ACUS11 KWNS 172249
SWOMCD
SPC MCD 172249
GAZ000-ALZ000-MSZ000-LAZ000-180015-

Mesoscale Discussion 0212
NWS Storm Prediction Center Norman OK
0549 PM CDT Wed Mar 17 2021

Areas affected...Much of southeastern Mississippi and central
Alabama

Concerning...Tornado Watch 29...33...

Valid 172249Z - 180015Z

The severe weather threat for Tornado Watch 29, 33 continues.

SUMMARY...The risk for tornadoes, a couple of which could become
strong and particularly damaging, is expected to continue to
increase through mid to late evening as an organizing squall line
overspreads the region. This may also be accompanied by more
general strong to severe surface gusts. A new tornado watch will be
needed by 7 PM CDT.

DISCUSSION...Large-scale ascent, aided by lower/mid tropospheric
warm advection beneath difluent high-level flow, continues to
support discrete thunderstorm development within a relatively broad
warm sector. Areas of the warm sector not substantially impacted by
prior convection remain characterized by CAPE of 1000-2000 J/kg, and
wind profiles across the region exhibit strong deep-layer shear and
sizable, clockwise-curved low-level hodographs. This environment
remains potentially conducive to long-lived supercells with strong
low-level mesocyclones posing a risk for tornadoes.

While the onset of diurnal cooling could result in at least some
decrease in instability by 00-01Z, favorable large-scale forcing for
ascent seems likely to maintain discrete storm development across
central Alabama, as a linear convective system continues to evolve
upstream, across southeastern Louisiana through southern and eastern Mississippi. This is occurring ahead of a vigorous short wave
trough turning east-northeast of the southern Great Plains. As this
feature progresses into the lower/middle Mississippi Valley through
mid/late evening, south-southwesterly 850 mb flow is forecast to
strengthen in excess of 50 kt in a corridor along/ahead of the
evolving squall line.

Further enlargement of low-level hodographs will maintain the risk
for tornadoes with both the discrete supercells preceding the the
squall line and those forming within the squall line. This will
include the potential for strong tornadoes. Otherwise, corridors of potentially damaging wind gusts will probably begin to increase as
the evolving squall line continues to organize and accelerate
northeastward.

..Kerr.. 03/17/2021

ATTN...WFO...FFC...BMX...HUN...MOB...JAN...LIX...

LAT...LON 31958982 33108866 34018760 34198650 33098473 32388488
31968596 31388687 30858797 30398875 30648987 31958982

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ACUS11 KWNS 182157
SWOMCD
SPC MCD 182157
VAZ000-NCZ000-SCZ000-182300-

Mesoscale Discussion 0225
NWS Storm Prediction Center Norman OK
0457 PM CDT Thu Mar 18 2021

Areas affected...far northern South Carolina...much of North
Carolina...and southern/southeastern Virginia

Concerning...Tornado Watch 42...43...

Valid 182157Z - 182300Z

The severe weather threat for Tornado Watch 42, 43 continues.

SUMMARY...Tornadoes and damaging wind gusts are possible with
clusters of ongoing convection. This threat will persist for at
least the next couple of hours.

DISCUSSION...Convection initially over north-central North Carolina
has organized and acquired rotation while favorably interacting with
a warm frontal zone over far southern Virginia. These storms are in
a strongly sheared environment with lingering instability upstream
from an undisturbed environment along/south of the front containing
1000-1500 J/kg MLCAPE. The general clustered nature of the
convection suggests potential for several cell interactions, though
the combination of shear, localized vorticity ingest along the
front, and moderate instability suggests that the tornado threat
will exist for at least the next couple hours. Hail is also
possible near supercellular convection exhibiting stronger updrafts.

Farther upstream, another quasi-linear segment was located very near
the Greensboro, NC area and has also exhibited occasionally strong
rotation on radar. Brief tornadoes and wind damage are likely as
this area of convection migrates/propagates east-northeastward along
the remnant frontal boundary in that area.

More isolated cells farther southwest into north-central South
Carolina may also exhibit a hail/wind and isolated tornado risk
given the strong shear and weak instability downstream, although
slightly veered low-level flow may temper the tornado threat in this
area compared to farther downstream.

..Cook/Guyer.. 03/18/2021

ATTN...WFO...AKQ...MHX...RAH...ILM...RNK...CAE...GSP...

LAT...LON 36487971 36897935 37167841 37527744 37627672 37357586
36617574 36037597 35527667 35137773 34697891 34467989
34448040 34708075 35308087 35978039 36487971

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