Late April severe weather risk ~Mon thru next Mon 4/24-5/01

[David Reimer]

1 hour ago, jameswx said:

Everybody loves a smartass

 

12 minutes ago, Stebo said:

Agreed, unnecessary to post that by him

Meh, better get used to the harsh reality of storm chasing humor if you plan on being out much. If you can't take a sarcastic jest then I suggest y'all not attend the more 'hard core' chaser gatherings.

Meanwhile... FWIW the 12Z CIPS analogs were pinpointing at a higher potential for severe on Tuesday. Graphic is for 10 or more severe reports. 

 

[CGChaser]

6 minutes ago, David Reimer said:

 

Meh, better get used to the harsh reality of storm chasing humor if you plan on being out much. If you can't take a sarcastic jest then I suggest y'all not attend the more 'hard core' chaser gatherings.

Meanwhile... FWIW the 12Z CIPS analogs were pinpointing at a higher potential for severe on Tuesday. Graphic is for 10 or more severe reports. 

 

Been saying this for the past day despite more hype end of the week. Both GFS/Euro initiate. If moisture can return.

[bjc0303]

2 minutes ago, CGChaser said:

Been saying this for the past day despite more hype end of the week. Both GFS/Euro initiate. If moisture can return.

not looking likely 

[CGChaser]

1 minute ago, bjc0303 said:

not looking likely 

Ya not sure what I'm saying. Good point!

[Stebo]

41 minutes ago, David Reimer said:

 

Meh, better get used to the harsh reality of storm chasing humor if you plan on being out much. If you can't take a sarcastic jest then I suggest y'all not attend the more 'hard core' chaser gatherings.

Meanwhile... FWIW the 12Z CIPS analogs were pinpointing at a higher potential for severe on Tuesday. Graphic is for 10 or more severe reports. 

 

Humor tends to actually be funny...

[Stebo]

32 minutes ago, bjc0303 said:

not looking likely 

What part? Moisture return late in the week should be fine unless the models get dramatically worse.

[CGChaser]

00z shows the volatility of this even. Slight change in timing. General idea is consistent Thursday/Friday thread somewhere, maybe not from chasing standpoint, but meteorologically

[brettjrob]

lol, 00z GFS is back to an I-35 outbreak scenario for Friday. Buckle up for at least the next couple days of models.

[jojo762]

Just now, brettjrob said:

lol, 00z GFS is back to an I-35 outbreak scenario for Friday. Buckle up for at least the next couple days of models.

Had to figure that models were going to be hot or cold for the next few days. There was no way we were getting off that easily with a synoptically obvious severe threat and nearly perfect model runs. Interested to see what euro shows now for Friday, as that was originally its big day.

[Stebo]

5 minutes ago, CGChaser said:

00z shows the volatility of this even. Slight change in timing. General idea is consistent Thursday/Friday thread somewhere, maybe not from chasing standpoint, but meteorologically

 

2 minutes ago, brettjrob said:

lol, 00z GFS is back to an I-35 outbreak scenario for Friday. Buckle up for at least the next couple days of models.

Yeah all that was needed was a bit of wave spacing between Tuesday/Wed and Friday/Saturday and we end up with a high end potential again.

[bjc0303]

18 minutes ago, Stebo said:

What part? Moisture return late in the week should be fine unless the models get dramatically worse.

Tuesday.

 

And yeah I think most of the pessimistic crowd including myself already stated that subtle changes aloft would lead to huge changes in surface feature placement. Thursday gets wiped out by a cold front surge Wednesday and we, thankfully, hold off on substantial cyclogenesis until Friday... yielding the 00z. 18z, 12z and 6z did not. 

[Stebo]

1 minute ago, bjc0303 said:

Tuesday.

 

And yeah I think most of the pessimistic crowd including myself already stated that subtle changes aloft would lead to huge changes in surface feature placement. Thursday gets wiped out by a cold front surge Wednesday and we, thankfully, hold off on substantial cyclogenesis until Friday... yielding the 00z. 18z, 12z and 6z did not. 

I don't see Tuesday as a huge potential but I would still say it could be decent if moisture does return.

[bjc0303]

"if it returns" but moisture looks pretty limited for tornado potential. 

[jojo762]

Honestly moisture verbatim on the 00Z GFS/NAM looks fine for Tuesday to me. Honestly I'd be more concerned about CI actually occurring as the cap looks fairly stout and neither the GFS nor the NAM convect despite the impressive 70kt H5 jetcore punching into the most favorable parameter space in the warm sector in C/E OK at 00z. 

[Stebo]

1 minute ago, jojo762 said:

Honestly moisture verbatim on the 00Z GFS/NAM looks fine for Tuesday to me. Honestly I'd be more concerned about CI actually occurring as the cap looks fairly stout and neither the GFS nor the NAM convect despite the impressive 70kt H5 jetcore punching into the most favorable parameter space in the warm sector in C/E OK at 00z. 

Yeah mid to upper 60s on both along with the 12z Euro. The 850mb temps would be the issue I would have with Tuesday.

[bjc0303]

I must have misremembered or looked at outdated stuff because Tuesday looked like a typical low tornado potential day due to high T/td spreads and capping. 

[Stebo]

1 minute ago, bjc0303 said:

I must have misremembered or looked at outdated stuff because Tuesday looked like a typical low tornado potential day due to high T/td spreads and capping. 

The T/Td spreads could be a touch better but they aren't absolutely terrible. The capping though is an issue at this point.

[jojo762]

00Z Euro isn't quite fast enough with the wave for Friday, so cyclogenesis occurs a tad too late, low-level winds aren't ultra impressive during prime-time as a result, and moisture doesn't get as far north as the GFS... but still shows what would appear to be at least some potential on Friday. Saturday would feature at least some potential as well.

[Stebo]

12 minutes ago, jojo762 said:

00Z Euro isn't quite fast enough with the wave for Friday, so cyclogenesis occurs a tad too late, low-level winds aren't ultra impressive during prime-time as a result, and moisture doesn't get as far north as the GFS... but still shows what would appear to be at least some potential on Friday. Saturday would feature at least some potential as well.

It does have an absurd amount of CAPE starting at 18z and especially 00z Saturday over most of OK. 3500-4500 J/kg.

[weatherextreme]

New outlook text (Updated maps are edited on the first post)  

 

The ECMWF and GFS solutions are in good agreement on Wednesday/Day
   4, moving an upper-level trough across the southern and central
   Plains. At the surface, a cold front is forecast to move into the
   mid Mississippi Valley. Strong to severe thunderstorms are expected
   to develop along the front from central Arkansas into southeast
   Missouri during the late afternoon and early evening.

   ...Thursday/Day 5...
   The ECMWF and GFS solutions move the cold front into the central
   Appalachians extending back southwestward into the Tennessee Valley.
   A marginal severe threat will be possible along parts of the front
   Thursday afternoon.

   ...Friday/Day 6...
   The ECMWF and GFS solutions are in better agreement for Friday/Day
   6, moving an upper-level low in the Four Corners region as a
   mid-level jet rounds the base of the system. Strong moisture
   advection is forecast to take place in the southern Plains where
   both solutions show a well-developed dryline by late afternoon. As
   the exit region of the mid-level jet moves out into the southern and
   central Plains late Friday afternoon, thunderstorms should develop
   along the dryline and move eastward across parts of Kansas and
   Oklahoma. The mid-level jet is forecast to couple with the low-level
   jet creating deep-shear profiles favorable for supercells,
   tornadoes, large hail and damaging wind gusts. A higher-end severe
   weather event could occur Friday afternoon and evening in the
   southern and central Plains. For this reason, have added a 30
   percent contour inside the original 15 percent contour.

...Saturday/Day 7...
   The medium-range models move the upper-level system across the
   central Rockies on Saturday/Day 7 as the mid-level jet core ejects
   northeastward across the southern and central Plains. Thunderstorms
   are expected to develop across much of the region due to strong
   large-scale ascent associated with the upper-level trough. This
   along with moderate instability and strong deep-layer shear should
   be enough for a severe weather event across parts of the southern
   and central Plains, where a 15 percent contour has been added.

   ..

[1900hurricane]

I'd say the 00Z suite in general looks very robust for Friday. The GFS/GEFS/ECMWF/EPS/UKMET all appear to be in relatively good agreement with the trough positioning and rapidly deepening a surface low in the vicinity of the Texas Panhandle. With rich Gulf moisture overtopped by impressive lapse rates, strong wind fields, and backing isallobaric flow. The CAPE/shear combo has the potential to be very high end (not that anyone didn't know that already).

 

 

 

[Quincy]

Thoughts on early in the period, as models seem to be in fairly good agreement through Wednesday:

 

Monday - Probably no robust convection. Despite a surface low developing and moving into the OK/TX panhandle vicinity during peak heating and an EML producing steep to very steep lapse rates across the southern High Plains, inadequate low-level moisture return and large T/Td spreads through the boundary layer should offset any realistic potential and severe. Can't completely rule out a rogue cell trying to go up just ahead of the dryline, but the potential is close to zero. 

 

Tuesday - Likely the first in a series of greater threats across the region. With that said, it has its own issues too. A frontal system is progged to drop through the Plains to lower Missouri Valley during the afternoon. Models converge on the most convection firing in the southeastern KS/northeastern OK/western MO area. Despite modest instability, deep shear vectors should align largely parallel to a surface boundary, suggesting mixed/messy storm modes and clustering of convection. The EML plume outruns the front, as mid-level lapse rates become less favorable with time. Capping becomes a greater concern with southward extent. Despite a seemingly favorable CAPE/shear overlap into central/southeastern OK and adjacent North TX, warm air in the mid-levels should work to make any severe threat in this area highly conditional.

 

Wednesday - The frontal system moves east into the Mississippi Valley region. Some severe threat may materialize from the middle MS Valley, southeastward into the Arklatex vicinity. Like Tuesday, shear vectors continue to be more or less parallel to the surface front, but guidance does suggest backing of low level wind fields in the open warm sector with modest 0-1km hodographs. The main issue is that considerable convection may fire along and just ahead of the front during the afternoon, favoring more of a squall line with time. Should any discrete convection be able to form farther east, then supercells would appear possible.

[Superstorm93]

The 12z GFS severe parameters over OK on Friday look like something the NAM would try and pull. 

Impressive to say the least. 

 

[Jim Martin]

7 minutes ago, Superstorm93 said:

The 12z GFS severe parameters over OK on Friday look like something the NAM would try and pull. 

Impressive. 

 

Oklahoma City, Oklahoma sounding for Friday evening. To what Superstorm93 is referring to...

 

[jojo762]

Found an STP of 18.5 on the 12Z GFS in central OK... pretty sure that'd be a record, definitely one of the higher (if not the highest) model parameter outputs I've ever seen. Unseasonably strong CAPE (by April standards), unseasonably impressive low-level moisture (on the upper-end of the scale for late-April), highly impressive low-level wind-fields and impressive deep-layer winds as well... nasty combo of ingredients coming together per the last three GFS runs in addition to other previous runs. Was a tad surprised that SPC pulled the gun on the 30% probabilities for D6 given some run-to-run variability, but also not surprised given who issued the outlook. 

[WhiteoutWX]

GFS looks good for Friday but it can't really afford to be much slower with the trough. Mid level flow is a somewhat late arrival as is and any slower with the wave and upper level support for convection may be too weak to overcome the cap. 

[bjc0303]

I probably would have done so myself as well, so I'm not exactly surprised.

[andyhb]

Not reposting the graphic, but the 12z Euro has most of Oklahoma under some pretty incredible parameters by 00z Sat thanks to a 40-50 kt LLJ and some exceptional backing of the low level flow. Timing will obviously modulate the degree of initiation that occurs on Friday given the current setup, but it's worth noting that there are bound to be subtle shortwaves leaking ahead of the main trough that should encourage initiation if moisture reaches anywhere near the levels it is projected to.

The fact that the trough doesn't just blast right through the warm sector would probably portend a mostly discrete, isolated storm mode, which would of course imply serious problems with the parameter space that is presented.

[brettjrob]

To be fair, I these kind of parameters (12+ EHI, etc.) have featured on the medium-range GFS for at least a handful of other events from past years that we're repressing due to PTSD (e.g., April 26, 2016).

I'm pleasantly surprised at trends since yesterday morning, particularly on the Euro. Guidance is beginning to settle into a legitimate but flawed threat -- perhaps with a comparable number of caveats as 4/26/16 had at this range, but they're different this time. The lead wave from Tue/Wed is still a concern; it wouldn't take much more amplification to keep the warm front Friday from lifting north of I-40. The other major concern looks to be late timing and related capping. Having the H5 trough axis well W of the Four Corners at 00z Sat is not ideal, and the timing will have to speed up considerably for this to evolve into a textbook outbreak with the main forcing arriving Friday afternoon. All that said, unless the downstream system starts to re-amplify a lot on future guidance, this will no doubt be a setup that keeps us all on the edges of our seat this week.

[Stebo]

I think it is safe to say at this junction that the 12Z model suite from yesterday was an outlier compared to everything else. Not saying it can't revert back to that but at this point trends have moved away from that considerably.