Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 171136 AAA

National Weather Service Jackson KY
736 AM EDT Thu May 17 2018

Issued at 710 AM EDT THU MAY 17 2018

A few showers have developed over the past hour to hour and a half
near the TN border in the vicinity of I 75. Hourly grids have been
updated to account for this as well as to account for recent
observation trends and trends in fog. The fog is still expected to
lift and dissipate no later than the 9 AM to 10 AM period.


.SHORT TERM...(Today through Friday)
Issued at 445 AM EDT THU MAY 17 2018

Early this morning, a slow moving upper level trough extended
from the mid MS Valley region into the southeast while an upper
level ridge remains centered over the Atlantic in the vicinity of
Bermuda. At the surface, a frontal zone extends from the mid
Atlantic states into portions of the OH Valley and Appalachians
then southwest into the Lower MS Valley. The front is roughly
bisecting the area north to south. Deep moisture is in place
across the region for this time of year with analyzed PW of
between 1.4 and 1.6 inches. Mid and high clouds were moving across
the region though there were some breaks from time to time. Dense
fog or low clouds has been reported at times in several locations
with locations that picked up heavier rain on Wednesday generally
experiencing greater areal extent and persistence of this.

With the boundary expected to sag slowly south and southeast today
before inching back north tonight and Friday as a series of weak
waves move along the boundary, showers and even some thunderstorms
cannot be ruled out at any point. However, model guidance
including the NAM, GFS, and even the CAMS generally indicate a
diurnal increase in coverage of these and of the thunderstorms
corresponding to the diurnal cycle. Thunderstorm motions should
again be slow and propagation may to a large extent favor outflow
boundaries. PW is expected to remain high today generally in the
1.4 to 1.6 inch range. The main concern with thunderstorms today
will again be isolated heavy rain and the threat of localized
flash flooding and high water in locations that receive more than
one thunderstorm. Temperatures will again be above normal for
this time of year though rather extensive cloud cover should keep
the departures closer to 5 degrees, in the upper 70s to near 80.

Convection should generally decrease through the evening into
tonight, though with the boundary present across the area and
upper level trough/low to the west of the area showers or even a
stray thunderstorm cannot be ruled out during the overnight hours.
Coverage of showers and thunderstorm chances should again peak
during the afternoon and early evening on Friday. PW should
continue to remain in the 1.4 to 1.6 inch range though storm
motions should increase to 10 to 15 mph range. Localized heavy
rain will again be possible. After warm overnight lows generally
in the lower 60s tonight near anticipated dewpoints highs on
Friday should average similar to today in the upper 70s to near

.LONG TERM...(Friday night through Wednesday)
Issued at 436 AM EDT THU MAY 17 2018

Little change is expected during the long term period, with a warm
and fairly moist air mass remaining in place. Two primary factors
will determine precipitation trends-- weak upper level features and
diurnal destabilization/stabilization. The period will start with a
weak upper level trough over the mid Mississippi Valley and lower
Ohio Valley. It will be weakening as it moves slowly eastward and
gets absorbed into the main belt of westerlies. Its approach will
bring our highest POP of the long term period on Friday evening and
Saturday afternoon. A weak cold front associated with the trough is
only expected to make it as far south as the Ohio River, leaving us
without a change in air mass. Even after the upper trough passes,
there will still be a possibility of showers/thunderstorms, with
coverage likely to peak during the late afternoon and evening hours
each day. Another upper level trough developing over the northeast
CONUS at the end of the long term period will support another
southward moving cold front. At this point, it looks like it may
make it to KY on Wednesday, but struggle to pass through.


.AVIATION...(For the 12Z TAFS through 12Z Friday morning)

A slow moving area of low pressure and stalled frontal boundary
will keep a chance of showers and and thunderstorms for much of
the period, especially between 15Z and 3Z. Fog and some low
stratus is expected initially down into the IFR range and near
airport mins in several locations. This should gradually lift and
dissipate through about 14Z, giving way to VFR conditions. Any
location that is directly impacted by a shower or thunderstorm
will experience a period of MVFR or lower vis and or ceilings. Fog
and low clouds should return late in the period with MVFR to IFR
expected. SYM, JKL, and SJS could approach airport mins.




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