249
FXUS63 KJKL 042008
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
408 PM EDT Tue Jun 4 2024

.KEY MESSAGES...

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

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

&&

.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 through Tuesday)
Issued at 248 PM EDT TUE JUN 4 2024

General agreement continues with respect to the mid/upper level
patterns aloft. An elongated low and associated trough will have
spun its way into the Great Lakes region at the start of the
extended. The low...or mean low sets up residence over the Great
Lakes for the remainder of the period, sending additional short wave
impulses around the southern periphery of the mean low, into the
Ohio Valley. At the surface, a relatively strong surface cold front
will move through eastern Kentucky late Thursday or Thursday night.
A stacked low over the Great Lakes, will keep our area under the
influence of northwest flow. Subtle short wave disturbances passing
across the region combined with wrap around moisture and diurnal
heating will keep a general 20-30 PoP going through the period, with
a noticeable diurnal flavor to activity.

Sensible weather features generally dry weather for many, though
isolated to widely scattered showers, commonly referred to as hit or
miss showers and thunderstorms could impact anyone on any given day
and at any given time. However, the most likely window of time for
rain would be in the afternoon and early evening time frames. Other
than Thursday morning at the start of the period, Saturday
afternoon/evening and again Sunday afternoon are the next most
likely day of more widespread rain as PoPs increasing to around 30-
35% as another cold frontal system approaches and passes through the
Ohio Valley. After Thursday`s low to mid 80s for max temps, daily
highs will average around 5 degrees below normal, or mid 70s through
the period. Our coolest day through the extended will be Friday,
with Saturday being slightly warmer by a degree or two. With lower
surface dew points in the low 50s and a gradient wind around 10 mph,
Friday will feel the coolest. Overnight lows will run in the 50s,
though we may be flirting with upper 40s in some of our coolest
valley locations by Saturday morning.

Not seeing any solid signals with respect to hazards through the
period. Instability will be relatively low, with MLCAPES only
climbing to between 750 and 1250 J/kg Thursday afternoon.
Instability looks even weaker for Sunday. At this time effective
shear is not even reaching marginal levels. Thus any organized
convection will likely be limited to features such as frontal
boundaries.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 153 PM EDT TUE JUN 4 2024

An increase in moisture, combined with daytime heating and the
approach of a couple of disturbances from the southwest, has
allowed isolated to scattered showers and thunderstorms to
develop across portions of the region. The activity should linger
into the evening, but with a general decrease in coverage between
00Z and 06Z. Confidence in timing/placement is too low for
anything more than VCTS to be mentioned in TAFs at this point,
though KSJS and KSYM appear to have the best chance for thunder
possibly on station over the next hour or two followed by KLOZ
and KSME. Some periods of MVFR or lower vis and or ceilings are
anticipated where the stronger showers and storms pass and a
brief gust into the 20 to 30KT is also possible. Fog could be a
concern tonight where rain occurs if clearing becomes substantial
enough, but due to lack of confidence is not included at this
time. After an anticipated lull in activity between about 06Z and
12Z, coverage may again increase to end the period.

&&

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

$$

SHORT TERM...JP
LONG TERM...RAY/CMC
AVIATION...JP