Area Forecast Discussion
Issued by NWS Jackson, KY

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FXUS63 KJKL 271640 AAB

National Weather Service Jackson KY
1240 PM EDT Mon Mar 27 2017

Issued at 1235 PM EDT MON MAR 27 2017

Pops have been updated to account for convection trends near the
northward lifting warm front and also trends in temperatures and
more clearing in the south to the south of the warm front. This
led to higher pops early this afternoon across the northern part
of the area. This activity should lift to near the OH River and on
into OH through mid afternoon. Additional convection should
develop during peak heating during the late afternoon to early
evening as an upper level trough and surface low pressure system
nears. CAPE and shear will be conducive for a few strong storms.
An isolated severe thunderstorm is possible mainly 5 PM EDT and
after. More vigorous convection is expected to develop from
western and middle TN into western and central KY and could
congeal into lines or lines of convection during the evening and
move into East KY.

UPDATE Issued at 659 AM EDT MON MAR 27 2017

Biggest issue this morning has been breaks in the clouds leading
to areas of dense fog. Did opt to beef up the wording in the
products and we did send out of graphical now to deal with the
issue. Otherwise forecast updated with latest obs and trends.


.SHORT TERM...(Today through Tuesday)
Issued at 407 AM EDT MON MAR 27 2017

This morning the surface analysis shows a weakening frontal
boundary to our west and another surface low across western OK.
This weakening surface boundary to the west is having little
influences on surface winds or temperatures. The bigger influence
on temperatures this morning has been with the breaks in the
clouds which is leading to some temperature splits. Also the fog
is locally dense which could also be holding back temperatures to
an extent. This surface boundary will likely lift north through
the day, as more of a warm front if anything. Therefore we remain
in the warm airmass across eastern KY today. The locally dense fog
is expected to lift through the early morning hours.

All eyes turn to the aforementioned surface low in western OK and
upper level short wave expected to lift into the midwest through
the day. This will induce height falls through the day from west
to east across the Ohio and Tennessee Valleys. Also this will
induce a LLJ that will creep north today and lead to further lift
and moisture. It does look like we will see breaks in the clouds
early in the day and this could lead to modestly unstable
environment. Cloud cover will also be the caveat as it could rob
the potential destabilization. Given the previously mentioned LLJ
and increasing winds with height we will have sufficient shear in
place across the region for strong storms. The shear is more
unidirectional and therefore think storm mode will be more
multicell or perhaps line segments. Model soundings do show a EML
in the mid levels with better reflection in the 00Z NAM. Given
this and dependent on low level lapse rates nearing the 8 C/km
through the day will be enough to support marginally severe wind
risk. Also the EML, reasonable shear, and low freezing levels at
or below 10 KFT will support marginal hail risk as well. Given
some of the caveats and climatology think the marginal risk from
SPC is reasonable. The best chances of seeing stronger storms
right now would be along and west of the I-75 corridor. However,
many of the CAMs suggest a line segment could in fact move
northeast along and near the I-64 corridor this afternoon.
Therefore did increase POPs across that area this afternoon, but
This will have to be monitored in subsequent updates.

This Surface low is expected to move into the Ohio Valley tonight
and overall best lift will come tonight where height falls will
be maximized. Therefore did opt to bring the CAT POPs through
tonight into the overnight from west to east. POPs will wane
through the day on Tuesday, as the upper level wave moves east and
front pushes across the region. This wave will dampen out and
front will weaken therefore not expecting a big airmass change.

.LONG TERM...(Tuesday night through Sunday)
Issued at 405 AM EDT MON MAR 27 2017

The models are in decent agreement aloft at the start of the
extended portion of the forecast with questions arising quickly by
the end of the week as spread increases. They all depict a
weakening wave departing to the east of Kentucky early in the
period - pushed along by a northern stream trough pivoting
through New England. This leaves ridging behind over the Ohio and
Tennessee Valleys ahead of a deep trough rolling east through the
Southern Plains. Already at this time, though, the models are
slightly out of step - the ECMWF further east and north with the
core of its trough compared to the GFS and laggard CMC. These
differences are steady state through Thursday as the individual
models move their trough centers north and east into the Central
Plains while ridging slips east of our area and mid level
southwest flow commences over Kentucky bringing some energy
through by evening. The broad trough will progress into the Ohio
Valley on Friday as the GFS hangs back when compared to the more
progressive and weaker ECMWF. As this occurs, a general weakening
of the trough itself will spread its energy more broadly through
the region with its 5h axis passing later that night. Another
bout of ridging follows for the weekend over Kentucky while
the next broad and deep trough plows its way through the Desert
Southwest. With the models still settling into a stable solution
will favor a general blend - accepting the broader trend as
represented by their consensus.

Sensible weather will feature a generally mild to warm period of
weather through the extended due to eastern Kentucky finding
itself in the midst of ridging aloft and mainly on the warm side
of the wx system moving across the region through the rest of the
week. While there may be some fluctuation or brief movement south
of a cold front to the north of the state on Wednesday, this will
occur in an environment of rising heights and climbing low level
thickness yielding a mild and near normal day with temperatures
hindered more by cloud cover than any advection. Thursday will see
warm and increasingly humid conditions as low pressure lifting to
the northwest of the area will bring its warm sector over the
state along with a threat of showers and thunderstorms. The
fairly slow movement of this relatively stacked low will linger
the shower and thunderstorm chances for the area through the day
Friday, though temperatures will be down a bit from Thursday - but
still mild. By Saturday, the low will be well east of the area
and result in some CAA on northwest winds for our area as high
pressure moves in to dry out the region. This high will gradually
moderate through the latter part of the weekend, but readings will
not get too far from normal for this time of year. The best
chances for any severe weather appears to be Thursday afternoon
and evening as the upper system, and its winds, will be stronger
than on Friday with more instability available ahead of the
system`s occluding cold front.

Made some minor - terrain based - changes to lows for most nights
of the extended considering the times that appear favorable for
inversions and radiational cooling of the sheltered valleys. As
for PoPs - did not deviate much from the consensus guidance as it
appeared reasonable for the main wx system and its structure
passing through from Thursday into Friday night.


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

TAFs have been slightly tricky overnight, as some sites cleared
and subsequently saw MVFR/IFR VIS at times. Otherwise the lower
VIS has been confined to the usual trouble spots. The fog is
expected to clear through the morning and lead to VFR conditions
through the day. The only issue is showers and thunderstorms will
be on the increase through the day and this could lead to isolated
lower CIGS/VIS issues. Overall better chances of showers and
thunderstorms will be late this afternoon and evening. There is
also a isolated chance a few of the stronger storms could contain
small hail and gusty winds. Late tonight thunderstorms will give
way to lingering showers, but the the lower cloud deck is expected
to lower leading MVFR CIGs for most toward dawn Tuesday. Overall
winds will be light out of the south to southwest, but again any
stronger thunderstorms could contain strong gusty winds.




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