April 24-30th Severe Potential

[Chicago Storm]

Still 5+ days out, but enough agreement and confidence for some sort of severe potential, associated with one or more troughs ejecting out into the Plains.

Looks like decent agreement on Tuesday and late week-early weekend threats.

We'll see how it goes...

[andyhb]

As I mentioned on the other thread, shear profiles seem to be shifting upwards in the latest guidance for Tuesday. With the steep mid level lapse rates and good quality moisture for April in place, that spells trouble.

 

Euro also is getting a substantial threat into the Lakes on Wednesday.

[IllinoisWedges]

Wow, SPC just came out with Day 6, 7, and 8 day outlooks. 30, 15, 15. Mention severe weather outbreaks possible on both day 6 and 7. Also, when was the last day 8? 

 

 

 

...DISCUSSION...
THE MEDIUM RANGE MODELS BEGIN THE DAY 4 TO 8 PERIOD WITH AN
UPPER-LEVEL TROUGH IN THE CNTRL ROCKIES AND MOVE THIS FEATURE EWD
INTO THE GREAT PLAINS ON SUNDAY/DAY 4. AHEAD OF THE UPPER-LEVEL
TROUGH...AN ISOLATED SEVERE THREAT MAY DEVELOP SUNDAY AFTERNOON
ALONG AN AXIS OF INSTABILITY EXTENDING NNEWD FROM THE SRN PLAINS
INTO THE MID MO VALLEY. ON MONDAY/DAY 5...THE MODELS BRING A
SHORTWAVE RIDGE NEWD ACROSS THE CNTRL PLAINS AND MAINTAIN AN AXIS OF
INSTABILITY IN THE SRN PLAINS WHERE AN ISOLATED SEVERE THREAT WILL
AGAIN BE POSSIBLE. ON TUESDAY/DAY 6...THE ECMWF AND GFS CONTINUE TO
MOVE A NEGATIVELY-TILTED UPPER-LEVEL TROUGH AND ASSOCIATED MID-LEVEL
JET ENEWD ACROSS THE SRN ROCKIES AND INTO THE SRN PLAINS. THE MODELS
SHOW A WELL-DEVELOPED DRYLINE ACROSS THE SRN AND CNTRL PLAINS
TUESDAY AFTERNOON. TO THE EAST OF THE DRYLINE...SFC DEWPOINTS IN THE
MID TO UPPER 60S F AND STRONG DESTABILIZATION SHOULD BE FAVORABLE
FOR SUPERCELLS. AS THE EXIT REGION OF THE MID-LEVEL JET OVERSPREADS
A VERY MOIST AND UNSTABLE AIRMASS...A SEVERE WEATHER OUTBREAK WILL
BE POSSIBLE WITH TORNADOES...LARGE HAIL AND WIND DAMAGE TUESDAY
AFTERNOON AND EVENING. THE MODELS HAVE BEEN CONSISTENT ENOUGH TO
WARRANT ADDING A 30 PERCENT CONTOUR ACROSS PARTS OF NORTH TX...OK
AND SRN KS. ON WEDNESDAY/DAY 7...THE MODELS ARE IN REASONABLE
AGREEMENT MOVING THE UPPER-LEVEL TROUGH INTO THE MO VALLEY AND
HAVING AN AXIS OF INSTABILITY IN THE MID MS VALLEY EXTENDING SWWD
INTO THE SRN PLAINS. SEVERE THUNDERSTORMS MAY OCCUR ALONG PARTS OF
THIS CORRIDOR WEDNESDAY AFTERNOON AND EVENING WHERE A SIGNIFICANT
SEVERE WEATHER EVENT WILL BE POSSIBLE. ON THURSDAY/DAY 8...ANOTHER
UPPER-LEVEL TROUGH IS FORECAST TO DEVELOP IN THE SWRN U.S. WITH
SOUTHWEST FLOW IN PLACE IN THE SRN PLAINS WHERE SEVERE THUNDERSTORMS
WILL AGAIN BE POSSIBLE THURSDAY AFTERNOON AND EVENING.

..BROYLES.. 04/21/2016 ( ͡° ͜ʖ ͡°)

[Stebo]

Can't disagree with anything in that outlook, as it stands right now, the potential is sky high from central KS to Dallas on Tuesday. Anything beyond that has too many question marks though still great potential.

[Quincy]

The top 10 GEFS analogs all showed some active periods including at least five tornado outbreaks. In order by ranking:

1. 4/26/1991: Outbreak with 53 tornadoes, including the Andover, KS F-5 tornado.

2. 5/10/1953: Localized outbreak of strong tornadoes in the Upper Midwest.

3. 4/17/1995: Outbreak with 21 tornadoes.

4. 4/9 - 4/10/2009: Outbreak with 86 tornadoes.

5. 5/8/1979: 21 tornadoes, though mostly in Florida, two were reported in Iowa, including an F-3.

6. 5/3/1994: 29 tornadoes in Texas.

7. 4/30/1978: 15 tornadoes in the southern Plains, including 6 strong tornadoes and a mile-wide F-4 on the northwest side of Oklahoma City.

8. 5/13 5/14/1994: 33 tornadoes across Texas.

9. 4/25 - 4/29/1994: 124 tornadoes in five days, including an outbreak from the 25th into the 26th.

10. 4/11 - 4-15/2007: 46 tornadoes in five days

A couple of these analogs don't seem like the best match with events in the Southeast, but nonetheless.

[ClicheVortex2014]

[ClicheVortex2014]

Forbes upped the TORCON to 4. At this rate, it can still reach 10 by game day.

[jojo762]

Forbes upped the TORCON to 4. At this rate, it can still reach 10 by game day.

he has only issued a 10 once. On April 27, 2011.

[FHSC Sam]

he has only issued a 10 once. On April 27, 2011.

Honestly, at this point it wouldn't surprise me to see numbers in that range, this could be one of those events..

[tornadohunter]

he has only issued a 10 once. On April 27, 2011.

 

Nope....also on 3/2/12

[jojo762]

Nope....also on 3/2/12

huh. Didn't remember/ know that one.

[FHSC Sam]

12z GFS looks pretty impressive, area of focus likely North-Central OK through Central, SE Central KS. 

[nrgjeff]

Thankfully forecast wind fields are not nearly as strong as those over Dixie 4/27/11. Pretty safe to take that and the other Superoutbreak off the table. Some of the Plains analogs shown might be close, but I would peel off the highest end ones. Wind fields were stronger all levels than what is forecast. Also I would note what Brett wrote in the Mid-Range thread regarding the downstream 500 mb short-wave ridge. It is not as far east as in some other cases. Ditto for the surface ridge northeast of the low. With upstream energy Tuesday should remain progressive, but it is not a slam dunk six days out.

 

What interests me most about next week is the sequence of days, not necessarily one widespread tornado outbreak. Tuesday of course looks like a regional tornado event. Sunday could be the preview and more action is likely after Tuesday. Models are debating days and placement later in the week. At any rate Tuesday, even if not historic, looks like an excellent chase day.

[ClicheVortex2014]

huh. Didn't remember/ know that one.

 

Yup, I think he issued 10/10 for central KY.

 

Thankfully forecast wind fields are not nearly as strong as those over Dixie 4/27/11. Pretty safe to take that and the other Superoutbreak off the table. Some of the Plains analogs shown might be close, but I would peel off the highest end ones. Wind fields were stronger all levels than what is forecast. Also I would note what Brett wrote in the Mid-Range thread regarding the downstream 500 mb short-wave ridge. It is not as far east as in some other cases. Ditto for the surface ridge northeast of the low. With upstream energy Tuesday should remain progressive, but it is not a slam dunk six days out.

 

What interests me most about next week is the sequence of days, not necessarily one widespread tornado outbreak. Tuesday of course looks like a regional tornado event. Sunday could be the preview and more action is likely after Tuesday. Models are debating days and placement later in the week. At any rate Tuesday, even if not historic, looks like an excellent chase day.

This is off topic but it's interesting how both Super Outbreaks happened outside of traditional tornado alley and there's not really an event in tornado alley that even comes close to either outbreak in magnitude or areal extent. It seems they get relatively smaller events (i.e., a few strong/intense tornadoes) more frequently, but we get the massive events on a less frequent basis. I'm curious why they haven't gotten their own Super Outbreak yet.

 

12z GFS looks pretty impressive, area of focus likely North-Central OK through Central, SE Central KS. 

 

GFS took a step back on the parameters... still generally impressive.

[Stebo]

Thankfully forecast wind fields are not nearly as strong as those over Dixie 4/27/11. Pretty safe to take that and the other Superoutbreak off the table. Some of the Plains analogs shown might be close, but I would peel off the highest end ones. Wind fields were stronger all levels than what is forecast. Also I would note what Brett wrote in the Mid-Range thread regarding the downstream 500 mb short-wave ridge. It is not as far east as in some other cases. Ditto for the surface ridge northeast of the low. With upstream energy Tuesday should remain progressive, but it is not a slam dunk six days out.

 

What interests me most about next week is the sequence of days, not necessarily one widespread tornado outbreak. Tuesday of course looks like a regional tornado event. Sunday could be the preview and more action is likely after Tuesday. Models are debating days and placement later in the week. At any rate Tuesday, even if not historic, looks like an excellent chase day.

I would be careful to discount the wind fields at this point, they have been steadily strengthening run to run, and there is very good directional shear regardless to the wind speeds.

[andyhb]

Thankfully forecast wind fields are not nearly as strong as those over Dixie 4/27/11. Pretty safe to take that and the other Superoutbreak off the table. Some of the Plains analogs shown might be close, but I would peel off the highest end ones. Wind fields were stronger all levels than what is forecast. Also I would note what Brett wrote in the Mid-Range thread regarding the downstream 500 mb short-wave ridge. It is not as far east as in some other cases. Ditto for the surface ridge northeast of the low. With upstream energy Tuesday should remain progressive, but it is not a slam dunk six days out.

 

What interests me most about next week is the sequence of days, not necessarily one widespread tornado outbreak. Tuesday of course looks like a regional tornado event. Sunday could be the preview and more action is likely after Tuesday. Models are debating days and placement later in the week. At any rate Tuesday, even if not historic, looks like an excellent chase day.

 

The wind fields forecasted by the Euro I think easily fall into that realm, with 60+ kt 500 mb flow overlapping the dryline and a 40-50+ kt LLJ by 00z.

[jojo762]

The wind fields forecasted by the Euro I think easily fall into that realm, with 60+ kt 500 mb flow overlapping the dryline and a 40-50+ kt LLJ by 00z.

yeah absolutely. The Euro looks a deal better than the GFS with the wind fields at all levels

[brettjrob]

This is off topic but it's interesting how both Super Outbreaks happened outside of traditional tornado alley and there's not really an event in tornado alley that even comes close to either outbreak in magnitude or areal extent. It seems they get relatively smaller events (i.e., a few strong/intense tornadoes) more frequently, but we get the massive events on a less frequent basis. I'm curious why they haven't gotten their own Super Outbreak yet.

 

This is a fair characterization. The Plains typically get a lot more tornado days per year, especially due to constant "mesoscale setups" in the late spring that are less common out east. Even our biggest outbreaks are normally focused along initiating boundaries: the dryline and/or warm front. Events like the Superoutbreak are characterized by a swarm of tornadic supercells throughout the open warm sector, sometimes in multiple waves that track over the same regions. It's not necessarily impossible to get an event like that further west, but it's typically not what's seen here.

[andyhb]

Not seeing much in the new Euro to temper anything. LLJ is significantly stronger/broader at 120 than yesterday's 12z run was at 144. I'm wondering if that ridge/surface high positioning further west may somewhat shrink the aerial extent of the threat, but intensify it over the areas affected, given that it means a stronger low level pressure gradient and thus stronger wind fields.

[ClicheVortex2014]

This is a fair characterization. The Plains typically get a lot more tornado days per year, especially due to constant "mesoscale setups" in the late spring that are less common out east. Even our biggest outbreaks are normally focused along initiating boundaries: the dryline and/or warm front. Events like the Superoutbreak are characterized by a swarm of tornadic supercells throughout the open warm sector, sometimes in multiple waves that track over the same regions. It's not necessarily impossible to get an event like that further west, but it's typically not what's seen here.

Yeah, that's my point. Those kinds of mesoscale setups are less common in the east, but we've had 2 Super Outbreaks while the Plains have had none that even comes close in magnitude or extent. 

 

My hypothesis is that it's because "our area" east of the Plains sees more mature systems than the Plains.

[andyhb]

Yeah, that's my point. Those kinds of mesoscale setups are less common in the east, but we've had 2 Super Outbreaks while the Plains have had none that even comes close in magnitude or extent. 

 

My hypothesis is that it's because "our area" east of the Plains sees more mature systems than the Plains.

 

It's also partly a function of LLJ trajectories. SW LL flow works E of the Plains because it means that moisture is being advected still from the Gulf rather than the Mexican Plateau if it was in the Plains. The Plains are closer to the EML source -> stronger capping -> stronger forcing for ascent needed to break that capping -> potential of more storms firing too quickly when the cap does break -> storm mode often becomes messy after the first few hours.

 

And as Brett said, open warm sector events tend to be less common in the Plains as opposed to the weaker capped areas E of the Mississippi River.

[brettjrob]

Pretty major nosedive on the 12z ECMWF for the whole string of (potential) events. So it begins. Never, ever trust setups with significant eastern troughing before mid-late May.

[Hoosier]

I agree with what Brett said.  On average, more focused events in the Plains with capping issues tending to be less prevalent once you move eastward from there.  And of course there are various reasons for the mega death tolls we've seen in outbreaks outside of the Plains.

[Hoosier]

It's also partly a function of LLJ trajectories. SW LL flow works E of the Plains because it means that moisture is being advected still from the Gulf rather than the Mexican Plateau if it was in the Plains. The Plains are closer to the EML source -> stronger capping -> stronger forcing for ascent needed to break that capping -> potential of more storms firing too quickly when the cap does break -> storm mode often becomes messy after the first few hours.

 

And as Brett said, open warm sector events tend to be less common in the Plains as opposed to the weaker capped areas E of the Mississippi River.

 

 

Agree with you too...didn't see your post before. 

[andyhb]

Pretty major nosedive on the 12z ECMWF for the whole string of (potential) events. So it begins. Never, ever trust setups with significant eastern troughing before mid-late May.

 

Tuesday still looks pretty major to me, shifted east a bit.

 

There seems to be a whole range of scenarios for what happens after that, I wouldn't focus too much on that yet.

[Stebo]

Pretty major nosedive on the 12z ECMWF for the whole string of (potential) events. So it begins. Never, ever trust setups with significant eastern troughing before mid-late May.

What are you talking about, there are several potentials on the 12z run...

[ClicheVortex2014]

Holy crap... the 12z Euro is just trough after trough after trough...

[Chicago Storm]

Pretty major nosedive on the 12z ECMWF for the whole string of (potential) events. So it begins. Never, ever trust setups with significant eastern troughing before mid-late May.

Definitely a step in the wrong direction.

Trough/jet streak eject out earlier Tuesday, and the set-up is further east.

Then the trough for Thur-Sun ends up with potential generally near and east of I-35, and into the jungles...for the most part.

[Stebo]

Definitely a step in the wrong direction.

Trough/jet streak eject out earlier Tuesday, and the set-up is further east.

Then the trough for Thur-Sun ends up with potential generally near and east of I-35, and into the jungles...for the most part.

It is one run of an inconsistent model, lets not all jump off a bridge and they are still chaseable events regardless to the changes.

[brettjrob]

What are you talking about, there are several potentials on the 12z run...

 

These wavelengths are just too short... this is not how you get major outbreaks in April. Tuesday is going to produce tornadoes somewhere, but if it's MO/AR, the chaser jubilation over the past 24 h will prove highly unwarranted. I'm not saying that's what's going to happen for sure, but I'd be somewhat surprised to see the ECMWF lurch like this and then completely back off later.

 

After that, on the 12z ECMWF, I'm seeing multiple shortwaves right on each others' heels. On Thursday, sub-freezing air at 850 mb is wrapping down into KS and NW OK as the next wave begins to progress through the Rockies. And then a similar (albeit less ugly) situation by Sat/Sun. In this scenario, TX/LA/AR would probably be the focus for anything noteworthy after Tuesday, at least in this subforum.