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jaxjagman

Tn Valley Severe Weather 2017

221 posts in this topic

On 5/20/2017 at 9:35 AM, nrgjeff said:

Decent tornado if 250 yards wide for 8 minutes. Remember average time OTG is only 10 minutes. Their language downplays it I suppose because it's only EF-0. Seems unchasable given witnesses all say hidden in rain. Glad nobody hurt!

Was out of town but monitoring radar when the warning was issued. Velocity showed a definitive couplet for 5-6 scans prior to warning issuance. Looks like touchdown occurred roughly 10 min after the warning. Per reflectivity, it was certainly wrapped in rain. 

Side note: I have clients in the Mountain City community. After the 2011 EF2, they're terrified of strong storms. Ominous clouds all scream "tornado" to them. Hate that another tornado struck there.

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Mesoscale Discussion 0824
   NWS Storm Prediction Center Norman OK
   0641 AM CDT Wed May 24 2017

   Areas affected...Northeast Alabama...eastern Tennessee...northwest
   Georgia...eastern Kentucky

   Concerning...Severe potential...Watch possible 

   Valid 241141Z - 241415Z

   Probability of Watch Issuance...40 percent

   SUMMARY...Storms should continue to gradually develop through the
   morning and early afternoon, with an isolated tornado, strong wind
   gusts and marginal hail possible.

   DISCUSSION...Storms are beginning to intensify ahead of a strong
   vort max aloft. Although instability is weak, it may be sufficient
   for at least isolated severe storms given cooling aloft and strong
   lift with deepening surface low. Visible satellite imagery shows
   extensive cloudiness is present downstream of these storms, which
   may temper their severity somewhat. However, as storms lift
   northeastward out of Alabama and across Tennessee and into Kentucky,
   some diurnal intensification is expected. Trends will continue to be
   monitored for a possible watch.

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Check of the 12Z Nam shows the LLJ pushing east to Chattanooga and Nashville by midday. It might still be present in the eastern Valley, TYS to MRX and TRI, later today. Upper pattern has a little VBV, but a decent LLJ would create more than adequate turning with height. East Kentucky could be interesting right east of the surface low, but oh that terrain LOL.

ATMO is getting overturned and the main show is to our southeast. Well, they said that in Kansas Saturday and a mesocyclone lasted two hours behind the CF with multiple brief tornado touchdowns. We're not in Kansas, but it is still late May...

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ww0264_radar_big.gif

 

URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 264
   NWS Storm Prediction Center Norman OK
   115 PM EDT Wed May 24 2017

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     central and eastern Kentucky
     western North Carolina
     eastern Tennessee
     southwestern Virginia

   * Effective this Wednesday afternoon and evening from 115 PM
     until 800 PM EDT.

   * Primary threats include...
     A couple tornadoes possible
     Isolated damaging wind gusts to 70 mph possible
     Isolated large hail events to 1.5 inches in diameter possible

   SUMMARY...Thunderstorms now forming near an upper disturbance over
   northern middle Tennessee are expected to increase in coverage and
   intensity through the remainder of the afternoon, while developing
   northeastward and eastward across the watch area.  Large hail and
   locally damaging wind gusts will be possible in strongest storms,
   along with a risk for tornadoes.

   The tornado watch area is approximately along and 105 statute miles
   north and south of a line from 40 miles west northwest of Crossville
   TN to 40 miles southeast of Jackson KY. For a complete depiction of
   the watch see the associated watch outline update (WOUS64 KWNS
   WOU4).

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Slight chance (risk) of anything interesting in Tennessee on Thursday. Models continue to settle on a solution of one or two MCS(s) with some straight line wind potential. It will be nothing like May 27. Derecho checklist is not met Thursday. WAA is missing at 850/700 mb. Height falls are not great enough at 500 mb. Speed lacks at 200 mb. Do not need much, but this is pathetic June gloom, lol.

Road to a better set-up might be a CIV (convectively induced vort max) coming out of the Plains or Mississippi Valley overnight. Otherwise I think 1-2 MCSs seems reasonable given the instability and boundaries left over from previous rain. If CAMs converge on a more likely corridor ENH risk for straight winds would not surprise me. I cannot see anything higher though. On the flip side there is a road to Marginal. Too much midday convection ahead of any MCS would stabilize/overturn the atmosphere, #2017ing in some circles.

Morning update: And sure enough 2017ing. Rain from Nebraska to South Carolina. Hopefully it is not the case August 21.

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On 6/14/2017 at 11:49 AM, nrgjeff said:

Slight chance (risk) of anything interesting in Tennessee on Thursday. Models continue to settle on a solution of one or two MCS(s) with some straight line wind potential. It will be nothing like May 27. Derecho checklist is not met Thursday. WAA is missing at 850/700 mb. Height falls are not great enough at 500 mb. Speed lacks at 200 mb. Do not need much, but this is pathetic June gloom, lol.

Road to a better set-up might be a CIV (convectively induced vort max) coming out of the Plains or Mississippi Valley overnight. Otherwise I think 1-2 MCSs seems reasonable given the instability and boundaries left over from previous rain. If CAMs converge on a more likely corridor ENH risk for straight winds would not surprise me. I cannot see anything higher though. On the flip side there is a road to Marginal. Too much midday convection ahead of any MCS would stabilize/overturn the atmosphere, #2017ing in some circles.

Morning update: And sure enough 2017ing. Rain from Nebraska to South Carolina. Hopefully it is not the case August 21.

Nothing much happened here.Some winds maybe 20-30.Some nice rain though with numerous lightning strikes around.Wind shear was weak as you mentioned.

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We had a good shelf cloud in Chattanooga on Thursday. However the GOES-16 vis loop from the day is probably more fun to watch. Today (Sunday) looks similar. Nah, it sucked. This is one of the least inspiring severe seasons I can remember.

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Cindy keeps severe hope alive. From SPC Day 2 valid Thursday:

...ArkLaMiss and surrounding region... 
   Models indicate a zone of stronger low and deep-layer shear will
   spread north in association with the migration of the northeast
   quadrant of Cindy---resulting in a conditional risk for mini
   supercells capable of isolated tornadoes.  Models vary
   considerably but some convection-allowing model guidance indicates
   cellular storms developing within a corridor of 500-1250 J/kg MLCAPE
   with enlarged hodographs.  A couple of tornadoes are possible with
   the stronger/more persistent low-level mesocyclones.  

I agree with the outside risk for something more than typical mini-sups with tropical systems. If clouds break up in Mississippi, as forecast between the cyclone and the slug of moisture into Alabama, instability will verify. Much of the wind shear is of course the LLJ, and it is somewhat unidirectional above. However NWP hints a just a bit of veering at the upper levels. If the upper levels can veer 30-40 degrees from the LLJ, hodographs would elongate. We'll see if all this happens. NWP may be allowing too much influence from the upper level westerlies to the north. If NWP is right though, Thursday could indeed feature a couple real mesocyclones.

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Finally Comcast is up and running here this afternoon.Been running slow as a turtle for past few days.Every time a tried to post i'd freeze up it's been so slow.

 

Not much of any severe here.Little bit of wind and rain other than that ...blah

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