April 24-30th Severe Potential

[Stebo]

I think it still has a lot more room to back west. The NAM has the dryline on Monday in a much more believable position, in far western Oklahoma, while the GFS has it east of 35. You'd think if the GFS wasn't already so far east with its initial positioning Monday that Tuesday's position would end up much further west as well.

Oh I do believe it will back further west than its current position. Maybe not as far west as the NAM but probably another 25-50 miles.

[jojo762]

The instability values popping up on the conservative GFS are downright scary.

3000J/KG MUCAPE across basically the entire warm sector, with 4000+ in the main threat area. Even if bulk shear ends up being just 30-40kts like the GFS shows right now at 00Z across the main area, that environment would be crazy. A mix of the timing of the euro and GFS along with the environment both are showing would be perfect. euro is quite a bit faster, and the GFS is a bit slower, so a mix would result in the MLVL jet core overspreading the warm sector at about the perfect time.

[chase_stormz]

Oh I do believe it will back further west than its current position. Maybe not as far west as the NAM but probably another 25-50 miles.

 

This is around that time that the longer range models struggle with the details of the setup as they pass it over to the hi-res short term models such as the NAM. It'll be interesting to see how the picture becomes clearer as this thing gets sampled.

[JoMo]

Some interesting changes. The dryline still looks to be retreating west through 06z and winds up in NW OK. 

[WhiteoutWX]

Also while the instability still looks good east of the dryline the good H5 flow stays a little further west, meaning the shear isn't quite as impressive this run. Still within the range of run to run wobbles though so nothing to worry about too much.

[jojo762]

Some interesting changes. The dryline still looks to be retreating west through 06z and winds up in NW OK.

surges east quickly after that though.

[chase_stormz]

Also while the instability still looks good east of the dryline the good H5 flow stays a little further west, meaning the shear isn't quite as impressive this run. Still within the range of run to run wobbles though so nothing to worry about too much.

 

Like JoJo said above, a good blend of the Euro and the GFS would provide quite the setup...

[Chicago Storm]

Some interesting changes. The dryline still looks to be retreating west through 06z and winds up in NW OK. 

 

 

surges east quickly after that though.

Many times the DL will retreat west to at least some degree after dark.

 

It's then picked up by the front, and races east thereafter. 

[jojo762]

Noticed this for a few runs, but it seems like the area with really the most unconditional tornado threat could end up being over central KS along the warm front and near the triple-point. That area likely will have something around 2000j/kg of cape, and will have significant deep-layer shear along with a very-backed low-level flow with winds east-southeast. 500-850mb crossover for that area will likely be nearly perpendicular.

[ClicheVortex2014]

Regarding the hype over strong tornadoes... remember that it isn't just TWC that's talking about it. SPC mentioned it yesterday in their day 4-8 outlook, as did a couple NWS offices. There comes a point where it seems it's likely an inevitable threat, and getting the word out is crucial. I say this as long as they at least hint that we're still almost a week out and things can change... however, a lot is going to have to change to mitigate the threat to the point where strong tornadoes aren't a primary concern. Under almost any other circumstance, I'd be against it... but I don't see this not yielding the threat for strong tornadoes.

[andyhb]

Sheesh, the 500 mb/upper level setup at 00z Wed on the 12z GGEM is basically classic for an I-35 mauling. Its low levels don't make any sense though with SSW winds at the surface (in the face of strong pressure falls east of the dryline).

 

Dprog/dt of the 12z Euro looks like it is slower/stronger especially with the surface low than yesterday's 12z run, doesn't seem to occlude as much as last night's run either.

[brettjrob]

Sheesh, the 500 mb/upper level setup at 00z Wed on the 12z GGEM is basically classic for an I-35 mauling. It's low levels don't make any sense though with SSW winds at the surface (in the face of strong pressure falls east of the dryline).

 

Yeah, I generally disregard the GGEM when it comes to sfc fields and use it primarily for synoptic-scale features. I believe due to the PBL scheme, it is often laughably dry and veered in any severe weather setup, at least around these parts.

 

 

Dprog/dt of the 12z Euro looks like it is slower/stronger especially with the surface low than yesterday's 12z run, doesn't seem to occlude as much as last night's run either.

 

Agreed. It looks more similar to the Wednesday afternoon run. Waiting to see the full fields, but it should at least be a step back in the right direction from the past couple runs.

[RCNYILWX]

Sheesh, the 500 mb/upper level setup at 00z Wed on the 12z GGEM is basically classic for an I-35 mauling. It's low levels don't make any sense though with SSW winds at the surface (in the face of strong pressure falls east of the dryline).

Dprog/dt of the 12z Euro looks like it is slower/stronger especially with the surface low than yesterday's 12z run, doesn't seem to occlude as much as last night's run either.

Agreed on the Euro, the trough is less meridional with excellent speed and directional shear as the surface and 850 mb winds back east of the dryline and 500 mb flow stays west-southwest. Dryline is also much farther west than the 12z run yesterday.

[capbreak]

Not liking those dry 850s punching in from NM/TX and advecting northward up to the warm front. That will cause deep moisture issues and might explain why the 18Z GFS dryline gradient looks so sloppy in the Barber/Pratt County areas.

[andyhb]

Wondering how much the cap is going to remain at bay later in the evening. Soundings would clearly support higher end supercells after dark with the nocturnal intensification of the LLJ and it's not like we're dealing with a pinched warm sector here like 5/10/10 or something like that (nor are we dealing with a setup that would lead to a rapid transition to linear storm mode in most depictions).

[ClicheVortex2014]

Forbes is pulling the trigger, calling for a tornado outbreak on Tuesday and Wednesday. TORCON up to 5 on Tuesday, 4 on Wednesday

 

TUESDAY 4/26

Computer models disagree on how far north and east the severe weather threat will extend. But it looks like at least a limited-area

severe thunderstorm and tornado outbreak will occur in late afternoon through late evening in north, south-central and southeast KS, west MO, extreme southeast NE, northeast and central OK, north-central TX near Wichita Falls. TORCON - 5 south-central and southeast KS, central, northeast and southwest OK; 3 rest of area except 2 southeast NE

 

WEDNESDAY 4/27

Computer models differ again on how far north the surface low and warm front will be. I'll go with a continuation of the severe thunderstorm and tornado outbreak, focused on the Midwest with with isolated severe storms trailing southwest into TX ahead of the cold front. Severe thunderstorms in extreme southeast SD, extreme northeast NE, IA, IL, central and south IN, west half KY, west TN, northwest MS, north LA, northeast quarter of TX, southeast OK, AR, central and east MO. TORCON - 4 southeast IA, northeast MO, north IL; 3 rest of area for now

 

 

[brettjrob]

So the 22/12z ECMWF has completely reversed stance from yesterday, pulling the dryline well W of I-35 and slowing down the shortwave by at least 6-8 hours. Verbatim, it actually does look like the strong tornado threat would be maximized in places like Chickasha/Enid/Harper (obviously the OKC-ICT corridor would still be in serious danger towards 00z).

 

Have to give credit to Stebo for not buying it as the start of a trend yesterday. The ECMWF is clearly struggling with this system right now - certainly possible it will go more progressive in future runs, but a fairly wide range of solutions remain in play.

[Stebo]

So the 22/12z ECMWF has completely reversed stance from yesterday, pulling the dryline well W of I-35 and slowing down the shortwave by at least 6-8 hours. Verbatim, it actually does look like the strong tornado threat would be maximized in places like Chickasha/Enid/Harper (obviously the OKC-ICT corridor would still be in serious danger towards 00z).

 

Have to give credit to Stebo for not buying it as the start of a trend yesterday. The ECMWF is clearly struggling with this system right now - certainly possible it will go more progressive in future runs, but a fairly wide range of solutions remain in play.

Thanks, though with it being one run it wasn't a trend IMO. Models sometimes goof up or ingest bad data leading to funky solutions. When any model does something radically different for no reason it is worth discounting until other models/runs do the same. 

[thewxmann]

I could see the depicted dryline position sloshing back and forth at least a few more times up to the day of the event.

[OKpowdah]

CMC has little change over the last 24 hours, and the synoptic comparison with May 24th is pretty impressive. 

 

[ClicheVortex2014]

Reed Timmer upgraded the tornado threat on Sunday

 

https://warningaware.com/blog/2016/04/22/tornado/

 

Previously, it looked like the moisture return would not yet be sufficient by Sunday east of the dry line for significant severe weather with this lead upper-level shortwave, but now I think that the cap will easily be breached along the dry line well south into western OK by evening.

 

[andyhb]

We don't really need updates on TOR:CON and Reed's site every time (not a shot at you).

[chase_stormz]

CMC has little change over the last 24 hours, and the synoptic comparison with May 24th is pretty impressive. 

 

Screen Shot 2016-04-22 at 2.22.18 PM.png

 

That was a very impressive event...

[andyhb]

That was a very impressive event...

 

Issue with that event is that storms got messy after the first 3 hrs due to issues with the wind profile (and also the fact that too many storms went up off the dryline). Still didn't stop it from producing 4 violent tornadoes (I consider the Canton tornado violent) in OK though.

[chase_stormz]

Issue with that event is that storms got messy after the first 3 hrs due to issues with the wind profile (and also the fact that too many storms went up off the dryline). Still didn't stop it from producing 4 violent tornadoes (I consider the Canton tornado violent) in OK though.

 

Oh the Canton tornado was definitely violent. The motion with it was incredible. You're right though about that event and the storms getting messy after a few hours yet they still were able to produce. From a chasing standpoint it was obviously pretty rough. The two storms that fired after the Piedmont/El Reno EF5 that went on to each produce an EF4 (Chickasha/Blanchard/Newcastle) and (Washington/Goldsby) were fairly discrete and LLJ enhanced. 

[ClicheVortex2014]

We don't really need updates on TOR:CON and Reed's site every time (not a shot at you).

To be fair, it's only posted when there's a change... but point taken.

[andyhb]

12z Euro also looked impressive for the Red River Valley southward into W/Central TX on Friday afternoon/evening. Another broad, neutral/neg tilted, low amplitude shortwave trough with a 60+ kt 500 mb jet streak and strong instability across a broad axis.

[ClicheVortex2014]

DDC
 

.LONG TERM...(Saturday night through Friday)
Issued at 300 PM CDT Fri Apr 22 2016

The CAMs are still indicating storms to break out along the trough
tomorrow evening. Forecast soundings show a mixed profile with considerable
DCAPE. Have the highest pops along the northwestern and spreading to
the northern zones. Roughly Johnson to Hays. Storms could reach to almost
severe levels. Think the main threat is convective outflows of 50 to
60 mph. There might be some hail as well up to 1" as the LHP is forecasting
some higher amounts. The next shot at convection comes Sunday evening.
The NAM backs up the dryline in the evening. The main question is if
storms will form in the first place. The 4 km NAM does have storms just
southeast of Barber county. CAPE and shear will be more significant
and some of the forecast soundings do suggest a low tornado threat for
Barber county as the LLJ strengthens in the 00Z-03Z window. Again, the
main question is if a storm will be there in the first place. LHP values
are supportive of hail size up to baseballs, should a storm develop
Sunday evening. Monday should be a down day as far as convection is
concerned. Attention then turns to Tuesday for storm activity. There
is some trend in NWP data to suggest the dryline and warm front will
be east and north of the forecast district, respectively. The boundaries
will be critical in where the highest tornado threat will be. The 12Z
EC has backed off on the eastward extension of the dryline. Something
to watch over time and see how model trends evolve. Pattern recognition
and analogs still suggest tornadoes and giant hail. Would like to recall
April 14, 2012. Models showed the dryline to the east. On the day of,
the dryline and resultant supercells were much farther west. Again,
something to watch. Bottom line, tornadoes and softball size hail could
easily come into the picture Tuesday evening across portions of Kansas
and Oklahoma. Please keep up to date with the forecast as we can fine
tune all the mesoscale details.

 

[Torchageddon]

Yes. One in 2008 and one in 2012. 

 

I don't remember any D8 in 2012, maybe mistaking that for the D7 pointing to April 14, 2012.

[IllinoisWedges]

I don't remember any D8 in 2012, maybe mistaking that for the D7 pointing to April 14, 2012.

I believe there was one in July.