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

[Stebo]

10 minutes ago, brettjrob said:

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.

I don't see this like 4/26/16 the trough ejection, orientation, and amplitude are all different this time around. To be honest there really isn't a comparison.

Also I am unsure what you mean by the I-40 comment. Are you saying that the warm front could end up north of I-40?

[brettjrob]

14 minutes ago, Stebo said:

I don't see this like 4/26/16 the trough ejection, orientation, and amplitude are all different this time around. To be honest there really isn't a comparison.

Also I am unsure what you mean by the I-40 comment. Are you saying that the warm front could end up north of I-40?

I only said there are a comparable number of caveats for this. I agree that the troughs and setups are not all that similar, at least right now.

As far as the downstream wave for the early week system, I just mean that if it goes back to being more amplified and lingering around the Lakes region longer, the warm front would also go back to yesterday morning's nasty solutions with the warm sector confined to I-40 or worse.

[brettjrob]

Have to admit, this is pure weather porn and needs to be saved for posterity, no matter the outcome.

[Stebo]

5 minutes ago, brettjrob said:

I only said there are a comparable number of caveats for this. I agree that the troughs and setups are not all that similar, at least right now.

As far as the downstream wave for the early week system, I just mean that if it goes back to being more amplified and lingering around the Lakes region longer, the warm front would also go back to yesterday morning's nasty solutions with the warm sector confined to I-40 or worse.

If it is I-40 and south that should be fine too, I don't see the issue there. 

[1900hurricane]

I'm also beginning to become intrigued by Saturday in central Texas. Global guidance is developing a secondary surface low over the Big Bend area that backs surface flow over much of the state. The main speed max stays north of the area, but a well times shortwave may help overcome the often ironclad capping that occurs that far south. Adequate wind fields coupled with impressive CAPE could make things interesting if if storms can initialize and move off the dryline. Of course, I may be a bit biased due to my central Texas location.

 

[andyhb]

At face value, that setup on Saturday on the GFS has a 12/26/2015 or 4/2/1957 look to it at 500 mb.

[bjc0303]

1 hour ago, brettjrob said:

Have to admit, this is pure weather porn and needs to be saved for posterity, no matter the outcome.

even more pure: 

[Superstorm93]

Euro looks very impressive at this range once again. 

[Superstorm93]

European ensembles are actually in pretty great agreement about H5 

 

[Indystorm]

OKC afternoon discussion expecting front to penetrate the Gulf on Wed. but moisture to quickly return on Thurs. and Friday setting the stage for svr for a good portion of OK on Friday and perhaps Sat,

[Will (little rock)]

How is Central Arkansas looking for Wednesday?

 

[Indystorm]

58 minutes ago, Will (little rock) said:

How is Central Arkansas looking for Wednesday?

 

Could be some svr t storms with possible strong tornadoes per NAM model.  Little Rock afternoon discussion says to monitor the situation as Wed. nears.

[jojo762]

16 minutes ago, Indystorm said:

Could be some svr t storms with possible strong tornadoes per NAM model.  Little Rock afternoon discussion says to monitor the situation as Wed. nears.

What makes you think strong tornadoes are possible in AR on wednesday, even on the NAM? I would say there's a solid shot at severe storms with large hail and damaging winds, and perhaps an isolated tornado if a storm is discrete, but things look like they will be linear for the most part. Good deal of model variability in frontal position by 7pm wednesday, which could make a lot of difference in what exactly central Arkansas sees. 

[jameswx]

5 hours ago, Stebo said:

If it is I-40 and south that should be fine too, I don't see the issue there. 

I think Brett is looking at it from a chasing standpoint when he mentions I-40.  It can get dicey down there, especially as you go east.  Not the absolute worst terrain, but certainly not ideal. 

[Stebo]

2 minutes ago, jameswx said:

I think Brett is looking at it from a chasing standpoint when he mentions I-40.  It can get dicey down there, especially as you go east.  Not the absolute worst terrain, but certainly not ideal. 

The best potential is along and west of I-35 right now though, so that wouldn't make sense.

[jameswx]

4 minutes ago, Stebo said:

The best potential is along and west of I-35 right now though, so that wouldn't make sense.

Ah, gotcha......I agree

[brettjrob]

11 minutes ago, Stebo said:

The best potential is along and west of I-35 right now though, so that wouldn't make sense.

I wasn't even thinking about chasing much when I said that. I think we might be overanalyzing a bit on this one. All else being equal, a taller warm sector can only be a good thing. Classic outbreaks like 4/26/91 and 5/24/11 are classics because numerous storms produced sigtors over a wide latitudinal expanse. If the wave responsible for the Tue/Wed threat amplifies to the east, it's a net negative on Friday's setup; I don't think many would dispute that (it reduces the total area of overlap between the jet aloft and rich theta-e at the surface). Doesn't mean you can't still get a substantial threat in TX, but it caps the ceiling of the overall threat some.

[Stebo]

Just now, brettjrob said:

I wasn't even thinking about chasing much when I said that. I think we might be overanalyzing a bit on this one. All else being equal, a taller warm sector can only be a good thing. Classic outbreaks like 4/26/91 and 5/24/11 are classics because numerous storms produced sigtors over a wide latitudinal expanse. If the wave responsible for the Tue/Wed threat amplifies to the east, it's a net negative on Friday's setup; I don't think many would dispute that. Doesn't mean you can't still get a substantial threat in TX, but it caps the ceiling of the overall threat some.

Yeah I get what you are saying, I am just looking at face value of current model trends.

[Indystorm]

40 minutes ago, jojo762 said:

What makes you think strong tornadoes are possible in AR on wednesday, even on the NAM? I would say there's a solid shot at severe storms with large hail and damaging winds, and perhaps an isolated tornado if a storm is discrete, but things look like they will be linear for the most part. Good deal of model variability in frontal position by 7pm wednesday, which could make a lot of difference in what exactly central Arkansas sees. 

72 hr. sig tor parameter sounding NAM on Pivotal showing PDS tor possibilities.  (18z today) 

[Quincy]

1 hour ago, Indystorm said:

72 hr. sig tor parameter sounding NAM on Pivotal showing PDS tor possibilities.  (18z today) 

Severe weather parameters (such as SCP and STP) don't take all factors into consideration. For example, on Tuesday, the SCP is seemingly very favorable for supercells in North Texas, but with warm mid-level temperatures, it's not likely that the cap will be breached in order for deep convection to materialize.

As for central Arkansas on Tuesday, let's briefly analyze the 72hr forecast sounding for KHOT (Hot Springs, AR), which does show a "PDS TOR" sounding with effective STP values over 3.

Notice the flow in the 2-8km layer, which is not only unidirectional, but parallel to the forecast surface boundary. This strongly suggests a forced linear line of convection. Although there is some low level hodograph enlargement (0-1km), the 1km and 6km wind vectors essentially overlap. Also not the poor 0-3km lapse rates below 6 C/km. This is not a sounding for a strong tornado and almost certainly not a sounding for discrete supercells, although QLCS-type spinups would certainly be possible.

[1900hurricane]

1 hour ago, Indystorm said:

72 hr. sig tor parameter sounding NAM on Pivotal showing PDS tor possibilities.  (18z today) 

The environment in Arkansas does technically meet all the criteria for a PDS Tor forecast sounding this model run, but there are some things that do jump out as immediate negatives in the modeled scenario. Perhaps the most notable is the the extreme section of backing winds with height between 850 and 700 mb, leading to a looping hodograph. Such a wind profile is not very good for maintaining mesocyclones, and often leads to messy storms and clusters/lines. Storms may also be limited to right on the frontal convergence. It's not impossible for a strong tornado to occur, but I would have my doubts that one would actually transpire given the mitigating factors. It might not hurt to keep an eye on it as it draws closer though.

 

 

*EDIT: The things Quincy said above also apply.

[Indystorm]

Good to learn caveats even with soundings.  Thanks, guys.

[Jim Martin]

0z NAM not very impressive for Arkansas on Wednesday.

[vwgrrc]

6 hours ago, Superstorm93 said:

European ensembles are actually in pretty great agreement about H5 

 

Does this mean a big event for the DFW metro later this week?

[andyhb]

Well that 00z GFS run was an exercise in mitigating every day in this stretch essentially.

[CGChaser]

4 minutes ago, andyhb said:

Well that 00z GFS run was an exercise in mitigating every day in this stretch essentially.

And very plausible as well. Though as we see w/ every storm, we're merely just gauging threat days until we're <84hrs to the event when models finally start to converge.

[Superstorm93]

Oof...00z GFS has dews in the 40's across OK and TX at 12z Friday. 

That front on Wednesday/Thursday really clears the Gulf too. Vectors take a while to recover. 

[jojo762]

Yeah front dove further south this run, and SFC winds took several more hours to recover to southerly... not gonna make a big deal out of it though... we'll see what the king says in a couple hours. 

[weatherextreme]

[WhiteoutWX]

Well Friday's threat went south quickly last night. Anyone with better Euro access care to comment? The crappy maps I'm seeing make it look like the warm front barely makes it to the Red River by Friday evening.