Severe weather risk 4/30 - 5/3

[mfgmfg]

7 minutes ago, mob1 said:

Since I don't know how to embed the link, I'll just take a screenshot. Very impressive looking tornado.

Just link the tweet URL and the forum software takes care of it:

 

[Indystorm]

Wow...warning for softball size hail near Minneapolis KS.

[Torchageddon]

First YouTube video of the Culver KS Tornado hot off the press:

 

[Upper Level LOL]

...should this have been a PDS watch?

[jojo762]

9 minutes ago, Upper Level LOL said:

...should this have been a PDS watch?

Given questions about coverage AND questions about storm interactions near the triple point I'd say no. There was always the chance for multiple impressive tornadoes though. SPC did a great job today.

[mob1]

Confirmed tornado with this one. 

[SmokeEater]

WIBW is live for those cells.

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[Buckeye05]

This isn't over yet. Possibly a strong tornado south of Clay Center, with increasing rotation with the second cell near Oak Hill.

[SmokeEater]

170 kts G2G South of Clay Center, the one behind it is going nuts as well.

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[SmokeEater]

Still on the ground near Clay Center.

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[andyhb]

Best video I've seen of Trescott/Bennington 3.0.

[jojo762]

Looks like the 00Z NAM may have finally come on board... doesn't develop convection along the DL in OK until late in the afternoon/into the evening, and has quite the progged environment by 00Z. Can't get into too many specifics because I am at work, but I think it looks promising. 

[jojo762]

Going to need a TOR warning soon it appears on the supercell just west of Milford Lake in Kansas. 

[Drz1111]

2 minutes ago, jojo762 said:

Going to need a TOR warning soon it appears on the supercell just west of Milford Lake in Kansas. 

You mean the one with the massive hook and the TDS?  Yeah, you'd think the local office might want to get on that.

[Quincy]

11 minutes ago, jojo762 said:

Looks like the 00Z NAM may have finally come on board... doesn't develop convection along the DL in OK until late in the afternoon/into the evening, and has quite the progged environment by 00Z. Can't get into too many specifics because I am at work, but I think it looks promising. 

Have a feeling based on trends that there's going to be something significant tomorrow between southern Kansas and North Texas. 

The latest HRRR shows upwards of 2500 J/kg CAPEs over the eastern portion of the Texas panhandle into western Oklahoma by noon. Such strong heating results (model verbatim) in cap erosion by early afternoon and explosive storm development. 

Although low level shear looks modest, there are signs of favorably backed low level winds, especially down near the Red River. Large buoyancy can overcome modest shear.

Still need to review subsequent CAM solutions and see if there's a growing consensus. Very large hail seems likely, but the tornado threat is a bit more unclear. If storms did wait until mid/late afternoon, they would probably go nuclear, but I don't think the cap will be that strong. 

Another note is that assuming there isn't complete overturning of the environment during the afternoon, a bonafide tornado threat could continue into the night over a large portion of Oklahoma. 

Stay tuned. 

[Indystorm]

Fort Riley military reservation and Manhattan Kansas are just east of that lake.  Too close for comfort for me with those training cells coming in from the west.

[Buckeye05]

8 minutes ago, Drz1111 said:

You mean the one with the massive hook and the TDS?  Yeah, you'd think the local office might want to get on that.

Not seeing a ton on velocity or CC, but that is an extremely impressive storm. A little concerned for the Manhattan area.

[hlcater]

(FWIW)HRRR isn't terrible for 18z tomorrow, at least relative to other models. This sounding from W OK wouldn't be ideal for tornadoes but it is an 18z sounding. However I feel like a deep veering(w/ little or no VBV) profile like that would support supercells if nothing else? Also noteworthy is the 30kt LLJ at 18z, also higher than other models. Does this make me optimistic for tomorrow? Not quite yet.

[MattPetrulli]

Would start with either a large 5% or a 10% unhatched in west central OK to start the day and adjust as needed. CAMs and NAM paints that area best for supercells, could be a decent nocturnal threat too in Central and eastern OK.  

Still lots of uncertainties and will probably depend on HRRR and the CAM's 12z suite for tornado potential since they preformed pretty well today.

[WhiteoutWX]

That's a pretty sizeable westward shift in the threat area over OK from the 12z CAMs runs ^^

Would likely save most of the metro OKC area from much of a tornado threat if initiation is that far west. 

[jojo762]

This was definitely a significant tornado, not sure what damage indicators the storm survey will find (they'll have a tough time getting out tomorrow and doing a full survey) but videos I have seen show some pretty good motion, and the roar is classic. Looks like a drill bit. 

 

[Stebo]

A couple picts from 81 and 18 sw of Bennington earlier. 

[jojo762]

If you're buying what the 00z GFS is selling tomorrow then you're possibly buying into a regional severe weather outbreak for much of Kansas and Oklahoma, with significant tornado *potential* (in the evening) extending from Southern Kansas down into S/SW Oklahoma. 00Z GFS represents a similar scenario to today, with a few differences. 

1. The environment by 21Z is fairly similar to what it was today over the MDT and ENH Risk areas by 21Z (around the time the "top" will probably start to come off, if not before), with a few improvements... Kinematically we will be looking at ~100-150m2/s2 0-3KM SRH by 21Z with bulk shear on the order of 40-50kts, so that is the same as today at the same time. But thermodynamically and moisture wise we should be significantly better by 4pm than we were today. With areas east and along the dryline likely featuring 2500-4000J/KG CAPE between 21-00... PBL moisture will be significantly better than Tuesday with mid/upper 60s dewpoints covering most of the warm-sector.

2. By 00Z the low-levels dramatically improve as the LLJ begins to strengthen and surface/near-surface winds begin to back to a south-southeasterly direction along much of the DL from KS into OK. This results in 0-3KM SRH dramatically improving by evening (much like we saw today) with 200-400m2/s2 progged east of the dryline by 00Z, which when combined with a significantly moist PBL signals ample tornado potential.

 3. Given how close we are to the event, I think it is probably best to use CAM precip fields to gain an idea as to what type of convective schemes/regimes we are going to see tomorrow. Given what 00z CAMs are showing, I see two separate/obvious regimes tomorrow:

• In central/northeast KS where initially cellular convective development in SW/S KS congeals into a forward propagating bowing MCS, capable of swaths of damaging winds and perhaps large hail and a spin up tornado or two.
• In far southern Kansas and Western/Central Oklahoma where convective development will likely be more sparse and much more cellular. In this area we are much more likely to see several discrete supercells capable of producing all severe hazards. Much was the case today along the dryline, some of these storms *may* have issues with maintenance and becoming longer-tracking, in addition to maintaining a low-level mesocyclone earlier in the period due to relatively lackluster low-level winds. HOWEVER, any organized discrete supercells in this area between 23-03Z (or later) will have significant tornado potential, given the environmental conditions discussed above. 
• I am quite curious as to where the dryline ends up setting up as there is quite a spread among various models on where it sets up... This will have a significant impact on the tornado threat for the two biggest metro areas at play here (Wichita and Oklahoma City). \
• One last point, clearly if storms become too numerous or develop too early in the southern area, then the tornado potential would be mitigated significantly for the evening. But given the progged degree of CINH, I am not very confident in that scenario. But on the flip side of that I am not particularly confident in the number of or ability of supercells to sustain themselves... Complicated forecast for sure.

4. Needless to say, but if the RAP/12NAM end up being correct on the position of the dryline, then you can throw most of my thoughts out the window location wise.

 

 

[Quincy]

The GFS does show a pretty volatile environment near/west of the I-35/135 corridor late this afternoon. The forecast precipitation fields suggest discrete storm modes from southern Kansas down to roughly the Red River. Like its higher resolution counterparts, it shows a massive blob (developing MCS) over central Kansas. 

I don't put much stock into the GFS for mesoscale details, so take that with a grain of salt.

The moisture does look a bit better than Tuesday, by about 2-5F (dew-points) or so.

I think this has the potential of outperforming 5/18/17 for areas west of I-35/135, but not to the point of justifying high risk tornado probabilities. The two limiting factors I can see are limited low-level shear prior to 00z and a tendency for messy storm modes in Kansas.

[jojo762]

 Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Wed May 02 2018

   Valid 021200Z - 031200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM NORTHEAST
   KS INTO FAR NORTHWEST MO...

   ...SUMMARY...
   Severe thunderstorms are expected across parts of the southern and
   central Plains into the middle Mississippi Valley today and tonight.
    Swaths of damaging winds, large to very large hail, and a couple of
   tornadoes will be possible.  Isolated to scattered severe storms may
   also develop across parts of the Midwest, with hail and damaging
   winds the primary threat.

   ...Synopsis...
   Upper pattern at the beginning of the period will look much like it
   did on Tuesday with a deep upper trough extending from the Canadian
   Prairie provinces southwestward to an upper low center over the
   Lower CO River Valley and upper ridging over the Lower MS Valley.
   Upper trough is expected to be a bit more progressive Wednesday with
   a lead shortwave trough (and accompanying enhanced mid-level flow)
   ejected into the central Plains during the afternoon. 

   The surface pattern at the beginning of the period will feature a
   low over the Upper Great Lakes with a cold front extending
   southwestward to another low over central KS. Expectation throughout
   the day is for the central KS low to remain largely in place as the
   frontal zone remains stationary. Dryline extending southward from
   the low will sharpen as moisture return persists across the southern
   and central Plains. Forcing for ascent associated with the
   previously mentioned shortwave as well as convergence along the
   dryline provide the impetus for another day of strong to severe
   storms.

   ...Central KS northeastward into the Middle MS Valley...
   Another day of return flow is expected across the region with
   dewpoints likely reaching the mid 60s across central KS by this
   afternoon. This return flow will occur beneath a strong EML
   characterized by mid-level lapse rates at or above 7.5 deg C per km.
   Temperatures across central KS and vicinity are expected to reach
   the low to mid 80s which, when combined with favorable low-level
   moisture and steep mid-level lapse rates will result strong
   instability by the early afternoon. Despite the strong EML,
   convective initiation is possible as early as 18Z as a subtle
   shortwave trough moving through the central/southern High Plains
   begins to provide forcing for ascent. Most probable location for
   initial convective initiation is currently southwest KS and far
   eastern TX/OK Panhandles with initiation then expanding northward
   along the dryline to the triple-point. 

   Convective initiation will occur in a similar area as Tuesday (with
   perhaps slightly more southwestward extent) and the overall
   thermodynamic environment is comparable. However, subtle differences
   in the wind fields will exists with the low-level flow a bit weaker
   and more veered. Additionally, more favorable dewpoints and warmer
   temperatures will result in less convective inhibition. These
   factors as well as slightly stronger forcing for ascent will result
   in a more linear convective evolution, as opposed to the more
   discrete storms experienced Tuesday. Anticipated linear nature of
   the storms lends itself to a higher threat for damaging wind gusts,
   although large to very large hail and a few tornadoes are still
   possible, particularly with initial development and/or along the
   southern flank of the line. 

   Anticipated MCS will likely mature near northeast KS and vicinity
   with the potential for a few significant wind gusts in this area.
   Severe threat will continue farther downstream with the expectation
   that the northern portion of MCS tracks along the frontal zone from
   IA into southern WI and the southern portion moves through central
   MO. 

   ...Far Eastern TX Panhandle....Western OK...
   A more conditional severe threat exists across this region. Numerous
   factors, including the lack of stronger forcing for ascent, only
   weak convergence along the dryline, and slightly cooler temperatures
   than areas farther north (resulting from abundant high cloudiness),
   contribute to the expectation that the strong capping inversion will
   likely inhibit anything but isolated storm development. Given the
   favorable thermodynamics and anticipated discrete storm mode, any
   storm that does develop would have the potential to produce very
   large hail and perhaps a strong tornado.

   ...TX Big Bend northward into north-central TX...
   Afternoon development is possible with the warm, well-mixed
   environment in the TX Big Bend vicinity. Steep lapse rates and
   strong shear support the potential for very large hail with any
   afternoon storms. Additional thunderstorms are possible later into
   the evening as a subtle shortwave trough approach the region.
   Favorable thermodynamics and kinematics will persist, supporting the
   potential for additional severe thunderstorms. Hail would be the
   primary threat will this activity. Expectation is for theses storms
   to track northeastward into north-central TX overnight.

   ...Northeast CO...
   Post-frontal, upslope flow will provide the impetus for a few
   thunderstorms during the afternoon. Steep lapse rates will support
   the potential for hail with the strongest/most persistent updrafts.

   ..Mosier/Leitman/Bentley.. 05/02/2018

[jojo762]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0100 AM CDT Wed May 02 2018

   Valid 031200Z - 041200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
   THE MID MISSOURI AND MISSISSIPPI VALLEYS...

   ...SUMMARY...
   Scattered severe thunderstorms (capable of large hail, damaging
   winds, and a few tornadoes) are forecast from parts of the southern
   Plains to the mid Missouri and Mississippi Valleys on Thursday.

   ...Mid Missouri and Mississippi Valleys...
   Within the broader western US trough, a shortwave impulse will eject
   northeast toward the region during the afternoon. In conjunction
   with this evolution, 60-80 kt of southwesterly 500mb flow will
   overspread eastern Kansas, western/northern Missouri, and southern
   Iowa. Amplifying deep ascent ahead of this wave should favor a weak
   surface cyclone translating northeast across the mid Missouri Valley
   through the day, with a warm front to its east gradually lifting
   north. Although heating may be stunted some by lingering
   clouds/precipitation during the morning/early afternoon, clearing
   near the dry line (extending to the south across eastern Kansas) and
   warm sector dew points in the mid 60s are expected to support MLCAPE
   values upwards of 1000-2000 J/kg. Convergence near the triple point
   and dry line, combined with deep ascent overspreading the region,
   will likely encourage vigorous convective initiation during the
   afternoon.

   Organized by ample effective shear (with deep-layer vectors having a
   significant component perpendicular to the dry line), several
   supercells may develop near the mid Missouri Valley and spread
   east/northeast through the evening. Relatively straight hodographs,
   characterized by some counter-clockwise curvature aloft, may sustain
   a few left splits, resulting in a combination of supercells and
   perhaps small bows. These cells are expected to be capable of all
   severe hazards, with very large hail possible from initial discrete
   development.

   ...Texas to the Ozarks...
   Lingering convection may be ongoing Thursday morning, aided by a
   southern branch of an 850mb jet extending from Texas northeast to
   the Ohio Valley. These cells may present a residual damaging wind
   and large hail threat, but should weaken and lift northeast as the
   jet relaxes and veers. However, with the region still under the
   influence of broad southwesterly flow aloft, a dryline positioned
   from the Edwards Plateau to the Big Country may initiate new
   convection through the afternoon. Moderate mixed-layer buoyancy
   (around 1000-2000 J/kg) and ample effective shear would support a
   few severe storms, primarily capable of large hail and damaging
   winds, but perhaps a tornado as well. Relatively straight hodographs
   suggest one or more small convective systems may organize, with
   persistent upshear initiation over parts of central/eastern Texas
   during the afternoon/evening.

   ...Northeast...
   Within fast, zonal westerly flow, a series of low-amplitude impulses
   will cross the region on Thursday. The first will likely cross New
   England during the morning hours. While related ascent may yield
   shallow convection, an initial lack of heating should keep any cells
   weak. Ongoing high clouds through the day may temper afternoon
   heating as well, but downslope trajectories and low-level warming
   should generate modestly unstable boundary layer profiles. Isolated
   to widely scattered thunderstorms are expected by afternoon, given
   increasing forcing for ascent (related to the secondary impulse) and
   weak surface convergence along an inland trough. With unidirectional
   wind profiles and 850mb westerly flow around 40-50 kt, cells may
   organize into small bowing segments capable of locally damaging
   winds. Additionally, a brief tornado cannot be ruled out. If surface
   heating / instability appear stronger in later forecasts, a slight
   risk may be warranted.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     30%     - Enhanced
   Hail:     30% SIG - Enhanced

   ..Picca.. 05/02/2018

[Radtechwxman]

2 hours ago, Stebo said:

A couple picts from 81 and 18 sw of Bennington earlier. 

You must have been right by us! Had the same view. Tornado was on the right edge of that rain near the smoke

[Quincy]

No big changes this morning. The 12z OUN sounding shows a moist profile up to about 850mb. Modifications to the AMA sounding suggest (with support from mesoanalysis) that there is already 2000-3000 J/kg of SBCAPE in place near the western Oklahoma/Texas border region. High resolution models show some backing of surface winds to SSE/SE this afternoon near a dryline bulge in far southwestern Oklahoma. Low-level shear looks to be on the order of about 10 knots in the 0-1km layer, so any substantial tornado threat will probably hold off until late afternoon. Low-level shear looks slightly better farther north, but the tradeoff is somewhat less directional shear.

Any way you slice it, large buoyancy coupled with more than ample deep layer shear should result in at least isolated supercells in western Oklahoma layer today with significant severe possible, if not probable. Moisture is better than yesterday and upper level forcing is improved. If storms stay widely spaced, watch out. One has to be realistic and realize that there's always the potential for storm clustering, especially given stronger forcing. If yesterday taught us anything, if this happens, don't discount the increasing low-level jet toward 00z...

[CheeselandSkies]

Only way yesterday could have gone better than it did from a chasing standpoint was if the two southernmost, widely isolated cells had been able to really get cranking, and parameters/CAMs always suggested that was a long shot. Even so, one of them did produce that large funnel/likely tornado under very photogenic structure near the OK/KS line.

[mfgmfg]