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Severe 3/24-3/26 possible severe wx

Day 1 Convective Outlook
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
 
Huntsville AFD


A dangerous severe weather outbreak is forecast to impact the
Tennessee Valley region later this afternoon and into the evening
hours. This will be coupled with a significant threat for flash
flooding through the entire day and into the overnight hours. The
synoptic pattern checks nearly all the boxes for a Deep
South/Tennessee Valley outbreak. As is the case with all severe
weather events, the devil will be in the details, with mesoscale
features determining the ultimate magnitude and scope of the severe
threat with this event. It's impossible (even this close to the main
event) to know exactly how these features will align themselves,
including a secondary warm front/differential heating boundary that
will play an intrical role in bringing a very unstable and downright
volatile air mass into the region later this afternoon. Regardless
of this uncertainty, we're much better positioned for all modes of
severe weather with this setup, including strong to violent
tornadoes. Flash flooding issues are about as close to an absolute as
you can get given the significant deep layer moisture transport,
multiple rounds of heavy convection, and two week precipitation
anomalies of 200+ percent. This is an event that should have
everyone's attention and it's critical everyone stays weather aware
today and has multiple ways to get warning information.

The initial surface warm front is quickly lifting northward into the
Tennessee Valley as of 08z and its moving at a fairly decent pace
given a fairly stout 60 kt LLJ surging northward from the Gulf
Coast. The combination of strong lift along the front, deep
moisture, and favorable dynamics has created a broad area of moderate
rain, with embedded heavier thunderstorms (thanks to some decent
elevated instability). End result will be a threat for heavy rainfall
and localized flash flooding with convection along this boundary
through much of the morning hours. Models often struggle with QPF
with elevated storms such as these and as a result, we've bumped our
QPF a little bit during this window. The other issue will be the
threat for a few strong to marginally severe storms around daybreak
as the front works its way through the area, with hail and localized
damaging winds being the other impacts. Since this activity will not
be rooted in the boundary layer, the tornado threat will be very
minimal with this first round of storms.

As alluded to above, the magnitude of the low-level jet should be
able to push this early morning convection north into Tennessee
without much problem. This should allow for a rapid moistening of the
boundary layer in its wake (especially without a wedge front in
place in NE Alabama), and dewpoints should surge into the low to mid
60s as southerly flow helps to establish a warm sector over northern
Alabama and southern Middle Tennessee by 15z or so. The following
3-4 hours will be very crucial in determining the setup for a
potentially very dangerous second round of storms in the afternoon
and evening along and ahead of a cold front. Namely, how much
destabilization will occur during this window. If lingering rain shower
activity lingers into the early afternoon, it's possible this will
latch onto a differential heating boundary just to our south that
will slowly move north into our area in the afternoon. Should this
occur, this could somewhat lessen the potential for a higher- end
severe/tornado threat in the afternoon -- or at least limit the
northward advection of the more unstable air mass until the evening.
However, this solution doesn't appear to be likely, as a second (and
stronger) low-level jet will be nosing into the Tennessee Valley
after 18z. This should force this boundary further north and closer
to southern Middle Tennessee by the mid afternoon.

Global models and their ensembles as well as most hi-res guidance
now favor a very unstable, highly shear environment developing
across much of our forecast area later today. This will result in a
dangerous outbreak of severe thunderstorms during the afternoon and
evening window. The aforementioned LLJ will help to create
impressive low-level shear, with 0-1 km shear values as high as
40-50 kts. SBCAPE values of 1000-2000 J/kg will be realized in this
warm sector by the afternoon, coupled with plenty of low-level
moisture with upper 60s dewpoints on the table. The surface low will
be deepening as it shifts from the Ozarks into the Ohio Valley, with
models trending toward a more negatively tilted upper-level system.
All this should result in less contamined and somewhat pristine warm
sector that will be favorable for discrete supercells and strongly
rotating storms along and ahead of the surface cold front. Storms
will also be quite fast-moving which will be an equally dangerous
proposition. The end result will be a threat for some dangerous
severe weather, with strong to violent tornadoes possible, especially
across northwest and north central Alabama, as well as intense
damaging winds, and large hail. The main timeframe for our severe
threat looks to be 1 PM to 11 PM -- with northwest Alabama being
under the gun initially in the early afternoon, before this activity
spreads east during the afternoon and into the evening. Models have
been consistent the timing of the cold front being roughly between
00-04z and expect our severe chance will drop off significantly by
the late evening and Midnight from west to east.
 
Probably the 1st time ever that I've pulled hodographs from about 10 different locations all to have "PDS TORNADO" over such a broad area! This setup truly has me nervous and I'm praying for a bust here. I saw one skew-t with a nudge of a cap, but was only present for one run and it never really capped it off, but I was hopeful! OH by the way Jim Cantore is in Huntsville if it wasn't posted....soooooo were all gonna die!! (sarcasm)
 
NEWEST BMX GRAPHIC
Capture.JPG
.SHORT TERM...
/Updated at 450 AM CDT Thu Mar 25 2021/
Today through Friday.

So far this AM we have had widespread showers with embedded
thunderstorms as it spread NE across C AL. The activity has been
elevated and while we are watching for any rogue storms, severe
activity during the early morning hours should be marginal at
best until the warm front makes its way northward later today. We
have increased the severe threat in the NW half of C AL for this
afternoon and evening. This probably doesn`t come as much of a
surprise as this system is ramping up to be significant there with
strong tornadoes a possibility. The SE half of C AL is a
different story. While we have a marginal threat this AM for
portions of C AL, for the rest of the afternoon and evening,
parameters are much lower in the SE counties with convection not
as likely there until later this evening. After the current
convection currently on the radar pushes N, we should have a
somewhat lull in activity in the SE.

In contrast, by around 11am, our warm front should be to the N of
the area. Models suggest some cellular activity will likely pop
up in the NW first. MUCAPE will not be lacking, but will be
highest in the west for this afternoon. 0-6km bulk shear will be
in ample supply across C AL. However, 0-1km shear will be
decidedly higher in the NW. Although amounts vary, guidance is in
agreement decreasing this low level shear significantly after 6z
as the bulk of the instability skirts to the NE. This will be not
only with the front moving across, but our negatively tilted upper
shortwave that is expected to be over the Arklatex ~18z today
expected to race off toward IL/IN by midnight tonight. With the
bulk of the activity in the SE counties expected for later this
evening, this greatly decreases the chance for severe weather for
them S of the I85 corridor. This is the reason for the sharp risk
gradient in our severe graphics. Timing is pretty similar to what
we had yesterday except possibly starting in the NW at 11am
instead of noon. The front is expected to make progress after
midnight with the risk for TS in the SE counties much lower for
the day on Friday with lower dew points moving in behind the
front.
 
Last edited:
Latest HRRR now shows directional shear looking good until 03z tonight/tomorrow. That is a major change. If this continues, discrete convection could continue longer into central AL before congealing into a squall like. All this assumes that capping doesn’t weaken convection as well which is also being modeled.
 
I’m really afraid of complacency. Listening to a BHM talk show as I normally do in the morning. Last weeks it was weather, high risk, tornadoes, having the NWS on ext; this week it is joking and pointless chatter for most of the first segment with weather may be a problem you need to watch it sprinkled in one or two times. They haven’t even mentioned it is a high risk yet.

It is a massive difference and today is much more dangerous.
 
Let's hope the ef5 hiatus stays a hiatus today. What time is this supposed to start for central alabama? Cause I'm busting my butt trying to get done with work so I don't have to be out in the mess.
 
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