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weatherextreme

Late April severe weather risk ~Mon thru next Mon 4/24-5/01

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1 hour ago, Drz1111 said:

I'd love to hear a postmortem on how the Van Zandt Co. tornados happened today.  It didn't look like there was nearly enough bulk shear for strong rotating updrafts in the midlevels, and visually the updrafts looked barely sheared when everything was in the towering cumulus stage, so notwithstanding the good low-level shear I was completely skeptical of tornados literally until the first tail end storm started spinning up.  Then all of a sudden that starts strongly rotating; then it's flanking updraft starts to rotate (that turns into the Canton storm) and so on for the next 2 or 3 updrafts.  So whatever was happening there, it was repeatable and not a fluke.

Also, I was out with Silver Lining Tours thanks to a tip from someone on this forum back in 2016 and obviously today was a home run for me, so thanks to whoever dropped that recommendation back when.  They were great and professional. 

Actually the 0Z NAM last night was the first hint that something would go down today, and the 0Z 3-km NAM was downright impressive. Both models spun up a subtle low in S OK that backed the winds in E TX to southeasterly. Earlier runs, and the GFS, kept the sfc low buried in S TX/MX and so the sfc winds veered along the front.

The kicker was the 3-km NAM veered the 500mb flow slightly more towards 0Z and this allowed more of the stronger bulk shear magnitudes to overspread the free warm sector, earlier. These subtle changes in trof geometry were not captured really well by any models until late-game, but made a huge difference in keeping storms supercellular just long enough.

Finally, on the mesoscale level, the sfc obs indicated that there was not one main initiating boundary (the cold front out towards 35), but two... one ahead of the cold front, separating the backed windfield from more veered flow closer to the front. Many of the storms initiated on the latter boundary because convergence was stronger along it.

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34 minutes ago, BuffaloWeather said:

That had to be over 1 1/2 wide at one point. Unreal video

Yeah it was huge. Seeing the damage to the car dealership is impressive. Lots of cars tossed and the building shredded but the metal framing still mostly intact. Looks strong EF-3ish to me when it hit the dealership. No telling what damage exist we haven't seen yet so who knows what the rating will end up. 

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Also remember that all it takes is one location to experience the most severe damage for the EF rating to be increased. No doubt though that this was a strong/violent tornado and it was on the ground for quite a ways.

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1 hour ago, jojo762 said:

Believe the boundary put out by that HP supercell--turned compact MCS-- in Louisiana earlier on in the day played a significant role in storm intensification. The 00Z SHV RAOB was fairly impressive to begin with in the low-levels (ESRH of ~400 m2/s2), but that ambient environment coupled with the boundary and extreme instability in Texas made it all come together... Well all that and very low LCLs.

 

Just another reminder that the 0-1km/0-3km layer are really what matters the most.

If you have SHARPpy, you can actually use the KSRV sounding as a starting point and modify it to something close to the near storm environment. I probably overcooked the one I just did by a little bit (my temp/dewpoint is something I recorded a little before I was in position to intercept those storms, and I might have backed and strengthened my surface winds a little too much), but it at least gives you an idea.

 

5905779648196_Canton(ModifiedSHV).thumb.png.35ae538274b5fa496c96bc3f1ace345a.png

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5 minutes ago, 1900hurricane said:

If you have SHARPpy, you can actually use the KSRV sounding as a starting point and modify it to something close to the near storm environment. probably overcooked the one I just did by a little bit (my temp/dewpoint is something I recorded a little before I was in position to intercept those storms, and I might have backed and strengthened my surface winds a little too much), but it at least gives you an idea.

Pretty rare to see such steep mid level lapse rates with such a moisture-laden sounding through the column.

A low level environment like that can certainly overcome iffy wind fields further aloft. Saw it on days like 5/22/16, 5/6/15 in N KS, to a lesser extent Vilonia 4/27/14, etc.

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6 minutes ago, andyhb said:

Pretty rare to see such steep mid level lapse rates with such a moisture-laden sounding through the column.

A low level environment like that can certainly overcome iffy wind fields further aloft. Saw it on days like 5/22/16, 5/6/15 in N KS, to a lesser extent Vilonia 4/27/14, etc.

Extreme surface-based instability with substantial low-level shear. The mid and upper levels didn't appear to be all that iffy. Sure, more low-level shear than deep layer shear, but good crossovers and 700mb mesoanalysis suggests there wasn't much VBV at all.

Some 23z maps:

IMG_1470.thumb.JPG.54246f72dfbef9c28be75e0308a39f5e.JPG

IMG_1471.thumb.JPG.1b48d882c85258516e4c4ed1c77df6bb.JPG

IMG_1474.thumb.JPG.1e6401a82b16a8cbff8e1f877945e658.JPG

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These have to be two of the dumbest yet luckiest people alive tonight. Roof flies off your barn SEEK SHELTER. Nope they just stand outside in a tornado. Glad they are alive.

 

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I was referring more to the lack of stronger ventilating flow in a very high PWAT/modest bulk shear environment, which would generally result in rapid transition to HP mode and precip-saturated RFDs. Given the intensity of the low level SRH and favorable storm relative inflow (not to mention plenty of low level instability), the latter of those conditions was essentially rendered irrelevant and the results were strong/violent tornadoes.

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Pretty large area of 5% tornado for tomorrow. Most of the area is for the other sub-forums, but looks like we still have LA and some of AR/MO within the outlook.

 

day1otlk_1200.gif?1493532317216

 

day1probotlk_1200_torn.gif?1493532474326

 

Strong Tornadoes mentioned

 

 

Mississippi Valley to western slopes of the Appalachians...
   Taking into account the preceding discussion, uncertainties seem too
   large to allow for more than an outlook of a categorical slight risk
   at the present time.  But given the strength of the synoptic system
   and associated wind fields, and at least a corridor of pre-frontal
   boundary layer moisture characterized by surface dew points in the
   mid 60s to near 70F, it may not be out of the question that a window
   of opportunity for considerable severe weather potential could
   develop this afternoon and evening.  This seems mostly likely to be
   focused near or just east of the Mississippi Valley, and mostly in
   the wake of an initial north/south oriented band or two of
   thunderstorms spreading east of the Mississippi Valley, where
   guidance appears suggestive that breaks in the overcast could allow
   insolation to contribute to at least pockets of mixed layer CAPE on
   the order of 1000-2000 J/kg.  Of particular concern is that the
   environment could become conducive to at least isolated to widely
   scattered long lived discrete supercell development, initially
   anywhere from portions of eastern Missouri into Illinois, southward
   through portions of western Kentucky and Tennessee into northern
   Mississippi.  In the presence of clockwise curved low-level
   hodographs characterized by strong to extreme shear, some of these
   could become capable of producing strong tornadoes.

   

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9 minutes ago, andyhb said:

I was referring more to the lack of stronger ventilating flow in a very high PWAT/modest bulk shear environment, which would generally result in rapid transition to HP mode and precip-saturated RFDs. Given the intensity of the low level SRH and favorable storm relative inflow (not to mention plenty of low level instability), the latter of those conditions was essentially rendered irrelevant and the results were strong/violent tornadoes.

FWIW, this doesn't really come across in the chaser videos but all the tornadoes this afternoon were substantially rainwrapped. But it seemed that even the rain-cooled air was either buoyant or near-buoyant; we were under the meso for the (much weaker) tornado immediately preceding the big wedge and while there was no wall, you could see tendrils of scud extending almost all the way to the surface being pulled almost directly into the cloud base, while rapidly moving from left to right.  It was most impressive.

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Tornado Warning
LAC067-083-123-301030-
/O.NEW.KJAN.TO.W.0050.170430T0934Z-170430T1030Z/

BULLETIN - EAS ACTIVATION REQUESTED
Tornado Warning
National Weather Service Jackson MS
434 AM CDT SUN APR 30 2017

The National Weather Service in Jackson has issued a

* Tornado Warning for...
  Morehouse Parish in northeastern Louisiana...
  Northwestern Richland Parish in northeastern Louisiana...
  West Carroll Parish in northeastern Louisiana...

* Until 530 AM CDT

* At 433 AM CDT, a severe thunderstorm capable of producing a tornado
  was located over Swartz, moving northeast at 45 mph.

  HAZARD...Tornado and quarter size hail.

  SOURCE...Radar indicated rotation.

  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.

* This dangerous storm will be near...
  Galion around 505 AM CDT.
  Goodwill around 510 AM CDT.
  Jones around 520 AM CDT.

Other locations impacted by this tornadic thunderstorm include
Forest, Bonita, Collinston, Mer Rouge, Pioneer and Oak Ridge.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

TAKE COVER NOW! Move to a basement or an interior room on the lowest
floor of a sturdy building. Avoid windows. If you are outdoors, in a
mobile home, or in a vehicle, move to the closest substantial shelter
and protect yourself from flying debris.

&&

LAT...LON 3271 9201 3301 9170 3301 9141 3293 9130
      3288 9131 3287 9132 3287 9134 3284 9135
      3275 9135 3244 9194 3246 9194 3252 9190
      3260 9193 3266 9191 3267 9193 3266 9194
      3271 9197
TIME...MOT...LOC 0933Z 225DEG 37KT 3257 9194

TORNADO...RADAR INDICATED
HAIL...1.00IN

$$

NF

 

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8 minutes ago, MattPetrulli said:

In my opinion, lets just keep this forum for the entire event because there is NO ONE discussing it in the SE forum

Also debris ball going through Vicksburg, MS.

Rotation on this one not too shabby either   

Screenshot_20170430-083331.png

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In my opinion, lets just keep this forum for the entire event because there is NO ONE discussing it in the SE forum

Also debris ball going through Vicksburg, MS.


Nope, if it doesn't involve NC, SC or GA, they could care less about it over there usually.

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Just now, SmokeEater said:


Nope, if it doesn't involve NC, SC or GA, they could care less about it over there usually.

I once asked about the severe threat there (right before January 21-22) and why no one was covering it. They all said they wanted snow and lived in the carolinas. Quite annoying. 

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I once asked about the severe threat there (right before January 21-22) and why no one was covering it. They all said they wanted snow and lived in the carolinas. Quite annoying. 


Lol and most of the time don't care about severe in general. Snow year round though.

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28 minutes ago, MattPetrulli said:

In my opinion, lets just keep this forum for the entire event because there is NO ONE discussing it in the SE forum

Also debris ball going through Vicksburg, MS.

MS and AL usually are in here or Tennessee forum if they have a thread.....like Smoke said 95% of the SE forum posters live in NC/SC/GA and southern VA and most are not severe weather folks though there are a few of us but we usually end up in here. Also its like not even 9 am on a Sunday so there not a lot of traffic on the board in general. 

 

There was a pretty obvious TDS with CC on that line south of Vicksburg 

screenshot.png

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4 minutes ago, downeastnc said:

MS and AL usually are in here or Tennessee forum if they have a thread.....like Smoke said 95% of the SE forum posters live in NC/SC/GA and southern VA and most are not severe weather folks though there are a few of us but we usually end up in here. Also its like not even 9 am on a Sunday so there not a lot of traffic on the board in general. 

 

There was a pretty obvious TDS with CC on that line south of Vicksburg 

screenshot.png

I don't know how many frames you can go back on radar scope, but the debris signature was pretty evident for at least 16 scans. 

Screenshot_20170430-085347.png

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Just now, mob1 said:

I don't know how many frames you can go back on radar scope, but the debris signature was pretty evident for at least 16 scans. 

 

Yeah I saw it, is there a way to screenshot or to freeze previous images in a loop on radarscope? I just took a screenshot of the latest CC scan as I dont know how to capture any previous to that. 

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I don't know how many frames you can go back on radar scope, but the debris signature was pretty evident for at least 16 scans. 

Screenshot_20170430-085347.thumb.png.e63b52092fd8e1484dfcfa53a4cfe863.png


Oh yea, it first started right on top of Port Gibson, there's a tornado report from there with trees down.

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2 minutes ago, downeastnc said:

Yeah I saw it, is there a way to screenshot or to freeze previous images in a loop on radarscope? I just took a screenshot of the latest CC scan as I dont know how to capture any previous to that. 

I don't think you can pause a loop, I just kept taking screenshots of the loop till I had the right one (I'm just primitive that way) 

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