Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 251203 AAA
AFDMEG

Area Forecast Discussion...UPDATED
National Weather Service Memphis TN
703 AM CDT Tue Apr 25 2017

.UPDATE...
Updated for 12Z Aviation Forecast Discussion below.

&&

.PREV DISCUSSION... /issued 442 AM CDT Tue Apr 25 2017/

DISCUSSION...Surface analysis this morning places a ridge of high
pressure over portions of Tennessee, Mississippi, and Alabama.
Meanwhile, a surface low is located over the North Carolina coast
and a developing surface low was centered over the Texas/Oklahoma
Panhandle early this morning. As of 4 am CDT, temperatures across
the Mid-South are in the 50s at most locations. The potential for
severe thunderstorms late Wednesday afternoon into Wednesday
night, and additional periods of severe thunderstorms Friday into
Sunday across the Mid-South will remain the predominant concern in
this morning`s forecast issuance.

Clear skies, calm winds, and high humidity from recent rainfall
has resulted in the development of fog, locally dense at times
along the Tennessee River Valley. As a result, a Dense Fog
Advisory has been issued for portions of West Tennessee near the
Tennessee River through 8 AM CDT.

A ridge of high pressure will begin to gradually move east today,
allowing southerly winds on the back side of high pressure to
return to the region. This will help to warm temperatures into
the lower 80s across many locations this afternoon.

Short term models continue to indicate an upper level trough
becoming negatively tilted as it moves through the Middle and
Lower Mississippi Valleys Wednesday night. Impressive 60-100 dm
500 mb mid-level height falls, favorable upper level divergence, steep
700-500 mb layer mid-level lapse rates between 7-8 C/km, 0-6 km
bulk shear between 40-60 kts, 0-1 km storm relative helicity
values between 300-500 m2/s2, and most unstable CAPE values
between 1500-2000 J/kg suggest a good potential for severe
thunderstorms from late Wednesday afternoon into Wednesday evening
along and west of the Mississippi River, then spreading overnight
across the remainder of the Mid-South. Models do indicate some
weakening of surface based instability with time Wednesday night
but conditions should remain conducive for severe thunderstorm
potential. At this time, I think the convective activity should
evolve into a line with bowing segments, especially as the
evening progresses. Large hail, damaging winds, and tornadoes are
all possible threats for thunderstorms that reach severe limits.

Shower and thunderstorm chances are expected to diminish Thursday
as weak high pressure builds into the Mid-South. However, this
will be short-lived as long term models indicate the front
will return back north as a warm front later Friday afternoon
into Friday night. Ample shear and more instability may result in
the development of severe thunderstorms with large hail, damaging
winds, and tornadoes possible. Additional severe thunderstorms
will be possible Saturday night into Sunday as a strong upper
level trough and cold front move through the Lower Mississippi
Valley.

CJC

AVIATION...

&&

.AVIATION...
12Z TAFs

Patchy ground fog in the TN River valley and at MKL, TUP will
dissipate with daytime heating, leaving VFR areawide. Because the
shallow and patchy nature of the ground fog, expect widely-varying
ASOS-reported visibility through 13Z or 14Z.

A tightening low level pressure gradient will drive southerly
tail wind component in excess of 7 KTs at MEM for the late evening
cargo ops, with occasional gusts likely overnight. MEM FL020 winds
should prevail just below WS mention at 020/21045KT during the
arrival push. An MVFR deck associated with returning elevated gulf
moisture will impact MEM after the late evening inbounds complete.

PWB

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...Dense Fog Advisory until 8 AM CDT this morning for Benton TN-
     Decatur-Hardin.

&&

$$



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