Scientific Forecaster Discussion
fxus64 kmeg 202352
Area forecast discussion
National Weather Service Memphis Tennessee
652 PM CDT sun Oct 20 2019
updated 00z aviation discussion.
Previous discussion... /issued 231 PM CDT sun Oct 20 2019/
The main story this forecast continues to be the vigorous
surface/upper system and associated hazardous weather threats late
tonight into Monday. 12z short-range forecast guidance is in fairly
good agreement and continues the timing and trends from earlier.
For tonight and Monday - upper system centered over the Midwest
should take a slightly negative tilt as it pivots across the area.
Scattered warm advection showers/storms are expected this evening
and overnight. A squall line should develop along/ahead of the
surface front. Line should approach our east Arkansas counties by 9z Monday,
into west Tennessee/northwest MS by 12-14z, and into NE MS by 16-18z.
Deep-layer and low-level vertical wind shear are supportive of
organized storms/severe threat. Main question will be instability,
which should be weakening as storms move across. Main severe threat
should be early in the day over east Arkansas/SW Tennessee/northwest MS. May see some
enhancement in the line around midday Monday as heating increases
before line exits County Warning Area.
Damaging winds should be the primary threat. Heavy rain/localized
flooding will also be a primary threat with the line and with warm
advection showers/storms. Can't rule out an isolated tornado,
although relatively weak low-level instability should reduce this
Monday night through Thursday - relatively quiet weather expected as
front/precip exits and high pressure moves in. No precipitation and
fall-like temperatures are expected. Southerly return flow sets up
Wednesday afternoon, bringing increased temps and moisture by
Friday through Sunday - still much disagreement with next upstream
system. GFS keeps a progressive open trough, while the
Canadian/ukmo/ECMWF have some variation of a slower-moving closed
low over the south central/southwestern U.S. Will broad-brush low
pops in the Friday-Saturday night time frame for now and reassess as
details (and hopefully agreement) increase during the week.
Dynamic conditions over the next 24-30 hours will bring showers
and thunderstorms, llws, strong gradient winds and a wind shift to
the midsouth as a cold front moves across the area. Low level wind shear may
exceed 45kt as early as 06z, especially at jbr, mkl and mem before
the front moves through the area. A line of showers and
thunderstorms associated with the front will start to move into
jbr by 12-15z, mem by 13-16z, mkl 16-18z and tup before 18z. Brief
IFR or LIFR vsby due to heavy rain is likely along with gusty
wind in association with thunderstorms. Wind gusts should start to
taper off around 23z Monday at jbr, mem and mkl.