Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 231800 AAA
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
200 PM EDT Tue May 23 2017

.UPDATE...
Issued at 145 PM EDT TUE MAY 23 2017

Did a quick update mainly to fine tune the PoPs and Wx through the
rest of the afternoon as this initial batch of showers and
sprinkles work through eastern Kentucky. Did also tweak the T and
Td grids per the latest obs and trends.

UPDATE Issued at 1110 AM EDT TUE MAY 23 2017

14z sfc analysis shows a weak area of low pressure slipping by to
the east with general high pressure over the rest of Kentucky.
Some light rain showers and sprinkles are moving through eastern
Kentucky with this low. Accordingly, skies are mostly cloudy, but
some thinner spots are noted to the northwest. Despite the
difference in the clouds, temperatures are fairly uniform across
the area - running in the low to mid 60s with dewpoints generally
in the mid to upper 50s. Meanwhile, winds are light and variable.
Still look for a bit more coverage to the pcpn later this
afternoon - mainly in the east with a thunderstorm or two possible
by evening. Have updated the grids mainly to handle near term obs
and trends for PoPs, T, and Td. Also, issued a fresh set of zones
mainly to remove the early morning fog mention. The grids have
been sent to the NDFD and web servers.

UPDATE Issued at 640 AM EDT TUE MAY 23 2017

WSR-88D radar continues to indicate some returns across the region
and most of this is likely not reaching the ground given the dry
air in place. However, a few sprinkles are still possible and we
have seen some sprinkles at JKL this morning. Better moisture and
convection should remain mostly south of the the region. Other
than adding the sprinkles did opt to update with latest obs and
trends.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 404 AM EDT TUE MAY 23 2017

A low pressure system will continue to take shape as 500mb wave
aids in cyclogenesis. This surface low will deepen as it tracks NE
into NC through the day. We remain on the fringes of this synoptic
scale system and think better convection to the south and track
of low pressure could cutoff potential moisture in eastern KY.
That said thinking some of the CAMs are a bit overdone with QPF at
this time and will limit best POPs in the far SE toward VA. There
have been some returns on radar this morning, but this will
likely remain elevated as virga given the drier air in the lower
levels. While cloud bases are high the skies are mostly cloudy and
therefore did bring skies up in general.

Overall the CAMs and larger scale synoptic models are showing the
region in the middle of two systems by this evening. Therefore,
did opt to lower POPs through the evening in most spots, as
the forcing for accent slackens. All eyes turn to the deepen
upper level system across the Midwest, as it combines divergence
aloft and strengthening jet streak to deepen a surface low.
Therefore will increase POPs from SW to NE through the overnight
into the early morning hours Wednesday. Overall models are in
decent agreement with the evolution of this system, but still some
differences with regards to the depth of the surface low.

Wednesday could not resist bring CAT POPs across the region given
the forcing for ascent and the synoptic scale low/front coming
across the region. The peak timing will be late morning into the
afternoon for best overall POP chances. The thunderstorm chances
will be mainly in the afternoon, but morning convection is not out
of the question. This leads to complicated afternoon as
instability could struggle owing to early local convection/clouds
and convection to our SE. This will be the fly in the ointment
for any potential for stronger storms as shear environment will
be more than ample. Therefore, agree with SPC keeping us in the
general for now and see how later forecast data handles this.

.LONG TERM...(Wednesday night through Monday)
Issued at 404 AM EDT TUE MAY 23 2017

An overall unsettled period looks to be in store from mid this week
into next week as quasi-zonal to cyclonic flow remains over eastern
Kentucky. The first in a series of upper level lows, referenced in
the short term discussion, will move overhead Wednesday night into
Thursday. Shower and thunderstorm chances will be greatest across
far eastern and southeastern Kentucky Wednesday evening as a cold
front moves through. Some semblance of a dry slot will likely
materialize into the evening and overnight in wake of the front and
underneath the forcing aloft. This will fill back in on Thursday
downstream of a secondary surface low/convergence boundary across
the Ohio Valley. Forecast soundings show steepening lapse rates
Thursday afternoon, perhaps resulting in a few hundred J/kg of CAPE.
However, elected to keep thunder out of the forecast given a
plethora of low clouds and limited heating in a post frontal airmass
characterized by high temperatures likely only warming into the low
60s. Will have to continue monitoring thermodynamic profiles for the
possibility of seeing some graupel if saturation can sustain itself
aloft with low freezing levels in place.

A dry period should develop Friday underneath transient shortwave
ridging. Before then, may see at least a minor ridge/valley
temperature split Friday morning as the northern edge of surface
ridging over Florida noses into the lower Ohio Valley. High
temperatures look to rebound into the mid 70s, very close to normal,
as partial clearing occurs in conjunction with an influx of warmer
air aloft.

Shower and thunderstorm chances will return for the weekend as
another upper low traverses the Canadian Prairies into south central
Canada. Depending on the strength and latitudinal position of this
system, may see several shortwave perturbations dive south toward
eastern Kentucky, thus keeping a wet Memorial Day weekend in the
offing. However, could see a long duration of dry weather if this
system and forcing remain north. Temperatures will likely remain
near to just above normal south of this low, with a cooldown ensuing
at some point into next week if and when frontal passage occurs.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 200 PM EDT TUE MAY 23 2017

All sites are in the VFR range this afternoon and this should
hold through the evening. However, later tonight and into
Wednesday cigs will fall as the lower levels of the atmosphere
moisten up and showers/thunderstorms move in from the southwest.
Accordingly, expect the worse conditions, potentially down to
IFR, with the convection on Wednesday. Light winds will prevail at
all the TAF sites throughout the period.

&&

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

$$

UPDATE...GREIF
SHORT TERM...DJ
LONG TERM...GUSEMAN
AVIATION...GREIF



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