Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 250610 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
210 AM EDT Tue Jul 25 2017

.UPDATE...
Issued at 145 AM EDT TUE JUL 25 2017

Did a quick update to the grids through the rest of the night fine
tuning the fog and sky based on the latest obs, satellite, and
webcam trends. Expect the fog to be patchy most places with a
tendency toward locally dense areas later in the night,
particularly in any of the valleys where the skies go mostly
clear. Also, fine tuned the T and Td grids per the latest obs
and trends. These updates have been sent to the NDFD and web
servers.

UPDATE Issued at 1013 PM EDT MON JUL 24 2017

Showers continuing to wind down across southeastern Kentucky as
boundary layer cooling takes place. Dewpoints beginning to
decrease across northern Kentucky, with this trend continuing
to sag slowly south through the night. Nonetheless, still looking
at widespread fog with some of this becoming dense in sheltered
valleys and in locations that have received rain recently.

UPDATE Issued at 815 PM EDT MON JUL 24 2017

A broken band of showers and thunderstorms, stretching from
Norton, Virginia to Brodhead, continues to make slow progress off
to the southeast in advance of a cool front set to cross south of
the Ohio River. These will diminish by mid-late this evening as
instability further decreases and drier northwest flow gradually
oozes in. Still looking at widespread fog development tonight
given crossover temperatures generally in the mid 60s or higher.
Drier air will likely mix in above the valleys earlier tonight,
particularly north of Mountain Parkway and Interstate 64. Valleys
here, as well as most locales farther south, will however see
lingering low level moisture as subsidence builds into eastern
Kentucky. Rather sporadic summertime rainfall the past couple of
days, combined with this slow influx of drier air, looks to keep
dense fog from becoming widespread at this time.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 418 PM EDT MON JUL 24 2017

Coverage of showers/t`storms has increased this afternoon and
warrants a higher POP than was previously carried. Have used high
chance POPs with the broken line dropping south through the
forecast area. This line roughly agrees with what the mesoscale
models suggested, and have extrapolated the precip southeast
across the area and allowed it to dissipate this evening as
models depicted.

The precip was occurring near a cold front dropping south through
the area. It will bring slightly cooler and drier air southward.
However, there`s not a strong influx tonight, and it will be
difficult to scour out all of our surface air mass, especially in
valleys. With drier air arriving aloft, this will set us up for
fog. It seems a safe bet in valleys. Just how far it spreads in
breadth and depth is the bigger question. Suspect it could get
rather dense.

Fog and low clouds will dissipate on Tuesday morning. Following
this, high pressure passing by to our northeast will provide fair
weather through Tuesday night.

.LONG TERM...(Wednesday through Monday)
Issued at 427 PM EDT MON JUL 24 2017

The continued expansive ridge of high pressure will be in control
of Kentucky to start the extended on Wednesday. However, heights
will quickly lower into the day Thursday as upper level low moves
eastward across Canada, and shortwave develops in the troughing
pattern, pushing southward. As this shortwave continues to
strengthen throughout the day and into the overnight Thursday,
will will result in more NW to SE flow across the state, with the
upper level ridge retrograding westward away from the Ohio Valley.
Longwave troughing will continue to amplify across the eastern
U.S. into the weekend, with heights continuing to fall across the
state. Several more shortwaves are expected to follow this SE flow
into the Ohio Valley through the weekend.

At the surface, high pressure will be in control Wednesday and
Thursday. A cold front will push SE into the state starting
Thursday night, spawning from a surface low pressure system
located over eastern Canada, in coordination with the upper level
low. A secondary surface low will also be located along this
frontal boundary, passing through the Ohio Valley and just north
of the state Thursday. The cold front will push southward through
the state Thursday night into Friday, exiting by Friday evening.
Surface high pressure and more northerly flow will then take hold
for the remainder of the weekend.

As for sensible weather, expect dry and continued warm conditions
for the day Wednesday with the surface high and upper level ridge
in control. Temperatures will reach the upper 80s in the afternoon
under mostly clear skies and light winds. Chances for showers and
thunderstorms will expand across the CWA Wednesday night into
Thursday ahead of the approaching cold front, as winds turn more
southerly and a warmer and moister airmass moves into the region.
Likely coverage will be possible across the north in the afternoon
and across the central and south Thursday night as the front nears
closer. Chances will then quickly begin to dissipate from NW to
SE Friday into Friday evening as drier and cooler air moves in
behind the frontal system. The frontal zone will still likely be
in close enough proximity to our SE to spawn isolated to scattered
showers and thunderstorms, mainly across the SE portion of the
CWA, during the day Saturday. However, temperatures will only be
in the low 80s both Friday and Saturday as northerly winds take
hold.

Surface high pressure will continue to build into the region
through the weekend, keeping mostly clear skies in place across
much of eastern KY along with cooler temperatures. That being
said, upslope flow may lead to some isolated convection in the
high terrain in the afternoon. Temperatures will be in the low 80s
still with much lower humidity.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
ISSUED AT 210 AM EDT TUE JUL 25 2017

The earlier broken band of showers over the western parts of the
Cumberland Valley has faded out. This occurred  in advance of a
cool front slipping south through the northern parts of the JKL
CWA where winds are veering northerly. Drier air will gradually
filter into the area behind this front later tonight, but enough
low level moisture will remain to likely produce areas of fog
across eastern Kentucky - locally dense. This should be more
prevalent in sheltered valleys, as well as further south of
Mountain Parkway where the drier air will be delayed in mixing
down into the lower levels. IFR/MVFR visibilities look very
possible for all sites, but SYM at some point later tonight -
ridges early and valleys later, with periods of sub-IFR conditions
certainly possible at SME and perhaps LOZ. Conditions will
improve to VFR with the onset of daytime mixing by mid morning
though winds will remain light, near 5 knots or less, mainly from
the northeast.

&&

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

$$

UPDATE...GREIF
SHORT TERM...HAL
LONG TERM...JMW
AVIATION...GUSEMAN/GREIF



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