2021 Weather/Storm Thread

Diggin It · Mar 24, 2021

This may be a busy year, as if it hasn't been already. Rather than doing a thread for each event, I'll stick to one. Primarily will be advance warnings and threat advisories. Feel free to chime in with reports if you've been affected.

Diggin It · Mar 24, 2021

For Thursday, 3/25, TN, MS, AL

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1228 PM CDT Wed Mar 24 2021

Valid 251200Z - 261200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE LOWER MISSISSIPPI VALLEY/MID-SOUTH INTO THE TENNESSEE VALLEY AND
SOUTHEAST...

...SUMMARY...
The potential for an outbreak of severe storms including several
long-track strong tornadoes, scattered large to very large hail, and
severe/destructive winds, will exist Thursday into Thursday evening
across a portion of the lower Mississippi Valley, Tennessee Valley,
and Southeast.

...Synopsis...
A shortwave trough with attendant 70-100 kt+ mid-level jet will
eject northeastward from the southern Plains across the lower/mid MS
Valley on Thursday, and continue over the OH Valley and lower Great
Lakes region Thursday night. At the surface, a weak low over
northeast TX at the beginning of the period Thursday morning is
expected to likewise develop northeastward to the mid MS Valley
through the day while deepening. A warm front attendant to this
cyclone will likely lift northward across the lower MS
Valley/Mid-South and TN Valley towards the lower OH Valley by
Thursday evening.

...Lower Mississippi Valley and Southeast...
Storms will likely be ongoing at the start of the period from
northeast TX into southern AR and northern MS/AL and TN. This
activity will likely be supported by a southerly low-level jet and
related warm advection. These storms should shift northward through
the morning, allowing for destabilization via diurnal heating to
occur across the lower MS Valley. Rich low-level moisture with at
least mid to upper 60s surface dewpoints (perhaps lower 70s), should
advect northward across parts of the lower/mid MS Valley, TN Valley,
and Southeast by Thursday afternoon. This increasing moisture,
coupled with diurnal heating, will likely support MLCAPE of
1500-2000 J/kg developing over a fairly broad portion of these
regions.

A pronounced low-level jet (50-60+ kt) will overlie much of this
region as well, as large-scale ascent from the ejecting shortwave
trough overspreads the lower/mid MS Valley vicinity. Strongly
veering and strengthening wind profiles from the surface through mid
levels will support supercells. 0-1 km SRH along/south of the
surface warm front will likely reach 300-500 m2/s2, and low-level
mesocyclones capable of producing strong, long-track tornadoes
appear likely with any supercells that can form. Scattered large
hail, some of which may be 2+ inches in diameter, and
severe/destructive winds also appear probable, both with supercells
and any bowing line segments that can develop. At this time, the
best potential for strong tornadoes appears to extend from parts of
central/northern MS into western/middle TN and central/northern AL,
mainly Thursday afternoon and evening as storms move generally
northeastward. Concern does exist regarding the effect of storms
forming during the morning on the development of instability, and
potential for destructive interference from too many storms
developing across the warm sector at the same time. Still, given the
very favorable environment forecast across this region and the
potential for numerous supercells, an upgrade to High Risk for
multiple strong to potentially violent, long-track tornadoes may be
needed in a later outlook update.

...Ohio Valley...
Fairly widespread precipitation should occur over a majority of the
lower OH Valley through the day. This should temper diurnal
destabilization to some degree, but weak instability will probably
still develop along/east of the surface low and northward-moving
warm front. At least an isolated severe threat may develop late
Thursday afternoon into the evening as the southerly low-level jet
strengthens over this region and low-level moisture increases. The
potential for a low-topped line of storms capable of producing
damaging wind gusts and tornadoes will exist given the strength of
the low-level flow and related shear. These storms will likely be
tied to a cold front as it tracks northeastward through the evening
and overnight hours.

..Gleason.. 03/24/2021

CLICK TO GET WUUS02 PTSDY2 PRODUCT

Diggin It · Mar 25, 2021

Upgraded to High Risk ... again. Very rare for two so close together in the same area.

NWS Storm Prediction Center Norman OK
1259 AM CDT Thu Mar 25 2021

Valid 251200Z - 261200Z

...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL...EASTERN AND NORTHERN MISSISSIPPI INTO NORTHWESTERN ALABAMA
AND SOUTHERN TENNESSEE...

...SUMMARY...
A tornado outbreak is expected today into early this evening across
parts of the Southeast northward into the Tennessee Valley. Several
long-track strong tornadoes, destructive winds and very large hail
are forecast from the Lower Mississippi Valley, eastward across
parts of the Southeast and northward into the Tennessee and Ohio
Valleys.

...Tornado Outbreak Expected Across Parts of the Southeast and
Tennessee Valley Today into Early This Evening...

...Southeast/Tennessee and Ohio Valleys...
A potent shortwave trough and an associated 75 to 90 kt mid-level
jet will eject quickly northeastward across the southern Plains
today. At the surface, a low will move northeastward and deepen
across the Arklatex and mid Mississippi Valley today. Strong
moisture advection will take place in the lower Mississippi Valley
as a 50 to 65 kt low-level jet strengthens. Surface dewpoints will
increase into the 65 to 70 F degree range by late morning throughout
much of eastern Louisiana, Mississippi and western Alabama. The
low-level moisture combined with surface heating will result in a
moderately unstable and volatile airmass by late morning. A band of
strong large-scale ascent, in advance of the shortwave trough, will
move quickly northeastward across the Arklatex this morning.
Convection appears likely to initiate around midday ahead of this
band of ascent from southeast Arkansas southward into northeast
Louisiana and eastward into southwest Mississippi. This cluster of
thunderstorms is expected to organize and rapidly intensify, moving
northeastward across central and northern Mississippi into
northwestern Alabama during the afternoon. Moderate instability,
strong deep-layer shear and impressive amount of lift on a large
scale will be favorable for widespread severe thunderstorm
development, and a tornado outbreak is expected.

RAP and NAM Forecast soundings this afternoon across the warm sector
from central Mississippi northeastward into northwest Alabama show
an impressive environment for severe storms. MLCAPE is forecast to
increase into the 2000 to 3000 J/kg range across much of central and
northern Mississippi by midday. Surface winds are forecast to become
backed to the south-southeast across the eastern half of
Mississippi. This combined with 60 kt of flow near 850 mb will
result in 0-3 km storm relative helicities in the 400 to 500 m2/s2
range. In addition, the progressive nature of the mid-level jet will
be optimal for the development of tornadic storms. Supercells are
forecast to develop rapidly after initiation across central
Mississippi early this afternoon and move quickly
north-northeastward into northeast Mississippi. Significant tornado
parameter is forecast to increase to near ten across northeast
Mississippi and northwest Alabama by 21Z, making conditions very
favorable for long-track strong tornadoes. As the low-level jet
consolidates and couples with the progressive mid-level jet, a
violent long-track tornado will be possible.

The cluster of severe thunderstorms is expected to move from parts
of northern Mississippi and northern Alabama into the Tennessee
Valley late this afternoon and early this evening. Supercells and
bowing line segments will likely be severe, producing wind damage,
tornadoes and large hail. Hailstones greater than 2 inches in
diameter may occur with the stronger updraft cores. The wind damage
threat is forecast to become more widespread as a squall line
organizes along a cold front in the Mississippi Valley. This line of
severe storms is forecast to move quickly eastward across the Ohio
and Tennessee Valleys this evening, producing widespread wind
damage. Wind gusts of greater than 65 knots will be possible.

Further north in areas near the Ohio River, instability is forecast
to be considerably weaker than in areas to the south. In spite of
the weaker instability, enhanced lift and strong deep-layer shear
will make severe storms possible. As storms move north-northeastward
across the Ohio Valley this evening, isolated large hail and wind
damage will accompany supercells and bow echoes. An isolated tornado
threat will also exist.

..Broyles/Cook.. 03/25/2021

Diggin It · Mar 28, 2021

"The city of Nashville on Saturday night quickly became one of the hardest hit areas, as torrential rain pounded the region.

As storms continued to deluge the Music City overnight Saturday, a life-threatening flash flooding situation developed very quickly across the Nashville metro. The NWS issued a rare flash flood emergency for Metro Nashville as well as Brentwood, Franklin and Mount Juliet, Tenn., overnight, warning of "an extremely dangerous and life-threatening situation."

As of midday Sunday, local news reported that at least four people were killed in the flooding in the Nashville area. The Nashville fire department said a third possibly flood-related death in the region was still being investigated.

Just before midnight, local time, an apartment building in the southeastern part of Nashville partially collapsed as floodwaters inundated the area. At least five people were trapped in the area as fire rescue units struggled against "swift water" to reach them, according to local media."