Area Forecast Discussion
Issued by NWS Jackson, KY

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186
FXUS63 KJKL 250632 AAC
AFDJKL

AREA FORECAST DISCUSSION...UPDATED
National Weather Service Jackson KY
132 AM EST Sun Feb 25 2018

.UPDATE...
Issued at 1140 PM EST SAT FEB 24 2018

A line of showers and thunderstorms continues to move east toward
the region. This line is more progressive than earlier convection
over Central KY, but area still producing some heavy rain rates
and wind gusts up to severe limits. Current radar trends and
mesoanalysis of instability parameters continue to indicate that
the thunderstorms could still be near severe limits as they
approach Pulaski and Wayne Counties. However, CAPE and lapse
rates are quite limited so strength of gusts as the line moves
east is limited. Gusts of 30 to 40 mph are expected, with stronger
gusts possible in any bowing segments that might occur. The core
of the low level jet is moving more into northern KY at this time
though winds aloft in the west are still in the 50 to 60KT range.
Mesoanalysis has PW in the 1.3 to 1.4 inch range across the north
and southwest. Much of this area received rainfall, some of it
heavier earlier today. With thunderstorms capable of locally
heavy rain in these areas overnight, opted to expand the flood
watch further south to near the Mtn Parkway corridor and also to
portions of the Cumberland Valley.

UPDATE Issued at 745 PM EST SAT FEB 24 2018

Convection continues to stream from southwest to northeast across
portions of central and western TN and KY. The discrete cells that
were closer to the I 65 corridor and track into the Bluegrass
earlier this evening have weakened, with heavier rain rates noted
in convection near I 65 over the past couple of hours. Cells
further southwest over parts of western KY and TN remain strong to
severe along a line. Across East KY, there has mainly just been
some sprinkles falling from mid clouds this evening. Winds above
2500 feet have been a bit gusty, sustained at 15 to 20 mph with
gusts of 30 mph or better at times.

Convection will continue to move east northeast toward the area
this evening and should remain strong to possibly severe as it
approaches East KY. Dewpoints and instability do decrease further
east so uncertainty remains in both timing and how strong it may
be when it reaches the area. The convective allowing models such
as HRRR and ARW appear close though they may be around an hour
slow in moving the convection east. With this in mind, strong
convection may approach the Lake Cumberland region by midnight.
Damaging winds would be the main threat.

Only some slight adjustments to timing of higher pops was made to
account for recent trends with the remaining hourly grids adjusted
for recent trends. Winds and wind gusts for the remainder of the
night were increased over the higher terrain above 2500 feet.
Convection is expected to be more progressive when it reaches East
KY, but rain rates will also need to be monitored.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 458 PM EST SAT FEB 24 2018

Precip has finally just about left the southeast part of the
forecast area, just in time for a reload coming out of central KY.
The showers and thunderstorms to our west are occurring as
warm/moist advection increases ahead of a cold front, and the flow
impinges on a warm front laid out from WSW to ENE across KY. Some
of this activity may affect the northwest portion of the JKL
forecast area this evening, well ahead anything attributable to
the long anticipated cold front. The northwest part of the area
still looks to be the most at risk for any hydro problem based on
expected rainfall and antecedent conditions, and the Flood Watch
is being allowed to continue. A band of showers near the cold
front will affect the entire area late tonight into early Sunday
morning. Instability looks marginal and barely supportive of
thunder. However, environmental winds will be very strong, and any
mix down could cause problems, even from intense rain showers.

The cold front will exit to the east on Sunday and any showers
lingering in the morning will end. Clouds will break up during the
day as high pressure builds in from the west.

Another wave traveling along the front well to our south may push
some clouds or precip back into the far southeast part of the
area late Sunday night. The NAM was more aggressive than the GFS
with this, and confidence is low that any showers will materialize
this far north. Have only used a 20-30 percent in our far
southeast counties.

.LONG TERM...(Monday through Saturday)
Issued at 458 PM EST SAT FEB 24 2018

Overall have a bit lower confidence in the extended portion of the
forecast than usual, mainly due to unusually inconsistent ECMWF runs.
In general our area remains under the influence of southwest flow at
the surface and aloft, at least until late in the week. Short wave
trough does move through the region at the beginning of the period,
reflecting a sfc wave of low pressure that skirts just to our south
and east Monday. Thereafter models depict southern stream energy
moving out of the deep southwest and phasing with northern stream
energy over the Midwest or Great Lakes by late Thursday or Thursday
night. A quick peak at the 12Z ECMWF shows a strong move towards the
GFS solution as compared to the 0Z run. As often seems to be the
case the Canadian takes the middle ground, measuring up right in
between the GFS and ECMWF, at least until the 12Z European came out.
At the surface a deepening surface low spins up rapidly as it pushes
through the Ohio Valley and Great Lakes Thursday-Thursday night. A
cold or occluded frontal boundary swings rapidly through the
Commonwealth Thursday. All models build a ridge back into the Ohio
Valley at the end of the forecast window.

Sensible weather features a chance for some additional shower
activity early Monday morning as a disturbance tracks across the
southern Appalachians. Trends seem to be towards drier weather, with
scattered showers being restricted to the far south-southeast.
Surface high pressure then exerts itself keeping our weather dry
until mid week. Rapidly developing storm system will bring
widespread rain back to our area by Wednesday as it deepens over the
mid Mississippi Valley region. This potent storm system sweeps a
frontal boundary through the area Thursday. Showers will linger well
behind the front as wrap around moisture is pulled into eastern
Kentucky from the Great Lakes and upslope showers take form Thursday
night into Friday. Weather improves for the end of the forecast
window as high pressure builds back into the region, both at the
surface and aloft. Daily high temperatures remain above normal, in
the mid to lower 60s through Thursday, then drop back to normal
levels by Friday and Saturday, lower 50s. Overnight lows start out
near normal, mid 30s, Tuesday morning before climbing into the 40s
to near 50 for the latter half of the week. Lows finally manage to
drop to normal levels as well, lower 30s, by Saturday morning.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 132 AM EST SUN FEB 25 2018

VFR and some MVFR in showers and thunderstorms was initially in
place across the region. An area of showers and some embedded
thunderstorms is moving into the western parts of the area. Vis
and or CIGS should be down into the MVFR if not the IFR range at
times during heavier showers during the next 3 to 6 hours as well
as along and immediately behind the cold front. Once convection
exits with the cold front, VFR conditions should return along with
slackening winds between 12Z and 18Z. Winds will be gusty generally
in the 10 to 15KT range with gusts of 20 to 30KT out of the south
to southwest. Stronger showers or any thunderstorms may bring
gusts up to 40kt. Winds should shift to the southwest and then
west as the front moves from west to east through 13Z.

&&

.JKL WATCHES/WARNINGS/ADVISORIES...
Flood Watch until 7 AM EST this morning for KYZ044-050>052-
058>060-068-069-079-080-083>085-104-106>109-111-112-114.

&&

$$

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



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