Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 180546

National Weather Service Jackson KY
146 AM EDT Sun Mar 18 2018

Issued at 1051 PM EDT SAT MAR 17 2018

The forecast was updated to remove any last mention of
thunderstorms and to account for ongoing rain showers that will be
moving across the eastern third of the forecast area over the next
hour or two. The rest of the forecast was in good shape with the
latest obs used to establish new trends. The night shift will need
to issue one more update early in their shift once the last of the
ongoing rain showers finally exit the area.

UPDATE Issued at 900 PM EDT SAT MAR 17 2018

Now that the severe weather threat has ended across the area, the
severe thunderstorm watch has been cancelled. The forecast and the
hazardous weather outlook products have both been updated to
reflect this changes. Also updated the precipitation forecast for
the rest of tonight based on current radar trends and the latest
run of the HRRR model. Now have thunderstorms moving out of the
area between 2 and 3Z and precipitation overall moving out of
eastern Kentucky between 4 and 5Z. Will need to issue another
update toward the end of the shift to get rid of any remaining
evening wording and for areas where the ongoing precipitation will
have already ended for the night.

UPDATE Issued at 735 PM EDT SAT MAR 17 2018

Have updated the grids with the latest obs to establish new
trends. Will leave the severe thunderstorm watch and zone forecast
text product as is until we cancel the watch this evening after
the severe threat has finally ended. It does appear that the
severe weather threat will end across our area well before the
midnight EDT expiration time of the watch. It also appears that we
may be able to take precipitation out of the area a bit faster
than the inherited forecast has been indicating, but will continue
to monitor current radar trends and the latest model data to
before making that determination.


.SHORT TERM...(This evening through Sunday night)
Issued at 520 PM EDT SAT MAR 17 2018

A cold front was bisecting the forecast area from east to west
late this afternoon, with a low pressure system tracking along the
front from central into eastern KY. Showers and thunderstorms have
quickly developed along the front. The regime will shift southward
this evening. There is good speed shear in place, and dry mid
levels with steep lapse rates. The severe weather parameter which
is looking puny is the moisture. Strong heating has mixed drier
air to the surface with dew points only in the 30s and 40s over
most of the southern portion of the area late this afternoon. Can
not rule out severe weather in places where higher dew points
linger or redevelop, but for much of the area late afternoon
conditions don`t look all that favorable. Freezing level and wet
bulb zero height are quite low, which favors large amounts of
small hail. Any large hail would probably need to come from storms
with significant rotation. Storms should taper off from northwest
to southeast this evening after cold fropa.

Surface high pressure passing to our north will provide fair
weather Sunday into Sunday night. Another low pressure system
heading east from the southern plains will pull the front back north
toward KY as a warm Sunday night. Showers could make a return to
our southwest counties by dawn, but will more likely hold off
until the daytime on Monday.

.LONG TERM...(Monday through Saturday)
Issued at 520 PM EDT SAT MAR 17 2018

Model solutions are in decent agreement, sufficient enough to pick
out the main features of concern through the extended. Flow aloft
amplifies with time but remains fairly progressive, with implications
that our generally unsettled pattern will continue with only one
relatively short period of fair weather from Thursday through at
least part of Friday. Consequently our weather is active straight
out of the gate as a mid level low, upper level wave moves into the
region Monday. Additional shortwave disturbances follow Tuesday into
Wednesday before exiting to our east by Thursday. Solutions differ
on timing another shortwave disturbance into the region by the end
of the period, with the 12Z GFS bringing our next weather maker into
the area by late Friday into Saturday. The 0Z ECMWF and 12Z Canadian
hold off on this system until beyond the end of the period, and seem
to suggest a deeper, more organized storm system.

Closer to the surface, a low pressure system will pass through the
Tennessee Valley Region Monday/Monday night. Instability is marginal
but may be enough to kick of a thunderstorm or two late Monday into
Monday night. Shortwave disturbances following in the wake of the
initial low will be responsible for the redevelopment of another
surface low or two over the southern Appalachians through Tuesday
and Wednesday. If enough cold air manages to be drawn southward into
the region from the north, sensible weather may feature a wintry mix
of rain and snow showers for a period of time late Tuesday night
into Wednesday morning, particularly across the higher terrain.
However, details remain a bit too sketchy to provide any specifics
for now. Drier conditions will work into the area by Wednesday night
and Thursday as ridging moves in from the west. Fair weather should
continue through much of Friday before the next potential weather
maker moves in from the west by late week or early into the weekend.
Comparing models favored a slower arrival of the precipitation for
the end of the extended and would not be surprised if Friday winds
up dry in the end. But should not discount the GFS solution totally
based on its recent very good performance with the last few systems
to affect our area. Otherwise, near normal temperatures initially
will cool to well below normal for the mid week time frame. Temps
then rebound for the end of the week and following weekend. |


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)

The low pressure system that traversed eastern KY and brought us
showers and thunderstorms this past afternoon/evening, has now
exited SE of the state. However, lingering moisture from this
system will continue the llvl clouds across the region throughout
the overnight. Most locations will experience MVFR conditions,
however IFR or lower CIGS may hold on at KSJS and KJKL for the
next several hours. Drier air will then filter into the region
late tonight and into the day tomorrow, with CIGS improving to VFR
at all TAF sites by mid morning. Skies should begin to clear out from
north to south throughout the afternoon and remain so through the
rest of the forecast period. Winds are a bit breezy out of the
north at KSME and KLOZ currently, but should dissipate by the
morning. Otherwise, expect light and variable conditions though
the extent of the period at all TAF sites.




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