Memorial Day weekend severe threats

[andyhb]

The lack of amplification of the trough on Saturday is reminding me of those IL events over the past couple of years that yielded tornadoes, but never really reached their full potential because nothing could develop away from the synoptic warm front or mesoscale boundaries (i.e. everything turned into a blob relatively quickly). The strong EML associated with this only further suggests that scenario, especially further east. Dryline is a wild card given the southeastward moving cold front on the backside and relatively anemic wind fields early on. It would help if the trough was more neutrally tilted with a healthier surface low.

[Indystorm]

But what a MCS we're going to have in ne OK and Missouri on east!  Those CAPE values on both NAM and GFS are astounding.  And yes, I would focus on the WF for tor potential but only for armchair chasing.  Ozark topography is impossible for actual chasing.

[janetjanet998]

4 minutes ago, Indystorm said:

But what a MCS we're going to have in ne OK and Missouri on east!  Those CAPE values on both NAM and GFS are astounding.  And yes, I would focus on the WF for tor potential but only for armchair chasing.  Ozark topography is impossible for actual chasing.

Could be trouble in the Ozarks with people camping in the woods

[Indystorm]

44 minutes ago, janetjanet998 said:

Could be trouble in the Ozarks with people camping in the woods

Yep, 70 mph wind, baseball size hail, and camping don't go very well together as currently progged by Springfield MO in their Sat. outlook.

[jojo762]

46 minutes ago, Indystorm said:

Yep, 70 mph wind, baseball size hail, and camping don't go very well together as currently progged by Springfield MO in their Sat. outlook.

TSA is forecasting hail up to the size of grapefruits, 80mph winds, and tornadoes... Run of the mill type stuff, ya know. 

[jojo762]

Also, worth noting that the NAM has progressively trended toward the dryline being further west by 00z over the last couple days of runs... Perhaps putting part of Central OK in play, 18Z NAM also showed less veered surface flow by 00z, with even some SE surface winds near the quasi triple-point in NC/NE OK. 18Z NAM verbatim shows a significant parameter space developing over portions of MO along/near the warm front, which is something that will need to be watched. Lots of uncertainty regarding the ceiling of TOR potential at this point, but what does seem certain is we will get significant severe storms at least along the Cold Front and Warm Front, and possibly the dryline as well, capable of giant hail and damaging winds and perhaps tornadoes.

Just for some classic uncle NAM laughs, not 100% sure if this is really contaminated as convection is fairly far away from this point-sounding... Here is an 18Z NAM sounding across SC MO at 7pm Saturday along the warm front.

[Misstertwister]

I know it's been said to me before but for us non met type guys where or how do I locate the dryline at this point for Saturday? Typically, being an okie I look for dryline based on dew point separation but as I understand it, Sat isn't your typical DL day. 

Do I look at Theta-e to find dryline at this point?

[bjc0303]

Those Missouri soundings are definitely contaminated.. MCS the NAM forecasts alters the pressure/height field/wind field in the area.

[JoJo]

Saturday looks so complex and will not get any fine details of the day of, this regards from the Eastern Plains/Ozarks eastward through the Ohio Valley to the East Coast, just an large complex late-may severe weather outbreak scenario

[Quincy]

Even the large MCS/derecho idea seems to be far from a slam dunk. Overnight models, both convection-allowing and global, aren't as keen on maintaining or developing such a convective system by mid to late afternoon. It's clear that remnant boundaries will play a major role in convective evolution. 

If I had to venture a guess, I'd expect mixed modes with multiple clusters and lines of storms, but still a few more intense supercells.

I'll post the recent NCAR ensemble 22z Sat reflectivity images for just an idea of some possible scenarios: 

[bjc0303]

Not one to post NWS products or anything, but couldn't help but find it interesting the Tulsa HWO graphic says a few strong tornadoes possible.

[Weatherdemon]

3 minutes ago, bjc0303 said:

Not one to post NWS products or anything, but couldn't help but find it interesting the Tulsa HWO graphic says a few strong tornadoes possible.

LOL, was getting ready to post too

Hazardous Weather Outlook
National Weather Service Tulsa OK
453 AM CDT Fri May 26 2017

...SIGNIFICANT SEVERE WEATHER EXPECTED LATE SATURDAY AFTERNOON INTO 
   SATURDAY EVENING WITH DESTRUCTIVE WIND AND VERY LARGE HAIL...

...A FEW STRONG TORNADOES POSSIBLE LATE SATURDAY AFTERNOON/EVENING...

[bjc0303]

I also believe strong tornadoes will be possible, just confined to storm interactions with effective front/OFB, wherever that ends up. I know that is what they're worried about.

[Weatherdemon]

Just now, bjc0303 said:

I also believe strong tornadoes will be possible, just confined to storm interactions with effective front/OFB, wherever that ends up. I know that is what they're worried about.

Agreed.

[Quincy]

Yesterday kicked off the holiday weekend severe threat with a few supercell thunderstorms in eastern Colorado and western Kansas. I chased a few storms in the area. The first in a pair of photos below had a tornado warning issued, but any circulation was rain-wrapped, so I opted to stay south for some photos in the Elkader area.

After snapping a few photos, it was time to go south and see if discrete convection near Dodge City could get its act together. Ultimately, despite showing transient signs of organization, the cell begin to dissipate before sunset. Nonetheless, I was able to grab one last photo just west of Dodge City of a healthy-looking updraft, before the storm weakened.

[Radtechwxman]

I found it amusing that Broyles said around 4000 cape in his outlook but pretty much every model has 5000-6000+. Guess he is playing it conservative after the high risk bust

[Indystorm]

Amazed at NCAR variability that Quincy posted.  Would have expected more consistency at this time period.  Guess boundaries will play a major role and may then possibly enhance tornado threat from what was previously thought.

[nrgjeff]

Big question is a pair of morning MCSs possible; one near KCMO and the other north of MEM. The latter could cut calm down the KCMO monster through Missouri. Atmo would have time to recharge well in the Mid Mississippi Valley if so. The conflicting CAMs make a lot of sense. We will not know until Saturday morning. Derecho, WF tornado outbreak, or more 2017 trash? Just kidding; Saturday should be quite the interesting day one way or another.

[bjc0303]

Not sold at all on a WF tornado outbreak. Parameters there are only alarming because of convective contamination with the MCS on the NAM.

GFS has really ramped up the parameters over NE OK in the vicinity of the triple point associated with a stronger forecast LLJ. Seeing a pretty weird signal in the 3km NAM for strong capping in between N TX and NE OK. Moreover the GFS has started to show this perhaps as well, and a relative dearth in QPF in this area suggests perhaps a region that may stay convection free (between the N TX dry line and the NE OK triple point). NCAR ensembles while mixed, do show this scenario as well. Starting to think there will be two convective regimes - the first along the TP/WF and east where a mix of supercells and a perhaps long-lived MCS and the second along the dry line from extreme southern OK through Texas. Gonna be a tough choice tomorrow. Won't know until the day of what's going on.

[David Reimer]

Warm-sector over Southern Oklahoma looking more impressive tomorrow off the 12Z 3KM NAM. Would just need a storm to fire, which the 3KM NAM does if you look at the UH tracks between 0-3Z. Also has backing surface winds and the dryline a bit further west. Could be a day where the topographical features (Wichita Mountains, Arbuckles, etc) play a role in initiation. With 7000+ MLCAPE and 0-3KM SRH around 225-250 any storm that gets going will probably be a monster. SHIP values of 6 to 7 are just ridiculously favorable for giant hail. Of-course it is entirely possible we'll have to wait for the CF to arrive Saturday evening should capping remain in place. 

[MUWX]

Sounds like a day two moderate is coming. 

Ptetty big moderate risk. 

[yoda]

[hlcater]

I definitely feel like wherever that boundary(from the KS MCS) ends up is gonna be the play of the day. Some tornadoes should be possible with southward extent, but anything significant should be confined to the vicinity of that boundary where SRH will be locally enhanced. Threat would increase some if the MCS cloud debris from the north is able to clear out and heat up both sides of the boundary leading to less of an instability/temp gradient and more leniency for tornadoes on both sides of the boundary, enabling storms to straddle/move across boundary without choking out. However storms may tend to cluster up in time, regardless maybe an hour or two of tornado potential may exist. If I were chasing, I'd watch obs and play that boundary.

[bdgwx]

13 minutes ago, NWLinnCountyIA said:

I definitely feel like wherever that boundary(from the KS MCS) ends up is gonna be the play of the day. Some tornadoes should be possible with southward extent, but anything significant should be confined to the vicinity of that boundary where SRH will be locally enhanced. Threat would increase some if the MCS cloud debris from the north is able to clear out and heat up both sides of the boundary leading to less of an instability/temp gradient and more leniency for tornadoes on both sides of the boundary, enabling storms to straddle/move across boundary without choking out. However storms may tend to cluster up in time, regardless maybe an hour or two of tornado potential may exist. If I were chasing, I'd watch obs and play that boundary.

That's pretty much exactly what the HRRRX shows. It has an MCS starting around KC with supercells exploding along the southern flank in it's wake. I still think tornado potential may be tied more to mesoscale accidents, but regardless a big chunk of Missouri is inline for some very intense and likely severe thunderstorms.

[JoMo]

Well, tomorrow is going to be no fun. 

[jojo762]

Tomorrow continues, with possibly some increase in confidence because of recent model trends, to look like a day where something major could happen (I.e., large wedge tornado or two... given the expected environment)... but it likely won't be very photogenic.

[Quincy]

Don't forget that extreme instability can compensate a bit for otherwise more lower-end shear. With that said, remnant boundaries will be the main focus, for enhanced shear and lower LCLs, but if 6000 J/kg CAPE verifies (some model progs are over 8000 J/kg), you won't need much low-level shear for tornadogenesis. Also, deep layer shear is progged on the order of 50+ knots through most of the enhanced risk area, which when combined with extreme instability, creates an extremely favorable parameter space for supercells, especially early in convective life cycles. 

Based on estimations from forecast soundings through the region, 0-2km SRH should commonly be on the order of 100-200+ m2/s2 by 21z Sat.

[nrgjeff]

On 5/24/2017 at 4:26 PM, Weatherdemon said:

How meteorologically similar is Saturday to May 10, 2008 when just a few storms exploded and an EF4 wiped out most of what was left of Picher, OK?

May 6, 2003 is another example of an ugly veered LLJ, but with numerous tornadoes in the same region. Again, shortwave not as strong tomorrow. 2003 was also neutral tilt, tomorrow positive. However Saturday will have more CAPE. 18z data showing themes of lead cells in flatter Delta ahead of MCC.

[Quincy]

Just one possible evolution:

An early look from the 18z HRRR shows an interesting setup, in which overnight convection basically weakens and leaves an almost entirely undisrupted warm sector tomorrow. This scenario results in an unusually large area with both extreme CAPE and favorable shear. By 21-22z, cells start to blow up over Missouri near the warm front. Back west, 10m winds are backed to the south across eastern portions of Oklahoma and North Texas. 

[MUWX]

26 minutes ago, nrgjeff said:

May 6, 2003 is another example of an ugly veered LLJ, but with numerous tornadoes in the same region. Again, shortwave not as strong tomorrow. 2003 was also neutral tilt, tomorrow positive. However Saturday will have more CAPE. 18z data showing themes of lead cells in flatter Delta ahead of MCC.

May 6th or may 4th?