acus01 kwns 231952
Storm Prediction Center ac 231950
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0150 PM CST Sat Feb 23 2019
Valid 232000z - 241200z
..there is a moderate risk of severe thunderstorms from central
through northern Mississippi into southwest and south central
Tennessee and northwest Alabama...
Threat for a few strong tornadoes, scattered damaging winds, and
isolated large hail should persist through this evening across the
lower Mississippi Valley into the Tennessee Valley. The most likely
period for strong tornadoes is expected through 8 PM CST across
northern Mississippi, southwest and far southern middle Tennessee,
and northwest Alabama.
..lower Mississippi through Tennessee Valley region...
Primary change to previous outlook has been to trim from the west
behind broken line of storms. The warm sector continues to
destabilize from northeast la and especially central through
northern MS where pockets of diabatic warming have boosted
temperatures into the mid-upper 70s. The special 18z radiosonde observation data from
Jackson MS sampled the warm sector and indicated around 1000 j/kg
MLCAPE. Scattered pre-frontal showers and thunderstorms have been
slow to intensify due to an inversion present around 700mb. However,
as the primary zone of forcing along the warm conveyor belt shifts
eastward and interacts with the destabilizing boundary layer, some
storms should evolve into supercells given favorable wind profiles
with 60+ kt effective bulk shear and 200-400 m2/s2 0-1 km storm
relative helicity along the strengthening low-level jet.
Previous discussion... /issued 1018 am CST Sat Feb 23 2019/
..lower MS and Tennessee valleys...
No change made to previous outlook except behind ongoing convection
in The Ark-la-tex. Overall forecast scenario is anticipated to
unfold from midday through tonight.
A surface cyclone over far northwest OK will translate quickly
northeastward, reaching southern WI around midnight. The cyclone
will deepen rapidly in conjunction with an ejecting midlevel
shortwave trough and the left-exit region of a strengthening (100+
kt) mid-upper jet streak. The deepening cyclone will draw the moist
warm sector northward from the central Gulf Coast states into parts
of the mid-south to perhaps as far north as the lower Ohio Valley
later this afternoon/evening to the east of a cold front, as a 50-60
kt low-level jet shifts across the northern part of the warm sector.
Marginally severe hail could occur with the stronger elevated storms
across the mid MS valley, but the primary severe threat is expected
farther to the south in the warm moist sector.
Ongoing convection across the Sabine valley into southern Arkansas will
increase in coverage/intensity as large-scale ascent overspreads the
northwest portion of the rich moist sector characterized by upper
60s to lower 70s boundary-layer dew points. The most robust
insolation appears to be underway downstream of this activity across
northern la into central/northern MS where surface temperatures
should warm into the upper 70s. This will support afternoon MLCAPE
of 1000-2000 j/kg, with only weak convective inhibition.
Semi-discrete storms are expected within the lingering band of
ongoing convection, and in the open warm sector, given strong
deep-layer shear and substantial cross-boundary shear vectors. The
tornado threat will be greatest from about 20-02z across
central/northern MS into northwest Alabama and southwest Tennessee. A few strong
tornadoes appear probable given 0-1 km/effective srh of 300-500
m2/s2 and effective bulk shear near 60 kt in the rich moist
environment. Thereafter, storms should weaken by 03-06z, though
isolated tornado/damaging wind potential could persist into the
early morning across northeast Alabama/northwest Georgia where storms will
encounter a remnant wedge front.
acus11 kwns 232301
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 232301
Mesoscale discussion 0128
National Weather Service Storm Prediction Center Norman OK
0501 PM CST Sat Feb 23 2019
Areas affected...far eastern MS into west-central and northwest Alabama
and south-central Tennessee
Concerning...Tornado Watch 5...6...
Valid 232301z - 240100z
The severe weather threat for Tornado Watch 5, 6 continues.
Summary...corridor of greatest tornado potential the next few hours
will extend from far east-central MS into northwest/west-central Alabama
and far south-central Tennessee.
Discussion...radar trends over the last 30 minutes or so have
indicated some strengthening in mid and low level storm rotation
both in semi-discrete convection to the northwest of Meridian MS and
further north associated with bowing line segment in Monroe County
MS. Additional semi-discrete storms moving into far south-central Tennessee
also continue to show signs of rotation. Overall, storms appear to
be struggling due to a weakness in storm relative flow in the low to
mid levels. Additionally, stronger forcing for ascent remains well
west/northwest of the region and height falls have generally been
rather weak. All of these factors have impacted organization and
longevity of intense convection.
Convection currently moving out of eastern MS into western Alabama and
south-central Tennessee will encounter the best environment of the day,
with regional vwp data indicating increased flow through the lowest
3km over over the last 30-60 min. Weak backed low level flow has
also been noted in this narrow corridor as well. This should help to
maximize low level shear in axis of greatest heating and
instability. As such, the greatest severe threat, and tornado
potential, will exit the next few hours, mainly across west-central
into northwest Alabama and adjacent south-central Tennessee. In fact, recent
lsr from mem confirmed a tornado had been sighted in Alcorn County.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 33198866 34158835 35378802 35618778 35668748 35578708
35358686 34768679 33238704 32818728 32618765 32558832
32668864 32808881 33198866