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fxus64 kmeg 201740 
afdmeg

Area forecast discussion
National Weather Service Memphis Tennessee
1240 PM CDT Mon Aug 20 2018

Update...

Updated to include 18z aviation discussion.

&&

Previous discussion... /issued 1030 am CDT Mon Aug 20 2018/

Discussion...

Convection ongoing in the warm sector across north Mississippi
and east-central Arkansas will continue to push east toward
middle Tennessee and north Alabama this morning into the early afternoon.
North Mississippi, the Memphis Metro and southwest Tennessee have the
bets chance for rainfall over the next couple of hours.

As the area of morning showers and thunderstorms clears the
region expect some breaks of sun. The atmosphere will destabilize
during the afternoon with sbcapes climbing into the 2000-3000 j/kg
range across the Delta. Expect storms to initiate along the cold
front moving east across Arkansas this afternoon. A belt of
moderately strong mid level winds will spread over the area as the
mid level trough pushes east. 0-6 km bulk shear values of 30-35
kts should be adequate to support the organization of severe
storms. Expect a broken line of convection to develop along the
front as it pushes east into the mid-south. Damaging winds will be
the main threat with large hail a secondary threat. 0-1 km
helicity values greater than 100 m2/s2 and the initial broken
nature of the line may lead to a weak tornado or two across the
Delta Region.

Sjm

Previous discussion... /issued 424 am CDT Mon Aug 20 2018/

Showers featuring occasional thunder are moving quickly across
the midsouth, most numerous across east central Arkansas and north
Mississippi. Rainfall totals through sunrise should be less than
one half of an inch. No strong or severe thunderstorms are
expected through sunrise.

Another round of showers and thunderstorms is expected later this
afternoon as a deep trough and associated surface low track to the
east along the Missouri Iowa state line. A trailing cold front
will eventually sweep across the midsouth tonight. Ahead of the
front all of the midsouth will be in the warm sector of a
seasonably strong storm system. However, several factors may
limit the potential for severe thunderstorms. The lack of cold air
aloft will limit lapse rates and ongoing rain and associated
cloud cover will likely limit thermodynamic instability. Model
guidance keeps cape generally below 2000 j/kg this afternoon and
that may be generous if we don't see significant breaks in cloud
cover. On the other hand dynamic parameters are seasonably
strong. Low level southwest flow on the order of 30-40kt is
expected to move over the area late this afternoon during or just
after peak heating. Surface flow is expected to remain southerly
resulting in sufficient shear to support healthy updrafts.
Multicellular storms look most likely with the potential to
produce locally damaging winds. The Storm Prediction Center does
mention the potential for a tornado, but damaging wind is far more
likely. High resolution short term guidance brings a narrow, fast
moving line of strong to severe thunderstorms across the midsouth
between around 4 PM and 10 PM. Will include a low to moderate
confidence of severe thunderstorms in the severe weather potential statement...but my gut feeling
is that the limiting factors discussed above will curb our severe
potential.

Otherwise, there does not appear to be any significant impact
weatherwise over the next 7 days. Behind tonight's cold front,
cooler and drier air will move into the midsouth. The coolest day
should be Thursday when morning lows may dip into the 50s near the
Tennessee River. Most of US will be in the low to middle 60s.
Highs Thursday are expected to be in the lower 80s across most of
the area. A weak ridge aloft and surface high pressure will keep
US mostly dry through Friday, with a few showers returning late
Friday into Saturday. Temperatures will trend warmer Friday
through the weekend, rebounding to near normal by Sunday.

30

&&

Aviation...
18z taf cycle

Flight category will vary throughout the period as a line of
storms moves through the region. Winds will be from the south and
gusty this afternoon ahead of the front, but will subside and
become more westerly by late in the period. Have currently
prevailed thunderstorms in the vicinity for much of the PM hours at all terminals and timed
thunderstorms and rain with tempo based on latest thinking, but uncertainty
remains.

Conditions should recover back to VFR conditions by early morning
hours. Some fog development could hinder mkl visibility, but too
much uncertainty coupled with focus on storm timing led to the
omission of that at this time.

Zdm

&&

Meg watches/warnings/advisories...
Arkansas...none.
MO...none.

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