April 12 Severe Threat

[VOLtage]

Not April 27th bad. Maybe April 15th 2011 bad.

[crossbowftw3]

22 minutes ago, VOLtage said:

Not April 27th bad. Maybe April 15th 2011 bad.

Probably not April 15th either but 4/24/10 looks closest to this at first glance.

[jaxjagman]

NAM/WRF 40Km FORECAST FOR: MEM    LAT=  35.05 LON=  -90.00 ELE=   285

Not bad if you like severe



                                             2P APR10
                 SFC     SFC     MU      SFC    BEST     SFC    1000M      0       0 
                 PWW    CAPE    CAPE     LIX     LIX     CIN     HEL     900     500 
                (IN)    J/KG    J/KG     (C)     (C)    J/KG    M2/S2   SHEAR   SHEAR
FRI  2P 10-APR   0.2       0       0      20      21       0      -6    00001   08046                                        
FRI  8P 10-APR   0.3       0       0      16      16       0     -14    05002   09039                                        
SAT  2A 11-APR   0.4       0      57      18      15       0      79    10010   17042                                        
SAT  8A 11-APR   0.4       0      12      20      14       0     122    09011   15045                                        
SAT  2P 11-APR   0.6       0       0      12      12       0      13    00003   09043                                        
SAT  8P 11-APR   0.7       0       9       7       5       0      76    01016   06040                                        
SUN  2A 12-APR   1.3       0     219      10       4       0     114    03021   08048                                        
SUN  8A 12-APR   1.3       0     103       9       1       0     215    07022   10065                                        
SUN  2P 12-APR   1.7       0    1068       6      -3       0     305    05036   05066                                        
SUN  8P 12-APR   1.5    2165    2608      -7      -8     -13     388    02040   04086                                        
MON  2A 13-APR   1.0      43    1102       3      -3    -104     231    04036   03055                                        
MON  8A 13-APR   0.4       6       0      21      10       0     -46    02017   07061                                        
MON  2P 13-APR   0.4       0       0      16      15       0    -107    02017   08066                                        
MON  8P 13-APR   0.5       0       0      13      14       0     -49    01010   09067                                        
TUE  2A 14-APR   0.5       0       0      16      16       0     -18    02009   12070       

[jaxjagman]

National Weather Service Nashville TN
220 PM CDT Fri Apr 10 2020

.DISCUSSION...

Another dry day across the mid state, with dewpoints dropping into
the lower 20s and even upper teens. Winds have calmed down a
little bit, and should continue to do so this afternoon. With
clear skies and light winds overnight, temperatures should drop
into the mid to upper 30s, and even areas on the Plateau along
with low lying areas seeing temps around and just below freezing.
Areas that get into the mid 30s will see some frost by sunrise, so
have a freeze warning for the Plateau and a frost advisory for the
rest of the area in effect overnight into Saturday morning.
Another dry day will be in store Saturday before the next upper
low moves in for Sunday.

Some uncertainty on the track of the low still exists for Sunday,
however, the potential for a significant severe weather outbreak
will be in place for the southeast US Sunday, mainly during the
afternoon and evening. Strong upper trough will move northeast
from the southern Plains, bringing plenty of WAA and moisture into
the region. Warm front will move through the mid state in the
morning, with showers and thunderstorms at that time as well.
Some may be strong to severe, but main focus remains on developing
convection for the afternoon and evening. As we get into the
afternoon, wind speeds aloft increase quite a bit, with the LLJ
showing southerly winds around 60 knots and winds aloft around 100
knots. That additional strength in southerly flow near the surface
will bring more low and mid level moisture, and PWAT values
continue to trend upward with model runs, now exceeding 1.5 inches
for the afternoon and evening across the mid state. These values
are well above climatological max values, and with training of
showers and thunderstorms during the afternoon and evening, the
potential for flash flooding looks to be increasing no matter
which low track takes place.

The severe threat on Sunday is also trending upward in addition to
the flooding threat already in place, however, a shift in the
track of the low will make a HUGE difference in regards to where
severe weather occurs. As of right now, most of the higher
instability stays off to the south, but Sunday afternoon and
evening, models do have around 500 J/kg of MLCAPE over most of
the southern zones. The NAM remains the most bullish model showing
around 1000 J/kg of MLCAPE. Wind shear is extremely strong, and
has remained so over the past few runs, with 0-6km deep layer
shear staying consistent around 70 to even 90 knots. 0-1km shear
is also high thanks to the strong near surface winds and LLJ, with
shear values around 40 to 50 knots. With shear values that
strong, its no surprise that 0-1km and 0-3km helicity values
exceed 600 m2/s2 with each model run from Sunday afternoon through
around midnight Monday.

This all suggests that we can have very fast moving, strong to
severe thunderstorms during the afternoon and evening Sunday, with
the potential for damaging winds, hail, and tornadoes. Should the
low track further north, and allow for additional instability to
reach the mid state, the potential for a few long track,
significant tornadoes will be possible as well. Be sure you stay
up to date with the latest forecasts, and make a plan now to
prepare for heavy rainfall/flooding as well as a potential for a
significant severe weather outbreak. Should severe thunderstorms
develop, with incredibly strong wind speeds through the
atmosphere, storm motions will likely be over 60 mph, so you will
need to be prepared to take shelter very quickly should warnings
be issued.

Some things that could inhibit the severe potential on Sunday
would be a southerly track of the low, keeping even more
instability to our south, and shifting our focus to a heavy
rain/flooding event with a few strong to severe thunderstorms as
opposed to a more widespread severe weather outbreak. Another
factor that could limit severe potential is warm sector convection
behind the morning warm front and before potential severe weather
later in the afternoon and evening. Late morning/early afternoon
convection may dilute the instability through cooling the low
levels, and not allowing the atmosphere to reload additional
instability with the strong southerly flow. Again, its important
to stay updated on the latest forecast changes, and be prepared
just in case for the potential of severe weather on Sunday.

[Runman292]

Here’s MRX’s latest AFD concerning Sunday.

Next the severe weather: Questions remain how far N the surface warm
front will lift Sunday evening. There is agreement that it at least
reaches the southern plateau/southern valley by 00Z before surging N
immediately ahead of the cold front closer to 06Z. How much of the
CWA can get into the warm sector will be key to how widespread the
tornado threat can be. The southern plateau and southern valley
continues to have the greatest tornado risk with at least a few
hundred joules of surface based CAPE developing after 00Z behind the
surface warm front. Shear in the vicinity of this boundary will be
extreme with 0-1 Km SRH of 600-800+ m2/s2, 0-1 Km shear of 50+ kts,
and 0-6 Km shear of 80-100 kts per latest NAM forecast soundings for
CHA. As would be expected in this environment, hodographs are sickle
shaped. It will not take much surface CAPE, combined with projected
low LCL heights, to see tornadoes in this environment. A couple of
strong, long track tornadoes will also be possible, especially in
discrete cells that can form ahead of the main line and cross over
the warm front. The current SPC day 3 outlook has an enhanced risk
across the the S plateau through SE TN, but would not be surprised
to see this upgraded to moderate. With questions remaining how far N
the surface warm front can move Sunday evening, the tornado threat
appears much less at this time from the N plateau through NE TN and
SW VA, however widespread damaging winds and pockets of large hail
will occur with the strongest cells as the QLCS crosses. As
mentioned earlier, rough timing of all this is 00-06Z, so brought
pops back to categorical before tapering off from W to E after 06Z.

[jaxjagman]

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
418 PM EDT Fri Apr 10 2020
 
Day 3
Valid 12Z Sun Apr 12 2020 - 12Z Mon Apr 13 2020 

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF 
THE TENNESSEE VALLEY TO PARTS OF THE SOUTHERN APPALACHIANS ON 
SUNDAY AND SUNDAY NIGHT...

2030z Update: Still looks like a good setup for excessive rainfall 
Sunday into Sunday night across northern MS/AL/GA into central and 
southern TN and the southern Appalachians. A strong mid level 
wave, favorable upper jet pattern, impressive low level moisture 
transport, and instability advecting northward...should set the 
stage for an active day of convection and heavy rainfall. Both PWs 
and IVT are forecast to be at or near record levels for mid April 
with this system. The system as a whole will remain progressive, 
which will cap the upper magnitude of rainfall potential...however 
still expecting a swath of rainfall greater than 3", with 
localized amounts of 4-6" a possibility. The best threat for these 
heavier rains will be near the northern gradient of the CAPE 
axis...where we will see the best overlap of lower and upper level 
forcing and enough instability for higher rainfall rates. Still 
some uncertainty on exactly where this sets up...but the model 
consensus is across the Moderate risk area. There is enough of a 
QPF and environmental ingredient signal to warrant an expansion of 
the Moderate risk westward over more of AL/MS and TN with this 
update. The Slight risk was also expanded to include more of the 
OH valley...as instability advecting ahead of the strong mid level 
vort should allow for convection making it this far north.

[Windspeed]

Not familiar with this model. Viper based? At any rate, reckon that's about as much a worst case scenario as I've seen. I actually lol'd when I saw this on the SE thread. Hopefully this is slightly overdoing things.

 

 

Edit: Nevermind, this is a proprietary model based off the WRF.

[jaxjagman]

The Euro this afternoon continues to show a more westward trend.This afternoon shows the LP into the lower Mo/Valley with even a strong LLJ  up to 75kts probably around Paducah

[jaxjagman]

The GFS the same time shows the LP around the Delta the NAM is further N than the Euro,they aren't playing along very nicely even in the short range

[Windspeed]

The GFS the same time shows the LP around the Delta the NAM is further N than the Euro,they aren't playing along very nicely even in the short range

Could see a scenario where modeling really doesn't start coming into line until around 18z tomorrow. This mainly due to differences in handling phase timing and tilt so far. You'd think within 24 hrs they should be close enough that those differences get ironed out for a better consensus. Perhaps? By that point we'll all be focusing on 3km mesoscales anyway.

[jaxjagman]

13 minutes ago, Windspeed said:

17 minutes ago, jaxjagman said:

The GFS the same time shows the LP around the Delta the NAM is further N than the Euro,they aren't playing along very nicely even in the short range

 

Could see a scenario where modeling really doesn't start coming into line until around 18z tomorrow. This mainly due to differences in handling to phase timing and tilt so far. You'd think within 24 hrs they should be close enough to those differences get ironed out for a better consensus. Perhaps? By that point we'll all be focusing on 3km mesoscales anyway.

Agree,the last shift of the Euro brought up the SBCapes in Mid Tn. and more into an overnight

 

 

ECMWF Deterministic FORECAST FOR: BNA    LAT=  36.12 LON=  -86.68 ELE=   591

                                            12Z APR10
                 2 M     SFC     SFC     3/6     3/6     3/6     500    1000 
                 TMP     DEW    CAPE     HR      CVP     NCP     HGT     500 
                 (C)     (C)    J/KG    (IN)    (IN)    (IN)    (DM)     THK 
SAT 12Z 11-APR   5.1    -0.3       3    0.00    0.00    0.00     566     551    
SAT 15Z 11-APR  12.6    -1.3       0    0.00    0.00    0.00     568     552    
SAT 18Z 11-APR  17.6    -0.8       0    0.00    0.00    0.00     569     555    
SAT 21Z 11-APR  18.7     1.3       0    0.00    0.00    0.00     569     557    
SUN 00Z 12-APR  14.9     4.9       0    0.00    0.00    0.00     569     559    
SUN 03Z 12-APR  13.0     3.7       2    0.00    0.00    0.00     570     559    
SUN 06Z 12-APR  12.1     3.4      51    0.01    0.01    0.00     570     560    
SUN 09Z 12-APR  12.9     4.0       1    0.01    0.01    0.00     570     560    
SUN 12Z 12-APR  12.6     6.9      30    0.02    0.02    0.00     570     560    
SUN 15Z 12-APR  12.7    10.7       0    0.06    0.03    0.03     571     561    
SUN 18Z 12-APR  12.7    12.3      22    0.39    0.05    0.34     571     562    
SUN 21Z 12-APR  14.6    14.4     263    0.21    0.07    0.14     569     566    
MON 00Z 13-APR  17.1    16.8     148    0.55    0.33    0.21     568     568    
MON 03Z 13-APR  19.1    18.4     130    0.45    0.08    0.37     566     571    
MON 06Z 13-APR  18.8    18.2     521    1.01    0.20    0.81     562     565    
MON 09Z 13-APR  15.9    13.5       3    0.01    0.00    0.00     559     558    
MON 12Z 13-APR  12.7     9.7      31    0.01    0.00    0.00     564     557    

 

 

[jaxjagman]

SREF 

[VOLtage]

5 hours ago, crossbowftw3 said:

Probably not April 15th either but 4/24/10 looks closest to this at first glance.

You hit the nail on the head here. I just checked the CIPS analogs and that comes up as the 2nd most similar to this scenario.

 

[MUWX]

28 minutes ago, jaxjagman said:

SREF 

Pretty big step back isn’t it? 

[Santa Clause]

9 minutes ago, MUWX said:

Pretty big step back isn’t it? 

Yeah one was higher probs I remember seeing yesterday.

[Runman292]

33 minutes ago, jaxjagman said:

SREF 

I got a question. What is this showing?

[MUWX]

1 minute ago, Runman292 said:

I got a question. What is this showing?

It was showing a large 90% area. Now barely a 75%

[Santa Clause]

19 minutes ago, VOLtage said:

You hit the nail on the head here. I just checked the CIPS analogs and that comes up as the 2nd most similar to this scenario.

 

4/24/10 may still be higher end than Sunday...remains to be seen, but that was big day with Yazoo City.

[Indystorm]

Barely a 75?   It's also at a later hour, isn't it?

[MUWX]

2 minutes ago, Indystorm said:

Barely a 75?   It's also at a later hour, isn't it?

Not sure, just saying that it’s a size able step back from a large 90% to and very small 75%. 

[jaxjagman]

Euro slightly east with the 18z run

[Matthew70]

9 minutes ago, MUWX said:

Not sure, just saying that it’s a size able step back from a large 90% to and very small 75%. 

This is at a later hour.  Plus the higher % moved into TN at that hour.  So wether it’s 90% or 75%.  Still do not like that being in my backyard.  No thank you please.  My brother is just now having his house rebuilt.  

[jojo762]

Surprised nobody mentioned that the significant tornado ingredients SREF map that was posted was valid for 10pm...

[jaxjagman]

46 minutes ago, jojo762 said:

Surprised nobody mentioned that the significant tornado ingredients SREF map that was posted was valid for 10pm...

That's close to Yazoo,MS,i dont know what it is about that town but they are a tornado magnet

[yoda]

10 minutes ago, yoda said:

 

 

[jaxjagman]

6 minutes ago, yoda said:

 

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Sat Apr 11 2020

   Valid 121200Z - 131200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR
   CENTRAL/NORTHERN LOUISIANA...SOUTHEAST ARKANSAS...MUCH OF
   MISSISSIPPI...WESTERN/CENTRAL ALABAMA......

   ...SUMMARY...
   An outbreak of severe thunderstorms appears likely Sunday into
   Sunday night, with the greatest threat expected from Louisiana
   through much of the Southeast and Tennessee Valley. Strong
   tornadoes, potentially widespread damaging winds, and large hail are
   all possible.

   ...Synopsis...
   The ejecting shortwave trough initially over the southern High
   Plains on Sunday morning is forecast to move quickly eastward to the
   lower MS Valley by early evening, and then accelerate northeastward
   toward the Ohio Valley late Sunday night into Monday morning, as it
   becomes absorbed within an amplifying longwave trough that will
   encompass nearly all the CONUS by 12Z Monday. In conjunction with
   the ejecting trough, a broad surface low centered over the
   central/southern Plains on Sunday morning will move eastward to the
   mid-MS Valley by 00Z Monday, and then move northeastward and rapidly
   intensify into an intense cyclone over the lower Great Lakes by 12Z
   Monday. A warm front will surge northward ahead of the low across
   the lower MS Valley and Southeast, while a strong cold front will
   move southward through much of the Plains in the wake of the
   departing cyclone. 

   ...East TX northeastward through much of the Southeast and TN
   Valley...
   One or more clusters of deep convection will likely be ongoing at
   12Z Sunday morning somewhere over east TX and potentially into
   portions of the lower MS Valley. The intensity and areal extent of
   any such clusters remain uncertain, but ample shear and instability
   will favor a threat of hail and damaging wind with any organized
   convection at the start of the period. Some tornado threat will also
   be present Sunday morning with any semi-discrete storms that begin
   to interact with the richer low-level moisture in the vicinity of
   the warm front. As this convection spreads northeastward,
   intensification is possible into portions of the ArkLAMiss region,
   with an increasing tornado threat in late morning/early afternoon
   with any surface-based storms, given rapidly increasing low-level
   moisture and shear. North of the warm front, evolution into a QLCS
   will be possible, with a corresponding risk of damaging wind into
   portions of the TN Valley. 

   Meanwhile, further south, moderate to locally strong instability is
   forecast to develop along/south of the warm frontal position, which
   will be modulated by the impact of outflow from any early convection
   described above. Midlevel flow will increase to 70-100 kt as a
   south-southwesterly low-level jet intensifies into the 40-60 kt
   range. These wind profiles combined with ample instability (MLCAPE
   of 1500-3000 J/kg) will support the potential for intense
   supercells. Any surface-based initiation along and east of a
   pseudo-dryline moving into western LA by late afternoon could evolve
   into one or more long-tracked supercells capable of producing strong
   tornadoes, large hail, and damaging wind gusts. The extent of
   development within the warm sector remains somewhat uncertain, given
   the presence of a capping inversion and generally subtle foci for
   initiation. 

   While the conditional risk of all severe hazards will be quite high
   if supercells develop, uncertainty remains regarding how convection
   will evolve from the morning into the afternoon. Any remnant outflow
   related to early convection will determine the northern extent of
   the higher-end tornado potential, and some guidance suggests the
   potential for elevated convection within a midlevel moist plume
   across the warm sector during the afternoon, which could either
   dampen the severe potential, or evolve into surface-based convection
   with a substantial severe threat. Given these factors, there is too
   much uncertainty to upgrade the ongoing outlook at this time. 

   Evolution into more of QLCS is suggested by most guidance by Sunday
   evening, which would pose an increasing threat of widespread
   damaging winds and a few tornadoes across much of AL into
   western/central GA through the overnight hours. Higher wind
   probabilities may be needed in subsequent outlooks if confidence in
   this scenario grows. 

   ...Central/southern Plains into the Ozark Plateau...
   While widespread convection to the southeast will likely limit
   transport of deeper Gulf moisture into the Plains/Ozarks, more
   modest moisture that was advected into the region on Saturday should
   remain in place ahead the advancing surface low and cold front
   Sunday afternoon. Steep lapse rates and cold midlevel temperatures
   associated with the primary shortwave will support moderate
   destabilization. Wind profiles will likely not favor classic
   supercells, with some backing of mid/upper-level flow expected, but
   effective shear will be supportive of organized structures. Large
   hail (potentially significant) will be the primary threat, with some
   wind potential if any upscale growth occurs. Wind profiles will not
   generally favor tornado potential, though robust updrafts
   interacting with locally enhanced vorticity near the surface cyclone
   could produce a tornado or two. 

   ...TN Valley into the OH Valley -- Sunday night...
   Substantial uncertainty remains regarding the potential for
   destabilization from northern portions of the TN Valley into the OH
   Valley, due to the potential for widespread convection to the south
   of this area. However, rapidly strengthening wind fields in advance
   of the deepening cyclone will support the potential for damaging
   wind and perhaps a tornado risk by Sunday evening should even modest
   destabilization occur, as strong convection attempts to move in from
   the southwest in tandem with the deepening cyclone. 

   ... Eastern Georgia into the Carolinas/Mid Atlantic...
   Substantial low-level moistening is expected over eastern GA into
   the Carolinas/Mid Atlantic through the period. There is a nonzero
   risk of organized convection along/north of the warm front during
   the day into the evening, which would pose some risk of locally
   damaging wind or perhaps a tornado, but confidence in this scenario
   is low at this time. A more likely scenario is for widespread
   upstream convection to evolve into multiple clusters or a QLCS and
   move into this region sometime early Monday morning. Intense wind
   profiles will support a risk of widespread damaging wind and a few
   tornadoes, given sufficient instability. 

   The magnitude and coverage of the severe threat in this region will
   be determined in part by how fast organized convection approaches
   from the west. If convection accelerates and arrives faster that
   current guidance would indicate, then there is less time for
   low-level moistening and destabilization, and the magnitude and
   northward-extent of the threat may be limited. If convection does
   not arrive until very late in the period, then a more substantial
   severe threat could evolve. If some of the slower guidance turns out
   to be accurate, then the primary severe threat in this region may
   not come until the D3/Monday period. Probabilities may need to be
   increased in this area once the details come into better focus.

[TellicoWx]

Strong wording in MRX AFD..kinda surprised me considering they are usually leaning conservative:

 

the
favorable jet coupling aloft, this event has the potential to pose
the most significant tornado threat we have had since April 27,
2011

[McMinnWx]

1 hour ago, TellicoWx said:

Strong wording in MRX AFD..kinda surprised me considering they are usually leaning conservative:

 

the
favorable jet coupling aloft, this event has the potential to pose
the most significant tornado threat we have had since April 27,
2011

Absolutely terrifying. 

[nrgjeff]

Seems somebody forgot about March 2, 2012. Southeast Tennessee got rocked but it's no April 27.

My analog is that Enhanced Risk day that busted a few weeks back due to rain. Well at least here in Tenn. Mississippi and Alabama may get lit up, especially Miss. 

Honestly I'm a little surprised the HRRR is not more amped up. No true line of pearls. That tells you something's up. Sure they could all be wrong, but no pearls on the HRRR.

Let's look under the hood. Soundings are not all that thick, even mid-levels. Low level CAPE could really be meager due to the inversion and cool rain. Oh but the parameters! Well, that's how forced QLCS or two gets going. Yeah they could have embedded tornadoes; but, long-track strong? Nah.

Winds turning with height remains impressive. However some issues have cropped up, namely short-wave timing. Kissing jets are great, unless they miss (Nickelback song, lol) and subsidence is left. Oh, but the EML? Great, unless it comes in at night. That's not really how Dixie rolls w/o low-level CAPE.

So many ways for MDT to bust and be more like ENH. On the other hand, slightly different timing of things (namely that EML) could still go nuts in Mississippi and Alabama.

My confidence is growing that East Tennessee only faces wind rather than tornadoes Sunday night.

[Matthew70]

So really no reason to worry here in mid TN?  Just possibly high winds and lots of rain?