Severe WX Severe Weather Threat 3/14-3/16

[Bama Ravens]

The couplet on lead storm near Isola, MS looks to have weakened a good bit. Hopefully it’s no longer producing a tornado.

 

[US_Highway15]

New MCD released for the next Tornado Watch in Alabama:

"SUMMARY...THE SEVERE THREAT WILL INCREASE THROUGH THE AFTERNOON,
INCLUDING THE POTENTIAL FOR MULTIPLE INTENSE, DESTRUCTIVE TORNADOES.
A PARTICULARLY DANGEROUS SITUATION TORNADO WATCH WILL BE ISSUED IN
THE NEXT HOUR.

DISCUSSION...THUNDERSTORMS, INCLUDING SUPERCELLS, CONTINUE TO
INCREASE IN COVERAGE AND INTENSITY OVER IN MS WITH THE RAPID
APPROACH OF A POTENT MID-LEVEL TROUGH. A PRONOUNCED 500 MB SPEED MAX
WILL GLANCE THE REGION TO THE WEST, PROMOTING THE MAINTENANCE OF
ONGOING STORMS, WHILE ALSO CONTRIBUTING TO ADEQUATE DEEP-LAYER
ASCENT FOR THE DEVELOPMENT OF NEW SUPERCELLS IN WARM-SECTOR
CONFLUENCE BANDS. AS THIS OCCURS, THESE SUPERCELLS WILL MATURE IN A
MOISTENING LOW-LEVEL AIRMASS, WITH DEWPOINTS IN THE MID 60S F,
OVERSPREAD BY 8 C/KM MID-LEVEL LAPSE RATES. MLCAPE SHOULD REACH
AROUND 2000 J/KG AMID 400+ M2/S2 EFFECTIVE SRH (DRIVEN BY LARGE,
ELONGATED/CURVED HODOGRAPHS THAT ARE ALREADY EVIDENT VIA REGIONAL
VADS). THE ANTICIPATED PARAMETER SPACE WILL BE HIGHLY SUPPORTIVE OF
TORNADIC SUPERCELLS. THE MORE DISCRETE, DOMINANT SUPERCELL
STRUCTURES WILL BE CAPABLE OF INTENSE, DESTRUCTIVE TORNADOES, AND
VIOLENT TORNADOES CANNOT BE RULED OUT. A SEVERE HAIL/WIND THREAT
SHOULD ALSO ACCOMPANY ANY ROBUST, SUSTAINED THUNDERSTORMS. A
PARTICULARLY DANGEROUS SITUATION TORNADO WATCH WILL BE NEEDED IN THE
NEXT HOUR TO ADDRESS THE IMPENDING SEVERE THREAT. "

 

[ColdFront]

Given that this event still has 6-8 hours left, plenty of time for that development to occur, especially as E MS/W AL continues to warm throughout the day

That may be true, but as that line of storms continues to move east, you’re going to need the right spacing and orientation for those cells to not only form, but have the space & time to move off and actually get a chance to mature. With that rain mass, it’s really going to put pressure on the cells to develop and move out and away from it quickly.

My messaging isn’t about this turning into a dangerous situation, that is a given. I’m more talking about this event reaching its ceiling

We have seen other high potential days run into the same issue. cells run straight into a more stable air mass and fail to produce.

 

[Chris3024]

Discussion out for Alabama now

 

[Brice W]

The couplet on lead storm near Isola, MS looks to have weakened a good bit. Hopefully it’s no longer producing a tornado.

I think that’ll be the last of that storm, you’ll have have to worry about straight line winds. Which should be taken seriously as much as a tornado.

 

[sak]

Hrrr looks just convection for Birmingham! I don’t buy that one bit

but why? what makes you think the HRRR had a good grip on things 48-60 hours out but is out to lunch within 6-12 hours?

 

[PopPop]

I think Alabama is where you’ll really start seeing things get violent. It’s eerily quiet there.

Quiet, sunny and a balmy 76° in Moody, AL just east of Birmingham

 

[ColdFront]

but why? what makes you think the HRRR had a good grip on things 48-60 hours out but is out to lunch within 6-12 hours?

IMO, the HRRR has had a good handle so far.

 

[TornadoFan]

SUMMARY...The severe threat will increase through the afternoon,
including the potential for multiple intense, destructive tornadoes.
A Particularly Dangerous Situation Tornado Watch will be issued in
the next hour.

 

[Kds86z]

Storm Report: houses damaged with possible injuries in Grace, MS from the first couplet.

So it was on ground,…

 

[UpperLevelLOL]

but why? what makes you think the HRRR had a good grip on things 48-60 hours out but is out to lunch within 6-12 hours?

HRRR has a known issue when modeling areas with ongoing convection at the time of run. Obs > models at this point, and the obs are potent. For example, here's the HRRR vs. obs from Jackson:

 

[keithGA]

 

[US_Highway15]

New Mesoscale Discussion for PDS Tornado Watch 45:

"SUMMARY...Strong to intense tornadoes are likely through
mid-afternoon across northern Mississippi.

DISCUSSION...Several mature, embedded supercells are starting to
emerge out of the larger area of precipitation across northwest
Mississippi with additional development possible from showers
evident on radar across northeast Mississippi. One of these
supercells, in Humphreys County, has had a persistent very strong
mid-level mesocyclone and tops over 50kft. In addition, structural
damage has been reported from this storm indicating the potential
for a tornado. This supercell and any other mature supercells which
develop are expected to persist east across the state through the
early-to-mid afternoon. 0-1km SRH from the GWX VWP is around 350
m2/s2 and increasing. The instability is not as great across
northern Mississippi where extensive cloud cover has muted daytime
heating somewhat. However, there is still ample instability for
maintenance of ongoing supercells. The combination of instability
and shear has yielded STP values of 2 to 3 which should increase
through the early afternoon as both shear and instability increase.
The 15Z WoFs shows several moderate low-level rotation tracks across
the northern part of the state over the next several hours which
supports expectations based on the aforementioned observational
data. Therefore, several strong to intense tornadoes are likely over
the next 2 to 3 hours across northern Mississippi within PDS Tornado
Watch 45."

 

[sak]

do we think the threat is now over in Memphis down the MS river towards a little north of Vicksburg, or might more SVR or TOR form later? if it's over for those areas, the event seems to be a little ahead of schedule, no?

 

[Baxter]

I'm really curious to see if they expand the MDT/High into Mid TN or if they stretch it across the eastern side of AL.

I would say more eastward into Georgia. Your atmosphere has really been worked over with all the rain, Atlanta is wide open. 73 degrees and climbing.

 

[UncleJuJu98]

Hate when I see these, because they are usually accurate. Seen too many of these individual area mesoscale discussion for strong/intense tornadoes. @JPWX watch out.

 

[SmokeEater]

Major structural damage and injuries in Grace, MS.

 

[Maxis_s]

That's a lot of prefrontals... Hoping they congeal and turn linear pretty quickly but it seems like they're going to stay semi-discrete at least.

 

[AJS]

That's a lot of prefrontals... Hoping they congeal and turn linear pretty quickly but it seems like they're going to stay semi-discrete at least.

Definitely looks like some of the storms may be becoming discrete.

 

[TornadoFan]

Brett Adair has a wall cloud on his stream.