Tn Valley Severe Weather

[CheeselandSkies]

Goodness, look at that trough digging into the western US on the 12Z NAM with unfettered southerly flow off the western and central Gulf. Where was that in May?

[nrgjeff]

Saturday afternoon events Middle Tennessee and points west might luck out if rain can get out before events start. John I hope the Christmas parade works out. I've lost interest in thunderstorms; so, I will hope for fair weather.

Appears severe starts Friday in the Ozarks; even more LOL with early sunset. Saturday dynamics seem to drift north of instability; so, rain here should be fairly benign. Rain timing should be in the morning many areas, including Mid-Tenn. Might still be afternoon showers in East Tenn. GFS is slower (wetter for Mid-Tenn) but ECMWF and NAM both push out the rain in time.

[CheeselandSkies]

Enhanced (30% risk) for ARKLATEX into lower MS valley Friday. Slight risk for Dixie Saturday. Not an ideal setup but wouldn't sleep on an isolated impact event or two. This is the time of year when tornadoes in the South can strike any time of day, often out of a previously innocuous-looking QLCS, and people aren't as aware as they might be in the spring.

[jaxjagman]

One more chance of severe weather should be Monday then close this thread out for the year.This threat looks  more west of I-65 Monday,but we'll see, looks to be quick moving system .Clouds could be a limiting factor as SPC mentions.Euro shows a line of low level convergence through the western Valley to mid Valley,wouldn't be surprised to see a slight risk tomorrow in parts of the Valley,if the models don't flip tonight's run

 

Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0358 AM CST Fri Dec 28 2018

   Valid 311200Z - 051200Z

   ...DISCUSSION...
   Cyclogenesis and a strong low-level jet will evolve Monday (day 4)
   over the mid MS, TN and OH Valleys in response to a deamplifying,
   northeast-ejecting shortwave trough. The cyclone will undergo some
   deepening as it develops northeastward, but model differences
   persist regarding the intensity of the low. Nevertheless at least
   partially modified Gulf air will advect northward through the
   pre-frontal warm sector contributing to a narrow corridor of weak
   instability from LA through MS and west TN. Weak lapse rates and
   widespread clouds will serves as limiting factors, and at least a
   shallow near surface stable layer might persist, especially with
   northward extent through the TN Valley. A band of showers and
   thunderstorms will develop along and just ahead of the cold front,
   and this activity will be embedded within wind profiles favorable
   for organized severe storms. While at least low severe probabilities
   will likely be introduced in the next update, too much uncertainty
   still exists regarding the evolution of the thermodynamic
   environment to introduce a 15% or greater risk area at this time. 

[jaxjagman]

Still a chance of storms in the western Valley,GFS isnt as good compared to yesterday

Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0205 AM CST Sat Dec 29 2018

   Valid 311200Z - 011200Z

   ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
   OF THE LOWER MISSISSIPPI VALLEY...

   ...SUMMARY...
   A few strong to severe storms with damaging wind the main risk are
   possible over a portion of the lower Mississippi Valley on Monday.

   ...Lower Mississippi Valley region...

   A cyclone will evolve over the lower to mid MS Valley region early
   Monday in response to forcing accompanying a northeast-ejecting but
   deamplifying shortwave trough. Trailing cold front should extend
   from a weak low in AR southwest through eastern TX at the start of
   the period, before continuing into the southeast U.S. as the cyclone
   develops northeastward through the OH Valley and lower Great Lakes.
   A corridor of modifying Gulf air with mid 60s F dewpoints should
   advect northward through pre-frontal warm sector along an intense
   (70 kt) southerly low level jet. This process will contribute to
   some destabilization, but CAPE will remain very marginal (less than
   500 J/kg) owing to widespread clouds and weak mid-level lapse rates.
   Showers and a few thunderstorms will be ongoing along the warm
   conveyor belt from eastern TX/LA into AR, and some intensification
   might occur during the day as this band continues east and interacts
   with the moistening boundary layer, though a near-surface stable
   layer could persist especially with northward extend toward the TN
   Valley. Though wind profiles will be favorable for organized severe
   storms, expected weak thermodynamic environment will remain a
   limiting factor. Nevertheless, some potential will exist for some of
   the convection to organize into mostly low-topped line segments
   capable of a few locally strong wind gusts later in the day into the
   early evening.

[jaxjagman]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 AM CST Sun Dec 30 2018

   Valid 311200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MONDAY AFTERNOON
   AND EVENING ACROSS PARTS OF MID SOUTH INTO LOWER OHIO AND TENNESSEE
   VALLEYS...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the Mid South into
   lower Ohio and Tennessee Valley region Monday afternoon and evening,
   accompanied by a risk for potentially damaging wind gusts and
   perhaps a couple of tornadoes.

   ...Synopsis...
   Mid/upper flow appears likely to remain broadly confluent across
   eastern North America, between a prominent subtropical high centered
   over the Bahamas and a polar low centered east/northeast of Hudson
   Bay, while amplified positively tilted ridging/troughing persists
   across the eastern Pacific into western North America, within a belt
   of westerlies emanating from the mid-latitude Pacific.  However, in
   response to further digging of a vigorous short wave impulse within
   the troughing inland of the Pacific coast, models continue to
   indicate that the remnants of a significant mid-level closed low
   will accelerate northeastward out of the Mexican Plateau during this
   period.  The lead impulse is forecast to progress across/northeast
   of the Texas South Plains by 12Z Monday, before continuing
   northeastward, then eastward, through the middle Mississippi Valley
   and lower Great Lakes region (generally around the western/northern
   periphery of the subtropical ridging) by 12Z Tuesday.  

   Model output remains indicative that forcing for ascent associated
   with this feature will support modest to strong surface cyclogenesis
   along a frontal zone currently stalled across the Gulf States/Gulf
   coast region.  This may commence across the Ozark Plateau by late
   tonight, as the front advances northward/northeastward, with most
   rapid deepening currently expected across the Ohio Valley into lower
   Great Lakes region Monday afternoon and evening.

   In response to these developments, a strengthening southerly flow
   off a modifying boundary layer over the western Gulf of Mexico
   appears likely to allow for a substantive plume of returning
   moisture.  Within the warm sector of the cyclone, where wind fields
   are forecast to strengthen to 50-70+ kt in the 850-500 mb layer,
   this is expected to include lower/mid 60s+ surface dew points east
   of the lower Mississippi Valley, at least as far north as the lower
   Ohio Valley.  These conditions may contribute to an environment
   conducive to organized severe thunderstorm development, including a
   risk for potentially damaging wind gusts and perhaps a couple of
   tornadoes.

   ...Lower Mississippi Valley through Ohio Valley...
   Possible weak destabilization appears the primary potential
   mitigating factor concerning the severe thunderstorm risk Monday
   through Monday night.  Despite the degree of low-level moisture
   return, lower/mid tropospheric lapse rates within the warm sector
   appear likely to remain weak, due to the absence of northeastward
   advecting warm elevated mixed-layer air, while the mid-level cold
   core of the upper system also generally remains displaced to the
   west/north.  Boundary layer heating may also be limited, and it
   appears CAPE may not exceed 500 J/kg.  Still, it appears that this
   will be sufficient to support thunderstorm development of sufficient
   strength to at least augment the downward transfer of high momentum,
   and potentially damaging wind gusts, to the surface.

   Maximum severe probabilities are expected to become focused across
   parts of the Mid South into lower Ohio and Tennessee Valley region,
   on the general southern periphery of the stronger mid/upper forcing
   for large-scale ascent, where destabilization may become sufficient
   to support an evolving squall line Monday afternoon and evening.  It
   might not be out of the question that this line may be preceded by
   isolated discrete supercell development while advancing
   northeastward across parts of Kentucky/Tennessee and northern
   Mississippi/Alabama, with additional discrete thunderstorm
   development possible across parts of southeastern Louisiana into
   southern Mississippi and Alabama, where forcing for ascent is
   expected to be much weaker, but the boundary layer may be a bit more
   moist and unstable.  This convection may be accompanied by a risk
   for tornadoes, in addition to strong outflow wind gusts.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     15%     - Slight
   Hail:     <5%     - None

   ..Kerr.. 12/30/2018

[jaxjagman]

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1126 PM CST Sun Dec 30 2018

   Valid 311200Z - 011200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   CENTRAL AND NORTHERN MISSISSIPPI...NORTHWEST ALABAMA...TENNESSEE AND
   SOUTHERN KENTUCKY...

   ...SUMMARY...
   Severe thunderstorms, including a potential for damaging wind gusts
   and a few tornadoes, will be possible today from parts of central
   Mississippi and northwest Alabama north-northeastward into Tennessee
   and southern Kentucky.

   ...Lower Mississippi Valley/Central Gulf Coast States/Tennessee and
   Ohio Valleys...
   An upper-level trough will move quickly northeastward from the
   southern Plains into the mid Mississippi Valley today. A surface low
   will gradually deepen ahead of the upper-level trough with a surface
   trough extending southward into the lower Mississippi Valley. Ahead
   of the surface trough, moisture advection will continue as a
   corridor of low-level moisture sets up across Mississippi and
   western Tennessee. Convection is forecast to develop along and to
   the east of the surface trough late this morning into the afternoon,
   spreading eastward across Mississippi and western Tennessee.
   Although instability should remain weak along the moist corridor, a
   60-70 kt low-level jet will create strong low-level shear profiles.
   Forecast soundings from east of Jackson, MS north-northeastward to
   near Nashville, TN early this afternoon show 0-3 km storm-relative
   helicities in the 350 to 500 m2/s2 range along with 0-6 km shear of
   65-75 kt. This impressive shear environment will support low-topped
   fast-moving supercells capable of producing a few tornadoes. 

   The greatest tornado threat should occur with the stronger discrete
   cells that develop near the axis of the low-level jet. These storms
   will also have a wind-damage threat. Later in the afternoon,
   increasing low-level convergence should aide the development of a
   line of storms along the surface-trough. This line should have a
   wind-damage and isolated tornado threat as it moves eastward across
   middle Tennessee, Mississippi and into western and central Alabama
   this afternoon. 

   Further north across west-central Kentucky into far southern
   Indiana, forecast soundings show very weak instability this
   afternoon. This will likely minimize the tornado threat across most
   of the Ohio Valley. Wind damage will still be possible with the
   greatest threat from far southern Kentucky southward into middle
   Tennessee, where forcing associated with the low-level jet and
   upper-level trough will aide the intensity of a fine convective
   line.

[jaxjagman]

URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 449
   NWS Storm Prediction Center Norman OK
   1145 AM CST Mon Dec 31 2018

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Western and northern Alabama
     Central and Eastern Mississippi
     Western and Middle Tennessee

   * Effective this Monday morning and evening from 1145 AM until
     700 PM CST.

   * Primary threats include...
     A couple tornadoes possible
     Isolated damaging wind gusts to 70 mph possible

   SUMMARY...An increasingly well-organized squall line is expected to
   race east-northeastward across parts of the region, with other
   potentially more isolated storms ahead of the line across
   Mississippi into western/northern Alabama. Although the air mass is
   not overly unstable, very strong low-level/deep-layer winds will
   support bowing segments along with embedded mesovortices capable of
   wind damage and some tornado risk. The overall severe risk should
   wane by early evening in most areas.

   The tornado watch area is approximately along and 60 statute miles
   east and west of a line from 35 miles north northwest of Nashville
   TN to 65 miles south southeast of Jackson MS. For a complete
   depiction of the watch see the associated watch outline update
   (WOUS64 KWNS WOU9).

[Carvers Gap]

Good call, @jaxjagman!  You all keep us updated.  We are nearing record highs in the eastern valley.  TRI is just four degrees from it and TYS is just one degree from it.  Should be plenty of warmth for those storms to work with over here.

[jaxjagman]

5 minutes ago, Carvers Gap said:

Good call, @jaxjagman!  You all keep us updated.  We are nearing record highs in the eastern valley.  TRI is just four degrees from it and TYS is just one degree from it.  Should be plenty of warmth for those storms to work with over here.

Best cell in our area looks to be by Holenwald,least there is some storm markers with bowing structure

[jaxjagman]

Seen some wind reports by the Rim,65 mph with trees down,only tornado around us has been into Ky

[Carvers Gap]

That is a nasty looking line.  Really pulling up the warm air in front of it on SSW/SW winds....

[jaxjagman]

Glad it's moving fast,drove by the Harpeth creek this morning in Franklin,it's rising.The creek by our house is the highest since we've moved here

[Carvers Gap]

Just now, jaxjagman said:

Glad it's moving fast,drove by the Harpeth creek this morning in Franklin,it's rising.The creek by our house is the highest since we've moved here

Man, forgot about that.  Everything here is really high.  The mountain streams and rivers were out of their banks on Friday afternoon.  The were barely back in by Saturday AM.

[jaxjagman]

Flood Advisory
National Weather Service Nashville TN
557 PM CST Mon Dec 31 2018


...The National Weather Service in Nashville, Tn has issued a flood advisory for
the following rivers in middle Tennessee...

  Harpeth River At Bellevue affecting Davidson and Williamson Counties

.Water levels on the Harpeth River will continue to rise this evening, and crest
below Flood Stage overnight.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Stay tuned to noaa weather radio or other local media for further information
from the National Weather Service.

&&

TNC037-187-011157-
/O.NEW.KOHX.FL.Y.0095.181231T2357Z-190101T1800Z/
/BELT1.N.ER.000000T0000Z.000000T0000Z.000000T0000Z.OO/
557 PM CST Mon Dec 31 2018

The National Weather Service in Nashville, Tn has issued a
* Flood Advisory for
  The Harpeth River At Bellevue
* At 05PM Monday the stage was 14.3 feet and rising.
* Flood stage is 20.0 feet.
* The river will rise overnight to near 16 feet, then fall to near 11.5 feet
  Tuesday morning.
* At 14.0 feet...Portions of the Harpeth River Greenway begin to be inundated,
  and water begins to inundate the parking lot of the Harpeth River State Park
  at Highway 100.

[jaxjagman]

HARPETH can be a bitch in our world.Creeks around our house are maxed out,should start to settle down the next couple hours

[nrgjeff]

ECMWF and CFS monthlies both show April better than May. Fits El Nino climo. So I will look early and often in Dixie. Plains may be yet another crap May. No EML in the Plains means slop. If I'm going to chase slop, Dixie is a whole lot closer!

[jaxjagman]

Sam Lillo‏ @splillo

FollowFollow @splillo

More

Here's the final gridded tornado-day anomaly map and timeline for 2018. Several hot spots of note. The big story of course is the substantial negative anomaly both spatially and temporally - across the popularly defined tornado alley, and tornado season.

11:05 AM - 1 Jan 2019

 

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      This is based on integrating the practically perfect forecast defined in Hitchen, Brooks and Kay 2013. I.e. you could do the same for SPC tornado probs through the year, and a value of -1 would mean an anomaly from "average" total annual forecast probs of -100%.

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      Since there have been a lot of questions about trends, here they are for the last 30 years of EF1+ tornadoes, in tornado-days / decade. The second plot removes 2011, which negates trends in the seasonal cycle, but spatial trends in the Southeast remain.

      

       

      

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[nrgjeff]

Saturday showcase includes thunderstorms. CAMs mostly line out the activity which is not a surprise. Line will be very forced with limited instability. Kinematics and wind field looks excellent. Rain and clouds should keep it a little cool though. If instability somehow verifies higher it might be worth a second look on a weekend.

Otherwise the real show is the ESPN Saturday Showcase; lots and lots of good college basketball.

Sunday evening should clear out in time for the lunar eclipse. Yes, back to fair weather chasing.

[AMZ8990]

On 1/18/2019 at 8:37 AM, nrgjeff said:

Saturday showcase includes thunderstorms. CAMs mostly line out the activity which is not a surprise. Line will be very forced with limited instability. Kinematics and wind field looks excellent. Rain and clouds should keep it a little cool though. If instability somehow verifies higher it might be worth a second look on a weekend.

Otherwise the real show is the ESPN Saturday Showcase; lots and lots of good college basketball.

Sunday evening should clear out in time for the lunar eclipse. Yes, back to fair weather chasing.

  Had some serious thunder and heavy rain come through last night from about midnight to 3am.  The pond in my yard has now gone from half full to 85% full.  Roughly a 4 foot rise in the level to give you a better idea.  Easily an inch of rain has already fallen, probably closer to 1.5 though.  Hopefully the old addage about thunder during winter holds true because we had quite the thunderstorm last night.

[AMZ8990]

Pretty stout cell moving over my house at the moment.  Winds gusting up to 50.  

[CheeselandSkies]

2018's over, guys. New thread time.

[jaxjagman]

4 hours ago, CheeselandSkies said:

2018's over, guys. New thread time.

I was waiting on the shutdown to end for data.I'm not going to get in any political debate here so with this thread only 14 pages, i went ahead and included 2019 in the topic,let's just run with it for right now for 2019.

[Holston_River_Rambler]

Have a buddy in Wetumpka, AL. Tornado hit 3 blocks from his house. 

[AMZ8990]

14 hours ago, jaxjagman said:

I was waiting on the shutdown to end for data.I'm not going to get in any political debate here so with this thread only 14 pages, i went ahead and included 2019 in the topic,let's just run with it for right now for 2019.

 Sounds good to me.  I don’t know why the guy from Wisconsin cares about our thread but whatever.  And for the record- I had some pretty good cells come through my house the past 2 days.  The snow wasn’t far behind the thunder either which was kinda cool. 

[nrgjeff]

Cheeseland is passionate about severe wx and welcome here. Note the smiley face.

I was going to take down my Christmas tree MLK Day weekend. If it is still up Monday, I will also use the shutdown reasoning as a later deadline.

Wetumka tornado is an unfortunate verification of the 5%. These things can happen with a dynamically forced line marginal instability.

Most importantly sky will clear out in time for the lunar eclipse tonight! High clouds could come into the northwest quad of our Region but not a show stopper.

[AMZ8990]

2 hours ago, nrgjeff said:

Cheeseland is passionate about severe wx and welcome here. Note the smiley face.

I was going to take down my Christmas tree MLK Day weekend. If it is still up Monday, I will also use the shutdown reasoning as a later deadline.

Wetumka tornado is an unfortunate verification of the 5%. These things can happen with a dynamically forced line marginal instability.

Most importantly sky will clear out in time for the lunar eclipse tonight! High clouds could come into the northwest quad of our Region but not a show stopper.

  @CheeselandSkies I didn’t mean anything bad about my comment saying I don’t know why you care about our thread.  I hadn’t seen you in our thread before and thought you might of been a lurker trying to stir the pot like so many others around here try to do to get a rise out of people.  My apologies if I offended you.

[CheeselandSkies]

It's all good. I do lurk around here a lot because it's usually the only part of the forum where severe wx discussion is ongoing this time of year.

[AMZ8990]

2 minutes ago, CheeselandSkies said:

4 minutes ago, CheeselandSkies said:

It's all good. I do lurk around here a lot because it's usually the only part of the forum where severe wx discussion is ongoing this time of year.

  I understand that, we definitely don’t lose our severe wx chances during any season of the year which is fun if your into tracking those kinds of threats.  You guys getting lots of snow up there this year??

[CheeselandSkies]

Not really, just got the first decent event of the winter Friday night into yesterday. 61-page thread (and growing) devoted to tracking that one!