Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 270239

Area Forecast Discussion
National Weather Service Memphis TN
939 PM CDT Wed Apr 26 2017


A line of sub-severe thunderstorms from Jackson TN to Calhoun
City MS continues to trek east. This line has been struggling for
the last few hours. First cut off by a gust front that moved out
ahead of the storms in NE AR earlier this evening and now
hampered by diminishing instability as MLCAPES are now around 100
J/KG. The severe thunderstorm watch continues until 11 pm for
parts of West Tennessee. A storm or two may become severe though
most likely scenario are some gusty winds to around 40 mph with
the line. There has been a good deal of moderate rain behind the
line and this has started to diminish and that trend will continue
as the line exits the area. Will continue to update and peel off
counties from the watch.



PREV DISCUSSION... /issued 315 PM CDT Wed Apr 26 2017/

Widespread showers and thunderstorms continue from the Arklatex
area into southeast MO. This line of storms appears to be located
along a pre-frontal trough ahead of a weak cold front that will
move east across the Mid-South overnight. Instability is modest in
the warm sector, with MLCAPE values on the order of 1000 J/kg
with effective layer shear of 45-55 kts. However, a strong capping
inversion over the area has prevented convection from developing
downstream of the current convective activity. This cap will
weaken this evening and, combined with strong frontal forcing,
will aid in sustaining the QLCS as it moves across the Mississippi
River before storms gradually weaken during the the mid/late
evening hours as they continue east. A few embedded supercells
will pose the most significant severe weather risk, with large
hail and damaging winds being the primary hazards. The linear mode
of this convection will limit the tornado potential, but the
possibility still warrants mention.

Average QPF amounts for tonight are near 1 inch across much of
the Mid-South, but higher amounts will be possible in northeast
AR where the deep-layer shear vector will be nearly parallel to
the surface boundary, promoting strong, training cells. Rain will
move east of the area late tonight, with generally dry weather
anticipated Thursday and Thursday night across much of the CWA.

Thunderstorms will be possible across portions of the Mid-South on
Friday, mainly during the evening and overnight period. A surface
low is progged to develop over MO, with a warm front extending
east into the Tennessee Valley. Surface temperatures in the 80s
will result in strong instability but a strong cap will limit the
thunderstorm potential through the afternoon hours. However, a few
storms could break through the cap, so low PoPs were continued.
Rain chances increase Friday night as the cap weakens and storms
develop along the warm front. Strong shear profiles may result in
strong to severe thunderstorms Friday night. In addition, locally
heavy rainfall will be possible, mainly north of I-40.

Strong to severe storms remain in the forecast for the Mid-South
for the weekend, especially Saturday night and Sunday. There may
be a lull during the morning and early afternoon hours on
Saturday, but a strong shortwave trough will approach the area and
will help precondition the atmosphere for intense convection later
in the day. Deep layer shear and instability will be impressive
downstream of this upper-level cyclone, supporting a potential
for all modes of severe weather. Again, heavy rainfall will be
possible across the area. QPF amounts from 7 PM Friday to 7 PM
Sunday are generally in the 2-5" range across the Mid-South, with
higher amounts of 4-6" over northeast AR and the MO Bootheel. Of
course, higher amounts will be possible in areas where the
stronger storms train, but that will rely on mesoscale features
that aren`t yet apparent. Flash flooding will certainly be a
concern over the weekend and a watch may be needed as early as
tomorrow. In addition, some Mid-South rivers are likely to move
into flood.

Dry weather is anticipated early next week on Monday and Tuesday
in the wake of the departing trough. Temperatures will take a hit
as well behind the cold front. Rain chances return by the middle
of next week.




A line of thunderstorms just moving over the Mississippi River and
will continue to move east tonight, otherwise VFR conditions will
continue through the evening hours. Lower clouds are expected to
move into the region overnight producing IFR ceilings. Clouds will
lift Thursday morning with VFR conditions returning. Winds will be
mainly from the south at 10 to 15 knots with higher gusts tonight
with winds shifting to the west overnight at around 10 knots and
continuing through much of Thursday.




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