Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 060919
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
519 AM EDT Thu Aug 6 2020

.SHORT TERM...(Today through Friday)
Issued at 452 AM EDT THU AUG 6 2020

Other than a lingering shower or two along the Virginia border, the
overnight has generally been quiet. While valley fog is present
according to the latest satellite, it is not as prevalent or dense
as previous night, and most automated observing sites have received
little impacts. There was some concerns about showers popping up
across the central portion of the CWA around this time according to
several of the CAMs, due to a convergence boundary across the area.
However, so far this hasn`t materialized, and satellite imagery does
not show the clod cover to support it either. As a result, kept out
of the forecast period through the early morning.

As we head into the daytime hours, any fog will lift and dissipate
generally before 9am. High pressure will remain in place across the
northern Ohio Valley throughout the day, dipping down into the
Mississippi Valley and keeping much of the western and central
portions of the Commonwealth dry. While this is likely to extend
into the western JKL CWA, the convergence boundary will remain
across our far eastern CWA, with a stationary frontal boundary just
east of the state. This will provide enough lift and moisture
advection to spawn another round of showers and thunderstorms across
the Central Appalachians during the day, spreading westward into our
CWA. Best coverage will once again be along the Virginia border, but
can`t rule out some scattered activity making it as far west as JKL
and Monticello. Temperatures will be similar to that of yesterday,
if not modifying a degree or two warmer, especially in areas that
see more sunshine. Highs are currently forecast in the low to mid
80s.

Tonight will see a quick end to any convective activity as daytime
heating is lost. A fairly quiet night is in store, with the main
concern just being the fog set up. With more moisture expected to
advect into the region during the day today, and slightly cooler
temps given more NW flow aloft, it is possible that fog could be
more prevalent tonight than it was during the current overnight.
Also kept with some ridge/valley splits as clouds clear out and
subsidence increases, with best fog once again expected to be in
these valley locations.

A very similar set up is on tap for Friday as for today. The only
difference is that winds will become more NWrly as the upper level
trough in place continues to slowly slide eastward. This will advect
drier air into the region, and may leave any shower/storm activity
confined closer to the VA border once more, while the remainder of
the CWA will be dry. Despite the NW flow, the subsidence and
sunshine in place will continue to warm temperatures just a bit,
with highs in the low to mid 80s.

.LONG TERM...(Friday night through Wednesday)
Issued at 515 AM EDT THU AUG 6 2020

The period is expected to begin with an upper level ridge centered
near Bermuda, an upper level trough extending from Quebec and
Ontario to the Appalachians, an upper level ridge extending from
the Southern Plains into the central Plains and portions of the
mid and lower MS Valley and southeast, a trough over the southwest
Conus, a shortwave nearing BC and the Pacific northwest, and an
upper level low centered over Saskatchewan with an associated
shortwave trough south into the Northern Rockies vicinity. At the
sfc, high pressure is expected to initially be centered near Lake
Huron with ridging southwest into the lower OH Valley. An inverted
trough may still be lingering into far southeast KY at that
point. East of the area a wavy sfc front zone is expected to
extend west into the mid Atlantic south and then southwest across
the Carolinas and GA and then west across portions of the Gulf
coast states and then north form eastern TX to the Dakotas.

Friday night through Saturday night, the upper level trough the axis
of which should be moving east of the area around or the start of
the period should continue east and northeast moving across the
northeast to the Maritimes and off the eastern seaboard.
Meanwhile, the upper level ridge should remain centered over the
Southern Plains, but will build into the southeast with height
rises extending into the southeast and eventually into east KY
much of Friday night through Saturday. A shortwave should reach
the western Great Lakes by Saturday evening with a convectively
induced vort possibly nearing the mid MS Valley on Saturday night.
At the same time, the frontal zone should move off the mid
Atlantic coast while the southern extent of the front should reach
near the coast of the Carolinas before stalling out or nearly
stalling out from there west into GA and AL before becoming a warm
front as it extends northwest and then west into the midsouth to
Central Plains. The ridge of sfc high pressure should build into
the Commonwealth during this time before moving east and becoming
centered over the central Appalachians late Saturday night.
Meanwhile, across the western Conus, ridging should build west
into the southwest Conus while the shortwave trough continues east
across the Pacific northwest and into the northern Rockies and
begins to merge with a shortwave further to its north.

From Sunday into Monday, the upper pattern should remain more or
less quasi zonal with mid and upper level ridging generally
extending from portions of the western Atlantic to the southwest
Conus. This ridge will be a bit dirty or have a weakness over the
southeast Conus. A shortwave trough should move from the eastern
Great Lakes and into the northeast and into the Maritimes one or
more additional shortwaves moving near the US/Canadian border in the
westerlies. These shortwaves will move east ahead of a stronger
shortwave trough moving from the northern Rockies across the
northern Plains and nearing the upper MS Valley late Sunday night.
An associated upper level low should develop over Saskatchewan and
move into Manitoba during this time. A couple of shortwave further
south or a convectively induced shortwave or two may move into the
the OH and TN Valley vicinity and across the area during this
time as they move around the ridging centered southwest of the
area. There is plenty of uncertainty with timing and even
existence of particular shortwave crossing the area during this
time. Meanwhile, the sfc ridge of high pressure is expected to
slide east of the area as the warm front to the west beings to
approach the area in response to the trough moving across Canada
and the northern US. This warm front may move into eastern KY on
Monday though it may become somewhat diffuse with time. Further
northwest, a cold front will move into the toward the central
Great Lakes with the southwest extent becoming sheared out from
east to west. Even if the warm front becomes diffuse before
reaching eastern KY, some return flow of deeper moisture should
occur with sfc dewpoints should creep into the upper 60s by late
Sunday.

Monday night to Wednesday, the upper level low will continue east
reaching Quebec to end the period with the trailing trough moving
across the Great Lakes and approaching the northeast. One or more
shortwaves moving through the trough may move closer to the OH
Valley during this time, but there remains uncertainty in the
strength and position of the ridging across the southern Conus
which leads to uncertainty in the track and timing of shortwaves.
Nevertheless, the cold front initially extending from the western
Great Lakes to Central Plains should continue east reaching the
northeast Conus Tuesday night and Wednesday with the western
extent across the OH Valley to the central Plains becoming
stationary or nearly stationary north of East KY. As the warm
front moves further east of the area or at least moist advection
occurs south of the approaching boundary, the GEFS mean PW
increases toward 1.5 to 1.7 inches by Tuesday and remains near
these levels into Wednesday.

Height rises on Saturday and lower sfc moisture and PW should
suppress convection, while the axis of ridge of sfc high pressure
extends across the region. Some cumulus should develop, particularly
near the VA border and possibly extend into McCreary County from the
TN northern Cumberland Plateau. Overall, a drier trend for the past
48 hours for this period continues.

There remains a bit more uncertainty with timing details with any
passing shortwaves that could lead to subtle height falls as
moisture begins to increase a bit by late on Sunday. A warm front
southwest of the area and some isentropic lift could also play a
role in leading to generally isolated to scattered showers or a
thunderstorm on Sunday. Moisture will continue to increase into
Monday and Tuesday and remain in place into Wednesday as the warm
front or at least moisture advection continues ahead of the cold
front slowly approaching from the northwest. Daytime heating will
probably lead to diurnal increase in coverage each day from Sunday
into Wednesday. However, with the warm front potentially nearing
the area on Sunday night and then moving east of the area by
Monday night combined with the cold front nearing from the
northwest and potentially multiple hard to time shortwaves or
remnants of upstream convection, showers and thunderstorms cannot
be completely ruled out at night Sunday night, Monday night, and
Tuesday night.

Temperatures should initially be near normal to slightly above
normal to begin the period on Saturday, but are expected to warm
to above normal levels over the weekend and persist through the
end of the period. Temperatures should near or reach the 90
degree mark in several areas by Sunday, and reach near 90 or the
lower 90s for locations below 2000 feet. Deeper moisture should
lead to more cloud cover and greater coverage of convection on
Tuesday and into Wednesday as the cold front nears the OH
Valley. This should lead to slightly lower temperatures on these
days in the upper 80s to near 90 for most. Heat indices should
peak in the mid to upper 90s and perhaps near 100 in a couple of
spots from Monday to Wednesday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
ISSUED AT 223 AM EDT THU AUG 6 2020

VFR conditions are expected to prevail throughout the period at
the TAF sites. River valley fog is once again forecast for
tonight, along with more fog in the far SE portion of the state
where rain showers were ongoing throughout the afternoon/evening.
However, this fog should not affect the TAF sites. Some of the
CAMs are still pointing at developing showers across portions of
SE KY along a boundary during the early morning hours, which could
affect several of the TAF sites. Uncertainty and light impacts did
not warrant inclusion in the current TAF, but will updated as
necessary if these do, in fact, materialize. By morning, once the
fog (and any rain) dissipates, expect another day of high
pressure, with VFR conditions that include diurnally driven fair
weather CU and light winds. Another round of scattered showers
and thunderstorms could occur along the VA border during the
afternoon with a stalled boundary to our east. However, these
should remain out of the TAF sites and will diminish heading into
the evening hours. Winds should remain light and variable
throughout the period.

&&

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

$$

SHORT TERM...JMW
LONG TERM...JP
AVIATION...JMW


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