Area Forecast Discussion
Issued by NWS Memphis, TN

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FXUS64 KMEG 241108

Area Forecast Discussion
National Weather Service Memphis TN
608 AM CDT Mon Apr 24 2017

Updated to add 12Z Aviation Discussion.

.PREV DISCUSSION... /issued 416 AM CDT Mon Apr 24 2017/


The upper level low pressure centered over Alabama early this
morning will continue to drift further southeast as high pressure
builds over the Mid South. This should support dry weather
conditions with morning clouds clearing out of eastern areas.
Temperatures will be much warmer today with highs ranging from
around 70 degrees east to the middle 70s west. High pressure will
move east of the area tonight with southerly low level return flow
setting up by Tuesday. Dry and warmer weather can be expected for
Tuesday with highs in the lower 80s with lows in the 50s to
lower 60s by early Wednesday morning.

An upper level shortwave trough will eject from the Plains across
the Mid South by Wednesday evening. This shortwave trough will
take on a negative tilt as it progresses across the region. This
should allow the atmosphere to become moderately unstable as
colder air aloft overspreads a moistening low level airmass Wednesday
afternoon and evening, especially along and west of the
Mississippi River. Steep mid level lapse rates approaching 7.5-8.0
c/km along with SBCAPES between 1000-1500 j/kg will develop over
these locations Wednesday afternoon and evening. This instability
will combine with strengthening low and deep layer shear,
associated with a 50-60 kt low level jet and 70 kt cyclonically
curved mid level jet respectively, to support severe weather
potential. Damaging winds and large hail will be the primary
severe weather concerns through Wednesday evening mainly along and
west of the Mississippi River. In addition, 0-1 km SRH will range
from 100-200 m2/s2 in advance of a surface low that will lift
northeast into southeast Missouri. This should support a threat
for embedded tornadoes as well, associated with any supercells
that develop in advance of a convective squall-line or with
embedded meso-vortices that develop within the line itself. A
slight risk for severe thunderstorms exists along and west of the
Mississippi River for this time period. Instability should
decrease with eastward extent from the Mississippi River late
Wednesday night, therefore severe potential should wane further
east with time.

High pressure will briefly build over the region behind a
departing cold front for Thursday. Dry and cooler temperatures can
be expected along with lower humidity levels. The front should
stall across central Mississippi and Alabama through Thursday. The
initially stalled front should begin to lift back to the north as
a warm front late Thursday night and Friday as a strong upper
level disturbance digs across the western states. A belt of
strong southwesterly winds associated with a subtle shortwave
disturbance lifting northeast from the Southern Plains into the
Mid South will overspread the lifting warm front. The atmosphere
along and south of the front should become moderately to strongly
unstable on Friday. The upper shortwave combined with the
instability should support the development of thunderstorms along
the lifting warm front. Strong shear, especially in the vicinity
of the warm front could support rotating supercells with all
severe threats possible. Overall storm coverage is in question but
storms that do develop will evolve within a favorable environment
supportive of severe storms. Plan to keep mention of severe
weather potential in the Hazardous Weather Outlook.

Another shortwave disturbance will rotate across western portions
of the Mid South by Friday evening which will support additional
thunderstorms along the western portions of the warm front over
northwest portions of the Mid South. Strong shear and instability
should keep a severe weather threat ongoing.

The region will remain entrenched within an unstable warm sector
into the weekend. Storm coverage to the east of an approaching
upper level low moving east from the southern Plains is less
certain on Saturday afternoon as a capping inversion may
strengthen over much of the region ahead of the approaching upper
feature to the west. There may be some storms west of the
Mississippi River during peak heating Saturday afternoon. The
environment will remain quite favorable for severe weather as a 50
kt low level jet remains over the region providing substantial
shear. In addition, instability parameters should also be
conditionally favorable with moderate to potentially strong
instability in place. Again, the primary uncertainty remains the
strength of any capping inversion and trigger for storms.

The strong upper low will move northeast into the Middle
Mississippi Valley by Sunday and Sunday night. Surface low
pressure should develop in response to this upper level feature
and deepen as it lifts northeast from the vicinity of the Arklatex
into the Middle Mississippi Valley by Sunday afternoon. A trailing
cold front will push across the Mid South Sunday afternoon and
night. Numerous to widespread showers and thunderstorms should
develop along and ahead of the front. Environmental conditions
will still feature strong shear and at least moderate instability.
Therefore an additional threat for severe storms is expected
across the area for Sunday afternoon into Sunday night.

Dry and cooler weather will build behind the front for early next
week with near seasonable temperatures expected.



12Z TAFs

Low clouds associated with an upper level low over East Tennessee
are expected to return to MKL/TUP today producing MVFR conditions
today then gradually improving to VFR conditions for the remainder
of the period. Otherwise, VFR conditions expected to prevail
through the period. light winds will increase to N winds between
6-8 kts today then become light by this evening.




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