synoptic agreement at
the start of the period before spread increases this weekend/early
next week. Initially, an ~548 dam low is in place over the Upper
Great Lakes, embedded within a swale extending northwestward in
the Yukon. This relative troughing is sandwiched between a
prominent ridge over the western CONUS and another orphaned ridge
axis aligned from Labrador/Quebec northwestward into the eastern
Beaufort Sea. At the surface, a regional analysis shows an ~991 mb
low south of James Bay while its cold front extends southward in
to the Central Appalachians and then extends southwestward along
the southern side of the of Ohio River, including across Kentucky,
and beyond across the Ozarks. High pressure is found just north
of the boundary across the the Central and Northern Plains.

The cold front sags across southeast Kentucky late Thursday
evening as the parent upper low drifts toward the Lower Great
Lakes. The upper level forcing with this system remains well
north of of the Commonwealth, leaving just the weak low-level
convergence along the front to spark convection under a strong
~600 mb cap. The potential for lingering scattered convection is
depicted by a majority of the 00z CAMs suite. Once that front
clears the area, a drier and cooler air mass will move in on
northwesterly breezes late Thursday Night and Friday as surface
high pressure sinks southeastward into the Tennessee Valley/Mid-
South Saturday night. Meanwhile, a vort max over the Canadian
Prairies, will pivot, either in part or whole, around the upper
low over the Lower Great Lakes, bringing another surface cold
front to the Eastern Kentucky Coalfields. The system`s evolution
will have a significant bearing on the rain chances late this
weekend and early next week, depending upon whether this vort max
remains more of a progressive open wave or forms a slow-moving
closed low.

Sensible weather will feature a diminishing threat for showers on
Thursday evening. Once the precipitation ends, fair weather can
be expected into Saturday morning with slightly cooler temperatures,
ranging mainly in the mid to upper 70s for highs and in the lower
to mid 50s for lows. A few of the coldest hollows could see upper
40s on Friday night. While the specifics are still uncertain, the
daily threat for showers and even a few thunderstorms is very
likely to return on Saturday and persist into early next week as
the next cold front and upper level system approach. Forecast
high temperatures generally range from the mid to upper 70s
through the remainder of the forecast period while nighttime lows
bottom out in the mid to upper 50s.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
ISSUED AT 825 PM EDT TUE JUN 4 2024

Scattered shower and thunderstorm activity will linger through
the evening, but with a general decrease in coverage through 04Z.
Some periods of MVFR or lower vis and or ceilings are anticipated
where the stronger showers and storms pass along with a brief gust
into the 20 to 30 kt range. Fog could also be a concern tonight
where the rain occurred, if clearing becomes substantial enough.
Have included a tempo at many terminals for some late night
restrictions due to fog. After an anticipated lull in activity
between about 06Z and 12Z, shower and storm coverage will probably
increase through Wednesday afternoon. Outside of any storms,
winds will be mainly from the south to southwest at less than 10
kts through the aviation forecast period.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...GREIF
SHORT TERM...JP
LONG TERM...GEERTSON
AVIATION...JP/GREIF