May 15-20 Severe Threat

[bjc0303]

Reason you want predominantly speed shear in the lowest km is it leads to a larger degree of streamwise vortex tubes in the lowest km... lending to rapid mesocyclogenesis. see 4/14/12

[andyhb]

14 minutes ago, bjc0303 said:

Reason you want predominantly speed shear in the lowest km is it leads to a larger degree of streamwise vortex tubes in the lowest km... lending to rapid mesocyclogenesis. see 4/14/12

To add on, basically those sickle shaped hodographs that people often look for in Plains tornado cases look that way because of this very thing.

[Superstorm93]

NSSL-WRF rolling in slowly...

21z and minimal activity breaking out in OK

 

[Paulie21]

14 minutes ago, bjc0303 said:

Reason you want predominantly speed shear in the lowest km is it leads to a larger degree of streamwise vortex tubes in the lowest km... lending to rapid mesocyclogenesis. see 4/14/12

I second this, think of the big boy observed soundings out there, in the hodograph, you essentially see almost a right angle occur after the first kilometer, that hard right turn would mean more speed shear than directional shear at the lowest level. I've spoken to Dr. Walker Ashley about this and noticed it as well and agrees, however, this goes against some theories because a right angle hodo would technically give you a bit less SRH than a curved hodograph, and thus technically less streamwise vorticity parallel to the storm relative inflow wind.  
Regardless, these forecast hodographs are so much more smoothed out than reality and the dynamics are there tomorrow, storm morphology and interaction will make or break tomorrow. Personally I also agree the HRRR is a bit overzealous with CI as we sit under the right exit region of the upper level jet. Shear vectors are favorable for discrete cells down the line tomorrow. Thinking triple point might be a bit messy however. Just a hunch though.

[jojo762]

Well most of the 00z CAMs (NSSL WRF-ARW/HRW-NMMB/HRW WRF-ARW/3km NAM) in addition to the 03Z HRRR did nothing to squelch uncertainty over storm-mode. Vectors would appear to favor supercells, but most CAMs show either 1. Clusters, perhaps supercell clusters, or 2. mixed storm-modes with Supercells and bowing segments/clusters. 

My current thoughts are that storms should fire sometime in the 18-20z time frame with initial supercells, perhaps remaining discrete or semi-discrete for at least a few hours with all severe hazards possible including strong tornadoes and giant hail, before coverage increases dramatically by 00z and clusters and bowing segments begin to become more prevalent with perhaps a discrete storm or two remaining along with transient supercell structures within the more organized convective clusters. Sort of like how 5/24/11 developed with intense semi-discrete supercells early before everything becomes messy (NOT comparing the setups, just how convective evolution occurred).

[CGChaser]

3 minutes ago, jojo762 said:

Well most of the 00z CAMs (NSSL WRF-ARW/HRW-NMMB/HRW WRF-ARW/3km NAM) in addition to the 03Z HRRR did nothing to squelch uncertainty over storm-mode. Vectors would appear to favor supercells, but most CAMs show either 1. Clusters, perhaps supercell clusters, or 2. mixed storm-modes with Supercells and bowing segments/clusters. 

My current thoughts are that storms should fire sometime in the 18-20z time frame with initial supercells, perhaps remaining discrete or semi-discrete for at least a few hours with all severe hazards possible including strong tornadoes and giant hail, before coverage increases dramatically by 00z and clusters and bowing segments begin to become more prevalent with perhaps a discrete storm or two remaining along with transient supercell structures within the convective clusters. Sort of like how 5/24/11 developed with intense semi-discrete supercells early before everything becomes messy (NOT comparing the setups, just how convective evolution occurred).

True, but it did diminish my beliefs in warm sector shenanigans farther east of dryline in mid-afternoon.

[jojo762]

2 minutes ago, CGChaser said:

True, but it did diminish my beliefs in warm sector shenanigans farther east of dryline in mid-afternoon.

Yeah, most of them show zero issue with anything south. Main issue ATTM would appear to be how storms evolve throughout the event, which will not be known at all until go-time. Today has a higher ceiling than Tuesday, but today also has more potential issues with convective mode than Tuesday had. Something to note is a lot of CAMs did pretty bad with convective mode in KS on Tuesday (showing a large convective system developing early/mid-afternoon... that did not happen).

[1900hurricane]

Day 2 for Friday is out.

 

   SPC AC 180533

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1233 AM CDT Thu May 18 2017

   Valid 191200Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM WESTERN
   NORTH TEXAS INTO SOUTHEAST KS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TX
   INTO KS...EASTWARD TO THE MID-MS VALLEY...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE
   SOUTHERN AND CENTRAL PLAINS TO THE LOWER OH VALLEY...EASTWARD TO THE
   VA/NC COAST...

   ...SUMMARY...
   Severe thunderstorms are expected across the central and southern
   Plains into the middle Mississippi Valley Friday and Friday night.
   The most intense storms are expected from parts of north Texas
   through central Oklahoma and into southeast Kansas. Very large hail,
   damaging winds and a few tornadoes are all possible with these
   storms. Additional isolated strong storms are possible across parts
   of the lower Ohio Valley to the middle Atlantic coast. Hail and
   gusty winds could accompany any storms that develop in that region.

   ...Synopsis...
   The upper low/trough centered over the central/southern Rockies will
   eject northeast across the central and southern Plains on Friday.
   This will bring a band of strong southwesterly flow aloft across
   northern TX into the mid-MS Valley. Strong low-level
   south/southeasterly winds ahead of a surface low and dryline will
   maintain transport of rich boundary-layer moisture across the
   southern/central Plains vicinity. As the southern Plains surface low
   shifts northeast through the night, a warm front draped west to east
   from near the KS/NE state line into the mid-MS Valley will advance
   slowly northward through the period into southern IA, northern IL
   and central IN. Meanwhile, a surface dryline will surge eastward
   across OK and KS. These boundaries will be the focus for severe
   thunderstorm development through the period. 

   Further east, A cold front located from southern OH into southern
   New England will track southward through the period. Thunderstorms,
   some potentially strong, may develop along/ahead of this boundary
   from the OH Valley into southeast VA/northeast NC in a moist and
   unstable environment.

   ...Southern/Central Plains to the Mid-MS Valley...

   A complicated scenario is unfolding across the region for Friday. A
   convective complex likely will be ongoing across parts of KS into
   MO/IL. This convection likely will be elevated but could still pose
   a hail threat given steep lapse rates and plenty of elevated
   instability.

   Additional morning convection is also possible across parts of TX
   into OK, though guidance varies on the extent and location of
   convection across this area. What guidance does agree on is that a
   very moist and unstable environment with very steep midlevel lapse
   rates and strong deep-layer shear will remain over the southern
   Plains. The position of the surface low will determine where the
   dryline and warm front are located and morning convection will
   impact where greatest destabilization in the vicinity of these
   boundaries occurs. At this time, it appears the most favorable
   boundary-layer conditions will exist from near the Red River
   vicinity of southwest OK/western North Texas into central OK
   along/ahead of the dryline. Discrete supercells capable of very
   large hail, damaging winds and perhaps a few tornadoes will be
   possible with these storms. The environment further to the north
   into southeast KS will be similar, though uncertainty is higher here
   given expected overnight convection on Thursday into Friday morning.

   Additional storms are expected to develop in the vicinity of the
   warm from north-central KS into northern MO. Capping concerns in
   this area, combined with likelihood of storms being elevated as they
   quickly move north of the front leads to greater uncertainty.
   However, very steep lapse rates and strong shear profiles will
   continue to support severe storms capable of very large hail.
   Heading into the overnight, one or more bowing complexes are
   expected to develop and track eastward across northern TX, OK, KS
   and MO. 

   Further south into central TX, forcing will be weaker and convection
   will be more isolated. Still, the environment will support
   supercells, mainly capable of large hail, strong winds and perhaps a
   tornado. 

   ...Lower Ohio Valley into Southeast VA/Northeast NC...

   Thunderstorms may develop in a moist and unstable environment ahead
   of a southward-sagging cold front. Upper forcing for ascent will be
   weak, as will deep-layer shear profiles. However, given steep lapse
   rates and moderate instability, brief, but strong storms are
   possible. Hail will be the main concern with these storms.

   ..Leitman.. 05/18/2017

[HillsdaleMIWeather]

...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF   SOUTHERN AND CENTRAL KANSAS INTO NORTHWEST OKLAHOMA...  

[HillsdaleMIWeather]

30 PERCENT SIG Tornado probs

[Central Illinois]

[JoJo]

Looks like an another high risk day, the best looking one for potential in the high risk this year

[jojo762]

Holy hell.

[jojo762]

BROYLES for the WIN. lol go figure... Who knows, he may be right.

[Upper Level LOL]

Of course it's Broyles...of course. 

[andyhb]

First 06z high risk since 11/17/2013.

[HillsdaleMIWeather]

[Central Illinois]

2 minutes ago, jojo762 said:

BROYLES for the WIN. lol go figure... Who knows, he may be right.

Better to be safe and get the word out than to be sorry at this point.

[jojo762]

Kerr, who normally is fairly aggressive with convective outlooks was fairly tame at the 1730Z D2, then Broyles pulled the trigger. First plains high risk since 4/14/12.

[CGChaser]

Just now, jojo762 said:

Kerr, who normally is fairly aggressive with convective outlooks was fairly tame at the 1730Z D2, then Broyles pulled the trigger. First plains high risk since 4/14/12.

Fwiw, it's a combo with Mosier.

[David Reimer]

Well this is either going to go quite well... or be a nasty bust. Regardless a very tight gradient. High risk for Enid with a Slight Risk for Norman. Interestingly enough, many of the OKC famous tornado days were under similiar 'outlook' circumstances. I'm curious where we'll be at 20Z. 

[jojo762]

For posterity...

 ...THERE IS A HIGH RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   SOUTHERN AND CENTRAL KANSAS INTO NORTHWEST OKLAHOMA...

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   HIGH RISK AREA ACROSS PARTS OF OKLAHOMA AND KANSAS...

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   MODERATE RISK AREA ACROSS PARTS OF THE SOUTHERN AND CENTRAL
   PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
   ENHANCED RISK AREA ACROSS PARTS OF THE SOUTHERN AND CENTRAL PLAINS
   INTO LOWER MISSOURI VALLEY...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER GREAT LAKES REGION...

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE SOUTHERN AND CENTRAL PLAINS NORTHEASTWARD INTO THE MID
   MISSISSIPPI VALLEY AND NORTHEASTERN STATES...

   ...SUMMARY...
   An outbreak of severe thunderstorms with tornadoes, very large hail
   and wind damage is expected to develop across parts of the southern
   and central Plains from this afternoon into this evening and
   overnight. Strong long-track tornadoes will be likely from parts of
   central and southern Kansas southward into western Oklahoma. Large
   hail and wind damage will also be possible outside of these areas
   across parts of the southern and central Plains. A severe threat is
   also expected across parts of the lower Great Lakes region late this
   afternoon and early this evening.

   ...DISCUSSION...

   ...Tornado Outbreak Likely Across Parts of the Southern and Central
   Plains Today and Tonight...

   ...Southern and Central Plains...
   An upper-level low will move eastward across the Four Corners region
   and central Rockies today as a lead shortwave rotates around the
   southeastern side of the system into the southern and central
   Plains. At the surface, a very moist airmass will advect northward
   across Oklahoma into southern and central Kansas with surface
   dewpoints reaching the mid 60s to lower 70s by afternoon. Strong
   instability should be in place to the east of a well-developed
   dryline situated from just east of Dodge City southward across far
   western Oklahoma by mid-afternoon. Thunderstorms are forecast to
   initiate rapidly during the mid to late afternoon along the dryline
   with numerous severe thunderstorms moving east-northeastward across
   the southern and central Plains during the late afternoon and early
   evening. A very moist airmass, strongly unstable warm sector,
   favorable deep-layer shear and impressive low-level shear appears
   likely for a tornado outbreak from central and southern Kansas
   southward across western Oklahoma.

   At this time, surface maps show a very moist airmass across the
   eastern third of Texas with lower to mid 70s F dewpoints at most
   observation sites.  This airmass is advecting northward quickly and
   appears certain to overspread the moderate and high risk areas by
   this afternoon. Deterministic and hi-res solutions suggest that a
   strongly unstable airmass will be in place by afternoon with MLCAPE
   values reaching the 3000 to 4000 J/kg range. In addition, the exit
   region of a 45 to 60 kt mid-level jet is forecast to be located
   across northwest Oklahoma and south-central Kansas by late afternoon
   which will create strong deep-layer shear profiles over the top of a
   pristine airmass. NAM forecast soundings late this afternoon show
   0-6 km shear in the 50 to 60 kt range to the east of the dryline
   with gradually veering winds with height in the low to mid-levels.
   This wind profile will support discrete supercell formation. Backed
   surface winds to the southeast, strong speed shear in the boundary
   layer and a strengthening 40 to 50 kt low-level jet will be very
   favorable for tornadoes. Low-level shear is forecast to increase
   during the early evening with 0-3 km storm-relative helicities
   reaching the 350 to 450 m2/s2 range across the moderate and high
   risk areas. This will be favorable for strong tornadoes with several
   long track tornadoes moving across the high risk and moderate risk
   areas. High-end tornadoes will also be possible across the high risk
   area. Forecast soundings also show very steep 700 to 500 mb lapse
   rates of 8.0 C/km. This combined with the strong deep-layer shear
   will make large hail likely with supercells. The more intense
   supercells will likely produce hailstones of greater than 2 inches
   in diameter. By late evening, MCS formation should take place as
   several severe storm clusters move eastward across northern Oklahoma
   and eastern Kansas. Some tornadoes along with large hail and wind
   damage should be associated with this MCS.

   Further south across west-central Texas, a dryline is forecast to be
   situated from near Vernon, Texas south-southwestward to just west of
   San Angelo, Texas. Widely spaced thunderstorms are forecast to
   initiate just to the east of the dryline along this corridor. Strong
   instability, moderate deep-layer shear and steep mid-level lapse
   rates evident on forecast soundings will support the formation of
   supercells. An isolated tornado threat along with a potential for
   very large hail will be possible with supercells that develop during
   the late afternoon and early evening.

   ...Lower Great Lakes Region/Mid Mississippi Valley...
   An upper-level trough will move eastward across the Great Lakes
   region today. At the surface, a cold front is forecast to advance
   southeastward into the lower Great Lakes region by late afternoon as
   moderate instability develops along to the south of the front. 
   Thunderstorms are expected to develop just ahead of the front from
   northern Indiana east-northeastward into northern Ohio and western
   New York late this afternoon. This convection will be supported by
   increasing low-level convergence along the front and be aided by
   large-scale ascent associated with the upper-level trough. NAM
   forecast soundings along this corridor at 00Z/Friday show MLCAPE
   vales in the 1000 to 1500 J/kg range along with 0-6km shear values
   of 35 to 45 kt. This environment may support isolated supercell
   development with large hail possible. However, multicell may be the
   preferred storm mode due to front being oriented parallel to the low
   to mid-level flow. A wind-damage threat will be most likely with
   bowing multicell structures.

   ..Broyles/Mosier.. 05/18/2017

[jojo762]

With the level of ingredients that will be in place... Impressive moisture, an untouched warm-sector with very impressive lapse rates (resulting in extreme instability), favorable deep-layer and low-level shear, along with a favorable mid-level jet timing, I suppose I can see why they/he pulled the trigger given the potential for a high-end event across the high/moderate risk areas... But after seeing the output from the 00Z CAMs I am quite surprised (given, i'm not sold on the messy crap they are showing shortly after CI either.) Guess we'll see how this pans out, David summed it up well. 

[nwohweather]

350-450 m2/s2 on top of dews in the 70s and CAPE of 3000-4000. Holy mother of god that's a powder keg

[HillsdaleMIWeather]

The media hype begins, TWC is in Storm Alert mode, every major news network has made an article about it, and High Risk is actually trending on Twitter.

[jojo762]

00Z NCAR ensemble is highly volatile across KS/OK today with numerous high-end UH tracks. 00Z SPC SSEO is also impressive, popping a 70% 24-hour probability of a UH >100m2/s2 across south-central Kansas. 

[andyhb]

39 minutes ago, nwohweather said:

350-450 m2/s2 on top of dews in the 70s and CAPE of 3000-4000. Holy mother of god that's a powder keg

Need to keep in mind that all of that means nothing if there are too many storms to take advantage of it.

[bjc0303]

One of the first Plains setups this season I can remember the moisture being well on its way... moisture will not be a problem folks. always look at your source regions.

[jojo762]

FWIW, 06Z 12NAM certainly ratcheted things (parameter space) up a notch across much of western and into central Oklahoma by 00Z, and continues to support a high-end parameter space in Kansas by as early as 21Z and continues to into the night. 

[1900hurricane]

Warm front is lifting north on schedule this morning.