April 19th Severe Event

[jrips27]

[WhirlingWx]

Oh shoot a moderate, SPC isn't loading properly for me yet though so I can't see the graphic and outlook text myself

[Quincy]

MDT risk:

 

[jojo762]

14 minutes ago, Orangeburgwx said:

Here they are for that time stamp

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Pretty saturated thermo profile all the way up to ~600mb... geez. Any storm would be pretty soupy... But the impressive LLVL (0-3km) CAPE, coinciding with that sickle-shaped hodograph is concerning. 

[DanLarsen34]

14 minutes ago, Quincy said:

MDT risk:

 

"It's April 12, all over again." lol

[andyhb]

2 hours ago, Snowstorm920 said:

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

 

Pressing X to doubt moisture mixing out that severely so close to the Gulf with unimpeded return flow. Not like the temps are in the upper 90s or 100s either.

[Orangeburgwx]

Pressing X to doubt moisture mixing out that severely so close to the Gulf with unimpeded return flow. Not like the temps are in the upper 90s or 100s either.

Which will only amplify the threat is the moisture doesn't mix out

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[Bob's Burgers]

I hate to say this, but I'm worried about the nocturnal tornado potential again with this system. Large area of EHI in the 3-5 range well after 0z Monday.

 

[Bob's Burgers]

That is not an innocent squall line 

 

[Snowstorm920]

58 minutes ago, andyhb said:

Pressing X to doubt moisture mixing out that severely so close to the Gulf with unimpeded return flow. Not like the temps are in the upper 90s or 100s either.

Ya I have my doubts to. CAMs seem to be to aggressive mixing out at times. Something to keep an eye on though 

[Upper Level LOL]

3 hours ago, Orangeburgwx said:

Is this bad?...

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Using Comic Sans as a default font? Yeah, that's bad

[StormySquares]

Are these meant to be supercells in central AL? No UH tracks with them

[Bob's Burgers]

HRRRV4 paints a more interesting image; possibility of strong boundary huggers possible

 

[MattPetrulli]

8 minutes ago, StormySquares said:

Are these meant to be supercells in central AL? No UH tracks with them

Yeah HRRR has a lot of intense cells but not a lot of UH tracks, was curious about that.

[StormySquares]

In this environment, any storms should be spinning but the lack of UH tracks in interesting. 

[JasonOH]

55 minutes ago, StormySquares said:

In this environment, any storms should be spinning but the lack of UH tracks in interesting. 

Sometimes that’s a sign that the storms are modeled to be elevated, similar to a lot of the crapvection last week. WAA loves to force elevated convection if there is a layer that supports it.

[jojo762]

1 hour ago, StormySquares said:

In this environment, any storms should be spinning but the lack of UH tracks in interesting. 

*any surface-based storms would be spinning.

It was only last week where we had plenty of storms, not all rotated (Because they were elevated junk), but a lot did — and those that did were surface-based, even if they were linear/clusters.

[Moderately Unstable]

8 hours ago, Hammer said:

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

Short version, giant hodograph, high critical angle.  Longer version...When you're looking for a strong tornado, you look for that big right turning hodograph. There's also a decent amount of academic literature now that discusses the link between critical angle and strong tornadoes. That's the angle between storm motion, and the low level shear. The closer to 90, the more likely you are to have an environment favorable for producing a strong tornado. Think about a boat, flowing down a river. That's the storm. Ok, now, imagine you tie a giant rope to that boat, and yank the back of it at a 90 degree angle. What happens? It spins. Or you fall into the river cause you thought you were stronger than a multi-ton boat in a current. Anywho, combined with a low LCL, large cape, AM cap, discrete cells...you have a problem on your hands. Hodographs let us plot wind speed and direction with height. It's an easy to read way to measure speed and directional shear together. When you combine those, we find that a large, right curving hodograph, signals that the *wind field* in an area is supportive of tornadoes. I feel compelled to add at this point...when we see a large, right curve, we're expecting a right-moving supercell. A "right mover", moves to the right of the mean flow. Hodographs are an easy way to determine this (and remember it). Large hodograph, in right quadrant, with right curve, equals right mover. Right movers tend to produce stronger and more frequent tornadoes due to some fancy dynamics. 

For tornadogenesis, we focus on the curvature of the hodograph in the first 2-3 km of the atmosphere. This is telling us about low-level shear. This is another area of tornadogenesis research that has become more clear in the last few years. It is part of why some supercells produce tornadoes, and others don't, and it is how the SPC can say now, x region will likely see supercells capable of "all hazards", where others will see a large hail threat. Basically, you start with a mid-level mesocyclone, and then that storm pulls in some additional rotational energy which enhances low level rotation. You can detect that on a hodograph through its low level curvature. You may also have noticed folks talking about the low "ground scraping" LCL's. That is, in essence, the cloud base. The closer that is to the ground, the easier it is for that strong low-level rotation to actually get to the ground.  Skew-T's, and hodographs, tell us all of this information. 

At the end of the day, hodographs are one plotting method used to tell us what's *possible*. The reason we use hodographs to prog wind profiles in severe setups, is they allow us to *easily* and *quickly* identify how risky a particular setup is, for a certain area. Thus when you read something "looks bad", it's because that chart or graph, is designed to allow us to easily interpret what we're viewing and come up with solutions. We could just look at the wind barbs on a Skew-t, or winds on pressure surfaces, but hodographs give us a better snapshot of what's happening at different heights, when it comes to shear and spin.

A tip for the future: don't overcomplicate chart analysis. When you forecast, you're considering many parameters. What's the starting setup? Do the models correctly capture this? Which capture it best? OK, what are the models that understand the situation to start with saying WILL happen in the future? How are they changing their forecasts with time? What do I know about the local area that could affect this setup? Do the models STRUGGLE with this setup, or area? What does this setup remind me of (or if you're me and have a bad memory, what does this remind a computer database of)? In all of that, you're going to look at many different charts, tables, plots, and figures.

Trying to get down deep into the weeds of a single hodograph in a scenario like this, isn't something anyone has time to do (or I suppose...should have time to do). Same is true for a Skew-T. I see folks overcomplicate them all the time, and you can come up with plenty of interesting things from them, some of which are useful. At the end of the day though--for a skew-t, what I'm going to look at....: what's the temp profile, what's moisture look like, is there a lot of CAPE, ok, where's that concentrated (aka, what's the profile), is it surface based, what's the wind, any significant advection occurring, anything else jumping out at me? If it's particularly noteworthy, what are possible analogs of that setup?  Ok, got it, NEXT. Thus, for a hodograph--long curvy rightward turning hodograph = bad. The bigger, and stronger the curve, in general = more bad. . 

 

[jburns]

57 minutes ago, Moderately Unstable said:

Short version, giant hodograph, high critical angle.  When you're looking for a strong tornado, you look for that big right turning hodograph. There's also a decent amount of academic literature now that discusses the link between critical angle and strong tornadoes. That's the angle between storm motion, and the low level shear. The closer to 90, the more likely you are to have an environment favorable for producing a strong tornado. Think about a boat, flowing down a river. That's the storm. Ok, now, imagine you tie a giant rope to that boat, and yank the back of it at a 90 degree angle. What happens? It spins. Or you fall into the river cause you thought you were stronger than a multi-ton boat in a current. Any who, combined with a low LCL, large cape, AM cap, discrete cells...you have a problem on your hands. At the end of the day, hodographs are one plotting method used to tell us what's *possible*. The reason we use hodographs to prog wind profiles in severe setups, is they allow us to *easily* and *quickly* identify how risky a particular setup is, for a certain area. Thus when you read something "looks bad", it's because that chart or graph, is designed to allow us to easily interpret what we're viewing and come up with solutions. We could just look at the wind barbs on a skew t, or winds on pressure surfaces, but hodographs give us a better snapshot of what's happening at different heights, when it comes to shear and spin. Don't overcomplicate chart analysis. When you forecast, you're considering many parameters. Step one, what's the starting setup. Do the models correctly capture this? Which capture it best? Ok, what are the models that understand the situation to start with saying WILL happen in the future? How are they changing their forecasts with time? What do I know about the local area that could affect this setup? Do the models STRUGGLE with this setup, or area? What does this setup remind me of (or if you're me and have a bad memory, what does this remind a computer database of)? In all of that, you're going to look at many different charts, tables, plots, and figures. Trying to get down deep into the weeds of a single hodograph in a scenario like this, isn't something anyone has time to do (or I suppose...should have time to do). Same is true for a skew-t. People overcomplicate them all the time and you can come up with plenty of interesting things from them. At the end of the day though--for a skew-t, for instance: what's the temp profile, what's moisture look like, is there a lot of surface cape, ok, where's that concentrated, is it surface based, what's the wind, any significant advection occurring, anything else jumping out at me? If it's particularly noteworthy, what are possible analogs of that setup?  Ok, got it, NEXT. Thus, long curvy rightward turning hodograph = bad. The bigger, and stronger the curve, in general = more bad. 

You spent a good deal of time on that post.  Paragraphs would greatly help readability and therefore increase the number of readers.

[Moderately Unstable]

1 hour ago, jburns said:

You spent a good deal of time on that post.  Paragraphs would greatly help readability and therefore increase the number of readers.

Thanks, edited. 

[jojo762]

00z Guidance is in fairly good agreement on a QLCS traversing the MDT risk area, what CAMs are not in good agreement on is WHEN this happens and IF there will be discrete convection in the warm sector during the afternoon and evening hours. 4KNAM, HRRR, and the HRW WRF-ARW present what is probably the high-end potential of this setup. All three models to varying degrees develop discrete/semi-discrete convection *somewhere* in the broad warm sector. Whereas the WRF-NSSL and HRW NMMB present a lesser day with regard to discrete warm sector development. WRF-NSSL presents what is probably the most likely failure mode tomorrow with LOTS of junky WAA convection developing across large parts of MS/AL in the afternoon...

Bottomline is, as was the case Easter Sunday, CAMs have not provided a clear picture on what is going to happen. Personally lean to something mildly similar to last Sunday with regard to convective evolution, just with likely (many?) less tornadoes.

Unlike with most setups, there is not a clearly defined area that has higher tornado potential (maybe southern Mississippi??), but rather a fairly expansive area with conditionally higher-end potential.

[Quincy]

A few quick thoughts...

Elevated storms are likely in the morning across Alabama (like last Sunday) and Georgia as well. The warm front could eventually reach these storms and if they do, the severe threat would increase there as early as late morning. Round 1 could focus across AL/GA into early afternoon before the western part of the risk area heats up.

Out west, the trend may be just slightly slower an a tick SW, which was the trend last week as well. Expect storms to initiate in East Texas during the morning and spread into central/northern Louisiana during the afternoon. These storms, in vicinity of the warm front and surface low, will be the ones to watch for the most widespread severe weather. They'll eventually move into central Mississippi.

It's still unclear if there is much warm sector activity south of the warm front and early day complex of storms coming out of Texas. Even if there is not, expect several tornadoes. The storm mode looks mixed and clustered, which will be challenging from both a chasing and preparation standpoint. I wouldn't rule out some warm sector activity as well.

It's hard to say how this will verify compared to last week, but I would not be surprised if it is a higher end (but not historic) outbreak. The three things to look for in terms of how high the ceiling could be:

1. Do early day storms in AL/GA become severe and if they do, does the tornado outbreak start there? If this happens, then the tornado count will be off to a quick start and remember that this area might see a second round Sunday night.

2. Watch the storms coming out of East Texas and Louisiana. If it's a broken line of storms with embedded supercells, that's going to lead to quite an outbreak. Even if it's just a squall line with QLCS tornadoes, that would still result in several tornadoes.

3. Is there much, if any warm sector activity? Even just one rogue storm down by I-10/south of the warm front could have long residence time to produce significant severe, assuming such a storm or storms can initiate.

P.S. the large/very large hail threat seemed to be a bit overdone last week. That tends to happen in these parts, especially when storm modes are mixed. I think we'll see some hail reports, especially across TX/LA/AR, but not as many farther east. There, lapse rates will be somewhat less steep.

If anyone is interested, I toyed with a live discussion on this threat about an hour ago:

 

[jojo762]

Dig the live discussion idea, I always enjoy listening to others thoughts on a setup more than just reading. Some type of initial chase target discussion would be nifty too, in addition to a "technical" discussion.

[DanLarsen34]

From an SPC meteorologist. 

[Quincy]

4 minutes ago, DanLarsen34 said:

From an SPC meteorologist. 

The environment from southern AL into southern GA rapidly becomes very favorable for tornadoes in the morning. If early convection can latch onto the warm front and ingest surface-based parcels, it could get ugly in a hurry. Storm motions suggest that storms could ride along the front right to the GA coast. 

Time sensitive:

[David Reimer]

The 0Z HREF goes bonkers tomorrow. Note that this is the SREF-calibrated TOR probabilities, not the SIG-TOR one that tends to run hotter. 

 

[David Reimer]

16 minutes ago, Quincy said:

The environment from southern AL into southern GA rapidly becomes very favorable for tornadoes in the morning. If early convection can latch onto the warm front and ingest surface-based parcels, it could get ugly in a hurry. Storm motions suggest that storms could ride along the front right to the GA coast. 

Time sensitive:

 

You getting trolled out to Dixie tomorrow or did you get your fill last weekend? 

[MattPetrulli]

Man those high risk rumors are flying tonight on Twitter

[Quincy]

 

[Radtechwxman]

12 minutes ago, MattPetrulli said:

Man those high risk rumors are flying tonight on Twitter

I see that. Apparently several people have inside info. Lol. Heard Broyles is doing outlook