Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 031157 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
757 AM EDT Mon Aug 3 2020

.UPDATE...
Issued at 750 AM EDT MON AUG 3 2020

Hourly grids have been freshened up based on recent observation
and trends with the areal extent of fog. The fog is still expected
to lift and dissipate through around 9 AM or 930 AM EDT. Some
showers and a stray thunderstorm moving across the Appalachians
have spread into portions of East Tn and southwest VA. Some of
this activity may spread or expand toward the VA border and into
the VA border counties as the morning progresses as a disturbance
moves through the Appalachians.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 515 AM EDT MON AUG 3 2020

Early this morning, an upper level ridge as centered near Bermuda
with another upper level ridge extending from portions of the
eastern Pacific into the southwestern Conus and then north near
the Rockies. In between, the axis of a mid and upper level trough
extends from eastern Canada southwest to the northern and western
Great Lakes and then south through the MS Valley. A shortwave
trough moving through the mean trough was nearing the lower OH
Valley. Meanwhile, Isaias continues moving north northwest to the
east of the FL coast. At the sfc, high pressure was centered over
the central Appalachians with a boundary stalled out generally
near or east of the Blue Ridge. Meanwhile, an area of low pressure
was moving across the Great Lake region with a trailing cold
front nearing the Lower OH Valley at this time. Fog has developed
in the valleys overnight and has been dense in a few locations.
The fog appears to be more prevalent across the western two
thirds where skies have been mostly clear to clear overnight and
have experienced less or no passing cirrus and some occasional mid
level clouds. Temperatures were colder than what has been
experienced offering a break from the mild overnight lows
experienced for much of the past couple of weeks.

Fog, generally in the valleys will linger past sunrise before
lifting and dissipating around 13Z/9 AM EDT. Otherwise, a
disturbance moving from the Gulf coast states north through the
Appalachians and some moisture drawn west should interact with the
boundary stalled southeast of the area. Some showers or
thunderstorms associated with this may affect mainly the VA
border counties though convective allowing model trends support
much of this remaining southeast of the area. Meanwhile, as the
shortwave trough rotates through the mean trough and generally
passes northwest of the area and cold front moves across western
into central KY as the associated sfc low moves rather slowly to
the eastern Great Lakes some additional convection may develop.
Again model trends support much of this activity or at least the
better coverage of this closer to the front/shortwave track where
forcing will be better. This leaves eastern KY in between systems
more or less. Enough instability should develop for isolated to
scattered coverage of showers and storms during the afternoon to
early evening, especially nearer to the VA border and probably the
northwest as well. MUCAPE and SBCAPE are only expected to peak
from about 1000 J/kg to perhaps as much as 1750 J/kg per HREF mean
with bulk shear around 25 to maybe as much as 30KT. Overall, pops
were lowered a bit from the previous forecast and to below NBM
values as coverage appears to be limited in between systems,
perhaps owing to the drier airmass/lower dewpoints in the 60s,
despite some height falls at 500 and 700 mb. Both MOS pops and
convective allowing model runs suggest mainly isolated to
scattered coverage, except right along the VA border where likely
(60 pop) was used. Max temperatures should average near to a
couple of degrees below normal for early August.

Tonight and into Tuesday, the mid and upper level trough axis
will continue to move east across the OH Valley and into the
southeast, including the Commonwealth as an upper low closes off
over the northern Great Lakes/Ontario. Meanwhile, Isaias will
continue tracking north into portions of the eastern seaboard. The
sfc low will continue moving northeast in advance of the upper
trough and near the St Lawrence Valley at the end of the period.
The trailing cold front should enter eastern KY tonight, before
pushing east of the area on Tuesday. Chances for showers and
thunderstorms will linger into the evening, with thunderstorm
chances diminishing late in the evening. The threat for showers
will linger overnight in the far east ahead of the front.
Meanwhile, some low clouds and or fog should affect areas along
and behind the front tonight. Daytime heating, and a passing
disturbance/shortwave ahead of the mid and upper level trough axis
should combine for scattered showers and a few thunderstorms on
Tuesday afternoon to early evening. Temperatures should average 2
to 4 degrees below normal both tonight and on Tuesday.

.LONG TERM...(Tuesday night through Sunday)
Issued at 411 AM EDT MON AUG 3 2020

Heights will be slowly rising aloft to start the extended portion of
the period, as a strong upper level low over Ontario begins to shift
NEward. However, a shortwave will remain in place across the Ohio
Valley and points southward from Wednesday through Friday, finally
exiting eastward by Saturday as strong ridging takes hold from our
SW. This ridging will remain the dominant feature through the
remainder of the extended forecast.

That being said, the surface features and sensible weather are
somewhat a contrast to the upper levels. While a shortwave
remains present across the state for the second half of the work
week, at the surface, a strong area of high pressure will be
gaining control of the region from the NW throughout the day
Wednesday. This high pressure system will have hold of much of
the state through the rest of the work week. The only caveat is
the far SE portion of the state, generally in the high terrain.
The cold front that moved through and exited KY during the day
Tuesday will become stalled across the Appalachians and points SW.
This will help promote daily convection near the stalled boundary,
spreading as far westward as our SE border. Pops should generally
be scattered or less in our CWA, diminishing quickly as we head
into the evening and overnight hours. With much of the rest of
the area experiencing high pressure and mostly sunny skies, expect
the temperatures to modify warmer each day. Highs on Wednesday
will start out in the low 80s, but will be in the upper 80s by
Friday.

For Saturday, as the strong ridge takes hold of the region...at the
surface, the area of high pressure will be shifting east of the
state. The models start to diverge at this point, with the GFS
showing an additional shortwave developing and moving through the
state on the periphery of the ridge, providing pops for eastern
KY for Saturday evening and through the day Sunday. The ECMWF also
has a developing system in place, but keeps it well to our west,
with high pressure remaining the dominate feature across the CWA
during this time. If the ECMWF pans out, we may stay dry through
the entire weekend, or at least until Sunday evening/night. If the
GFS is correct, however, it`s going to be a wet weekend. Given
the uncertainty in which track and solution is correct, just kept
with the NBM at this time, which went generally isolated to
scattered chances throughout the weekend...breaking the difference
between the two. Expect that depending on which solution the
models end up trending towards, these current chances will either
be increasing or decreasing as we over the next few days.
Regardless, the temperatures will be warm, with highs expected to
continue rising. Highs on Saturday and Sunday will be in the upper
80s and low 90s. Expect these temps may sway some as well,
however, depending on how the models trend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
ISSUED AT 755 AM EDT MON AUG 3 2020

VFR should prevail throughout the vast majority of the period.
There will be a couple of exceptions. Fog, mainly in the valleys
initially should lift and dissipate by 1330Z. Otherwise, a
disturbance passing to the east of the area and a cold front and
disturbance approaching from the west should lead to isolated to
scattered convection generally from about 16Z on and could lead to
brief MVFR or IFR at a location. Some convection may spread into
locations near the VA border around or after 14Z. We have
continued to include VCTS for a few hours at all sites by around
18Z as there is remains uncertainty in coverage and timing.
Showers should generally diminish between 0Z and 6Z while a cold
front moves into East KY. Along and behind the front, or from
about 5Z on, some stratus buildown will probably lead to MVFR to
IFR and perhaps lower vis and or ceilings. Winds will be less than
10KT outside of any thunderstorm activity.

&&

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

$$

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



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