Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 211101

Area Forecast Discussion
National Weather Service Memphis TN
601 AM CDT Mon May 21 2018

.DISCUSSION... /issued 457 AM CDT Mon May 21 2018/

Similar upper air pattern to yesterday, with a ridge centered
over the southern Appalachians, and weak southwest flow aloft
around the ridge`s western periphery over thee Midsouth. A weak
stationary upper low will remain centered over the FL panhandle.

NAM Bufr soundings depict less CAPE over the Midsouth today,
roughly 1500 J/KG. Given the relatively widespread overnight
rains and residual cloud cover through the morning, this appears
reasonable. While instability will be somewhat reduced today, a
shortwave - already evident over southeast OK on GOES East water
vapor imagery - will lift into AR this afternoon. This feature
will likely aid in destabilization and storm organization/
persistence into the evening hours.

The shortwave will move only slightly east as it dampens out under
the upper ridge Tuesday. Combined with strong insolation, there
should be enough weakness in the upper ridge for a few afternoon
storms to develop. By Wednesday and Thursday, weaknesses in the
amplifying upper ridge become harder to find. Afternoon temps will
edge up to around 90, perhaps a couple degrees higher, with rain-
free conditions prevailing.

Height falls will arrive by Friday night, as an upper low drops
into the upper MS River valley from the Canadian prairies. Medium
range models continue to phase the associated trof axis over the
MS River valley with a deepening gulf coast upper low this weekend.
The models differ on the meridional placement of the phased trof
axis and upper low. With more widespread rain likely east of the
phased trof axis, this will affect rain chances for the Midsouth.
Of the medium range models, the ECMWF is furthest west and a
little more rainy for the Midsouth. Regardless of which solution
is correct, heavier more organized rains will likely occur to the
east of the upper low, along the gulf coast.




12Z TAF Set

Low confidence with TAF forecast as some of the CAM models did
not initialize well with the convection that occurred overnight.
Thus atmosphere along and west of the Mississippi River could be
worked over limiting redevelopment this afternoon. Left VCTS
wording in at KMEM and KJBR for the time being, but think best
chances for development will be along a corridor between KMKL and
KTUP. Expect convection that does develop to be diminishing in
coverage between 02-06Z. Fog may develop during the overnight
hours thanks to the rain that has occurred or is expected to fall.
Added TEMPO groups to the TAFS at all the sites. Winds will be
light and variable through the period.





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