Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 292320

Area Forecast Discussion
National Weather Service Memphis TN
620 PM CDT Wed Mar 29 2017

Updated for 00z Aviation Discussion.


.PREV DISCUSSION... /issued 325 PM CDT Wed Mar 29 2017/


..Two rounds of severe weather expected...

Currently...A strong upper low is located over the southern plains
this afternoon. A warm front is pushing north through the MId-
South and is roughly located from NE Arkansas into West Tennessee
at 19z. Temps are climbing into the lower 80s south of the front
with dewpoints in the lower 60s with some location mixing into the
upper 50s.

Tonight...Expect showers thunderstorms to develop the Arklatex
and across Western Arkansas over the next few hours. This activity
will move east during the evening impacting Eastern Arkansas
mainly after 03z. A potent shortwave rotating around the upper low
will punch into the area late tonight. This feature contains a
8O-90 kt mid level jet and a 40-50 kt low level jet. This low
level jet will feed and increasingly moist and unstable airmass
into the Delta region. Increasing lift associated with this
shortwave will result in the expansion of showers and
thunderstorms later tonight with perhaps maintain or even
increase the storms intensity. Strong mid level lapse rates of
7-8c/km will result in hail being the main threat initially
gradually shifting to a damaging wind threat later tonight as the
storms tend to congeal as they move to the MS River. A few
tornadoes are also possible. The enhanced risk tonight has been
moved to south and west of a Jonesboro Arkansas to Memphis to
Charleston Mississippi line.

Thursday into Thursday night...Expect a large area of showers and
thunderstorms west of the MS River during the morning hours. This
area of storms will be in a weakening stage and eventually lift
northeast of the area by mid-morning. Since the shortwave
rotating around the upper low is more potent late tonight/early
Thursday and the amount of shower and thunderstorm coverage is
potentially greater than previous models runs there is a good deal
of uncertainly concerning the severe weather potential Thursday
afternoon. The 12km and 3km NAM and some versions of the WRF take
an aggressive approach to destabilizing the airmass in the wake of
the morning convection. Meanwhile the GFS/ECMWF have less
destabilization occurring. At this point expect the upper low to
track across Missouri on Thursday with a cold front tracking east
into the Mid-South. Expect thunderstorms to develop along this
front as another potent shortwave rotates around the upper low on
Thursday. The degree of severity will depend on the amount of
destabilization which, as mentioned above, is in question. If
instability to the degree of SBCAPE values in the range of
1500-2500 J/KG can occur then a line discrete supercells with very
large hail and damaging winds will occur along the front. 0-1 km
helicity values over 200 m2/s2 are expected and strong tornadoes
are possible. The EML punching in from the southwest may help
maintain discrete supercells for a longer period of time before
merging into a line. Depending on the amount of destabilization
this line could develop as far west as the Bootheel to Memphis by
18z or further east if more time is needed to destabilize. A
moderate risk continues for most of West Tennessee and North
Mississippi. The line will eventually push into Middle Tennessee
and North Alabama by 8 pm at the latest. Cooler air and some
clearing expecting by Friday morning.

Friday through Saturday...The upper low will lift out on Friday
with some clouds across the north. Temps will be much cooler
across the north with readings in the lower to mid 60s....lower
70s across North Mississippi. By Saturday an upper ridge will
build in with sunshine and temps from about 70 north to 80s south.

Sunday into Monday...Looks unsettled with another upper low moving
through with increasing chances for showers and thunderstorms.
The low is tracking tracking right across the region so any
severe weather risk will probably stay across the south part of
the Mid-South or further south. Confidence too low to add to the
HWO at this time.

Tuesday and Wednesday...Tuesday looks quiet with another system
possible late Wednesday. Just went with small pops for now.




00z TAFs

Showers/thunderstorms affecting all sites this period...with
first round reaching JBR and MEM during the first half...and MKL
and TUP during the second. Worst conditions in storms will be IFR
along with strong wind gusts. MEM may see a second round between
sunrise and noon...but coverage warrants VCTS for now. MKL and
TUP run the risk for stronger afternoon storms...which may turn
out to be more severe. Cigs will bounce between VFR and MVFR with
gusty south winds veering southwest behind a passing cold front.




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