Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 181811 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
211 PM EDT Tue Apr 18 2017

.UPDATE...
Issued at 200 PM EDT TUE APR 18 2017

Hourly grids were freshened up based on recent observation and
radar trends. Some redevelopment of showers is expected through
late afternoon and early evening with a thunderstorm also
possible. Some of the recent HRRR develop some of the stronger
convection in the north where more intense heating is occurring at
this time.

UPDATE Issued at 1013 AM EDT TUE APR 18 2017

Light showers persist near the TN border closer to the frontal
zone extending from the TN Valley to the Carolinas and in advance
of a weak shortwave trough. As the shortwave nears and the
boundary returns north as a warm front as sfc low pressure moves
from the Northern Plains/MS Valley to the Great Lakes some
thunderstorms will be possible this afternoon and evening around
and after peak heating. Other than some adjustments to hourly
grids based on observation and radar trends no other changes were
needed at this time.

UPDATE Issued at 648 AM EDT TUE APR 18 2017

WSR-88D radar continues to show a few isolated showers or perhaps
sprinkles this morning. Dry air remains in place north of the
Mountain Parkway this morning and therefore could only justify
some sprinkles in those areas. Otherwise little intervention
needed with the grids set this morning.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 349 AM EDT TUE APR 18 2017

WSR-88D does indicate isolated showers continue to move east
across southern portions of the CWA this morning. These seem to be
aligned across a moisture boundary where dewpoint are in the mid
and upper 50s generally south of the Mountain Parkway. Also a high
level jet is exiting east and perhaps providing modest lift as it
does. Most guidance does indicate a upper level wave will move
east out of the Arkansas region through the day. This will
interact with a nearby boundary and increase the chances of
showers and perhaps a few thunderstorms through the day. Does seem
like the guidance would suggest the instability will meager
particularly in the east. The flow will also be
southeasterly/downsloped and this could lead to less overall
coverage in the east as well. That said did keep POPs in the
slight range in the east and northeast, and also keep thunder
limited to the south given little if any support in the MUCAPE
values.

Tonight think the deeper reflection of lift from the upper level wave
will move into the region. Therefore, do go at least chance POPs
area wide by around 4Z to 5Z. Right now limit the thunder to early
evening and wane after. Moisture return will be better on
Wednesday and lingering low level lift will lead to showers and
thunderstorms. Best area for this will be the far east, but the
lift will be fleeting in the afternoon hours based on the omega
sampling seen in the soundings. That said much of the western
portions of the CWA could see little in the way of showers by the
later afternoon hours.

.LONG TERM...(Wednesday night through Monday)
Issued at 418 AM EDT TUE APR 18 2017

The remnants of a shortwave trough will be to our southeast at
the start of the period, but advection of warm/moist air into the
region will persist in the lower levels Wednesday night and
Thursday. No clear focus/forcing mechanism is seen during this
time, but some sparse coverage of showers/thunderstorms can`t be
ruled out. A low pressure system crossing the Great Lakes will
send a cold front south through KY on Thursday night and early
Friday, providing a better shot at getting precip. At this point,
shear does not look too impressive, and the late night/early
morning timing of the system is not favorable for severe weather.

The front is forecast to stall just to our south, and remain close
enough to keep a threat of rain in the forecast Friday and Friday
night, especially in our southern counties. Models are consistent
in developing low pressure along the front in response to an upper
low (currently well offshore of the Pacific Northwest) moving east
in the flow aloft. This system would pass near our area during the
weekend, with our best chance at rain being on Saturday night.
Although models are consistent in developing the system and have
come into better agreement on timing, the track is still shifting.
The trend has been for a more southerly track, and the ECMWF now
takes the surface low by to our south. This would keep our area on
the cool side of the system and limit thunder probabilities. The
GFS still takes the surface low up the Ohio Valley before further
development occurs near the coast. The GFS scenario would bring a
thunderstorms potential, and a mention will still be made in the
forecast, but only in the chance range. With the upper low/trough
not passing over until Sunday night or Monday, showers will remain
a possibility.

&&

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

VFR conditions are expected to prevail through the first 12 hours
of the period outside of any showers and thunderstorms where
brief MVFR or even IFR would be possible. An upper level wave will
move through the area and interact with a warm front. This will
bring the threat of some showers and perhaps a few storms mainly
through 0Z, but instability will be limited. At least a small
threat for showers should linger through the end of the period.
Model consensus brings ceilings down to MVFR after 7Z, but begin
to improve from southwest to northeast late in the period. Winds
are expected to remain generally 10KT or less and veer from the
southeast around to the southwest through the period.

&&

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

$$

UPDATE...JP
SHORT TERM...DJ
LONG TERM...HAL
AVIATION...JP



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