Severe WX April 19-20, 2020 Severe Weather Threat

[J-Rab]

At first honestly thought they had somehow accidently copied the D4 outlook from the first event into the D4-8 again. Much deja vu here

Yep. A whole lot of deja vu. My anxiety from Easter Sunday hasn’t really even had a chance to dissipate yet.

Right back into the crosshairs. Hopefully, this one won’t be as robust as last Sunday’s.

 

[MUSH]

What was the risk area of the Chattanooga tornado from last weekend? Enhance?

 

[J-Rab]

What was the risk area of the Chattanooga tornado from last weekend? Enhance?

Yeah, I’m pretty sure that it was enhanced.

 

[Kory]

NAM is showing UH tracks along the 20/59 corridor. Here we go again.

 

[Richardjacks]

NAM is showing UH tracks along the 20/59 corridor. Here we go again.

View attachment 2947

I just don't know about that...based on everything I see, i think the real threat is well south of I20-/59. Sure, something could change but for now, I am not impressed.

 

[Kory]

I just don't know about that...based on everything I see, i think the real threat is well south of I20-/59. Sure, something could change but for now, I am not impressed.

The NAM is on northern end of guidance with the European. GFS and CMC guidance is more further south.

Most CAMs aren’t this far out.

 

[KoD]

With so many modeled rounds of convection, there leaves a lot of uncertainty. There's a stout cap and modest shear and there could be some enhanced boundary interactions if things time out favorably come afternoon/evening time.
Never disregard a storm system in Dixie during April though.

 

[MattPetrulli]

NWS Jackson AFD

Saturday night through Sunday night...

Several rounds of severe weather will be possible across the
region during this period as potent upper level shortwave pushes a
surface boundary across the Southern MS Valley region. A
preceding upper level disturbance embedded within the developing
southwest flow aloft across the region will help to enhance storms
along a warm front that will begin to lift across the region
early Sunday. The main threat with these elevated thunderstorms on
Sunday morning will be large hail and damaging wind gusts. An
unstable airmass will quickly develop during the ;ate morning
period as the warm front lifts out of the ArkLaMiss and teh cold
front begins to approach from the west. Dew points will increase
to near 70 while SB CAPE values will range from 2k-4k. Surface
based storms will begin to enter the region from the west late in
the morning as the surface boundary nears the region. Ample
amounts of deep layer shear will be available for storms to tap
into, helping them to become and maintain their severe status as
they track across the region. Guidance has also continued the
trend of increasing low level shear with each new run. The main
threats with storms across the region on Sunday late Sunday
morning through Sunday evening will be damaging straight line
winds between 60-70 mph, large hail up to tennis ball, and
tornadoes. Parameters suggesting a few strong tornadoes across
the region are continuing to improve, but will keep tornado
wording in the HWO the same for now.

 

[Kory]

WRF-ARW and NSSL certainly look a lot tamer than the NAM. A couple more notable UH streaks near the LA/MS border and Southern AL/GA, but they pale in comparison to last weekend as expected (the dynamics just aren't in the same ballpark).

 

[darkskys25]

WRF-ARW and NSSL certainly look a lot tamer than the NAM. A couple more notable UH streaks near the LA/MS border and Southern AL/GA, but they pale in comparison to last weekend as expected (the dynamics just aren't in the same ballpark).

Honestly id believe the gfs over the nam for severe wx. The models seem to be all over the place this year. But just stepping away from it all and looking at the big picture how can we stay destablized with round after round of storms and rain totals of 3 to 4 inches. It just doesnt seem realistic. Im feeling montgomery south right now has the best shot. Lets see how things look tomorrow night.

 

[Kory]

Trajectory of low level winds help. With the LLJ being more SWerly than our typical S/SSW, the more unstable air is able to slide in behind those storms. We will have a lot of elevated instability so hail and damaging winds still look like a very real possibility. The tornado threat is highly conditional and not as high as what it looked like 2 days ago.

 

[Kory]

NWS Birmingham.

A thermal gradient or effective front will develop as a result of
the morning convection and will be critical in determining the
northward extent of the afternoon and evening severe weather threat.
The most likely placement for this boundary at noon is somewhere
near Montgomery in a NW/SE orientation. A late morning to early
afternoon convective minimum appears likely which should give the
atmosphere a chance to become quite unstable. The most plausible
scenario is for a cluster of thunderstorms to form by early
afternoon in eastern MS and move eastward with the warm front
beginning to advance northeastward. The cluster of storms is likely
to grow upscale across our southwestern counties. Supercells may
also form ahead of the cluster along the advancing warm front in
response to warm advection with a strengthening low-level jet.
Dewpoints around 70 F in the warm sector and relatively cold
temperatures aloft could result in SBCAPE of 2000-3500 J/kg. 500 mb
flow of 50-60 kts and a strengthening low-level jet will be
supportive of supercells, bowing segments, and mesovortices mainly
across the southern half of our area. Large hail, damaging winds,
and tornadoes appear possible if this scenario unfolds. However,
there is still uncertainty regarding how the mesoscale details
will play out. Along and north of the warm front, training storms
could lead to flash flooding in an east to west corridor.

 

[Richardjacks]

Does tomorrow remind anyone of the Palm Sunday event...just positioned further south. I still think the warm front will not make much progress between Montgomery and B'ham, but will have to be watched for any surprises.

 

[Kory]

HRRR has supercells along a thermal boundary from Central MS ESE to near Montgomery tomorrow afternoon.

 

[Kory]

DO NOT think this boundary location is settled right now. Tomorrow morning convective pattern will determine that and we do not know as of now where that will set up.

 

[ARCC]

Does tomorrow remind anyone of the Palm Sunday event...just positioned further south. I still think the warm front will not make much progress between Montgomery and B'ham, but will have to be watched for any surprises.

Yep, and Lee county last year and possibly 4/8/98 as well. I don't think it will be of course as severe as this days, but I'm worried one storm will ride that boundary across a heavily populated area. As goofy and untrustworthy as the 3km NAM is, it's scary and it's been far too weak on UH the past few events.

 

[Richardjacks]

DO NOT think this boundary location is settled right now. Tomorrow morning convective pattern will determine that and we do not know as of now where that will set up.

True, also the morning convective pattern may be less widespread and move out much quicker, enabling the warm sector to freely expand. However, based on what I see right now, that morning rain falling into the cool, dry air will cause surface instability to pinched further south. We shall see....

 

[skelly]

Why is the large hail always called for and we rarely see it or get reports?

 

[MattW]

Looks like predominantly another overnight threat for Georgia unless I'm missing something.

 

[CAL]

The SHARPpy SARS is pulling an unusually high number of high impact analogs for tomorrow