Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 180431

Area Forecast Discussion
National Weather Service Memphis TN
1131 PM CDT Thu Aug 17 2017

Updated for 06z Aviation discussion.


.PREV DISCUSSION... /issued 821 PM CDT Thu Aug 17 2017/

UPDATE...Evening Update



The majority of the rain is now moving into Middle Tennessee and
North Alabama...although there is a bit of additional development
near Oxford, MS. Nevertheless little if any additional rain is
expected tonight. Lowered pops to 20% at best. A clearing line is
approaching East Arkansas. Much of the Midsouth West of the
Mississippi River should be clear by Midnight with mostly clear
conditions area wide by sunrise. A drier airmass tomorrow will
result in much lower Heat the low to middle 90s
instead of the tipple digits we saw yesterday and today.

The forecast for the eclipse still looks favorable...but not
perfect. For now we are expecting 30-40% cloud coverage. However
I have to wonder how much the reduced insolation will limit the
formation of cumulus.



.PREV DISCUSSION... /issued 618 PM CDT Thu Aug 17 2017/

A cold front is currently located west of the Mississippi River,
while a shortwave trough aloft exists across central Arkansas.
Showers and thunderstorms have developed ahead of these features,
supported primarily by subtle upper height falls and weak low
level forcing from the approaching front. This activity will
slowly progress east throughout the evening ahead of the surface
front, but all activity should remain sub severe as daytime
heating wanes.

The front will gradually ease through the region overnight and
into Friday. The most noticeable difference in the airmass change
will be a drier atmosphere on Friday, with heat indices only in
the lower 90s. By Friday afternoon conditions will be dry as the
front pushes south of the region. Models hint at an MCS
developing late Friday night and into Saturday morning across
central Missouri, and pushing through the southwestern half of the
region by Saturday afternoon. Highs will again be in the upper 80s
to lower 90s on Saturday, before a warming trend ensues for

Upper heights build over the region by early Sunday as an upper
ridge builds into the region, signaling the start of both a drier
and warmer period into early next week. Sunday will be pleasant
and highs will be in the low to mid 90s. The primary focus for
Monday will be the potential for clouds to eclipse the eclipse.
Models progress the upper ridge to the east on Monday, leaving
the local region on the western periphery of this feature, just as
surface flow becomes more southerly between a high to the east
and a deepening low to the west. This will be supportive of some
diurnal convection during the afternoon. However, I did go
slightly lower than guidance high temperatures on Monday
afternoon due to the cooling effect caused when the sun hides
behind the moon, at least partially, for a few hours during the
afternoon. Thinking this could partially aid lower sky cover, as
surface heating will be resultantly reduced by the eclipse. Thus
have 30 to 40 percent sky cover currently in the grids, with only
slight POPs for most of the region, and chance POPs for western
regions where the southerly flow both aloft and at the surface
will be most prominent.

Another upper trough begins to swing through the Midwest on
Tuesday, signaling a return to northwest flow aloft over the
region. Consequently, temperatures will again be a couple of
degrees cooler than average by midweek, while daily showers and
thunderstorm chances will exist as weak impulses embedded in the
flow aloft aid diurnal convection.




Conditions mostly VFR at the TAF sites. Only exception is a short
period of MVFR vis/cigs at MKL and TUP...though confidence at this
time is not overwhelming. Light westerly winds diminishing late.




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