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Area forecast discussion 
National Weather Service Memphis Tennessee
628 am CDT Sat Apr 18 2015

updated to add 12z aviation discussion.


Previous discussion... /issued 354 am CDT Sat Apr 18 2015/


A large upper level low pressure system continues to spin across
the intermountain west this morning while slowly lifting to the
northeast. A lead shortwave now ejecting across the Southern
Plains will continue to lift northeast towards the middle south
today. The airmass over the forecast area will become slightly
unstable as dewpoints remain in the lower 60s and temperatures
rise into the middle and upper 70s. This moisture/instability
combined with lift associated with the approaching shortwave
should support the development of scattered to numerous showers
and thunderstorms mainly later this afternoon...with the greatest
potential over southern sections. Rain and thunderstorms should
overspread the entire middle south tonight with the potential for
localized heavier rainfall. There remains uncertainty with respect
to which locations will receive the heaviest rainfall amounts and
also with respect to overall amounts. Due to this uncertainty...plan
to defer any decision regarding a Flood Watch to the day shift.

There should be a temporary end to widespread rainfall on Sunday
following the departing lead shortwave late tonight. As the upper
level low lifts northeast and transitions to an open wave on
Sunday...expect middle level height falls to overspread the middle south
later Sunday afternoon and especially Sunday night. This will be
aided by a 50+kt middle level jet ejecting across the Ozarks by
Sunday afternoon/evening. This will help to steepen middle level
lapse rates and destabilize the atmosphere. Destabilization will
also be aided by daytime heating and continued low level moisture
advection which should drive SBCAPE values to in excess of 2000
j/kg by Sunday afternoon and evening across much of the forecast
area. The middle level height falls associated with the upper trough
should erode any residual early day capping and allow for
scattered to numerous thunderstorms developing across the warm
sector...along and ahead of an approaching surface cold front that
will move through the region Sunday night. The combination of
strengthening deep layer shear and moderate instability should
support the potential for severe thunderstorm development. Initial
storm Mode may be a mix of supercells and short bowing
segments...especially along and west of the Mississippi River
Sunday afternoon. Storms should congeal into a squall line by
Sunday evening as middle level forcing strengthens. Weaker low level
flow and quick transition to more unidirectional flow should limit
the tornado threat. The primary severe weather concerns should
remain damaging winds and large hail. Considering the degree of
steepening lapse rates in excess of 7.5 c/km...there may be the
potential for some significant hail reports...especially if the
more robust NAM soundings prove true. Severe storms will be
continue eastward into the overnight hours and may persist through
a good portion of the night before exiting east by early morning

High pressure will build into the middle south for Monday through
Wednesday of next week with a return to dry and cooler weather
conditions. Temperatures will be pleasant but slightly below
normal for this time of year with low humidity. High temperatures
should range from the upper 60s to lower 70s with lows mainly in
the 40s and 50s.

Warmer and wetter conditions will return by the end of the
extended forecast period.



12z taf cycle

Low stratus and fog has developed this morning producing MVFR to
LIFR conditions at taf sites. Conditions expected to improve to
VFR conditions by late morning into this afternoon.
However...conditions expected to deteriorate back to MVFR/IFR
conditions by tonight as a shortwave moves across the lower
Mississippi Valley...producing showers with perhaps some


Meg watches/warnings/advisories...


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