JKL issues Area Forecast Discussion (AFD) at Jul 4, 1:19 PM EDT ...MESOSCALE UPDATE...905
FXUS63 KJKL 041719
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
119 PM EDT Thu Jul 4 2024
.KEY MESSAGES...
- Sultry weather continues through Friday. Afternoon heat indices
may reach near 100 in some locations. There is also a
persistent threat of thunderstorms through Friday, especially
during daytime hours. A few thunderstorms could produce locally
heavy rainfall and strong wind gusts.
- A cold front finally pushes through as we move into the weekend,
with dry and somewhat cooler and less humid weather arriving.
- Warmer and more humid conditions will make a noticeable comeback
on Monday and continue into the week, along with a potential for
more thunderstorms.
&&
.UPDATE...
Issued at 119 PM EDT THU JUL 4 2024
...MESOSCALE UPDATE...
A moist air mass over central and eastern Kentucky is beginning to
heat up and destabilize in the wake of earlier cloud cover and
convection, much of which is exiting into the mid-Ohio Valley.
Recent observations at LEX shows a temperature of 90F with a dew
point of 75F and Kentucky Mesonet observations indicate dew
points in the 72-80F range across across all of central Kentucky.
A strong line of thunderstorms has developed along a weak cold front,
extending from roughly Madisonville, KY to just west of
Louisville, KY.
CAMs are struggling to resolve this convection as it presses east
and forecaster confidence in their solutions is low. The latest HRRR
runs for example, largely show the line of storms dying out as
mixing causes dew points to fall back in the 60s -- improbable.
The latest mesoanalysis already shows 4,000 J/kg of SBCAPE across
central Kentucky (well above that indicated by most of the CAMS)
where heating has been most intense. Additionally, increasing flow
aloft will lead to increasing effective wind shear reaching 30 to
35 knots roughly near and north of the Mountain Parkway late this
afternoon. As long as heating over eastern Kentucky is not
substantially hindered by ongoing spotty shower and thunderstorm
activity, conditions appear favorable for this upstream line of
shower and thunderstorms to intensify as it moves through central
Kentucky and then only gradually weaken as it moves through
eastern Kentucky late this afternoon and early evening. North of
the Mountain Parkway, shear should be sufficient for a few
thunderstorm line segments and perhaps embedded supercell
structures with primarily a damaging straight-line wind threat.
An isolated weak tornado also cannot be ruled with any supercells
given moderate low-level bulk shear (up to ~20 knots from sfc-1
km) and modest turning in the low-level hodograph. South of the
Parkway, lower shear will tend to favor less organized storm
structures, though steep low-level lapse rates, PWATs values of
2.0 to 2.25 inches, and high levels of instability could still
favor precipitation-loaded downdrafts collapsing and leading to
sporadic downbursts/microbursts.
UPDATE Issued at 1205 PM EDT THU JUL 4 2024
Hourly grids were updated to account for observation as well as
radar/convective trends. Measurable rain was occurring with
showers and some embedded thunderstorms moving across the northern
and northeastern portions of the CWA. Much of central KY was
devoid of convection at this point, though a warm and moist
airmass was leading to increasing instability ahead of convection
that is nearing the OH River vicinity at this time. A shortwave
trough/instability was also helping to maintain this convection.
Convection ongoing over northern and eastern sections of the area
should depart over the next couple of hours. Then a round of
heating is anticipated over the entire CWA and during the mid to
late afternoon, when the activity to the west should approach. By
that point, MLCAPE may reach 1500 to 2500 J/kg courtesy of
dewpoints in the 70s while shear will be limited. In the south
near 20KT effective shear is forecast at 20Z, but 25 to 35KT
effective shear is forecast at that point in the north. Some
organized convection is possible with these parameters, with
locally heavy rain a threat as PW should remain around the 2 to
2.2 inch range along with a threat of locally strong to damaging
wind gusts. Some recent HRRR runs track a more robust cell from
north central/northern KY with decent 2-5km UH toward the Fleming
County vicinity during the late afternoon or roughly into the
area when SPC 13Z SWODY1 added in a slight near and north of
Interstate 64. Convective trends for mid to late afternoon to
early evening will continue to be monitored. After the potential
for stronger activity during the late afternoon and evening
sliding across at least northern portions of the area, a decrease
in coverage of activity should occur toward sunset.
UPDATE Issued at 841 AM EDT THU JUL 4 2024
Showers are starting to break out over our western counties. These
should continue to expand today. Have updated the POP based on
latest model runs, which incorporates a slight shift northward for
the likely POP.
&&
.SHORT TERM...(Today through Friday)
Issued at 546 AM EDT THU JUL 4 2024
A weakening, stalled frontal boundary is laid out north of the
Ohio River early this morning. Its exact position is a bit muddled
due to weak surface winds and prior convection. In the upper
levels, we reside along the southern edge of the prevailing
westerlies, with a weakening high over the Deep South and multiple
waves propagating through the westerlies to our our north.
Aside from a stronger wave over the northern plains, the features
aloft are very weak and difficult for the models to handle.
However, our atmosphere is warm/moist and easily destabilized
with lifting and/or diurnal heating. That being the case, will
look for more convection to develop along and south of the frontal
boundary today, but exactly how it plays out is uncertain.
Mesoscale features will play a significant role. Using a blended
solution from models, will expect convection to pick up as we move
into the day, with the greatest coverage over our northern and
eastern counties today. The activity should again diminish to some
extent as we move into the night.
The aforementioned upper level wave over the northern plains will
strengthen as it moves east and will lead to a larger scale trough
developing over the Midwest by Friday. This will support a
strengthening surface low tracking east over the Great Lakes on
Friday, which will propel a cold front east southeast into
Kentucky. The front will work in combination with the deepening
upper level trough and strengthening flow aloft to bring a
likelihood of showers and thunderstorms area wide on Friday.
Precipitable water should remain near or above two inches through
the short term period, which will allow thunderstorms to be
efficient rain producers. Should any training of cells occur,
there remains a possibility of localized hydro problems. Pockets
of higher instability could lead to some strong storms in the
afternoon or evening hours. Flow aloft will also be increasing
during the short term period, which would be more supportive of
some organization and a severe threat. Even so, it does not look
overly impressive.
.LONG TERM...(Friday night through Wednesday)
Issued at 349 AM EDT THU JUL 4 2024
The forecast period begins with the CWA in the midst of FROPA as a
cold front is slowly moving through the area. A surface low moving
through the Great Lakes will drag the front through the area with
showers and thunderstorms occurring at the start of the period. The
front will gradually exit the region Saturday afternoon with high
pressure building in and remaining overhead for Sunday into Monday.
Models continue to hint at the continuation of an active pattern
into next week. However, in this evening/overnight model suite, long-
term deterministic models begin to diverge on how upper-level
forcing will play out for next week. The GFS continues with a dry
streak into Tuesday morning before dragging a cold front through the
Commonwealth late Tuesday evening. The ECMWF is a little more active
with PoP chances building in for Monday night before a surface low
moves through the Great Lakes and drags a surface boundary through
the area Tuesday afternoon. However, both models keep PoP chances
overhead through the remainder of the forecast period. Nonetheless,
with the discrepancies between deterministic runs, opted to stick
with a weighted NBM solution that keeps periods of showers and
storms through the remainder of the forecast period.
Overall, the period will highlighted with periods of showers and
thunderstorms that'll bring much needed rain to the area. Also,
temperatures will return to more seasonal ranges as daytime highs in
the mid-80s to low-90s and overnight lows ranging from the upper-50s
to upper-60s.
&&
.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
ISSUED AT 841 AM EDT THU JUL 4 2024
Showers/thunderstorms were starting to redevelop between KSME and
KIOB at the start of the period. They should continue to expand
in coverage as we move into the day, with the greatest coverage
likely to be north of the Cumberland Basin. Activity should
decline again as we move into the evening. They will not be
continuous at any given location, and it would be very difficult
to pin down timing. That being the case, VCTS was used in most
TAFs. Precipitation will bring sub-VFR conditions to many
locations for a time. Outside of precipitation, mainly VFR
conditions are expected. Valley fog is a possibility tonight, but
the extend will depend on the coverage of rain during the late day
and evening and the amount of cloud cover tonight (fewer clouds -
more fog).
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...GEERTSON
SHORT TERM...HAL
LONG TERM...VORST
AVIATION...HAL
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 4, 1:19 PM EDT ...MESOSCALE UPDATE...---------------
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