May 15-20 Severe Threat

[Jonbo]

Towers going up around me. 

[bjc0303]

1 minute ago, CGChaser said:

Some discrepancies tomorrow with regards to moisture return and dryline placement. Looks as though global models & NAM bring the dryline to TX/OK border, into TX on 00z euro. Meanwhile shorter-range guidance (NCAR, TTU, hrrrx) suggests dryline placement farther east with moisture not returning as quickly into W/NW OK. 

Eh, I'd say that all guidance pretty much suggest more or less the same thing, minus an outlier or two. 

[David Reimer]

That was a rather 'meh' sounding Day 2 IMO. I mean, better than going hype, but still a bit of a reduction in wording. 

[CGChaser]

8 minutes ago, David Reimer said:

That was a rather 'meh' sounding Day 2 IMO. I mean, better than going hype, but still a bit of a reduction in wording. 

Thought the same. Especially compared to overnight forecast.

[Jim Martin]

IAC167-171930-
/O.CON.KFSD.TO.W.0006.000000T0000Z-170517T1930Z/
Sioux IA-
209 PM CDT WED MAY 17 2017

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 230 PM CDT FOR EASTERN
SIOUX COUNTY...
    
At 209 PM CDT, a confirmed tornado was located west of Hospers, or 
near Orange City, moving northwest at 25 mph.

HAZARD...Damaging tornado and quarter size hail. 

SOURCE...Weather spotters confirmed tornado. 

IMPACT...Flying debris will be dangerous to those caught without 
         shelter. Mobile homes will be damaged or destroyed. Damage 
         to roofs, windows, and vehicles will occur.  Tree damage is 
         likely. 

[MattPetrulli]

Tomorrow is beginning to  really look like a high end/outbreak day. Especially across a populated area across the Plains (I-35 corridor).

[OceanStWx]

I do like the look of hodographs across southern KS and northwestern OK. There is model agreement on the sickle look around 1 km.

[WhiteoutWX]

18 minutes ago, MattPetrulli said:

Tomorrow is beginning to  really look like a high end/outbreak day. Especially across a populated area across the Plains (I-35 corridor).

I think the vast majority of the tornado threat looks to focus to the west of the 35 corridor. 

[Jonbo]

Didn't expect a storm coming up here earlier to collapse quickly and produce a likely marginally strong microburst (I think the cold front or dry line cut it off). Started recording right before it arrived in case of a good lightning/thunder moment and that plan changed real fast.

Edit: Fairly certain it was a microburst. This large branch on a healthy tree wasn't down from yesterday's wind event. I walked down the trail after yesterday's and didn't see much damage besides leaves.

[brettjrob]

Tomorrow's a tough nut to crack. Don't feel comfortable ruling out a large event/outbreak, but certainly don't have high confidence in that scenario. Overall, the environment along the DL looks better than yesterday by 23-01z, both due to less VBV and less likelihood of capping/cool air downstream of CI. On the other hand, wave timing seems off, with some indications in the guidance of warm sector storms exploding early-mid afternoon closer to the I-35 corridor. Plus, this is a neutral to slightly positively-tilted trough, which I never like seeing for more intense systems like this. Obviously, the cold air lurking up north isn't ideal, either. With all that being said, it's mid-May... if the warm sector is still relatively clean by 21z and CI is imminent along the DL at that point, this *should* be the biggest Plains event of the season thus far.

[jojo762]

Looking at various pieces of 18Z guidance, it seems that the MDT risk may need to be moved/expanded further east AND south. Not a perfect setup necessarily, but I have little doubt that at least one or two significant tornadoes will occur tomorrow - as long as stuff doesn't become junky too fast.

[brettjrob]

HRRRx has been consistent in firing "junky" cells well east of the DL on each of its long-cycle runs today, in agreement with MPAS and the NCAR ensemble from last night. Meanwhile, the NSSL WRF and 3-km NAM nest are much different, with classic supercells initiating along the DL and streaking across the warm sector. Confidence in the broad convective evolution appears below average for this lead time, and makes a lot of difference in the outcome.

A consistent theme in the junky-looking guidance is early (17-19z) development of an intense complex across C/N TX, which sends off outflow and/or left splits to the N and screws up most of the OK threat.

[Jim Martin]

Radar-confirmed tornado east of Matherville, Illinois currently, moving northeast.

[David Reimer]

For any newer weather weenies visiting this thread and wondering about the Texas severe weather potential... My evening thoughts (summary and very detailed blog post) below. 

 

[jojo762]

00z 3NAM has CI by 21Z along the dryline. It has a favorable parameter space developing by as early as 20-21Z across the warm sector with strong deep-layer shear, sufficiently strong low-level shear, upper 60s/low 70s dewpoints and extreme instability with MUCAPES of 4000-5500J/KG widespread across the warm sector. Verbatim the simulated reflectivity is a mixed storm-mode fairly early with bows/clusters and supercells. I highly doubt that things get that messy as early as the 3km NAM shows, but we'll have to see what other 00z CAMs show.

00z 12NAM develops a favorable parameter space by 00z from Central KS down into SW OK... With the highest tornado threat likely residing closer to the triple point where LLVL winds will be most impressive, so pretty much over C/SW/SC Kansas. Also, Friday continues too look potentially interesting across Oklahoma. 

[1900hurricane]

There is a strong signal for convective initiation between 18-21Z across central Texas, and this will definitely need to be watched, but I think it's fairly likely that it won't impact the main portion of the warm sector (which I'm defining roughly as the latest SPC Day 2 Enhanced Risk area) too much. Based largely on the SSEO and NCAR Ensemble >40 dBZ neighborhood probabilities, the earlier storms appear most likely to fire in the Concho Valley, in SJT's forecast area. When running a NAM HYSPLIT trajectory matrix for the main warm sector at elevations of 100, 500, and 1000 m AGL from 18Z to 00Z, parcels appear to originate north and east of the area of most likely early convection. Now, a few of the members do initiate convection well north and east into the heart of FWD forecast area, and that convection would have an impact on at least a chunk of the main warm sector. However, based on what I see so far, this is a less likely scenario in my opinion.

 

00Z May 17 NCAR Ensemble >40 dBZ neighborhood reflectivity probabilities at tau 45, valid 21Z May 18.

 

12Z May 17 SPC SSEO Ensemble >40 dBZ neighborhood reflectivity probabilities at tau 33, valid 21Z May 18.

 

 

18Z NAM HYSPLIT backward trajectories from tau 24 to tau 30, ending 00Z May 19 for 100, 500, and 1000 m AGL, respectively.

[1900hurricane]

Also, here are reflectivities of the individual members of the aforementioned runs of the NCAR Ensembles and SSEO valid 21Z tomorrow. There are a few solutions that would mitigate things, but most look alright. Not a slam dunk either way though, although as I've stated, it appears to me more likely that the earlier storms won't be overly impinging on the main warm sector.

 

[MUWX]

I've seen some mention of tomorrow being a high risk type of day, what needs to improve for the spc to agree?

[MattPetrulli]

Just now, MUWX said:

I've seen some mention of tomorrow behind a high risk type of day, what needs to improve for the spc to agree?

Evolution of moisture and whether CI will be too early and if convection will go linear and junky.

[jojo762]

5 minutes ago, MattPetrulli said:

Evolution of moisture and whether CI will be too early and if convection will go linear and junky.

Moisture is not an issue tomorrow. But the other two certainly are. I personally also have some questions about the low-level wind field overall. In the lowest 1-kilometer there really isn't that much turning tomorrow in most soundings south of the triple point, like into Oklahoma, primarily because almost all the winds in the lowest 1km of the profile are backed to the south-southeast. 

[MattPetrulli]

Just now, jojo762 said:

Moisture is not an issue tomorrow. But the other two certainly are. I personally also have some questions about the low-level wind field overall. In the lowest 1-kilometer there really isn't that much turning tomorrow in most soundings south of the triple point, like into Oklahoma, primarily because almost all the winds in the lowest 1km are backed to the south-southeast. 

Only reason why I say this is because a METAR in Western OK is currently 70/41. A little concerning given the issues we've had so far this year.

[bjc0303]

1 minute ago, jojo762 said:

Moisture is not an issue tomorrow. But the other two certainly are. I personally also have some questions about the low-level wind field overall. In the lowest 1-kilometer there really isn't that much turning tomorrow in most soundings south of the triple point, like into Oklahoma, primarily because almost all the winds in the lowest 1km of the profile are backed to the south-southeast. 

Want speed shear more than directional shear in the lowest kilometer.. 

[bjc0303]

Just now, MattPetrulli said:

Only reason why I say this is because a METAR in Western OK is currently 70/41. A little concerning given the issues we've had so far this year.

Look at 00z SHV sounding and areas downstream

[jojo762]

4 minutes ago, bjc0303 said:

Want speed shear more than directional shear in the lowest kilometer.. 

I'd say both are equally important. ESRH is what matters more in the end I guess, rather than 0-1km SRH anyways as it is the true helicity that the storm inflow is ingesting. ESRH values are still very impressive across the entire threat area.

Also on moisture. DPs have already increased markedly across W/C OK compared to what they were this afternoon. Source soundings (like the SHV sounding referenced) are very impressive with upper 60s/low 70s across most of the region that our moisture is coming from tomorrow. Most, if not all, global models and CAMs show more than sufficient moisture tomorrow along and east of the dryline as well with upper 60s to perhaps 70 Dt.

[MattPetrulli]

1 minute ago, bjc0303 said:

Look at 00z SHV sounding and areas downstream

Yeah I take that back, nice airmass coming in. Just checking 00z NAM its initialization is close to actual, off by maybe 1 or 2 degrees.  I take back moisture concern, but still concerned about convective evolution. 

[Stebo]

5 minutes ago, MattPetrulli said:

Only reason why I say this is because a METAR in Western OK is currently 70/41. A little concerning given the issues we've had so far this year.

I am not concerned at all, look south of Dallas, low to mid 70 dew points that are rapidly advecting northward.

[JasonOH]

5 minutes ago, Stebo said:

I am not concerned at all, look south of Dallas, low to mid 70 dew points that are rapidly advecting northward.

Heck, there's already upper 60s advecting into SE Oklahoma (almost 70 far SE).

 

 On a side note, on the mobile website is there a way to get the met names red? I recognize them but the names are white. I'm too lazy to learn the app.

[Stebo]

Just now, JasonOH said:

Heck, there's already upper 60s advecting into SE Oklahoma (almost 70 far SE).  

Yeah, if it looked like this right now 12 hours from now, then there would be a problem. Moisture isn't going to be an issue at all tomorrow.

[JasonOH]

15 minutes ago, bjc0303 said:

Want speed shear more than directional shear in the lowest kilometer.. 

I'll take your word on that since I don't read too many severe weather Papers. I know his expertise and trust his knowledge.  (He is going to get the red name pretty soon)

[jojo762]

Gotta love how crappy, and utterly useless, the HRRR is sometimes when it shows CI occuring and shortly thereafter, or just in general (overconvecting bigly)... Either way, shows CI between 19-20z along (actually a bit east) of the dryline.