April 23rd Severe Event

[Bob's Burgers]

Figured it's time to start another thread (this is exhausting to see round after round of severe wx in the southeast) after seeing the last few runs of the UKmet, and the 0z NAM tonight.

 

[MattPetrulli]

Woof that NAM run would certainly be a higher end setup if it were to verify. Also, would think SPC puts out at LEAST a slight risk for Wednesday, gotta watch this closely. 

[WhirlingWx]

Either early today in the morning or yesterday I remember seeing that the timing of this system was going to temper the severe threat (moving through overnight without a very destabilized atmosphere). Those runs definitely show the system slowing down and I think in ABC 33/40's most recent Xtreme Weather video James Spann noticed a slower trend as well which meant a higher severe threat. Yikes.

[hlcater]

Lots of variation in guidance. Unsurprisingly, the models that are more significant with the parameter space are also the ones that have the slowest progression (NAM/UKMET). Will have to watch to see if their solution becomes favored. 

As this had been modeled up until today, the surface low was lifting out far too quickly, leading to a veering of the LLJ/surface winds by midday thursday. The 12z UKMET is slightly more backed with each, while the 00z NAM is substantially more backed. This system will also be pulling some sort of an EML with it from the plains, so thermodynamics are pretty good on all models. 

 

[andyhb]

SREF popping a 90 this early (FH 72) is a pretty good indicator of a problem on Thursday.

[yoda]

4 hours ago, MattPetrulli said:

Woof that NAM run would certainly be a higher end setup if it were to verify. Also, would think SPC puts out at LEAST a slight risk for Wednesday, gotta watch this closely. 

ENH risk issued... large area of hatched 30 percent

[yoda]

Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Tue Apr 21 2020

   Valid 231200Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MAINLY OVER
   ALABAMA...GEORGIA...AND NORTHERN FLORIDA INCLUDING THE PANHANDLE...

   ...SUMMARY...
   Significant severe storms are expected over parts of the Southeast
   on Thursday, including the potential for strong tornadoes.

   ...Synopsis...
   A positive-tilt upper trough with 70-80 kt midlevel speed max will
   move from the lower MS Valley Thursday morning toward the
   Appalachians by 00Z, with a 50-60 kt low-level jet core shifting
   from AL to the Mid Atlantic during the day.

   At the surface, low pressure will move from northeast AR into KY
   through 00Z, and toward the Delmarva by 12Z Friday. A dryline will
   extend southwestward from the low, and will move across AL, MS and
   LA during the peak heating hours. East of this boundary, 65-70 F
   dewpoints will be common, beneath cooling temperatures aloft.

   Models differ with how quickly the dryline will move, and early day
   storms may dictate where the quasi-stationary warm front sets up
   latitudinally. Regardless, the warm sector will become very
   unstable, with shear favoring tornadic supercells along the dryline
   and warm front/outflow boundary. At this time, it appears the bulk
   of the activity will occur over AL, GA, and the FL Panhandle into
   northern FL.

   The NAM solution, if taken literally, suggests strong and perhaps
   violent tornadoes will be possible over parts of MS, AL, and GA.
   However, this solution is much slower with the dryline than other
   models, and may be overdone with instability and low-level shear.
   Using the preferred ECWMF solution, the dryline will extend from
   southern MS into central AL Thursday afternoon, with early day
   storms reinforcing a warm front roughly from Birmingham AL to
   Atlanta GA. Outflow could potentially push the warm front farther
   south. Supercells will be possible both along the dryline and along
   the warm front, with strong tornadoes possible. The strongest lift
   will occur early in the period related to warm advection, and this
   will lift northeast during the day. However, subtle lift along the
   dryline will favor supercells, as opposed to a linear storm mode.
   MUCAPE of 2000-3000 J/kg is possible, with midlevel lapse rates of
   6.5 to 7.0 C/km aiding updraft vigor. Regardless of preferred model,
   this event will be adjusted with time as predictability increases,
   with categorical upgrades possible.

   Elsewhere, lift associated with a low-amplitude shortwave trough
   moving into the central Plains may support isolated strong storms
   along a cold front over NE, KS and OK where weak instability will
   develop beneath a northwest flow regime.

   ..Jewell.. 04/21/2020

[cheese007]

4 hours ago, yoda said:

Regardless of preferred model,
   this event will be adjusted with time as predictability increases,
   with categorical upgrades possible.

Will we have yet another day 2 mod?

[DanLarsen34]

4 hours ago, yoda said:

Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0228 AM CDT Tue Apr 21 2020

   Valid 231200Z - 241200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MAINLY OVER
   ALABAMA...GEORGIA...AND NORTHERN FLORIDA INCLUDING THE PANHANDLE...

   ...SUMMARY...
   Significant severe storms are expected over parts of the Southeast
   on Thursday, including the potential for strong tornadoes.

   ...Synopsis...
   A positive-tilt upper trough with 70-80 kt midlevel speed max will
   move from the lower MS Valley Thursday morning toward the
   Appalachians by 00Z, with a 50-60 kt low-level jet core shifting
   from AL to the Mid Atlantic during the day.

   At the surface, low pressure will move from northeast AR into KY
   through 00Z, and toward the Delmarva by 12Z Friday. A dryline will
   extend southwestward from the low, and will move across AL, MS and
   LA during the peak heating hours. East of this boundary, 65-70 F
   dewpoints will be common, beneath cooling temperatures aloft.

   Models differ with how quickly the dryline will move, and early day
   storms may dictate where the quasi-stationary warm front sets up
   latitudinally. Regardless, the warm sector will become very
   unstable, with shear favoring tornadic supercells along the dryline
   and warm front/outflow boundary. At this time, it appears the bulk
   of the activity will occur over AL, GA, and the FL Panhandle into
   northern FL.

   The NAM solution, if taken literally, suggests strong and perhaps
   violent tornadoes will be possible over parts of MS, AL, and GA.
   However, this solution is much slower with the dryline than other
   models, and may be overdone with instability and low-level shear.
   Using the preferred ECWMF solution, the dryline will extend from
   southern MS into central AL Thursday afternoon, with early day
   storms reinforcing a warm front roughly from Birmingham AL to
   Atlanta GA. Outflow could potentially push the warm front farther
   south. Supercells will be possible both along the dryline and along
   the warm front, with strong tornadoes possible. The strongest lift
   will occur early in the period related to warm advection, and this
   will lift northeast during the day. However, subtle lift along the
   dryline will favor supercells, as opposed to a linear storm mode.
   MUCAPE of 2000-3000 J/kg is possible, with midlevel lapse rates of
   6.5 to 7.0 C/km aiding updraft vigor. Regardless of preferred model,
   this event will be adjusted with time as predictability increases,
   with categorical upgrades possible.

   Elsewhere, lift associated with a low-amplitude shortwave trough
   moving into the central Plains may support isolated strong storms
   along a cold front over NE, KS and OK where weak instability will
   develop beneath a northwest flow regime.

   ..Jewell.. 04/21/2020

This is a really strongly worded outlook for Day 3. Models really shifted in the past 24 hours towards a more dangerous set-up. 

[nwohweather]

What is this Oklahoma? Dryline barreling through the SE just miles away from the ocean with solid lapse rates is absolute trouble.  Also the lift in place will create more of a string of pearls type setup instead of a bunch of spinning QLCS.  

Other than warm front placement I don't know what there isn't to like about tornado chances on Thursday, and violent ones at that.  With such good thermodynamic properties and lift, SRH on the order of 300+ will be more than sufficient to produce some monsters

[Orangeburgwx]

What is this Oklahoma? Dryline barreling through the SE just miles away from the ocean with solid lapse rates is absolute trouble.  Also the lift in place will create more of a string of pearls type setup instead of a bunch of spinning QLCS.  
Other than warm front placement I don't know what there isn't to like about tornado chances on Thursday, and violent ones at that.  With such good thermodynamic properties and lift, SRH on the order of 300+ will be more than sufficient to produce some monsters

Dixie Alley has been Tornado Alley this year

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[DanLarsen34]

8 minutes ago, Orangeburgwx said:

Dixie Alley has been Tornado Alley this year

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Dixie Alley is tornado alley at this point.

[Bob's Burgers]

Looks like a real hoot

[olafminesaw]

44 minutes ago, DanLarsen34 said:

Dixie Alley is tornado alley at this point.

Yup

[DanLarsen34]

30 minutes ago, Bob's Burgers said:

Looks like a real hoot

This is fine gif. 

[cheese007]

28 minutes ago, olafminesaw said:

Yup

Would be interested in seeing a 2009-2019 map

[Snowstorm920]

1 hour ago, DanLarsen34 said:

Dixie Alley is tornado alley at this point.

Mean number of EF2+ tornado days per decade from 1986-2015

[jpeters3]

6 minutes ago, DanLarsen34 said:

This is fine gif. 

One thing to watch is that this run shows an early day MCS taking a substantial chunk out of the warm sector, which could end up being a bust mode.

[SnowGoose69]

1 hour ago, Orangeburgwx said:

Dixie Alley has been Tornado Alley this year

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The western ridge/East trof pattern is a disaster for the Plains severe weather season.   There are some signs the pattern may shift 5/5-5/10 but by that point many areas of TX/OK are nearing the slowing point of their season which ends around 6/1 usually 

[Santa Clause]

Dixie Alley has kinda taken over in recent history. Tornado alley has had its moments obviously, but it feels we’re tracking Alabama, MS, TN far more often.

[buckeyefan1]

For the third time in 10 days, this thread is now pinned for easier access.  Thank you all once again for the great discussions and learning opportunities. Now......back to your regularly scheduled program     

[nwohweather]

8 minutes ago, Wmsptwx said:

Dixie Alley has kinda taken over in recent history. Tornado alley has had its moments obviously, but it feels we’re tracking Alabama, MS, TN far more often.

Yeah this is obviously one of the hallmarks of climate change.  In addition until recent years we have also seen a drastic decline in landfalling hurricanes as well

[audioguy3107]

12z NAM sounding on Thursday afternoon evening for points just west of Atlanta, Ga.  

[Snowstorm920]

18 minutes ago, Wmsptwx said:

Dixie Alley has kinda taken over in recent history. Tornado alley has had its moments obviously, but it feels we’re tracking Alabama, MS, TN far more often.

I always found this chart from this article interesting. Study period was 1974-2015. Large outbreaks are almost always focused east of Tornado Alley

 

[weunice]

Now that we can literally "see" almost every tornado from radar we know what we have now. Furthermore, with the ready availability of cell phone cameras and whatnot we have seen a drastic increase in weak tornadoes reported. Let's face it, you all watch the chases in the south. You tend to get a whole lot of three things: 

1. Rain wrapped
2. Night time
3. Trees

At least you can see in the plains so historically it might have seemed obvious to us that was tornado alley. I don't doubt a shift to the SE so don't get me wrong but I wonder to the extent that this has always been the case. There have been some epic tornado outbreaks in the south long before climate change was involved. I am thinking of a few oldies like the April 24, 1908 outbreak and the Enigma Outbreak just to name a couple. 

[janetjanet998]

One of these days the Birmingham  area luck is going to run out

by luck I mean one one of those F4-5 wedges moving NE along I-20 starting near Bessemer ...if one can track just right it will move over 30 miles of dense urban areas..

Most of these wedges seem to hit the less populated north suburbs rather then I-20 itself or the more heavier populated south areas

the 1998 F5 and 4-27 storms are examples

 

[SnowGoose69]

13 minutes ago, Snowstorm920 said:

I always found this chart from this article interesting. Study period was 1974-2015. Large outbreaks are almost always focused east of Tornado Alley

 

You don’t get many outbreaks in KS/OK/TX where you see like 50 plus tornadoes.  It’s more common to see violent tornadoes though vs outbreaks with high numbers.  Those are more frequent to the east as those maps show as well as further north in the Plains   

[Bob's Burgers]

1 hour ago, jpeters3 said:

One thing to watch is that this run shows an early day MCS taking a substantial chunk out of the warm sector, which could end up being a bust mode.

The thing that is interesting to me is the timing. If it goes though early (12z or so) and the atmosphere can recover somewhat, couldn't we look at local hotspots with modifying outflow boundaries? 

[jpeters3]

11 minutes ago, Bob's Burgers said:

The thing that is interesting to me is the timing. If it goes though early (12z or so) and the atmosphere can recover somewhat, couldn't we look at local hotspots with modifying outflow boundaries? 

Yeah, the 12z run seems to indicate enough recovery for supercells behind the MCS.  Though CAMs seem to always under-estimate the southward component of MCS  motion.

[andyhb]

1 hour ago, SnowGoose69 said:

The western ridge/East trof pattern is a disaster for the Plains severe weather season.   There are some signs the pattern may shift 5/5-5/10 but by that point many areas of TX/OK are nearing the slowing point of their season which ends around 6/1 usually 

What? Mid-late May is climatological peak season for these areas.