Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 301747

Area Forecast Discussion
National Weather Service Jackson KY
147 PM EDT TUE AUG 30 2016

Issued at 1250 PM EDT TUE AUG 30 2016

Forecast remains on track today with a few showers still possible
over the high-terrain along the Virginia border. The last few HRRR
model runs have been consistent with this as well. Otherwise, did
a quick refresh to the hourly temps and sky cover. Sent updates to
NDFD and web servers.

UPDATE Issued at 947 AM EDT TUE AUG 30 2016

The majority of the morning fog has now lifted and have therefore
removed mention of it in the HWO. Also freshened up the hourly sky
cover and temperature grids to reflect most recent obs.

UPDATE Issued at 630 AM EDT TUE AUG 30 2016

Clear and calm so far this morning across eastern KY, with varying
degrees of fog reported at the observation sites. Freshened up the
near term forecast with the latest observations to make sure they
matched up well with current conditions. Otherwise forecast seems
to be well on track. All changes have been published and sent to
NDFD/web. No new forecast package is needed at this time.


.SHORT TERM...(Today through Wednesday)
Issued at 356 AM EDT TUE AUG 30 2016

An upper level ridge will be in place across the region today and
tonight, keeping subsidence and calm weather across the region
during this time. Meanwhile, a closed upper level low will push
southeast along the shores of the Hudson Bay today. This will result
in upper level troughing as the low continues on into James Bay
overnight, and lowering heights across the eastern US during the day

As for sensible weather...
High pressure across the region has led to clear skies and light
winds early this morning. Locations that received rain yesterday
have been prone to patchy dense fog overnight, as have many of the
deeper river valleys. This fog will slowly dissipate through the
morning hours as temperatures begin to warm. Generally clear
conditions are expected through the day today under continued
light NE to N flow. That being said, afternoon heating could lead
to a few diurnal cumulus, and possibly an isolated shower or
thunderstorm. All hi-res CAM models are pointing at the best
potential for this occurring along the highest terrain in the far
southeast portion of the state, so did include some isolated pops
here. Under strong subsidence, temperatures will be similar to
that of yesterday, nearing 90 degrees by the afternoon. Thankfully
with the NE to N flow in place, this will keep some of the
humidity levels down, and apparent temps will remain close to the
actual temp values.

Any diurnal clouds will clear out once again tonight, with valley
fog formation being the only weather concern. Temperatures will fall
into the upper 60s to near 70, similar to that of this morning. The
big change will come during the day Wednesday. A surface low
pressure system associated with the above mentioned upper level
closed low will track southeast across Canada, pulling with it a
cold front. This cold front is expected to push eastward and towards
KY, reaching just north of the Ohio River by Wednesday afternoon. An
interesting thing to note, however, is that the winds never turn
southerly ahead of this front, instead they will shift from NE to NW
along and behind the frontal passage. That being said, a lot of the
convection along the frontal boundary will actually be diurnally
driven, with the aid of afternoon heat/instability. Clouds really
won`t start building in until just ahead of the frontal zone, along
with the best convection, given the lack of moisture. Did keep some
isl to sct pops in during the afternoon, though coverage may be
limited to the far northern portion of the CWA (closer to the actual
frontal zone), as well as in the high terrain as a result of upslope
NW flow across the CWA.

Overall, much of the CWA should see minimal impacts during the day
Wednesday, and much of the convection should cease by Wednesday
night with the loss of diurnally induced lift. Temperatures
Wednesday will still manage to boost back into the upper 80s, though
if cloud cover winds up being more extensive than originally
thought, this may keep temps a degree or two cooler.

.LONG TERM...(Wednesday night through Monday)
Issued at 450 AM EDT TUE AUG 30 2016

The models are in pretty good agreement aloft through the long
term portion of the forecast. They all depict a northeast trough
diving through the Ohio Valley and Central Appalachians from
Wednesday through Friday. This trough will be accompanied by
plenty of energy, but the best of it will stay to the north and
east of Kentucky. Some lingering patches will be scooped up out
ahead of the trough into Thursday morning - pushed into Kentucky
in conjunction with the best height falls. Later as the trough
moves out, another batch of energy will settle into the area
Friday afternoon into the night but heights will be rebuilding at
that time and should dampen the effects of this on sensible
weather. Strong ridging then will move over the region and
dominate the weather into next week. Given the model similarities
have accepted a general blend as a good starting point through the
extended portion of the forecast.

Sensible weather will feature a chance for showers and storms from
Wednesday night into Thursday morning as a cold front settles
through eastern Kentucky, pushed by a fairly strong area of high
pressure. This high will settle into the Ohio Valley by the end of
the week with a nice taste of the cooler and drier weather that
will soon be upon us as summer`s grip relaxes. However, a
resurgence over the weekend and into next week will bring very
warm temperatures and a slow build up of humidity back to our
forecast. The retreating high should keep any renewed threat of
convection out of the picture until beyond Monday, though.

Mainly made temperature adjustments to the extended grids -
capturing the ridge and valley distinctions, especially from
Friday night on through Monday morning. Also, tweaked the hourly
PoPs Wednesday night and Thursday tracking the front into our area
and its departure to the southeast by midday Thursday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)

Scattered diurnal CU will continue to develop throughout the
afternoon, with some isolated convection possible near the VA
border. But this should pose little threat to any of the TAF
sites. Tonight, fog could be a concern once again. However, this
will depend on if temperatures can reach the crossover
temperatures, and if any TAF sites see rain. Right now, SJS is the
only site that may see rain this afternoon so decided to put IFR
VIS, with MVFR at LOZ and SME, in the forecast late tonight. Winds
will remain light, generally from the N to NE and less than 5 mph.


.JKL Watches/Warnings/Advisories...


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