Tn Valley Severe Weather

[jaxjagman]

Chance for some strong storms towards the end of the work week by both the GFS and Euro.SPC don't sound to enamored by this

 

...Friday/Day 6 to Sunday/Day 8...
   On Friday, the models diverge in the solutions but on a broad-scale
   maintain a western U.S. upper-level ridge and eastern U.S.
   upper-level trough. The position of the trough is doubtful at this
   range but model consensus would put the greatest potential for
   thunderstorm development in the Ohio and Tennessee Valleys. An
   isolated severe threat would be possible Friday afternoon into the
   early evening. On Saturday and Sunday, the models move the
   upper-level trough slowly eastward but vary considerably on the
   amplitude of the system and amount of instability that will be in
   place. Thunderstorms with some potentially strong, would be possible
   ahead of the upper-level trough in areas that destabilize the most.
   Uncertainty is considerable at this range.

[jaxjagman]

Models still show a chance of some strong storms towards the end of the work week into the Valley.Took some soundings into the Mid Valley for Friday.The Euro is for BNA and the GFS is slightly S of BNA.All the models today show the Upper level trough more Southward than usual in the summer time.Instabilities right now look pretty decent for some strong storms upcoming.Who ever gets storms it should be like the SPC mentioned as there is a capping inversion into the evening hours,so storms will die off into the early evening,right now anyways

 

Nashville disco

 

Extended outlook...Rain chances will creep back into the forecast
on Thursday as another upper level trough moves southeastward
through the Midwest. Chances will increase further on Friday as
the trough approaches TN and moist southerly flow returns at
lower levels. The pattern for late next week and next weekend is
pretty interesting as extended models morph the trough into a
significant closed low over Michigan. This set up leaves Middle TN
in a period of significant northwest flow aloft...and probably
another cold front that could arrive Saturday. There is much
uncertainty in a Day 6-7 forecast, but don`t be surprised if we
see some strong storms in this pattern...given the moisture, a
cold front and unusually strong flow aloft proving unseasonably
strong wind shear.

[nrgjeff]

Friday and Saturday should offer at least something to watch. I would put it in the category of the June 21-28 weather with modest upper level flow and some severe wx reports.

ECMWF continues to show greater than seasonable upper level flow. It veers with height, but the low levels are far from backed to start. Looks like a straight line wind pattern. A hard right mover on a boundary (SSE motion) could spit out hail too. 06Z GFS trends toward the ECMWF with a more open wave, as opposed to broad but closed off, which creates a little more veering with height on the GFS. 

Wind direction at low levels does not favor rotation. However veering with height upstairs still supports the chance of severe wx mainly in the form of straight winds. We'll see if it holds.

[AMZ8990]

Had a pretty intense storm Last night, came in around 2:30am this morning.  picked up around .65 in the rain gauge and some epic lighting strikes.  Had several that shook the house and I haven’t got that all year so far.   It was the strongest cell of the summer so far in my opinion.  Anyone else get anything this morning??

[nrgjeff]

June 28 evening was my lightning show of record for 2018. In fact it's the best I have seen here in several years. We had frequent lighting for nearly an hour with nearly constant rumbling of thunder. On two occasions continuous lighting went for a few minutes. Separately, a few booms of thunder shock the house. Being at night of course helped with the light show.

We had stronger storms a few days before that. June 28 was more about the lighting and thunder. Hopefully modest flow aloft in a few days will bring more fun. Real storms please!

[nrgjeff]

Impressive video @*Flash* from June 26. Takes me back to the Plains with a disco strobe anvil topped thunderhead. Hopefully we can do it in the Valley (and Midsouth) later this week and over the weekend.

Modest flow is still forecast over that period, I'll say Friday through Monday. Turning with height is meager but the speed is pretty good for this time of year. SPC does not sound too impressed, but at least we get the marginal text mention. Should be enough for organized storms, vs just pop-up poop-out. All I'm asking for is a little straight wind, good shelfies, and lightning shows. 

You know, this summer still feels a little empty without the 2017 eclipse anticipation. 

[jaxjagman]

Besides the brief respite from the muggy air, the other story of
this forecast package revolves around the intense upper level low
that will develop in the Great Plains tonight and push into the
Great Lakes region Friday.  As it does, areas from the mid-
Mississippi Valley into the Tennessee Valley will be squarely in a
northwesterly flow aloft. Models continue to show a pre-frontal
MCS (though being depicted to arrive earlier in the day Friday now
in both the Euro and GFS) and a surface low developing to our
west Friday evening. While the MCS could be troublesome enough,
both the GFS and NAM are off the charts regarding the deep layer
shear being generated by this surface low. What was 40-50 kts of
0-6 km shear is now 60 kts and in the 00Z to 03Z Saturday time
frame (Friday evening), low level SRH values bounce up to about
300 m2/s2. Instability values are also sky-high due to the
southerly influx of surface moisture. The first thing that comes
to mind in the northwesterly flow aloft is a Friday evening
derecho. Obviously, a scenario like this carries with it damaging
straight line winds, heavy rains (PW values are running about 2
inches) and yes, the potential for July tornadoes. I am going to
add this Friday severe weather threat into the Hazardous Weather
Outlook.

 

Some decent shear for this time of year,much better than it was showing yesterday

https://forecast.weather.gov/product.php?site=OHX&issuedby=OHX&product=AFD&format=CI&version=1&glossary=1

[John1122]

The only tornado in my area in recent times was a July f3. Gonna be keeping an eye out for this one.

[nrgjeff]

Wow that's some bullish language from OHX. Keep in mind it is an internal discussion; and, they should go over all the possible solutions. Other solutions include the classic Dixie crap out scud nation.

Getting serious, I like a slight risk for part of the region. Wind fields certainly support it. I believe the high-res NAM is too amped with SRH. Might be locally higher on a boundary; but, the other NAM is less bullish overall. Either way CAPE will be high and storms will tap into those wind fields. While maybe not enough turning for tornadoes*, it is enough veering with height to promote organized severe storms. 

* Hard right mover on a boundary could still surprise. Yeah maybe look on the Plateau. I believe low level wind fields (its ground level) are stronger up there for two reasons.. higher elevation, and broad Bernoulli effect as mesoscale winds flow over the Plateau. 

Friday could offer a nice break from the Good Morning Vietnam forecast. Like the June 20-ish week we should start a few days with organized thunderstorms. Slight could also shift toward the Mid-South if the boundary sinks.

[yoda]

20 hours ago, nrgjeff said:

Wow that's some bullish language from OHX. Keep in mind it is an internal discussion; and, they should go over all the possible solutions. Other solutions include the classic Dixie crap out scud nation.

Getting serious, I like a slight risk for part of the region. Wind fields certainly support it. I believe the high-res NAM is too amped with SRH. Might be locally higher on a boundary; but, the other NAM is less bullish overall. Either way CAPE will be high and storms will tap into those wind fields. While maybe not enough turning for tornadoes*, it is enough veering with height to promote organized severe storms. 

* Hard right mover on a boundary could still surprise. Yeah maybe look on the Plateau. I believe low level wind fields (its ground level) are stronger up there for two reasons.. higher elevation, and broad Bernoulli effect as mesoscale winds flow over the Plateau. 

Friday could offer a nice break from the Good Morning Vietnam forecast. Like the June 20-ish week we should start a few days with organized thunderstorms. Slight could also shift toward the Mid-South if the boundary sinks.

Then you will like how SPC went ENH:

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1227 AM CDT Thu Jul 19 2018

   Valid 201200Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE OHIO AND TENNESSEE VALLEYS...

   ...SUMMARY...
   Scattered severe thunderstorms associated with large hail, wind
   damage and a tornado threat will be possible Friday afternoon and
   evening across parts of the Ohio and Tennessee Valleys.

   ...Ohio and Tennessee Valleys...
   An upper-level trough will move into the Ohio and Tennessee Valleys
   on Friday as an unseasonably strong mid-level jet moves through the
   southwestern side of the system. At the surface, a low is forecast
   to move east-southeastward across northern Illinois during the day
   as a cold front advances eastward across the mid Mississippi Valley.
   Ahead of the front, a very moist airmass should be in place with
   surface dewpoints in the lower 70s F. This should enable a corridor
   of moderate to strong instability to develop ahead of the front by
   afternoon. As low-level convergence increases along the front,
   thunderstorms are forecast to form during the early to mid afternoon
   in the mid Mississippi Valley with the storms moving southeastward
   across the Ohio and Tennessee Valleys during the late afternoon and
   early evening.

   Forecast soundings for Paducah, KY, Evansville, IN and Louisville,
   KY at 00Z on Saturday show MLCAPE values of 2500 to 3000 J/kg, 0-6
   km shear of 40 to 50 kt and steep mid-level lapse rates. This
   environment should be favorable for supercells with large hail.
   Hailstones of greater than 2 inches will be possible with the most
   intense cells. As the low-level jet strengthens during the early
   evening, 0-3 km storm-relative helicity is forecast to reach the 200
   to 250 m2/s2 range. This should be enough for a tornado threat with
   the more dominant supercells. Storm coverage is expected to increase
   markedly by early evening as an MCS organizes across the Ohio and
   Tennessee Valleys. In response, the wind-damage threat should
   gradually increase during the late afternoon and early evening as
   supercells or bowing line segments move southeastward across the
   instability corridor.

   At this time, the models are in good agreement concerning Friday's
   scenario. The environment will likely support a substantial severe
   threat across the Ohio and Tennessee Valleys so this outlook
   includes an upgrade to enhanced risk.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     30%     - Enhanced
   Hail:     30%     - Enhanced

   ..Broyles.. 07/19/2018

[nrgjeff]

I do like it! 

34 minutes ago, yoda said:

Then you will like how SPC went ENH:

Storm mode remains a question for me. About 1/3 CAMs still produce a line in the late afternoon. Most have one in the morning, which is fine if it lays down outflow. My question is the afternoon round. ARW (research version of WRF) just put out a junk scenario and I hope it is an outlier. At any rate the chance of afternoon storms quickly going into a squall line is real. All the shear and turning with height could just translate into a well-maintained straight line wind producing squall line. THEE checklist probably won't be met, not quite enough WAA. However a shortwave in northwest flow with lots of heat humidity and CAPE could get some damaging winds going. 

NAM version of the WRF mostly favors supercells. 06Z was a little messy but 00/12Z are supercells in the afternoon. I am still skeptical of the lowest levels 0-1km. Now the 0-3km SRH is robust for July (but average spring system). The 0-1km needs something more. How about a boundary? Morning convection would need to produce that just-right outflow boundary. Can't have a cool pool undercutting, a risk without vigorous inflow. If rain gets off the said boundary, it can cook for a few hours in the afternoon. NAM has a hard right mover on the boundary in Middle Tenn. I would not take that location seriously at 36 hours. Only the conceptual model is worth noting. If a lone supercell establishes on a cooking boundary (no other rain) then the large hail scenario gets more likely, perhaps even rotation. For the latter, I think a little more ambient 0-1km SRH is needed even if a boundary is present. 

Due to forecast overnight and morning convection the location is actually still up in the air. I like the Slight-Enhanced for Kentucky and Tenn. Ohio Valley also has a triple point forecast but that is another regional forum area.

[yoda]

LMK was going all in in morning disco it would appear

.Long Term...(Friday through Wednesday)
Issued at 300 AM EDT Thu Jul 19 2018

...Confidence Growing For Friday Severe Weather Episode...

A significant severe weather episode could unfold on Friday as the
combination of strong instability and anomalously strong shear
create an environment capable of initial supercell modes that would
ultimately (and perhaps quickly) congeal into an organized wind
producing line of storms. At this point, the greatest overlap of
strong shear and instability is expected to reside over the western
two-thirds of our CWA where SPC has decided to upgrade to an
Enhanced Risk for Day 2. More details below.

An anomalously strong shortwave trough will move from the upper
Midwest to the southern Great Lakes on Friday, with the associated
surface low dragging a cold front into our area by late Friday
night. Ahead of this front, a severe weather environment should set
up on Friday as the exit region of a 60-70 knot mid/upper level jet
will overspread the Ohio Valley through the day. Also of note will
be an unseasonably strong low level jet response around 30-40 knots
over southern IN and northern KY. This setup will create a very
strong and notably veered vertical wind profile supportive of
organized convection, including supercells and a tornado threat. 0-1
km SRH values should be over 200 M2/S2 for a time over much of the
area late afternoon/evening.

In addition to the shear and exit region forcing, expect the
environment to become strongly unstable in the afternoon. The
combination of heating and low level moisture return beneath
steepening mid level lapse rates will yield SB CAPE values north of
2500 J/KG, and perhaps as high as 4000 J/KG across SW Indiana and
western KY. As the previous discussion mentioned, forecast soundings
for Friday afternoon/evening look pretty impressive with a "fat"
CAPE profile given the steep mid level lapse rates. With the veering
profile mentioned above, hodographs also take on an ominous long and
looping look.

There is still some question as to how much any elevated morning
convection will limit the ability to destabilize later in the day.
However, models all suggest redevelopment by the afternoon/evening
and at this point it seems more of a "when" question rather than an
"if" question. Still thinking that early storm modes could be
discrete and supercellular, but do anticipate that a transition to
an organized cold pool driven wind producer is likely. Given this
scenario, would expect an initial tornado and large hail threat,
followed by a sizable wind threat into the evening hours. An
isolated tornado threat would also continue into the evening. Did
also want to mention an isolated flooding threat given high PWATs
and potential for some repeated storm occurrences over the same
area.

Still some timing and storm mode questions to answer, but overall
confidence is increasing in potential for some significant severe
weather. Stay up to date of the coming forecasts.

[jaxjagman]

Models still don't get along but the NAM seemed to join hands somewhat with the Euro bringing a MCS east of Nashville in the evening.Both the CAMS look the way.The WRF still shows multi cluster supercells until early morning sometimes.

I just want to see a light show

[yoda]

@nrgjeff @jaxjagman

 

[yoda]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1236 PM CDT Thu Jul 19 2018

   Valid 201200Z - 211200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR SOUTHERN
   IL/IN...CENTRAL/WESTERN KY...MIDDLE/WESTERN TN...NORTHERN MS/AL...

   ...SUMMARY...
   Scattered severe thunderstorms associated with large hail, wind
   damage and a tornado threat will be possible Friday afternoon and
   evening across parts of the MIssissippi, Ohio and Tennessee Valleys.

   ...Synopsis...
   An anomalously strong deep layer trough and associated surface
   cyclone are expected to move southeastward from the upper Midwest
   into portions of the lower Great Lakes on Friday. The surface
   pattern will be complicated by one or more convectively-induced
   outflow boundaries, with a synoptic-scale surface trough/cold front
   expected to progress eastward south of the surface low through the
   period. A stout EML will spread eastward from the southern Plains
   over rich low-level moisture, resulting in a volatile thermodynamic
   environment developing over portions of the MS/TN/OH River Valleys
   and the Midwest. 

   ...MS/TN/OH River Valleys into the Midwest...
   A potentially significant severe thunderstorm episode is possible
   across portions of the MS/TN/OH Valleys and the Midwest on Friday,
   though considerable uncertainty remains regarding convective
   evolution through the period. 

   One or more clusters of convection will likely be ongoing Friday
   morning, though the remnants of these clusters are expected to push
   east through the day, allowing for moderate-to-strong
   destabilization in their wake. The strongest focus for convection
   will be the surface trough moving through IL/IN/OH, though this area
   will be somewhat removed from the stronger shear and instability,
   especially with northward extent. 

   Foci for convective initiation will be more subtle further south and
   west, but the environment will also be much more volatile, with
   strong instability (MLCAPE of 2500-4000 J/kg possible) and effective
   shear (45-60 kt) in place. Scattered thunderstorms are expected to
   develop during the afternoon, potentially along the trailing surface
   boundary and also evolving out any early day elevated convection.
   Initially discrete storm modes will favor large hail (potentially
   greater than 2 inches in diameter), along with damaging wind gusts
   and a tornado or two. With time, evolution into one or more
   upscale-growing clusters is expected into the evening. Any such
   clusters would be capable of producing damaging wind swaths as they
   propagate to the southeast. 

 

 ...MAXIMUM RISK BY HAZARD...
   Tornado:   5%     - Slight
   Wind:     30%     - Enhanced
   Hail:     30% SIG - Enhanced

   ..Dean/Dial.. 07/19/2018

[nrgjeff]

Expanding the ENH and introducing hatched hail both seem reasonable. OHX afternoon discussion reads ever so slightly more interested in tornadoes; however, they are rightfully mainly focused on straight line winds. My previous post was after 12Z CAMs, so I have little to add there.

Interesting the 850/925 mb winds appear a little better in northern Kentucky. However the stronger 500/200 mb winds are down over Tenn. Could we have more than one or two good cells and spread out? Gee that would be something unusual in 2018!

I'm starting to actually think about this northwest flow event. Still doubt I'll chase due to awful terrain. I mean in 2018 something has to go wrong.

[Brick Tamland]

Good luck, folks. Looks like you are really under the gun today. The tornadoes in Iowa yesterday weren't even expected.

[yoda]

@nrgjeff

Mod risk... good luck!

[John1122]

The SPC reasoning for the moderate risk area. It's crazy that there's an excessive heat warning right where the storms are getting fired up in Arkansas and West Tennessee. Memphis is supposed to have a HI around 115 today. I'm not sure I remember areas having excessive heat warnings and enhanced/moderate risk outlooks for severe at the same time.

Quote

Lower MI to Mid-South and TN Valley...
   Scattered to locally numerous thunderstorms should develop in this
   corridor, perhaps evolving into multiple clusters or bands at
   different times from midday through at least late evening.  The
   environment across the enhanced and moderate risk areas will be the
   most favorable for supercells, bow echoes and organized convective
   clusters, with tornadoes, damaging winds and large/damaging hail all
   possible. 

   Tornado and significant/damaging-hail probabilities for now are
   maximized across parts of the lower Ohio Valley and Mid-South
   regions where seasonably steep lapse rates (7-8 deg C/km), very
   strong to extreme instability (MLCAPE 4000-6000 J/kg), rich moisture
   (70s F surface dew points, mean mixing ratios 17-20 g/kg), and
   strong deep shear 50-65 kt northwesterly effective shear vectors)
   are expected to juxtapose.  Tornado probabilities also have been
   increased/expanded in two directions:
   1.  Northward across the eastern IN/western OH corridor along and
   near an eastward-moving warm front, where thunderstorms developing
   in the warm sector or along the cold front may have time to evolve
   into mature supercells before interacting with the warm frontal
   zone's vorticity-rich, low-LCL environment.
   2.  Westward across the Mid-South and northeastern AR, where some
   discrete supercell modes are possible in a high-CAPE,
   adequate-shear, high-PW environment before upscale evolution occurs
   to more of a clustered mode and wind threat.  In that regard, some
   potential also exists for activity developing near either cold front
   in KS or southwestern MO to grow upscale near an already-observed
   moist axis, evolving into a southeastward-moving MCS with damaging
   wind over parts of the Ozarks region, and perhaps reaching parts of
   the lower Mississippi Valley.

 

[Brick Tamland]

1 hour ago, yoda said:

@nrgjeff

Mod risk... good luck!

[nrgjeff]

I am sitting out today, mainly due to terrain. Iowa tornadoes did pique my interest but they had greater low level turning. Iowa tornadoes is all or nothing like snow in Dixie, lol..

Today in TN/KY deep layer shear is downright robust for July. CAPE should achieve advertised levels. My issue is the lowest level shear. Even adjusted for a northwest flow event I don't like the lowest 100 mb or so. From 850 mb up turning is good. However from 850 mb down speed is meh. I know it's July. Still I like the lowest levels to close the deal for tornadoes. It requires a quality boundary. Attm (1643Z surface chart) winds do not kink well along the boundary near the TN/KY border. We'll see how things go.

Looks like plenty of straight line wind and even large hail for severe weather fans. OHX is rightfully hitting the straight winds in their comm. Can't take tornadoes off the table in the MDT and immediate surrounding ENH area (not all of it). Note max tornado probabilities are ENH. The other modes of severe wx could achieve MDT.

If the terrain were better, today might be worth a try in West Kentucky and adjacent parts of Tenn. The meteorology looks like few and brief tornadoes, easily missed in poor terrain. Appears the wind and hail will be the primary issues. 

[Runman292]

SPC has extended the enhanced risk to western parts of east TN.

[Witness Protection Program]

Edit:  Nevermind, radar false alarm

Of course on the one week I can't park in my garage because of construction.  How big is the Nashville hail risk for the 1am-6am rounds?

[Chinook]

SPC is expecting to issue a tornado watch for W Kentucky and western and central Tennessee.

[John1122]

Tornado warned cell in Lincoln/Casey Co in SE Kentucky. The storm will approach the I-75 corridor over the next hour.

Quote

Tornado Warning

Severe Weather Statement
National Weather Service Louisville KY
708 PM EDT FRI JUL 20 2018

KYC045-137-202330-
/O.CON.KLMK.TO.W.0029.000000T0000Z-180720T2330Z/
Lincoln KY-Casey KY-
708 PM EDT FRI JUL 20 2018

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 730 PM EDT FOR SOUTHERN
LINCOLN AND EAST CENTRAL CASEY COUNTIES...

At 708 PM EDT, a severe thunderstorm capable of producing a tornado
was located 10 miles west of Bee Lick, moving east at 25 mph.

HAZARD...Tornado and golf ball size hail.

 

[Holston_River_Rambler]

Cell in Monroe county, KY looks to be developing a hook. 

https://imgur.com/jomk03r 

 

 

[jaxjagman]

Tornado watch for the Eastern Valley

[Holston_River_Rambler]

Looks like it's all trying to consolidate into a line now over the upper Cumberland plateau. Hopefully that puts and end to most of the tornado threat for those folks. No disrespect meant to any chasers in any way.  

[AMZ8990]

10 hours ago, John1122 said:

The SPC reasoning for the moderate risk area. It's crazy that there's an excessive heat warning right where the storms are getting fired up in Arkansas and West Tennessee. Memphis is supposed to have a HI around 115 today. I'm not sure I remember areas having excessive heat warnings and enhanced/moderate risk outlooks for severe at the same time.

 

I’m 60 miles east of Memphis and we’ve had thunderstorms every night this week. I work in Collierville which is technically south east Memphis but when I got to the golf course this morning the course was a mess.  We had standing water in a lot of areas, and limbs down everywhere.  It’s been pretty cool to watch these storms unfold and develop every night this week.  

[John1122]

Just had a very high wind/heavy rain storm roll through. Winds justified the severe warning. Sideways sheets like you'd see in a hurricane, was hard to hold the car in the road from the wind.