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

[Radtechwxman]

0z nam doesn't attempt any CI till 06z. And what it does fire is north of front. So we got nam vs. every other model. I hate to be a pessimist but it also looked bad in Iowa last week while every other model looked great and it ended up being right. That late arriving llj or lack of one period is a huge caveat. Honestly if we had that it would help fire storms earlier and greatly enhance low level shear

[Quincy]

10 minutes ago, StormChaser4Life said:

0z nam doesn't attempt any CI till 06z. And what it does fire is north of front. So we got nam vs. every other model. I hate to be a pessimist but it also looked bad in Iowa last week while every other model looked great and it ended up being right. That late arriving llj or lack of one period is a huge caveat. Honestly if we had that it would help fire storms earlier and greatly enhance low level shear

The fact that the SREFs have such low probabilities (for convective precipitation in a favorable CAPE/shear environment) as well is a big red flag. These only improve slightly by 03-06z after this 00z SAT forecast image:

[brettjrob]

10 minutes ago, StormChaser4Life said:

0z nam doesn't attempt any CI till 06z. And what it does fire is north of front. So we got nam vs. every other model. I hate to be a pessimist but it also looked bad in Iowa last week while every other model looked great and it ended up being right. That late arriving llj or lack of one period is a huge caveat. Honestly if we had that it would help fire storms earlier and greatly enhance low level shear

I wouldn't worry about the NAM QPF in a situation like this. Its convective parameterization scheme is notoriously unreliable in Plains environments with dry air aloft.

Watching the 00z NAMs come in, dProg/dt is in the right direction, albeit small in magnitude. The 3-km nest, in particular, is veering surface flow across OK noticeably faster during the afternoon than the last couple runs, which means it's trending toward the global models. The fact that it doesn't show any convection before 03z is somewhat more concerning than the 12-km variant, but if the NAM is still in the process of correcting its representation of the shortwave toward the global models, it's not all that meaningful. Soundings W and NW of DFW at 00z show very little capping where EHI is maximized at the NW edge of the warm sector.

I know continuing to pin my hopes on Friday for a solid chasing opportunity is more likely than not to end in sorrow, but it looks like it'll be a long while until the next one, so might as well.

[Stebo]

1 minute ago, brettjrob said:

I wouldn't worry about the NAM QPF in a situation like this. Its convective parameterization scheme is notoriously unreliable in Plains environments with dry air aloft.

Watching the 00z NAMs come in, dProg/dt is in the right direction, albeit small in magnitude. The 3-km nest, in particular, is veering surface flow across OK noticeably faster during the afternoon than the last couple runs, which means it's trending toward the global models. The fact that it doesn't show any convection before 03z is somewhat more concerning than the 12-km variant, but if the NAM is still in the process of correcting its representation of the shortwave toward the global models, it's not all that meaningful. Soundings W and NW of DFW at 00z show very little capping where EHI is maximized at the NW edge of the warm sector.

I know continuing to pin my hopes on Friday for a solid chasing opportunity is more likely than not to end in sorrow, but it looks like it'll be a long while until the next one, so might as well.

Yeah we have seen this song and dance before in the plains with the NAM having poor convective initialization. Considering the amount of moisture advection into the warm front, I would be shocked if the NAM was correct. Also as you mention the trend in moisture return is favoring the global models, another tick or two in the right direction and Friday could be huge.

[Radtechwxman]

1 minute ago, brettjrob said:

I wouldn't worry about the NAM QPF in a situation like this. Its convective parameterization scheme is notoriously unreliable in Plains environments with dry air aloft.

Watching the 00z NAMs come in, dProg/dt is in the right direction, albeit small in magnitude. The 3-km nest, in particular, is veering surface flow across OK noticeably faster during the afternoon than the last couple runs, which means it's trending toward the global models. The fact that it doesn't show any convection before 03z is somewhat more concerning than the 12-km variant, but if the NAM is still in the process of correcting its representation of the shortwave toward the global models, it's not all that meaningful. Soundings W and NW of DFW at 00z show very little capping where EHI is maximized at the NW edge of the warm sector.

I know continuing to pin my hopes on Friday for a solid chasing opportunity is more likely than not to end in sorrow, but it looks like it'll be a long while until the next one, so might as well.

Good points Quincy. Nam has definitely been more east of other models. And I totally understand Brett, I'm feeling the same way but harder for me justifying a 10+ drive for a conditional tornado threat. Obviously if I lived in OK no doubt I would chase this. If Sat trended less linear and messy I would bite on it because if Fri busts I got Sat. But as you stated no good setups in the near future

[1900hurricane]

Here's a few dProg/dt chats I pulled for 00Z Saturday from the NAM:

 

 

[brettjrob]

Canadian RDPS has come into range for Fri and looks much like the GDPS/Euro, with the WF up to I-40 and a decent LLJ over much of the warm sector. Given its resolution is similar to the NAM, I'm leaning more toward the NAM being out to lunch for now.

[1900hurricane]

The 00Z NAM is also spitting out some pretty ridiculous 0-3 km CAPE over east Texas Saturday afternoon and evening thanks to modeled surface temperatures and dewpoints around 80*F (example). Color me skeptical.

[Radtechwxman]

7 minutes ago, brettjrob said:

Canadian RDPS has come into range for Fri and looks much like the GDPS/Euro, with the WF up to I-40 and a decent LLJ over much of the warm sector. Given its resolution is similar to the NAM, I'm leaning more toward the NAM being out to lunch for now.

Not use to you being so optimistic, haha, esp with a setup with quite a few caveats. But that's certainly a good sign because the LLJ was my biggest fear. Moisture looks good on all models. CI looks probable. I'm just wondering how long of a tornado threat there will be with this occurring late and CIN setting in after dark. Will storms remain surface based or go elevated? Def not a slam dunk but at least most models are trending up

[bjc0303]

At least near the warm front there certainly seems potential for storms to remain surface based within a strong WAA regime overnight.

[CGChaser]

00z gfs remaining consistent with decent LLJ kicking in sooner than NAM and initation along RRV before 00z.

[Radtechwxman]

4 minutes ago, CGChaser said:

00z gfs remaining consistent with decent LLJ kicking in sooner than NAM and initation along RRV before 00z.

Hard to ignore its consistency the last several runs. Somewhere near or just east of Wichita Falls looks good for CI on Fri. Great moisture and cape. Nice backed surface flow east of TP. 850 weakness continues to be my concern but gfs looks far better than nam. Like night and day. If stuff goes it will be explosive. Trough looks more east on this run than before

[Quincy]

47 minutes ago, brettjrob said:

Canadian RDPS has come into range for Fri and looks much like the GDPS/Euro, with the WF up to I-40 and a decent LLJ over much of the warm sector. Given its resolution is similar to the NAM, I'm leaning more toward the NAM being out to lunch for now.

Limited forecast sounding sites, but here are OKC (near warm front) and DFW (very large buoyancy) at 00z SAT:

[brettjrob]

1 hour ago, StormChaser4Life said:

Not use to you being so optimistic, haha, esp with a setup with quite a few caveats. But that's certainly a good sign because the LLJ was my biggest fear. Moisture looks good on all models. CI looks probable. I'm just wondering how long of a tornado threat there will be with this occurring late and CIN setting in after dark. Will storms remain surface based or go elevated? Def not a slam dunk but at least most models are trending up

Yeah, there are plenty of caveats/weaknesses that still relegate this to a run-of-the-mill late April setup, for now. I'm just increasingly skeptical of the NAM scenario where cyclogenesis is slow and meager enough to ruin the whole surface map. If the Euro and Canadian prove to have the right idea on the large scale, I can still see the cap posing a hindrance to getting multiple storms that traverse the open warm sector S of the frontal zone.

EDIT: Well, now that I see what the 00z NCEP HRW runs want to do with the surface fields, I'm back to fearing the NAM may score another coup. Saggy frontal zone that refuses to budge out of N TX. Wouldn't eliminate any tornado threat, but would confine it to E TX and the Arklatex... because we haven't seen that enough this spring.

[jojo762]

17 minutes ago, brettjrob said:

Yeah, there are plenty of caveats/weaknesses that still relegate this to a run-of-the-mill late April setup, for now. I'm just increasingly skeptical of the NAM scenario where cyclogenesis is slow and meager enough to ruin the whole surface map. If the Euro and Canadian prove to have the right idea on the large scale, I can still see the cap posing a hindrance to getting multiple storms that traverse the open warm sector S of the frontal zone.

Still important to remember that it only takes one storm/tornado to change one's entire perspective of a day. 

[CGChaser]

For what it's worth.. majority of GEFS members initiate down along RRV before 00z.

[Chinook]

Alright, this might sound dumb. The 3km NAM at 48 hrs (00z Saturday) has crazy CAPE in Texas,  weakening MLCINH near the Red River, and no storms, except for some nighttime storms in OK and AR, pretty far north. There must be some storm in Texas, (or extremely close to the Red River,) right?

[weatherextreme]

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Reed Timmer‏ @ReedTimmerAccu  2h2 hours ago

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Holy cow does Saturday look significant for severe weather in northeast Texas. Good heavens

[jojo762]

2 minutes ago, weatherextreme said:

Latest from Reed Timmer

 

Reed Timmer‏ @ReedTimmerAccu  2h2 hours ago

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Holy cow does Saturday look significant for severe weather in northeast Texas. Good heavens

I still have some issues with Saturday, but potential is there for something...  I'm interested to see SPC's take in the D3. 

[jojo762]

Not very many changes to the outlook for Friday. SPC outlining concern about if CI will occur near the triple point or along the warm front before dark... more concerned about severe threat after dark it would appear as numerous storms will fire off. Highlighting risk for large to very large hail, and a few tornadoes.

[thewxmann]

FWIW, for severe wx the NAM is absolutely elite within 48 hours, even over global models that have consistent solutions (an example: April 2013). If the NAM continues with its solution in the 12Z run, consider the LLJ and the tornado threat for Friday nuked.

My best guess as to what's happening here is that convection in the mid-Mississippi Valley has a "tug" on the LLJ that keeps its axis veered off to the east. The globals aren't properly resolving the convection, so they're prematurely backing the LLJ to the west. Given the weak and delayed cyclogenesis off to the west and the anafrontal nature of this setup, I'd side with the NAM scenario.

I'll also have to take back what I said earlier about CI since it *does* look now like the embedded impulse that we need to trigger convection is about 3-6 hours too late.

All in all, I'd be beyond shocked if Friday even verifies an enhanced risk at this point.

[andyhb]

3 minutes ago, thewxmann said:

FWIW, for severe wx the NAM is absolutely elite within 48 hours, even over global models that have consistent solutions (an example: April 2013). If the NAM continues with its solution in the 12Z run, consider the LLJ and the tornado threat for Friday nuked.

My best guess as to what's happening here is that convection in the Ohio Valley has a "tug" on the LLJ that keeps its axis veered off to the east. The globals aren't properly resolving the convection, so they're prematurely backing the LLJ to the west.

I'll also have to take back what I said earlier about CI since it *does* look like the embedded impulse that we need to trigger convection is about 3-6 hours too late.

All in all, I'd be beyond shocked if Friday even verifies an enhanced risk at this point.

What does this even mean to be fair?

The dprog/dt of the NAM has been showing a tendency to shift slowly towards the global models with the low level jet further west as illustrated earlier by Ryan's (1900hurricane) gif.

[Stebo]

1 minute ago, thewxmann said:

FWIW, for severe wx the NAM is absolutely elite within 48 hours, even over global models that have consistent solutions (an example: April 2013). If the NAM continues with its solution in the 12Z run, consider the LLJ and the tornado threat for Friday nuked.

My best guess as to what's happening here is that convection in the mid-Mississippi Valley has a "tug" on the LLJ that keeps its axis veered off to the east. The globals aren't properly resolving the convection, so they're prematurely backing the LLJ to the west.

I'll also have to take back what I said earlier about CI since it *does* look like the embedded impulse that we need to trigger convection is about 3-6 hours too late.

All in all, I'd be beyond shocked if Friday even verifies an enhanced risk at this point.

The NAM in the Plains has a tendency to be terrible especially in situations like this. It also is by far the weakest with the LLJ due to its terrible low evolution.

As for Friday, it will verify an enhanced risk, I guarantee that. Models explode convection after 00z that would be severe with very large hail and winds at the very least over a large area. That would verify an enhanced risk easily if that projection is correct.

[thewxmann]

4 minutes ago, andyhb said:

What does this even mean to be fair?

The dprog/dt of the NAM has been showing a tendency to shift slowly towards the global models with the low level jet further west as illustrated earlier by Ryan's (1900hurricane) gif.

What it means- convection fires off in the mid-Mississippi Valley on Friday. Convection tends to pull low-level flow towards it. That effect is usually not very significant, but without strong cyclogenesis over W TX, it may just be enough to delay the LLJ backing back towards N/NW TX.

Regarding the NAM- it's looks like to me that it's been jumping around. Not much of a strong, sustained trend. I guess the latest run does look a little better, but I'll have to wait a few more runs before acknowledging that as a real trend.

[Stebo]

Also if we are considering the NAM being elite, we would have had a few tornado outbreaks and hell today would have been much bigger than it was. It busted on today in several ways.

[thewxmann]

8 minutes ago, Stebo said:

The NAM in the Plains has a tendency to be terrible especially in situations like this. It also is by far the weakest with the LLJ due to its terrible low evolution.

As for Friday, it will verify an enhanced risk, I guarantee that. Models explode convection after 00z that would be severe with very large hail and winds at the very least over a large area. That would verify an enhanced risk easily if that projection is correct.

What do you even mean the NAM is terrible in situations like this? I mentioned April 2013 -- do you have a counterexample?

Hail *might* verify the enhanced, but a lot of convection Friday night is anafrontal in nature which gives me pause about considering having a cluster of large hailers. Winds are not likely to be as significant of a threat given the high PWAT's and the elevated nature of the Fri night storms.

[andyhb]

5 minutes ago, thewxmann said:

What it means- convection fires off in the mid-Mississippi Valley on Friday. Convection tends to pull low-level flow towards it. That effect is usually not very significant, but without strong cyclogenesis over W TX, it may just be enough to delay the LLJ backing back towards N/NW TX.

Regarding the NAM- it's looks like to me that it's been jumping around. Not much of a strong, sustained trend. I guess the latest run does look a little better, but I'll have to wait a few more runs before acknowledging that as a real trend.

On the mesoscale. We're looking much more at the synoptic scale here when you refer from the Mid-Mississippi/Ohio Valleys back towards the Plains.

If you're looking for something that could veer the low level jet like the NAM has, it would be the passage of the lead 500 mb shortwave to the north on Thursday evening/Friday morning encouraging early pressure falls.

April 2013 (I'm assuming you're talking April 17) was an intense, anafrontal, surging cold front. None of guidance has anything like that on Friday regardless of the extent of the warm frontal retreat/LLJ characteristics/etc. You're going to have to do a bit better than that IMO if we're talking similar setups.

[Stebo]

Just now, thewxmann said:

What do you even mean the NAM is terrible in situations like this? I mentioned April 2013 -- do you have a counterexample?

Hail *might* verify the enhanced, but a lot of convection Friday night is anafrontal in nature which gives me pause about considering having a cluster of large hailers. Winds are not likely to be as significant of a threat given the high PWAT's and the elevated nature of the Fri night storms.

Yes April 2012 is the counter example, the NAM consistently showed nothing through the day because of a late ejection, ended up being completely wrong.

Friday night isn't an anafront, what are you talking about... There isn't an anafrontal interaction until Saturday morning on the NAM and Saturday afternoon on everything else. I mean you are just throwing darts at a dart board at this point.

[thewxmann]

9 minutes ago, Stebo said:

Also if we are considering the NAM being elite, we would have had a few tornado outbreaks and hell today would have been much bigger than it was. It busted on today in several ways.

What are you talking about? NAM hinted at VBV and had SSW 500mb flow superimposed on top of S sfc flow with a sharp trof axis and a NNE-SSW oriented boundary. If I said that and nothing about CAPE or SRH values you'd scoff at me for even mentioning an outbreak.

[brettjrob]

Up-too-late musings: situations where the models break into these camps regarding frontal position are among the most frustrating short-range problems in convective forecasting. The event wxmann alluded to (2013-04-17) definitely comes to mind. When you look at the past 4-6 runs of the ECMWF, and especially considering that it only got more bullish about lifting the WF well into OK on tonight's run, it's hard to believe it will be 100-150+ mi. off on synoptic-scale features at this range (e.g., if the HRW runs verify on the frontal position at 00z Sat). It is, after all, the elite global model.

It's true that in the 2013 event, the global models were embarrassingly overzealous about lifting the WF (which pretty much ended up just being a CF). The Euro was bad, and the GFS was just disastrous, trying to pull it up to I-70 in KS. But that day also had legitimately chilly air trying to ooze down the southern High Plains. This one is still a tough call, to me, because it's not like the airmass progged over W OK and the TX PH during the day is even cold. Overall, it's a very different synoptic situation, with the only commonality being that the global models may be underestimating the push of cool air out west. I don't recall what the RDPS had in 2013, but the fact that it's worlds apart from the NAM is the one thing that gave me hope out of tonight's suite.

Ultimately, when the camps break down like this, the "cold air wins" camp virtually always has something to say about reality. So, for now, I'd go with a compromise that's not too far off from the 3-km NAM. Unfortunately, even that compromise is likely flawed enough to make the daytime threat pretty low key (at least W of the Arklatex/Ozarks).