This is a developing situation. Please monitor local TV and radio for local updates. We will update Saturday evening and Sunday morning:
The NWS and the NOAA Storm Center have been predicting a severe weather threat for this weekend for at least 72 hours. The severe event this weekend begins today in Texas and continues tomorrow across the South. Hee is what we know today:
- Severe storms with possible tornados will fire up this afternoon in Texas. San Antonio, Austin and Houston are under the gun.
- This system will come in waves. The first overnight and into the morning with heavy rains for many. The duration of these heavy rains will have a direct effect on the severity of storms for many. If they clear out quickly and the heat of the day is allowed to de-stabilize the atmosphere, then the severe threat increases.
- Tornados, flash flooding, high winds are the 3 main threats.
- New Orleans, Baton Rouge, Jackson, Birmingham are just some of the municipalities that are to be aware of the threat of long tracking tornados. Especially with the second wave expected Easter afternoon
- A 3rd wave is expected overnight into early morning.
- 2″-6″ of rain are expected in 24 hours across many areas including Alabama, Tennessee, and Georgia.
The official Saturday morning statement from the NWS and Storm Prediction Center:
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1259 AM CDT Sat Apr 11 2020
Valid 121200Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR
CENTRAL/NORTHERN LOUISIANA...SOUTHEAST ARKANSAS...MUCH OF
MISSISSIPPI...WESTERN/CENTRAL ALABAMA......
...SUMMARY...
An outbreak of severe thunderstorms appears likely Sunday into
Sunday night, with the greatest threat expected from Louisiana
through much of the Southeast and Tennessee Valley. Strong
tornadoes, potentially widespread damaging winds, and large hail are
all possible.
...Synopsis...
The ejecting shortwave trough initially over the southern High
Plains on Sunday morning is forecast to move quickly eastward to the
lower MS Valley by early evening, and then accelerate northeastward
toward the Ohio Valley late Sunday night into Monday morning, as it
becomes absorbed within an amplifying longwave trough that will
encompass nearly all the CONUS by 12Z Monday. In conjunction with
the ejecting trough, a broad surface low centered over the
central/southern Plains on Sunday morning will move eastward to the
mid-MS Valley by 00Z Monday, and then move northeastward and rapidly
intensify into an intense cyclone over the lower Great Lakes by 12Z
Monday. A warm front will surge northward ahead of the low across
the lower MS Valley and Southeast, while a strong cold front will
move southward through much of the Plains in the wake of the
departing cyclone.
...East TX northeastward through much of the Southeast and TN
Valley...
One or more clusters of deep convection will likely be ongoing at
12Z Sunday morning somewhere over east TX and potentially into
portions of the lower MS Valley. The intensity and areal extent of
any such clusters remain uncertain, but ample shear and instability
will favor a threat of hail and damaging wind with any organized
convection at the start of the period. Some tornado threat will also
be present Sunday morning with any semi-discrete storms that begin
to interact with the richer low-level moisture in the vicinity of
the warm front. As this convection spreads northeastward,
intensification is possible into portions of the ArkLAMiss region,
with an increasing tornado threat in late morning/early afternoon
with any surface-based storms, given rapidly increasing low-level
moisture and shear. North of the warm front, evolution into a QLCS
will be possible, with a corresponding risk of damaging wind into
portions of the TN Valley.
Meanwhile, further south, moderate to locally strong instability is
forecast to develop along/south of the warm frontal position, which
will be modulated by the impact of outflow from any early convection
described above. Midlevel flow will increase to 70-100 kt as a
south-southwesterly low-level jet intensifies into the 40-60 kt
range. These wind profiles combined with ample instability (MLCAPE
of 1500-3000 J/kg) will support the potential for intense
supercells. Any surface-based initiation along and east of a
pseudo-dryline moving into western LA by late afternoon could evolve
into one or more long-tracked supercells capable of producing strong
tornadoes, large hail, and damaging wind gusts. The extent of
development within the warm sector remains somewhat uncertain, given
the presence of a capping inversion and generally subtle foci for
initiation.
While the conditional risk of all severe hazards will be quite high
if supercells develop, uncertainty remains regarding how convection
will evolve from the morning into the afternoon. Any remnant outflow
related to early convection will determine the northern extent of
the higher-end tornado potential, and some guidance suggests the
potential for elevated convection within a midlevel moist plume
across the warm sector during the afternoon, which could either
dampen the severe potential, or evolve into surface-based convection
with a substantial severe threat. Given these factors, there is too
much uncertainty to upgrade the ongoing outlook at this time.
Evolution into more of QLCS is suggested by most guidance by Sunday
evening, which would pose an increasing threat of widespread
damaging winds and a few tornadoes across much of AL into
western/central GA through the overnight hours. Higher wind
probabilities may be needed in subsequent outlooks if confidence in
this scenario grows.
...Central/southern Plains into the Ozark Plateau...
While widespread convection to the southeast will likely limit
transport of deeper Gulf moisture into the Plains/Ozarks, more
modest moisture that was advected into the region on Saturday should
remain in place ahead the advancing surface low and cold front
Sunday afternoon. Steep lapse rates and cold midlevel temperatures
associated with the primary shortwave will support moderate
destabilization. Wind profiles will likely not favor classic
supercells, with some backing of mid/upper-level flow expected, but
effective shear will be supportive of organized structures. Large
hail (potentially significant) will be the primary threat, with some
wind potential if any upscale growth occurs. Wind profiles will not
generally favor tornado potential, though robust updrafts
interacting with locally enhanced vorticity near the surface cyclone
could produce a tornado or two.
...TN Valley into the OH Valley -- Sunday night...
Substantial uncertainty remains regarding the potential for
destabilization from northern portions of the TN Valley into the OH
Valley, due to the potential for widespread convection to the south
of this area. However, rapidly strengthening wind fields in advance
of the deepening cyclone will support the potential for damaging
wind and perhaps a tornado risk by Sunday evening should even modest
destabilization occur, as strong convection attempts to move in from
the southwest in tandem with the deepening cyclone.
... Eastern Georgia into the Carolinas/Mid Atlantic...
Substantial low-level moistening is expected over eastern GA into
the Carolinas/Mid Atlantic through the period. There is a nonzero
risk of organized convection along/north of the warm front during
the day into the evening, which would pose some risk of locally
damaging wind or perhaps a tornado, but confidence in this scenario
is low at this time. A more likely scenario is for widespread
upstream convection to evolve into multiple clusters or a QLCS and
move into this region sometime early Monday morning. Intense wind
profiles will support a risk of widespread damaging wind and a few
tornadoes, given sufficient instability.
The magnitude and coverage of the severe threat in this region will
be determined in part by how fast organized convection approaches
from the west. If convection accelerates and arrives faster that
current guidance would indicate, then there is less time for
low-level moistening and destabilization, and the magnitude and
northward-extent of the threat may be limited. If convection does
not arrive until very late in the period, then a more substantial
severe threat could evolve. If some of the slower guidance turns out
to be accurate, then the primary severe threat in this region may
not come until the D3/Monday period. Probabilities may need to be
increased in this area once the details come into better focus.
