Tn Valley Severe Weather Nov 5-6

[jaxjagman]

I wasn't going to do this after this afternoon run on the GFS, but the GFS looks better this evening.Negative tilted trough and there also a possibility of some discrete storms in the afternoon in the Western Valley Monday afternoon.But the main threat looks to be towards late evening/early morning hours.

[AMZ8990]

I had been keeping an eye on this as well, definitely has some potential to produce dangerous storms.  Keep me posted Jax, I know severe is in your wheelhouse!!

[jaxjagman]

 Day 3 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0233 AM CDT Sat Nov 03 2018

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM A PORTION
   OF THE LOWER MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY...

   ...SUMMARY...
   Numerous severe storms with potential for damaging wind and
   tornadoes are expected Monday evening into the overnight from a
   portion of the lower Mississippi Valley into the Tennessee and Ohio
   Valleys.

   Primary change to previous outlook for Monday has been to expand the
   severe risk areas farther north and east based on latest trends in
   model guidance.

   Potential still exists for significant severe weather to transpire
   Monday evening and overnight, mainly from the lower MS Valley into
   the Tennessee Valley regions. Though the NAM and GFS are slightly
   less amplified with approaching upper trough compared to the ECMWF,
   models have demonstrated reasonably good consistency. Cyclogenesis
   should commence by Monday evening over the lower MS Valley in
   response to ascent within exit region of an approaching, intense jet
   streak within base of an amplifying shortwave trough. The low is
   forecast to deepen as it lifts northeast into the OH Valley
   overnight with trailing cold front advancing through the TN and
   lower MS valley regions. Richer low-level moisture residing over the
   northern Gulf will advect rapidly northward through the warm sector
   in response to the strengthening low-level jet, contributing to
   destabilization with modest instability (1000-1500 J/kg MLCAPE).
   Mixed storm modes including a squall line and supercells are likely
   to develop along and ahead of advancing cold front Monday afternoon
   initially over the lower MS Valley, and continuing east into the TN
   Valley and Southeast States Monday night. Impressive wind profiles
   with large hodographs and an intense upper jet will promote a threat
   for mainly damaging wind and tornadoes, though some hail will also
   be possible.

[jaxjagman]

[jaxjagman]

MUCapes even look better this afternoon on the GFS,over 1k west of Nashville.But all in all you never want to see a over night severe threat while people sleep.Soundings show a possible tornado threat for the vast part of the Valley,right now anyways.

[Windspeed]

Sat 12z ECMWF didn't back off the Monday evening/night severe threat from earlier runs. If anything, it increased 50-60 kts of low-level shear between 6pm to 2am from the northern half of MS into Kentucky. An area stretching from central MS to Nashville looks particularly concerning between 9pm and midnight. CAPE values are obviously lower/decreased over Middle Tennessee as the evening progresses, but bulk shear continues to increase. Hoping this stays more linear, however any discrete cells probably will be the rotating variety and some likely tornadic through the lower half of the MS Valley and western half of the TN Valley. Given the strong low-level jet, linear storm mode will likely have severe frontline winds as well as the line advances into the middle and eastern Valley. Images courtesy of weather.us.

[Windspeed]

ECMWF simulated reflectivity for Mon by 11pm CST also still looks discrete in nature:

[jaxjagman]

1 hour ago, Windspeed said:

Sat 12z ECMWF didn't back off the Monday evening/night severe threat from earlier runs. If anything, it increased 50-60 kts of low-level shear between 6pm to 2am from the northern half of MS into Kentucky. An area stretching from central MS to Nashville looks particularly concerning between 9pm and midnight. CAPE values are obviously lower/decreased over Middle Tennessee as the evening progresses, but bulk shear continues to increase. Hoping this stays more linear, however any discrete cells probably will be the rotating variety and some likely tornadic through the lower half of the MS Valley and western half of the TN Valley. Given the strong low-level jet, linear storm mode will likely have severe frontline winds as well as the line advances into the middle and eastern Valley. Images courtesy of weather.us.

The Euro is more severe than the GFS  into the Western Valley into the late afternoon,early evening,with possible discrete storms ahead.The showalter even would suggest this with drier air into the mid levels for thunderstorms.Wind profiles no need to mention,they would be there by both GFS and Euro.The hatched area from the SPC still looks good to me via the Euro,but it could get expanded more into SW Kentucky,by this afternoons runs,but can surely change the next runs.

[jaxjagman]

The hatched area today

 

[jaxjagman]

Area Forecast Discussion
National Weather Service Nashville TN
251 PM CDT Sat Nov 3 2018

.DISCUSSION...

Our main concern continues to be severe thunderstorm potential.
Models are continuing to come together, focusing on Monday night
for a line of thunderstorms to cross Middle Tennessee. This line
of storms will likely produce some wind damage, and may contain a
few spinup tornadoes.

But first in the short term, we will have clear to partly cloudy
skies tonight with lows in the 40s. On Sunday, a low pressure
system will lift across the midwest with a trough trailing down
across Tn. This system will create gusty winds on Sunday with
gusts over 30 mph at times. A few limbs could come down with a
couple of midday gusts around 40 mph. Showers will develop from
west to east Sunday afternoon and early evening. Showers will be
mainly light with most locations having under one tenth of an inch
of rainfall.

We should start out Monday with only small chances for showers.
A potent low pressure system will be working out of the Rockies
on Monday. A trough will take on a negative orientation by Monday
night with a surface low deepening as it lifts northeastward out
of the Mid Mississippi Valley, and a trailing cold front that will
sweep eastward. There is no doubt this system will have more than
ample shear to work with as models show deep layer shear over
45KT, including favorable low level shear for spinup tornadoes
along the expected squall line. Models are showing a tongue of
500-1000 cape ahead of the cold front which should be adequate to
develop severe thunderstorms. Models are in good agreement with
storms coming into our west after 9 PM Monday evening and moving
off to our east before 8 AM Tuesday. SPC shows the western two
thirds in an enhanced risk for Monday night and the rest of the
area in a slight risk.

With the bulk of the showers and thunderstorms moving off early
Tuesday morning, election day should be pretty much rain-free,
partly cloudy, and breezy. Cooler and drier air will come in for
Tuesday night and Wednesday.

[jaxjagman]

If the SPC goes by the GFS and Euro the hatched area should get expanded  more into Mid Tn and Western Ky

[jaxjagman]

The wind profiles on the Euro are really impressive into the Mid Valley into the lower OV  before the system heads away.There still looks to be a tornado chance for the whole Valley until you might get to the TN/NC mountains

[Windspeed]

The wind profiles on the Euro are really impressive into the Mid Valley into the lower OV  before the system heads away.There still looks to be a tornado chance for the whole Valley until you might get to the TN/NC mountains

Yeah, even when convection becomes more linear, there could easily be rotation and spinups within the severe line through dawn and mid morning.

[jaxjagman]

20 minutes ago, Windspeed said:

26 minutes ago, jaxjagman said:

The wind profiles on the Euro are really impressive into the Mid Valley into the lower OV  before the system heads away.There still looks to be a tornado chance for the whole Valley until you might get to the TN/NC mountains

Yeah, even when convection becomes more linear, there could easily be rotation and spinups within the severe line through dawn and mid morning.

Yeah,we haven't seen this set-up in years in the Valley with fall severe.With the linear you mention both the GFS AND Euro shows winds of 50kts down to 1kMB in our area,so a good chance we could see winds around 60 mph here possibly even more with convection.But this looks more wind and possible tornado,not alot of dry air in the mid levels,otherwise this would be a potential loaded gun

[jaxjagman]

The Euro on tonights run shows the winds in the Mid Valley down to 60kts at 1kmb on the skew-t in middle Tn,would be winds around 70mph if its right and mixes down,sounding are BNA And it also shows some drier air in the mid levels

[jaxjagman]

The dry layer in the mid levels will pump the instability in the Mid Valley,if it's right of course.Hard to go against the Euro this time frames.Really still think the hatched area will go east next run and possible more north

[jaxjagman]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Sun Nov 04 2018

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE LOWER
   MISSISSIPPI VALLEY INTO A PORTION OF THE TENNESSEE VALLEY...

   ...SUMMARY...
   Numerous severe storms with potential for damaging wind and
   tornadoes are expected Monday evening into the overnight from a
   portion of the lower Mississippi Valley into the Tennessee and Ohio
   Valleys.

   ...Lower Mississippi into the Tennessee and Ohio Valleys...

   Only minor adjustments have been made to previous outlook, and
   guidance remains generally consistent. Potential still exists for
   significant severe weather to transpire Monday evening and night,
   mainly from the lower MS Valley into the Tennessee Valley regions.
   Primary zone of cyclogenesis should commence Monday evening over the
   lower MS Valley (northern AR or southern MO) in response to forcing
   for ascent in exit region of a progressive, intense upper jet streak
   located within base of an amplifying shortwave trough. The cyclone
   will deepen as it lifts northeast into the OH Valley Monday night
   with trailing cold front advancing through the TN and lower MS
   valley regions. 

   Latest observations indicate surface winds over the western Gulf
   have shifted to southerly, and this air continues to modify with
   dewpoints already in the low 60s F. Cold front now moving through
   east TX as of early Sunday morning will stall along the Gulf coast,
   allowing the Gulf boundary layer to modify further through Monday.
   Gulf moisture with mid to upper 60s F dewpoints will advect rapidly
   northward through the warm sector along a strengthening low level
   jet, contributing to destabilization with 500-1500 J/kg MLCAPE by
   Monday night, but mid level lapse rates will remain somewhat
   marginal. Mixed storm modes including a squall line and supercells
   are likely to develop along and just ahead of advancing cold front
   by late Monday afternoon, initially over the lower MS Valley, then
   continuing east into the TN and OH Valleys overnight. Impressive
   wind profiles with large 0-1 km hodographs and intense mid-upper jet
   should foster organized storms including embedded bowing segments
   and supercells with low-level mesocyclones capable of mainly
   damaging wind and tornadoes, though some hail will also be possible.
   A moderate risk upgrade might be warranted for a portion of this
   region in later outlooks.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     30% SIG - Enhanced
   Hail:     15%     - Slight

[Chinook]

In my opinion, this could be as potent as 10/31 ( a few days ago.) As a reminder, on 10/31 there were 192 wind reports and 56 preliminary tornado reports, (possibly 15 confirmed, as per Wikipedia)

 Watch out! The 3-km convection allowing models now show organized thunderstorms in Arkansas into W Tennessee and W Kentucky. Look at these  SRH values (500 m2/s2) that should exist with convection (surface based convection, or close enough). So, this isn't some sort of meaningless SRH plot, there should be surface-based convection, with a pretty high chance of wind reports after sunset in western Tennessee. The tornado situation should be watched closely.

 

[Runman292]

Per the latest update from the SPC, it looks like the threat is spreading eastward. 

[jaxjagman]

 Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1201 PM CST Sun Nov 04 2018

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
   ARKLAMISS REGION NORTHEASTWARD INTO CENTRAL KENTUCKY...

   CORRECTED SIGNIFICANT TORNADO PROBABILITY TO 10%

   ...SUMMARY...
   Severe storms capable of damaging winds and tornadoes are expected
   mainly Monday evening and overnight from northern Mississippi across
   Tennessee and into central Kentucky.

   ...Synopsis...
   Within a broad area of cyclonic flow aloft across the CONUS, a
   shortwave trough will move from the ArkLaTex Monday afternoon
   northeastward across the OH Valley during the night. This wave will
   take on a negative tilt, with the greatest height falls/cooling
   aloft from northern AR into OH while height tendencies remain
   neutral overnight across the Gulf Coast states. Winds aloft will
   continually increase through the period, with strong large-scale
   lift mainly from TN northward toward the Great Lakes.

   At the surface, a broad area of southerly winds will allow a
   northward return of 60s F dewpoints from eastern TX into the lower
   MS Valley during the day, and into TN and KY overnight. This will
   aid in gradual destabilization which when combined with very strong
   shear profiles will support the potential for corridors of damaging
   severe storms.

   ...ArkLaMiss northeastward into Kentucky...
   The rapid warm advection and moistening from the south will likely
   lead to extensive low cloud cover over much of the area ahead of the
   cold front which will limit low-level lapse rates/heating.
   Therefore, most of the destabilization will be due to low-level
   moisture advection and cooling aloft. This will occur first across
   AR and southern MO during the afternoon, and elevated storms capable
   of hail are possible. Not until after 00Z will destabilization occur
   farther north and east across northern MS/AL, TN, and KY, where
   shear will be strongest. Storms are expected to intensify along the
   southern periphery of the warm advection storms, as the air mass
   becomes more supportive of surface based convection, likely near the
   AR/MS border. It should be noted that too much coverage of these
   earlier storms could push the greatest threat corridor east, or
   diminish it faster than expected from the west.

   The cold front will then increase lift as it emerges into MS, TN,
   and KY, with a QLCS likely. Both damaging winds and tornadoes will
   be possible, with tornado potential more heavily weighted toward
   areas with warmer, more unstable air from northern MS across middle
   TN and perhaps southern KY and northwest AL. A strong tornado cannot
   be ruled out, with effective SRH potentially to 500 m2/s2.

   Severe wind gusts, along with a lesser tornado threat, will exist
   with storms along the trailing cold front across the remainder of MS
   and AL.

   ...MAXIMUM RISK BY HAZARD...
   Tornado:  10% SIG - Enhanced
   Wind:     30% SIG - Enhanced
   Hail:      5%     - Marginal

[jaxjagman]

The latest SWEAT index from this afternoons Euro in the Valley.In case you don't understand what the SWEAT index is,here's a link.The maps are 0Z AND 6Z Tuesday

http://www.theweatherprediction.com/habyhints/304/

[CheeselandSkies]

I'm really perplexed as to why the 3KM NAM isn't showing much stronger UH streaks late Monday afternoon into the overnight.

[jaxjagman]

26 minutes ago, CheeselandSkies said:

I'm really perplexed as to why the 3KM NAM isn't showing much stronger UH streaks late Monday afternoon into the overnight.

It has a more stronger capping inversion

[jaxjagman]

SREF is up to 30% West and Central Valley

[jaxjagman]

4 hours ago, Chinook said:

In my opinion, this could be as potent as 10/31 ( a few days ago.) As a reminder, on 10/31 there were 192 wind reports and 56 preliminary tornado reports, (possibly 15 confirmed, as per Wikipedia)

 Watch out! The 3-km convection allowing models now show organized thunderstorms in Arkansas into W Tennessee and W Kentucky. Look at these  SRH values (500 m2/s2) that should exist with convection (surface based convection, or close enough). So, this isn't some sort of meaningless SRH plot, there should be surface-based convection, with a pretty high chance of wind reports after sunset in western Tennessee. The tornado situation should be watched closely.

 

National Weather Service Nashville TN
220 PM CST Sun Nov 4 2018

...Main Concern Continues to be Severe Thunderstorm Potential
Monday Night...

.DISCUSSION...This afternoon, light showers were occurring over
the west half of the area. Look for the light showers to move
eastward through the evening. Rainfall amounts will continue to be
light, with less than one tenth of an inch expected. The
weakening front responsible for the showers was also producing
gusty winds approaching 40 mph at times. The winds will diminish
through the evening.

Monday will start out cloudy across Mid Tennessee. On the large
scale, a trough axis will be moving out of the Rockies with an
elongated area of surface low pressure over the central plains. As
the day progresses the trough will take on a negative orientation
and the surface low will deepen as it gains more upper level
support. As the surface low deepens, a cold front will take shape
over the Mississippi Valley. Gulf moisture will surge northward
ahead of the front helping to destabilize the prefrontal air. A
few showers may develop over Mid Tn during the day, but most of
the action will hold off until Monday evening, with the initial
development occurring off to our west.

Monday night, the deepening low pressure across the Midwest and
Ohio Valley will drag a trough / cold front from the Mississippi
Valley, eastward through Mid Tn late in the night. A tongue of
rich, Gulf moisture ahead of the front will cause enough
destabilization to achieve around 600 J/kg of mixed layer CAPE. A
50-65 kt low level jet will ramp up ahead of the cold front
leading to 40 kts of 0-1 km shear and 45-50 kts of 0-3 km shear.
The severe threat will be in the form of a QLCS capable of
damaging straight line winds and a few tornadoes.

Despite the overlap of impressive shear and modest instability,
this is not a slam dunk event. Pre frontal convection could
interfere with available instability. Also, the shear to
instability ratio may be too great. But, if deep updrafts
flourish, they will easily rotate, and low level SRH will be
supportive of tornadogenesis.

Timing still looks like storms will be approaching from the west
around 8 PM, crossing Metro Nashville between 11 PM and 2 AM, and
east of the Plateau around 5 AM Tuesday.

Most of Mid Tn is now under an enhanced risk from SPC, partly for
wind damage potential and partly for high SRH values that could
contribute to tornado development/strength.

[Windspeed]

Despite the overlap of impressive shear and modest instability, this is not a slam dunk event. Pre frontal convection could interfere with available instability. Also, the shear to instability ratio may be too great. But, if deep updrafts flourish, they will easily rotate, and low level SRH will be supportive of tornadogenesis.

This is probably why we won't see an upgrade to moderate until early tomorrow afternoon, if there is an upgrade at all. I suspect if high precipitation linear modes develop earlier, the tornado threat will be squashed, though certainly enough 0-3km helicity will be there for imbedded tornadoes to occur. The threat increases substantially if convection remains disorganized or holds off until late afternoon. We'll have to watch for any breaks in coverage by midday as 3-4 hrs of sunshine could really get things cranking by early evening for central MS up into SW Tennessee. It seems enough instability and low level shear will be there regardless for strong storms and frontline winds even if the mode is messy or linear.

[Chinook]

Now that we're in Standard Time, the NAM-3km maps regarding tomorrow'sevent are on the internet as soon as 7:15PM Mountain time. Nifty. The comment about the shear being too big for the instability may be an interesting one. That's something I haven't thought about for a long while, because instability is dominant in summer.

[jaxjagman]

24 minutes ago, Chinook said:

Now that we're in Standard Time, the NAM-3km maps regarding tomorrow'sevent are on the internet as soon as 7:15PM Mountain time. Nifty. The comment about the shear being too big for the instability may be an interesting one. That's something I haven't thought about for a long while, because instability is dominant in summer.

Yeah the NAM seems to be the strongest with wind shear at the surface to 6km,it backed down into Mid Tn to around 60 kts i've been wondering if they are going NAM by this?The LLShear is still impressive this evening,0z run.The post i posted from OHX the severe factor would or should be if any convection happens into Alabama and MS,which could or would cut off instabilities ,but if like you mentioned stronger shear is not always a good thing

[jaxjagman]

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1129 PM CST Sun Nov 04 2018

   Valid 051200Z - 061200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
   AR TO MIDDLE TN...

   ...SUMMARY...
   Severe storms capable of damaging winds and tornadoes are expected
   to concentrate Monday evening and overnight from southeastern
   Arkansas to Middle Tennessee.

   ...Lower MS Valley to TN Valley...

   Late evening water vapor imagery depicts a well-defined short-wave
   trough over the central High Plains region moving east in line with
   latest model guidance. Precipitation is expanding/developing east
   across NE/KS ahead of this feature and large-scale forcing for
   ascent should spread into the mid MS Valley region later today. The
   short wave will eject into the OH Valley late day1 as primary
   mid-level speed max ejects across the TX Panhandle into AR by
   06/00z...then into OH by the end of the period.

   In response to this short wave, LLJ should strengthen over the
   southern Plains which should aid northward advance of maritime
   tropical air mass over the western Gulf Basin into southeast TX
   where lower 70s dew points are possible ahead of the front. Even so,
   higher moisture content may struggle a bit to advance too far inland
   and 05/00z short-range models suggest modified boundary-layer
   moisture should return across the ENH risk region where 60s dew
   points are expected prior to convective development. Forecast
   soundings suggest the greatest buoyancy will remain south of I-20
   where large-scale forcing will be minimized.  While warm advection
   may drive some early-day convection across the lower MS Valley,
   further moistening/destabilizing will likely be warranted for more
   robust convection. Latest thinking is strong/severe thunderstorms
   are most likely to evolve along/ahead of the front during the late
   afternoon over eastern AR then mature downstream along a corridor
   from extreme northeast LA into middle TN. Forecast shear profiles
   favor supercells and if discrete storms can develop it would appear
   the greatest tornado threat will be concentrated over northern MS,
   though isolated tornadoes can not be ruled out where near-surface
   based thunderstorms can develop across the TN Valley. Otherwise,
   damaging winds are the primary severe threat with upward evolving
   squall line as it progresses toward the southern Appalachians by the
   end of the period.

   ..Darrow/Wendt.. 11/05/2018

[Araqiel]

So uh did they forget the SIG hatching again in today's 06Z D1 then? >_>

Long-time lurker finally got around to making an account btw so hi all.