951
FXUS63 KJKL 091717
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
117 PM EDT Thu May 9 2024

.KEY MESSAGES...

- Some showers and perhaps a storm or two are possible at times
  from this afternoon through early next week.

- Above normal temperatures are forecast today. However, a cold
  front passing today will usher in cooler temperatures from
  Friday through the weekend, with warming then returning.

&&

.UPDATE...
Issued at 1150 AM EDT THU MAY 9 2024

Looking at upstream ACARS sounding over SDF and CVG and matching to
latest hi-res guidance, the 14Z HRRR seems to have a better handle
on a low-level inversion across the region. That model has backed
off on precip chances for this afternoon, with just a smattering of
a few showers. NAM/RAP time-height sections keep moisture and lift
shallow across the area, perhaps a little deeper over NE and far
eastern KY. Thus will continue to trim pops down a bit, as well as
thunder chances for today.

UPDATE Issued at 945 AM EDT THU MAY 9 2024

Most of the rain has exited eastern KY this hour, with residual
high clouds streaming northeastward from ongoing convection over
northern Alabama. We could see a brief window of sunshine before
low clouds build in within the moist low-level environment. Have
backed off of rain chances a little, and kept the best chances for
scattered storms along and east of a line from Mt. Sterling to
Jackson to Middlesboro. These will be brief events, with not as
much deep moisture to work with. We could see some brief gusty
winds with these cells and cannot rule out small hail with any
taller cores that develop. Updated products will be out shortly.

UPDATE Issued at 730 AM EDT THU MAY 9 2024

Hourly grids were updated based on recent observations and trends
and with the rain rates not being all that substantial the Flood
Watch was cancelled early.

&&

.SHORT TERM...(Today through Friday)
Issued at 436 AM EDT THU MAY 9 2024

Early this morning, an upper level trough extended from the
Maritimes across portions of Ontario and Quebec to the Great
Lakes to southwest Conus. West southwest flow was in place
between this trough and upper level ridging, the axis of which
extended across Central America to portions of the Caribbean. A
shortwave trough was approaching eastern KY at this time. At the
surface, An area of low pressure was tracking across the Lower OH
Valley region with the associated frontal zone extending east to
the mid OH Valley to the mid Atlantic coast. Meanwhile an
instability gradient associated with outflow from rounds of
convection since Wednesday was in place southwest of eastern KY.
Recent mesoanalysis had very limited instability in place north
of this boundary with MUCAPE 250 to 500 J/kg in the southwest
portion of eastern KY, mid level lapse rates area wide no more
than 6 to 6.5C/km, and best shear parameters from the TN border
and locations to the south of the area. PW as high as 1.3 to 1.5
inches was in place from central KY to areas generally near and
west of Interstate 75. Convection was occurring across the OH and
TN Valley with the more robust/deeper convection from nearer to
the TN border and south in the instability gradient though
lightning was occurring into portions of central KY in a
stratiform rain regime.

The shortwave trough is expected to move east of eastern KY this
morning while the trough axis at 500 mb remains north of the the
OH Valley today. The western portion of the trough is progged to
close off/be left behind over the Four Corners region today and
then meander to the west and southwest through Friday. Meanwhile,
the 500 mb trough axis is expected to move south and southeast
across the Great Lakes and near the OH Valley and mid MS Valley
tonight, before this trough axis axis rotates across the OH Valley
and into the Appalachians to end the period. Shortwave ridging
should enter the OH Valley to end the period while another
shortwave trough moves into the evolving trough over the eastern
Conus and into the western Great Lakes and Upper MS Valley.

Chances for convection today should be greatest through the
morning though after a possible late morning to early afternoon
lull, a slight uptick in activity may coincide with peak heating
and the cold front crossing eastern KY. Recent convective
allowing models forecast as much as an inch or more over the next
few hours through about dawn in the southernmost tier or two of
counties nearest to the TN border. At this point have held onto
the Flood Watch through 8 AM across the south.

Chances for at least isolated convection will linger into the
evening and tonight as the 500 mb trough axis lingers upstream
though a lull during the evening into a part of the overnight is
possible. If and where clouds can clear out, fog may become a
concern following recent rainfall though a general increase in
cloud late tonight and toward dawn on Friday leads to uncertainty
in location and duration. Some patchy fog was included in the
grids for tonight, with somewhat lower visibilities for deeper
valleys. Chances for convection will increase on Friday during
peak heating as the trough nears with the best chances in the
southeast. Temperatures on Friday will be notably colder than
recent days with highs not expected to get out of the 60s. Friday
highs should be nearly 10 degrees below normal for this time in
May.

.LONG TERM...(Friday night through Wednesday)
Issued at 542 AM EDT THU MAY 9 2024

Our weather at the beginning of the long term period will be under
the influence of a longwave trough over the northeast CONUS and
shortwave troughs rotating around it. A cool air mass will persist
over our area in this regime. One shortwave trough will be
departing to our east on Friday night, and in its wake, transient
surface ridging will build in from the west. This results in skies
becoming mostly clear. Another shortwave trough moves southeast
over the Ohio Valley on Saturday, and with it we can look for a
potential for showers to return. The greatest probability will be
over the northeast portion of the area, closest to the shortwave.
Have included a slight chance of thunder over our northeast
counties based on NAM forecast soundings, but it looks very
marginal. This wave departs to the east by evening and precip and
most clouds dry up again.

At this point, the heart of the longwave trough also shifts east,
and ridging aloft approaches from the west on Sunday and passes
over on Monday. This brings dry weather and mostly clear skies
from Sunday night through at least Monday morning. At the surface,
high pressure passes eastward south of our area on Sunday and
departs eastward on Monday. Increased sunshine will allow for
temperatures to return to near normal on Sunday, with a further
climb on Monday as warm air advection becomes more pronounced.

Our next weather system will begin to affect the area already by
late Monday. A nearly stationary closed upper level low centered
over UT today will eventually open up and get absorbed back into
the flow. Timing of these features can be tricky, especially at
longer time ranges. At present, a model blend suggests it will
approach us from the west late Monday and arrive on Tuesday. It
is expected to support a weak surface low which will help to pull
moisture northward on the back side of the departing high. The
GFS is faster than the ECMWF with the system and shows some light
precip reaching our southwestern counties by Monday evening. Both
models have precip here on Tuesday. Based on this, have used only
a slight chance late Monday, increasing to likely by Tuesday
evening. It looks like there will be little change in air mass
behind the system, and models try to generate more convection with
heating on Wednesday. Have used a chance POP on Wednesday, with
the best upper level support departing to the east.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
ISSUED AT 117 PM EDT THU MAY 9 2024

High clouds clearing off to the east, but low clouds moving in from
the west to fill the gap. KSJS/KSYM may briefly dip below the
MVFR/VFR threshold with these clouds. Isolated to widely scattered
showers/storms may impact those sites. Winds will pick up from the
west at all sites with gusts of 15-20 kts. Should be a break in the
cloud cover/rain chances/wind gusts this evening before low clouds
develop again toward daybreak Friday.

&&

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

$$

UPDATE...JP/SHARP
SHORT TERM...JP
LONG TERM...HAL
AVIATION...SHARP