April 13 Severe Threat - TX, OK, LA, ARK, KS, MO, IA

[jojo762]

12Z NAM seems to want to veer surface winds a bit to either just slightly west of due south OR due south across eastern KS (and along pretty much the entire dryline), not sure im buying it, but that would greatly hinder tornado potential. 12Z GFS also wants to do the same with surface flow. Need surface winds to be at least slightly south-southeasterly to maximize tornado potential with this setup.

[Chinook]

Not sure if anybody is discussing this... There may be a chance for supercell tornadoes/ QLCS tornadoes near the Gulf Coast on Saturday. Right now, the models show the best instability in the southern 2/3rds of Alabama and Mississippi. SPC has already put out an enhanced risk for this area. 

[yoda]

New Day 2 OTLK from SPC is late...

[jojo762]

7 minutes ago, yoda said:

New Day 2 OTLK from SPC is late...

Nearly 20 minutes late already. Which is VERY late for an SPC outlook. Anecdotally i've found that late outlooks don't necessarily equate to outlook changes/upgrades.

[yoda]

 

[yoda]

 Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1250 PM CDT Thu Apr 12 2018

   Valid 131200Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PARTS OF
   SOUTHERN IA TO NORTHEAST TX AND NORTHERN LA...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   ENHANCED FROM IA AND SOUTHEAST NE TO EAST TX AND THE LOWER
   MISSISSIPPI VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
   SLIGHT FROM FAR SOUTHERN MN TO THE NORTHWEST GULF COASTAL REGION...

   ...SUMMARY...
   Strong/severe storms are expected to develop Friday afternoon and
   continue into the overnight hours extending from Iowa and part of
   the middle Missouri Valley southward across the Arklatex region, and
   lower Mississippi Valley.  All severe hazards are possible with very
   large hail and a few tornadoes, one or two of which could be strong,
   being the primary threats.

   ...Synopsis...
   An upper trough moving through and amplifying across the western
   states into the Rockies during D1, will undergo further
   amplification Friday into Friday night across much of the central
   United States.  An embedded closed low, likely forming by the start
   of D2 across the central Rockies, is expected to deepen as it tracks
   through the central Plains toward the mid Missouri Valley. 
   Meanwhile, an upstream shortwave trough digging southeast through
   AZ/NM to far west TX and northern Mexico by later Friday night will
   aid in the expected amplification of the central Plains parent
   trough.

   Given the slow eastward shift of the large closed mid-upper level
   low, the associated surface low is forecast to move from near the
   north-central KS/NE border into southeast NE to near Omaha, where it
   should occlude Friday night.  By mid-late Friday afternoon, a warm
   front will extend east across IA (generally in vicinity of I-80),
   while a cold front trails southwest from the low into south-central
   KS to western OK and the TX Panhandle.  A dryline, mixing eastward,
   is expected to extend south from a secondary low near ICT through
   east-central OK into central TX Friday afternoon.  The cold front is
   expected to sweep east Friday night toward the middle and lower
   Mississippi Valley.

   ...Eastern NE/IA to northern and western MO/eastern KS...
   The Enhanced and Slight risk area, including the significant severe
   potential, have been expanded north across northern MO, more of IA
   and eastern NE, given run-to-run consistencies and confidence of the
   ECMWF and NAM continuing to show the warm front moving into southern
   IA before the start of D2.  

   An increasingly favorable environment for severe storms is forecast
   to evolve during the day Friday, across the northern extent of the
   warm sector, ahead of the advancing cold front.  As the deepening
   upper system shifts slowly eastward, a very strong deep-layer wind
   field will overspread the evolving warm sector.  Diurnal heating
   combined with low-level moistening beneath cooling mid-level
   temperatures will result in moderate destabilization during the
   afternoon, with MUCAPE up to 1500-2000 J/kg from eastern KS to
   southeast NE and southern IA. 

   Operational and CAM output suggest discrete storm development will
   occur by late afternoon near the southeast NE low and southward
   along the cold front and dry line.  These storms will track quickly
   to the north-northeast as strengthening deep-layer wind fields
   spread across the warm sector.  The environment will support
   strong/rotating updrafts, with very large hail and a tornado threat
   expected.  A strong tornado or two will be possible, especially
   across parts of northern MO into southern IA.  Farther north, very
   steep midlevel lapse rates associated with the EML suggest hail,
   some very large, will be possible north of the warm front, with a
   marginal risk extending into far southern MN.  

   ...Rest of MO to Arklatex, east TX and lower Mississippi Valley...
   Although stronger forcing for ascent is not expected to spread
   across the southern extent of the D2 severe risk areas until Friday
   night, a modifying warm sector becoming moderately unstable and
   strongly sheared will support strong to severe storms from Friday
   afternoon into the overnight.  Mixed-layer CAPE up to 2500 J/kg
   suggests sustained updrafts will be likely with storm rotation. 
   This will result in all severe hazards being possible.  The Enhanced
   and Slight risk areas have been expanded east to the lower
   Mississippi Valley region, as the a strong southerly low-level jet
   shifts toward western MS Friday night.  Mixed storm modes, initially
   cellular, are expected with the mode possibly becoming linear as
   stronger forcing for ascent spreads across this region Friday night.
    Given some uncertainty in the overall evolution of storms across
   this part of the severe risk areas, a moderate risk is not being
   introduced at this time.

   ..Peters.. 04/12/2018

[jojo762]

12Z CAMS paint a fairly clear, yet some what questionable picture for tomorrow. HRW NSSL-WRF, HRW NMMB, HRW WRF-ARW, and the RGEM all depict scattered discrete supercells developing along the dryline in Eastern Kansas southward into Eastern Oklahoma by 21Z with an environment that is conducive for all severe hazards, with the NSSL-WRF probably being the most impressive of the four... Storm-mode across eastern Kansas stays almost exclusively supercellular with modes further south becoming more messy/linear with time. Across the Arklatex and northeastern Texas, things are definitely a bit more questionable leading to the uncertainty mentioned in the 1730z D2 outlook. CAMs paint a bit of a messy picture in this region with a mix of supercells and clusters, but one thing does appear to be for sure - any supercell with any kind of breathing room will almost certainly be capable of producing tornadoes.

I'm not 100% buying into the idea of fairly sparse storm coverage across Eastern Kansas given the very strong dynamics at play AND the fact that CIN is negligible by as early as 20Z across the area. But it is probably best to trust NWP, as it normally beats human skill. 

Not much more we can do but sit back and enjoy the first interesting plains setup of the year.

[andyhb]

Can't help but think the ill-timing of occlusion with this system is going to be its undoing if it doesn't yield something more significant. If the 500 mb setup at 12z tomorrow was shifted 6-12 hrs later, I would tend to think we'd be looking at a pretty major severe wx outbreak. This is somewhat analogous to 4/10/2008, which had similar ill-timing.

[Drz1111]

I am merely whelmed by tomorrow’s setup.  The best low level wind field is either displaced from the best lift or in places with messy storm mode likely (IA/NE, or N LA/AR).  Winds seem likely to be more veered in KS/OK near dryline than was previously expected.  And just gut-pattern- recognition-wise, it doesn’t ‘feel’ like a big one.  

 

That being said, seems odd to me that the official discussions have been so muted on this.  If there is any sort of outbreak, the ‘crappy chase terrain’ simultaneously means higher population densities.  Lot more to run into in MO or LA than out by I-35.

[bjc0303]

1 hour ago, jojo762 said:

12Z CAMS paint a fairly clear, yet some what questionable picture for tomorrow. HRW NSSL-WRF, HRW NMMB, HRW WRF-ARW, and the RGEM all depict scattered discrete supercells developing along the dryline in Eastern Kansas southward into Eastern Oklahoma by 21Z with an environment that is conducive for all severe hazards, with the NSSL-WRF probably being the most impressive of the four... Storm-mode across eastern Kansas stays almost exclusively supercellular with modes further south becoming more messy/linear with time. Across the Arklatex and northeastern Texas, things are definitely a bit more questionable leading to the uncertainty mentioned in the 1730z D2 outlook. CAMs paint a bit of a messy picture in this region with a mix of supercells and clusters, but one thing does appear to be for sure - any supercell with any kind of breathing room will almost certainly be capable of producing tornadoes.

I'm not 100% buying into the idea of fairly sparse storm coverage across Eastern Kansas given the very strong dynamics at play AND the fact that CIN is negligible by as early as 20Z across the area. But it is probably best to trust NWP, as it normally beats human skill. 

Not much more we can do but sit back and enjoy the first interesting plains setup of the year.

Do you have statistics for this? Because I'm gonna venture out and say that is pretty false lol. 

 

I'm just not feeling a moderate risk tomorrow. Can't really see it for hail, given modest lapse rates at best (though very strong effective bulk shear is on the higher end for this area). Definitely am not seeing it for tornadoes, even in the Arkansas vicinity. I could kind of see a moderate for wind in Arkansas (kind of.. would be a stretch).

[andyhb]

18 minutes ago, bjc0303 said:

Do you have statistics for this? Because I'm gonna venture out and say that is pretty false lol. 

 

I'm just not feeling a moderate risk tomorrow. Can't really see it for hail, given modest lapse rates at best (though very strong effective bulk shear is on the higher end for this area). Definitely am not seeing it for tornadoes, even in the Arkansas vicinity. I could kind of see a moderate for wind in Arkansas (kind of.. would be a stretch).

NAM/NAM 3 km both have solid 7-8+ C/km mid level lapse rates across the entire risk area before convection tomorrow. I don't think I'd consider that modest, especially east of the High Plains, and particularly for a rather amplified system such as this.

[hlcater]

1 hour ago, andyhb said:

Can't help but think the ill-timing of occlusion with this system is going to be its undoing if it doesn't yield something more significant. If the 500 mb setup at 12z tomorrow was shifted 6-12 hrs later, I would tend to think we'd be looking at a pretty major severe wx outbreak. This is somewhat analogous to 4/10/2008, which had similar ill-timing.

This is kind of a stupid question, but what about the pretty extreme veer back signals at 12z? Those seem to iron themselves out by 21-00z.

[Chinook]

The relatively new HREF system shows this for the updraft helicity tracks. There is a greater concentration of UH tracks on the north side and the south side of the outlook. I'm not even sure that this HREF system is really all that different than looking at the 3km NAM, WRF-ARW,  WRF-NSSL, and WRF-NMMB at the same time.

 

[OUGrad05]

1 minute ago, Chinook said:

The relatively new HREF system shows this for the updraft helicity tracks. There is a greater concentration of UH tracks on the north side and the south side of the outlook. I'm not even sure that this HREF system is really all that different than looking at the 3km NAM, WRF-ARW,  WRF-NSSL, and WRF-NMMB at the same time.

 

Basically skips OK so that'll probably verify 

[jojo762]

2 hours ago, bjc0303 said:

Do you have statistics for this? Because I'm gonna venture out and say that is pretty false lol. 

 

I'm just not feeling a moderate risk tomorrow. Can't really see it for hail, given modest lapse rates at best (though very strong effective bulk shear is on the higher end for this area). Definitely am not seeing it for tornadoes, even in the Arkansas vicinity. I could kind of see a moderate for wind in Arkansas (kind of.. would be a stretch).

https://www.nssl.noaa.gov/users/brooks/public_html/future/technology.html

Quote

"The accuracy of NWP guidance has reached the point that, in many cases, there is little that human forecasters can do to improve upon it. In this regard, NWP is seen by many as a threat to the existence of human forecasters. Rather than being an ally, as in the case of making observations, technology is viewed as an "enemy" of humans involved in the forecast process. There is no reason to believe that the quality of NWP will not continue to improve and, perhaps more importantly, the lack of opportunities to add significant value to NWP guidance leads some to envision a future in which forecasts are made without human intervention."

https://www.nssl.noaa.gov/users/brooks/public_html/papers/stuart.pdf

I don't really feel like junking up the thread too much. But the idea, nowadays, that a subjective human forecast can beat out NWP, or at least the average consensus of NWP on any given day is a thing of the past. Back in the early to mid 2000's, forecasters brought significant extra value to a forecast. But in this current day and age, that simply is not the case in most instances. NWP does most of the job for us, we simply add a bit of subjectivity in our model preferences and climatological beliefs, among other things.

[Drz1111]

28 minutes ago, jojo762 said:

https://www.nssl.noaa.gov/users/brooks/public_html/future/technology.html

https://www.nssl.noaa.gov/users/brooks/public_html/papers/stuart.pdf

I don't really feel like junking up the thread too much. But the idea, nowadays, that a subjective human forecast can beat out NWP, or at least the average consensus of NWP on any given day is a thing of the past. Back in the early to mid 2000's, forecasters brought significant extra value to a forecast. But in this current day and age, that simply is not the case in most instances. NWP does most of the job for us, we simply add a bit of subjectivity in our model preferences and climatological beliefs, among other things.

Which is crazy because this is true even while convection still (mostly) needs to be parameterized.  Once convection can be modeled explicitly . . . whoosh.

Also, the machine learning that's solved Go and Chess would be phenomenal for identifying relevant parameters for severe risk.  I'm shocked that hasn't been done already because its a classic overfit problem that those programs are much, much better than humans at.

[andyhb]

Models were quite overdone on moisture return today, although some of this was almost certainly related to their inability to properly mix the boundary layer.

[CheeselandSkies]

14 minutes ago, andyhb said:

Models were quite overdone on moisture return today, although some of this was almost certainly related to their inability to properly mix the boundary layer.

...which is why human forecasters are (theoretically) still necessary, understanding and accounting for these biases. Unfortunately it seems like a lot of times they don't bother.

[Radtechwxman]

1 hour ago, andyhb said:

Models were quite overdone on moisture return today, although some of this was almost certainly related to their inability to properly mix the boundary layer.

You thinking moisture quality might be an issue tomorrow?

[bjc0303]

2 hours ago, jojo762 said:

https://www.nssl.noaa.gov/users/brooks/public_html/future/technology.html

https://www.nssl.noaa.gov/users/brooks/public_html/papers/stuart.pdf

I don't really feel like junking up the thread too much. But the idea, nowadays, that a subjective human forecast can beat out NWP, or at least the average consensus of NWP on any given day is a thing of the past. Back in the early to mid 2000's, forecasters brought significant extra value to a forecast. But in this current day and age, that simply is not the case in most instances. NWP does most of the job for us, we simply add a bit of subjectivity in our model preferences and climatological beliefs, among other things.

As far as day-to-day goes.. can’t beat NWP. 

 

As far as high-impact weather goes, things specialist centers like SPC take on.. NWP loses, and loses often. 

[bjc0303]

3 hours ago, Chinook said:

The relatively new HREF system shows this for the updraft helicity tracks. There is a greater concentration of UH tracks on the north side and the south side of the outlook. I'm not even sure that this HREF system is really all that different than looking at the 3km NAM, WRF-ARW,  WRF-NSSL, and WRF-NMMB at the same time.

 

It’s he exact same thing as you suspect, but laid out in a way that extracts a signal. Not as cool as NCAR. 

[andyhb]

17 minutes ago, StormChaser4Life said:

You thinking moisture quality might be an issue tomorrow?

Further south, probably not given the strength of the LLJ overnight and into the morning. Further north, there might be some questions.

[Radtechwxman]

6 minutes ago, andyhb said:

Further south, probably not given the strength of the LLJ overnight and into the morning. Further north, there might be some questions.

I'm more worried about depth of moisture and how much mixing will impact it. Dews are in the upper 50s already at the sfc up there looking at mesonet data

[Chinook]

I posted that HREF image partially to talk about the forecast at hand. I wonder if the lower number of updraft-helicity tracks in the mid part of the risk area will translate to few storm reports there tomorrow. I don't really know.

I am wondering how forecasters, (and fans like us,) will use the HREF information in the next couple of years. Apparently it is a collection of 8 models that use 3 km grid spacing . It may be using the exact same 3-km NAM, HRW-ARW, and HRW-NMM, NSSL model that are shown on the Pivotalweather.com web site. 

The NCAR-ensembles (hi-res) *had* some nice stuff.  I believe it *had* a collection of 10 models that were distinct from the main NCEP hi-res models. And it went to 48 hrs, but it only ran at 00z, not 12z like everything else.

[andyhb]

Well the 00z NAM certainly just took it up a notch across the southern portion of the threat area.

Should add that I'm still a bit concerned that the iffy wind fields early on (due to what appears to be a subtle shortwave passing through the flow) may lead to storm mode becoming messy before the parameter space becomes more favorable.

[jojo762]

13 minutes ago, andyhb said:

Well the 00z NAM certainly just took it up a notch across the southern portion of the threat area.

Wind profile and thermodynamics both improved and are very favorable on this run. Most notable change to me is that the mid/upper level profile has improved markedly from a directional stand point. The tornado threat also appears to last well into the night from both a semi-discrete/transient supercell and a QLCS standpoint.

[Radtechwxman]

What about the northern target? I haven't had time to look at things. Gotta crash soon. Leaving early to get to chase target

[Indystorm]

At 3 a.m. CDT I must say it's been a long time since we have seen a low this deep...988mb in central Kansas, and excellent lapse rates and helicity over a wide area.  Now if dew points can just advect northward we might have a significant day weatherwise that we haven't seen in quite awhile.

[OUGrad05]

2 hours ago, Indystorm said:

At 3 a.m. CDT I must say it's been a long time since we have seen a low this deep...988mb in central Kansas, and excellent lapse rates and helicity over a wide area.  Now if dew points can just advect northward we might have a significant day weatherwise that we haven't seen in quite awhile.

Possible but the directional profiles of the winds are lacking.  Plenty of speed shear across the risk area but directional shear could be significantly better.  CAPE values while adequate are nothing spectacular.  There will be some tors today for sure but there's still significant disagreement in model solutions as it relates to dry line position, veer-back, convection and timing...  

Having said that it won't take a lot of changes to make things pretty interesting especially east of US75 in the southern portions of the risk area.  Arkansas could get lit up today.

[Jonbo]

With the way models are going, probably won't have to go too far outside of Des Moines to see something today (budgeting reasons). Maybe not a tor but I gotta end the severe wx withdrawals.