Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 220133
AFDJKL

AREA FORECAST DISCUSSION
National Weather Service Jackson KY
933 PM EDT Mon Aug 21 2017

.UPDATE...
Issued at 933 PM EDT MON AUG 21 2017

No substantive changes are needed this evening as forecast is
tracking obs nicely. Forecast may be a tad too fast ramping up
PoPs tomorrow based on some of the 18z guidance but decided in the
end to leave it alone and let midnight shift digest the 00z data
before making any changes. The timing for the greatest severe
threat tomorrow remains as early as mid afternoon in our northwest
counties through the evening for the remainder of the area. Have
a great night...

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 324 PM EDT MON AUG 21 2017

With the partial eclipse reaching a maximum of about 95 percent
here at the NWS office in Jackson we observed a temperature drop
of 6 degrees with the fall beginning around 1750Z. The temperature
fell from 87 to 81. The temperature had risen back to 84 by 1912Z.
The few cumulus clouds we had also diminished during the partial
eclipse. Pretty interesting!

Anyway, the focus now turns from the weather for the eclipse to
the threat for severe thunderstorms on Tuesday into Tuesday
evening. As a strong short wave moves along the U.S Canadian
border on Tuesday surface low pressure will deepen as it moves
from the upper Great Lakes into Ontario and eventually Quebec. A
cold front trailing from the low will move into KY Tuesday night
and will pass southeast of our area Wednesday morning. Models have
been suggesting some scattered storm development well ahead of
the front with some outflow boundaries from upstream convection,
so we could see storms as early as early Tuesday afternoon. Storms
should become more numerous as the afternoon progresses and the
front nears and low level wind fields increase. Instability will
increase Tuesday afternoon as well with MLCAPE in excess of 2500
J/kg expected. Shear values in the 0-6km range will also be better
than in recent events. The freezing level and wet bulb zero
height will still be elevated so the main severe threat looks to
wind and not hail. SPC has most of the area in a slight risk for
Tuesday and since this is the best chance for severe storms we`ve
had in a while we`ll be highlighting the threat in our messaging.
Also with PW in excess of 2 inches, locally heavy rains will also
be a threat, and WPC has placed the area in a marginal risk for
excessive rains for Tuesday. We will also be highlighting this
threat in our messaging.

.LONG TERM...(Wednesday through Monday)
Issued at 324 PM EDT MON AUG 21 2017

With the passage of the cold front Wednesday morning, much cooler
and drier air will invade the area, with an extended period of
below normal temperatures which will last into early next week. A
couple of short waves will move across the Great Lakes/Ohio Valley
from Thursday into Friday and again Sunday or Monday, helping to
keep a mean trough over the eastern United States. The drier and
cooler air mass will be noticeable with highs will mostly in the
upper 70s from Wednesday through Monday, with lows mostly in the
mid and upper 50s. Dewpoints will mostly be in the 50s through the
long term portion of the forecast but will begin to increase
again early next week. Confidence remains low on details and
timing for any shower or storm chances, but blended model load
keeps a small chance very close to the VA border on Saturday
afternoon, a better chance across the south on Sunday, and then a
chance area wide on Monday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
ISSUED AT 750 PM EDT MON AUG 21 2017

VFR conditions and light winds will prevail at the TAF sites
through early Tuesday afternoon. Valley fog is expected to develop
tonight with some local IFR conditions, however fog is not
expected to affect the TAF sites. Clouds will be on the increase
by around dawn but bases should remain VFR. An approaching cold
front will then bring scattered thunderstorms Tuesday afternoon,
with the storms becoming more numerous by Tuesday evening.

&&

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

$$

UPDATE...ABE
SHORT TERM...SBH
LONG TERM...SBH
AVIATION...ABE


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