461
FXUS64 KMEG 230219
AFDMEG

Area Forecast Discussion
National Weather Service Memphis TN
919 PM CDT Sun Sep 22 2024

...New UPDATE...

.UPDATE...
Issued at 903 PM CDT Sun Sep 22 2024

The severe weather threat for this evening has diminished due to
the presence of nocturnal inversion across the Mid-South. Showers
and thunderstorms will continue to trek across the
Kentucky/Tennessee border over the next few hours, diminishing
around midnight.

00Z guidance continues to support a marginally severe environment
setting up over northeast Arkansas, the Missouri Bootheel, and
west Tennessee Monday afternoon. Exact timing of convective
initiation will determine the severity of impacts for the Mid-
South. The greatest parameters will setup in the late afternoon,
lasting until sunset. The main limiting factor for storms during
this time frame: mid level forcing. For example, 700-500mb lapse
rates are modeled around 5.5 C/km. This will limit the chance for
tornadoes, making for more of a damaging wind and large hail
threat. The remainder of the forecast is on track and does not
need additional updates at this time.

ANS

&&

.SYNOPSIS...
Issued at 320 PM CDT Sun Sep 22 2024

An approaching cold front will bring scattered showers and
thunderstorms to the Midsouth on Monday. A few of these storms may
reach severe limits north of Interstate 40 during the late
afternoon and evening. Damaging winds will be the primary severe
weather threat. This front will eventually stall over north
Mississippi on Tuesday, as a deep upper level low pressure system
approaches. This upper low will remain near the Midsouth through
much of the week, as a tropical system likely develops in the Gulf
of Mexico.

&&

.DISCUSSION...
(This evening through next Saturday)
Issued at 320 PM CDT Sun Sep 22 2024

Another day of summer temperatures on this first day of autumn.
Isolated showers were noted on radar this afternoon, aided by
lower 70s dewpoints, cooler midlevel temps a weak midlevel
shortwave evident on GOES water vapor imagery.

Deep layer shear will increase on Monday, as an approaching
positively-tilted midlevel trough dampens the upper ridge that
has brought mid-summer heat over the past few days. A belt of
stronger midlevel southwesterly flow will overspread the Midsouth
Monday afternoon, with 0-6km bulk shear increasing to around
40 knots. HREF ensemble mean surface-based CAPE is around 1100
J/kg late Monday afternoon, with 25th and 75th quartiles of 800
to 1500 J/kg respectively. The take-away: instability should be
adequate for severe storms, even if cloud cover results in
realized CAPE near the low end of the ensemble spread. Regarding
storm timing, CINH should weaken sufficiently for storms by
midafternoon Monday, but the severe threat will likely be focused
just ahead of a midlevel trough passage Monday evening.

A cold frontal passage will follow the passage of the midlevel
trough late Monday night. This front will likely stall over north
MS on Tuesday. A belt of strong midlevel flow will overspread
much of the Midsouth, as a closed upper low drops into western
MO. The stalled front will provide focus for storms on Tuesday,
particularly south of I-40. Modest instability should limit
Tuesday`s severe storm threat.

The closed low will deepen over the Ozarks through late Wednesday
night. By this time, 12Z global consensus develops what could
become Hurricane Helene over the central/eastern Gulf of Mexico,
lifting it rapidly north ahead of the mid-latitude closed low
over AR. GFS, ECMWF and Canadian model deterministic solutions all
depict the midlevel upper low and remnant tropical system
congealing into one large low pressure system over the mid- MS
River valley by Saturday. With so many moving parts, it`s too
early to say with confidence how this pattern will evolve through
the course of the week. While the mid-latitude closed upper low
appears a good bet, important details of tropical development over
the gulf remains uncertain. For that, be sure to follow the
latest forecasts and discussions from the National Hurricane
Center.

PWB

&&

.AVIATION...
(00Z TAFS)
Issued at 621 PM CDT Sun Sep 22 2024

As of 630 PM, spotty convection continues to approach JBR. Overall
confidence for activity to reach the terminal is low, but opted to
keep PROB30 in TAF for now. Most guidance keeps MVFR CIGs situated
just north of JBR. However, given proximity to the airport, added
MVFR CIGs to the site for Monday morning. Otherwise, little change
to TAFs outside of adding PROB30 groups for additional convection
Monday afternoon.

ANS

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$

PUBLIC FORECAST...PWB
AVIATION...ANS