April 19th Severe Event

[jojo762]

1 minute ago, cheese007 said:

Considering how prolific Sunday ended up being, that says a lot 

I probably should've clarified this as supercell tornado potential... Keyword being potential, last sunday's "potential" (for multiple long-tracking supercell tors) was hampered significantly by storm mode, low-level lapse rates, and WAA convection; that being sad, the two long-track sigtors in S MS provided an example of the upper-end tornado strength potential for Easter. 

Something similar to last Sunday is that CINH will not increase markedly (or really at all) well after dark, signaling the potential yet again for nighttime QLCS tornadoes.

[Quincy]

45 minutes ago, andyhb said:

Probably worth noting that while the progged warm sector on the models is not especially extensive in terms of northward extent, it is very extensive in the longitudinal (W-E) direction. This matters when you have a setup with westerly winds aloft.

This... meaning a broad warm sector, spells trouble, assuming you have discrete/semi-discrete convective initiation. Whether that happens on an isolated or more widespread basis remains to be seen. 

[buckeyefan1]

Once again, thank you all for the excellent discussion. For the second straight week, there is now a pinned thread for easier access. Now.....back to your regularly scheduled program   

[Orangeburgwx]

Once again, thank you all for the excellent discussion. For the second straight week, there is now a pinned thread for easier access. Now.....back to your regularly scheduled program   

Thanks Buckeye, you stay safe out there!

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[buckeyefan1]

9 minutes ago, Orangeburgwx said:

Thanks Buckeye, you stay safe out there!

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You too Shawn. Not sure where you are, but I'm not too fond of the soundings in the St.Matthews area

[rnj79]

I live in the SELA region, but that forum doesn't seem to have as much discussion going as this one. I hope its ok to hang out here!

Thank you to all who help contribute!!

[buckeyefan1]

43 minutes ago, rnj79 said:

I live in the SELA region, but that forum doesn't seem to have as much discussion going as this one. I hope its ok to hang out here!

Thank you to all who help contribute!!

Welcome! We look forward to having you hang around   

[calm_days]

On 4/16/2020 at 12:13 PM, Bob's Burgers said:

also, hrrrv4 is back on COD, so get ready for 48 hour HRRR forecasts haha

 

Here it is so far. I've put it away from immediate viewing in case it is not accurate enough.  It looks possible, but definitely an unusual setup.

 

Here it is so far ^^ I've put it away from immediate viewing in case it is not accurate enough.  It looks possible, but definitely an unusual setup.

[Orangeburgwx]

You too Shawn. Not sure where you are, but I'm not too fond of the soundings in the St.Matthews area

I'm on the Bamberg side between Orangeburg and Rowesville, and yeah... That NAMNEST sounding is kinda making me itch... And considering a saw a decent sized dust devil by my job today, I got a hunch that does not bode well...

 

Here was the NAMNEST from 18z btw

 

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[Quincy]

Some of the longer range mesoscale models show an evolution not all that much different than last week. Just a tick farther south and west. 

If taking the HRRRv4/4km NAM verbatim, a complex of storms evolves in East Texas and tracks across northern Louisiana into central Mississippi along the warm front. NSSL WRF is somewhat farther south. I think given the expected larger scale pattern, the warm front is more likely to verify near or south of current progs, as opposed to farther north. I also don’t see a rapidly surging warm front like last Sunday, meaning northern MS/northern AL and almost certainly TN will probably not be in the crosshairs.

There also seems to be support for modest capping to leave the broad warm sector largely uncontaminated through midday. Any time you see 2000-3000 J/kg CAPEs with substantial shear in the Deep South, that’s not good.

There is still time for this to evolve, but I’d say it’s not looking any less severe at this point. 

[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 late 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.

[SmokeEater]

Not good....

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[nwohweather]

Shear isn’t as wild as Easter but last week was a once in a lifetime outbreak in my opinion. Numerous strong tornadoes almost all apart of a QLCS? It was one of the oddest events I’ve ever witnessed, but showed the raw power of solid instability and insane helicity.

SRH is high, the LCL is ground scraping once again, decent hodographs, ample moisture, 2-4000 j/kg of CAPE, and strong wind shear. Things may not be off the charts but this looks like another big event, and once again night time issues for GA and SC

[brianc33710]

SPC/BMX has Bham in a slight risk. Not far north is only marginal, while not too far south is enhanced. I guess they're just waiting to see where the models take the low. I think that the slight risk means that the warm front makes it to about I-20.

The airmass won't be as cold & dry as Easter morning but still not conducive as needed for a significant outbreak. So, we need warm air invection, but not as much. But, we probably won't get as much as what came thru Easter either.

If later models move the low north, then the risks will shift with it. S AL could wind up with what weather they feared last Sunday but didn't get.

[Snowstorm920]

Lots of 0-3km CAPE showing up on the HRRRv4

1km SRH is also high

Several signs pointing to another dangerous tornado environment across the deep south Sunday

 

 

[Chinook]

3/15/2008 is a possible analog( listed as #3 analog) on CIPS (run: 4/17, 12z) I thought it was a better match to the low pressure area than the #1 analog. You better hope this storm report map doesn't happen. Interestingly the top analog is 4/6/82, a well-known blizzard from Chicago to Boston. 

other analogs:

[MattPetrulli]

Very large 10% for Sunday.

[jojo762]

SPC goes with 10% hatched TOR, 30% hatched wind, and 30% hatched hail at 06z. Fairly tame/nondescript discussion compared to what has been discussed on social media and on here, but given all the various uncertainties it makes sense.

[Orangeburgwx]

Very large 10% for Sunday.

Yep, and I'm in it

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[Quincy]

Not a whole lot has changed. The model consensus seems to focus from northern LA into central MS for the most likely daytime severe threat. Similarly to last Sunday, storms initiate early in the day in East Texas and track eastward into northern Louisiana. Here, the tornado threat could once again get going early as a sufficiently unstable airmass advects north.

The upper level pattern is progressive with a more westerly component to the upper level winds. The surface front is likely to lie W-E near or just north of I-20 from LA-AL. Note that even if surface winds tend to “veer” to SSW, hodographs will still be quite large with a robust SW low-level jet and W/WSW flow at 500mb.

Storms near the surface low and riding along the warm front should pose the greatest, most widespread tornado threat. I would not be surprised if SPC upgrades this area to MDT risk.

Storm mode looks mixed/messy in this zone, but like last Sunday, a swath of damaging winds and tornadoes looks probable from northern LA into central MS. Eastward from there, the threat should continue into central AL and possibly central/southern GA into the evening and overnight.

The wildcard will be the warm sector... do we get any isolated storms south of I-20 from LA to AL? If we do, all severe hazards would be possible, with the potential for strong tornadoes. 

[Orangeburgwx]

Not a whole lot has changed. The model consensus seems to focus from northern LA into central MS for the most likely daytime severe threat. Similarly to last Sunday, storms initiate early in the day in East Texas and track eastward into northern Louisiana. Here, the tornado threat could once again get going early as a sufficiently unstable airmass advects north.
The upper level pattern is progressive with a more westerly component to the upper level winds. The surface front is likely to lie W-E near or just north of I-20 from LA-AL. Note that even if surface winds tend to “veer” to SSW, hodographs will still be quite large with a robust SW low-level jet and W/WSW flow at 500mb.
Storms near the surface low and riding along the warm front should pose the greatest, most widespread tornado threat. I would not be surprised if SPC upgrades this area to MDT risk.
Storm mode looks mixed/messy in this zone, but like last Sunday, a swath of damaging winds and tornadoes looks probable from northern LA into central MS. Eastward from there, the threat should continue into central AL and possibly central/southern GA into the evening and overnight.
The wildcard will be the warm sector... do we get any isolated storms south of I-20 from LA to AL? If we do, all severe hazards would be possible, with the potential for strong tornadoes. 

Great synopsis, but the Lowcountry/Southern Midlands of SC is also in the Enhanced risked zone, I would not be surprised if a few weak tornados spawn

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[Snowstorm920]

Noticing the models are mixing out low level moisture in a large swatch across the risk area during the day tomorrow from surface heating. Check out the surface dewpoint map below. That could really lessen the tornado/severe threat atleast for a time tomorrow afternoon/evening. LCLs get pretty high

 

[Orangeburgwx]

Is this bad?...

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[Jessy89]

Is this bad?...

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Of course that’s bad


.

[Orangeburgwx]

Of course that’s bad


.

No sarcasm, I was actually asking a legitimate question

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[Bob's Burgers]

43 minutes ago, Orangeburgwx said:

No sarcasm, I was actually asking a legitimate question

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Very impressive critical angle

[Hammer]

No sarcasm, I was actually asking a legitimate question

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It would be helpful to those of us still learning or who do not know as much bad the rest of you if people could explain why something is bad.

Saw another post in this thread with a picture and the caption “Not good” (or similar).

My first thought: why doesn’t it look good?
Second thought, “Crap - it covers my area”.

Hammer


. Pro

[Quincy]

It helps to post thermodynamic profiles too. It’s one thing if there’s a large hodograph, but are thermodynamics favorable too?

[Orangeburgwx]

It helps to post thermodynamic profiles too. It’s one thing if there’s a large hodograph, but are thermodynamics favorable too?

Here they are for that time stamp

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[Orangeburgwx]

It would be helpful to those of us still learning or who do not know as much bad the rest of you if people could explain why something is bad.

Saw another post in this thread with a picture and the caption “Not good” (or similar).

My first thought: why doesn’t it look good?
Second thought, “Crap - it covers my area”.

Hammer


. Pro

Any time you see "PDS Tornado" on that Skew-T, that has a potential to drop EF4s, the ones that tore up Mississippi last weekend had that in their Skew-Ts

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