April 12 Severe Threat

[jaxjagman]

9 minutes ago, nrgjeff said:

Moderate rain moving into Chattanooga. Looking forward to a relaxing stable evening...

Just kidding! WF is trying to lift north, but I just can't get excited with my heat pump on while I'm wearing full sweats.

Real concerns remain from Mississippi through Alabama and perhaps Georgia though. Warm sector gonna be lit, though very sloppy.

Yeah keep seeing some strong inversion setting into the Valley soon by both the HRRR and RAP

[jaxjagman]

Have to wait and see but if the lid isn't that strong as advertised or breaks sooner.HREF shows some half way decent updrafts if its to be believed

[jaxjagman]

Tornado around Yazoo city,go figure

[dwagner88]

1 hour ago, Holston_River_Rambler said:

If that QLCS holds together, the HRRR suggests that it might be making it straight for the southern/ south central parts of the eastern valley

HRRR and GFS both have a significant flash flood event tonight. 6”+ qpf. 

[jaxjagman]

5 minutes ago, dwagner88 said:

HRRR and GFS both have a significant flash flood event tonight. 6”+ qpf. 

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1200 PM EDT Sun Apr 12 2020
 
Day 1
Valid 12Z Sun Apr 12 2020 - 12Z Mon Apr 13 2020 

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FROM THE MID 
SOUTH THROUGH PARTS OF THE TENNESSEE VALLEY TO THE SOUTHERN 
APPALACHIANS...  

...Southern U.S / Moderate Risk Area...
In the 16Z update the Moderate Risk is nearly the same as it was. 
We expanded coverage on the western end, over Arkansas, to account 
for what was an ideal heavy rain setup in the near term through 
19Z as well as some wet antecedent conditions from early morning 
rainfall.

While 00Z hi-res models did not fare well in handling the Texas 
MCS this morning, the expected axis of greatest rainfall totals 
did not change too much, as the synoptics will largely dictate 
that MCS activity rolls eastward along the advancing deep layer 
warm front, shallow upslope convection boosts totals in the 
Appalachians, and a separate round of moderate to heavy rain forms 
this evening ahead of the surface front in the Plains / Midwest. 
The 06Z NAM Nest had a decent handle on the Texas MCS, and many of 
the 12Z hi-res solutions looked well initialized. Overall, we 
prefer the details of the 12Z HRRR, WRF-ARW, and NAM Nest per 
their simulated reflectivity fields. A QPF blend using these 
sources and a base layer of broader resolution consensus QPF 
suggests the emphasis for higher-end rainfall continues to be 
north of the surface warm front from eastern Arkansas through 
southern Tennessee and all adjacent states to the south. This is 
essentially where a more cellular / supercellular regime 
transitions to one of QLCS activity with broader distribution of 
heavy rainfall. Rainfall will likely average 2-4 inches here, with 
local totals above 5 inches. Stronger capping limits the southward 
extent, and migration of rain-cooled air along the northern 
periphery limits northward extent of the heavier totals, thus 
giving us higher confidence in placement.
  
The whole weather system is strongly anomalous, with the strength 
of the mid-level systems at play 3-4 sigmas below the mean for 
mid-April and a surface cyclone 4-5 sigmas below the mean -- near 
record values for April -- from the Mid-South into the Lower 
Peninsula of MI.  Both Precipitable water and Integrated Vapor 
Transport values are near record levels for this time of year 
since the cyclone will drive a powerful low-level jet (approaching 
80 kts) -- with effective bulk shear to match -- that will invade 
from the Gulf coast into the lower MS Valley, TN Valley, and 
southern Appalachians this period.  ML CAPE is likely to build 
towards 3000 J/kg during the afternoon hours within the capped 
warm sector near LA where 700 hPa temperatures are expected to 
exceed 9C which should boost convective potential downstream into 
the evening hours.  The synoptic scale system will remain 
progressive, which will have a tendency to cap the upper magnitude 
of the rainfall potential.  With concerns for episodic training of 
convection along/near a warm front lifting north through the TN 
Valley/southern Appalachians, hourly rainfall totals are likely to 
max out in the 2-3"/hour range within mesocyclones, cell mergers, 
and periods of training.  Swaths of the Mid-South, Southeast, and 
southern Appalachians shows 50%+ chance of exceeding 3" of rain 
this period per the 00z HREF probabilities.  The 00z HREF 
probabilities for 5"+ maximize in southwest NC where the chances 
of exceedance lie above 90%.

[jaxjagman]

National Weather Service Nashville TN
133 PM CDT Sun Apr 12 2020

.DISCUSSION...

Showers have been pounding Middle Tennessee all morning, and a
line of enhanced echoes is currently making its way northward
across the mid state owing a weak surface trough or a meso-low
trying to spin off. The primary center of low pressure is still
situated near the Ozarks, and is forecast to move into the Ohio
Valley by 06Z while deepening to 991-993 mb. This will contribute
to a strong pressure gradient over Middle Tennessee for several
hours later this afternoon and tonight, hence the Wind Advisory.
Meanwhile, the environment across Middle Tennessee remains capped,
especially across the cooler northern zones. The NAM12 forecast
sounding for BNA valid at 21Z shows a SBCAPE of 0, but the MUCAPE
(900 mb) is nearly 500 J/Kg. The expected 0-3 SRH at the same
time is a whopping 1,160 m2/s2. We never really do get any SBCAPE
this far north, but the cap does erode somewhat as the surface
front approaches, and MUCAPE values should increase to around
1,000 J/kg, so the lift provided by the cold front should be able
to tap into that elevated instability. When combined with the
enormous shear values, don`t see any need to deviate from the
current severe weather messaging of damaging straight-line winds
and isolated tornadoes, especially south of I-40. Actual fropa
should occur between maybe 02Z and 07Z, with sharp subsidence
right behind the front. The surface low passes close enough to
Middle Tennessee that we will likely experience a swath of wrap-
around moisture toward morning and maybe some lingering showers
along the Cumberland Plateau Monday morning. Looking ahead, next
week looks to be much cooler than normal with only nominal chances
of rain. We could see areas of frost as late as Thursday morning.
Expect a pleasant warming trend by next weekend. After tonight,
we don`t see any severe weather risk at least through Saturday.

[TellicoWx]

18z HRRR continues increasing the UH up the valley 

[jaxjagman]

Mesoscale Precipitation Discussion 0139
NWS Weather Prediction Center College Park MD
245 PM EDT Sun Apr 12 2020

Areas affected...Northeast LA...Central/Northern
MS...Central/Southern TN...Far Northwest GA

Concerning...Heavy rainfall...Flash flooding likely

Valid 121845Z - 130045Z

SUMMARY...Heavy showers and thunderstorms will continue to impact
portions of the lower MS Valley and especially the Mid-South this
afternoon and into the evening. The threat for flooding and flash
flooding will remain elevated given the increasingly wet
antecedent conditions, and high rainfall rate potential.

DISCUSSION...The latest GOES-16 IR satellite imagery shows an
impressively diffluent flow pattern aloft from the lower MS Valley
to the Mid-South out ahead of an ejecting mid-level shortwave
trough over the southern Plains. This along with area radars
confirm an expansive area of cold-topped convection which includes
vigorous severe-mode thunderstorms impacting northeast LA and
west-central MS, and a notably elevated arc of heavy showers and
thunderstorms to the northeast from northern MS, northern AL and
through adjacent areas of western and central TN.

While being aided by strong synoptic scale ascent, the convection
is focusing within a highly favorable thermodynamic environment
that is being facilitated by a very strong southwest low-level
jet. In fact, as of 1800Z, VAD wind profiler data is depicting
flow ranging in the 50 to 70 kt range at 850 mb, and 40 to 50 kts
at 925 mb. This is fostering extreme low-level moisture transport
and is also transporting a significant amount of warm-sector
instability well north over an advancing warm front to promote and
sustain the convective threat.

Going through the late-afternoon and early evening hours, the
greatest rainfall threat will overwhelmingly be over the
Mid-South, with an emphasis on northern MS, northern AL, much of
central/southern TN and gradually edging into far northwest GA.
This is basically where the strongest warm-air advection, deep
layer ascent will overlap with the aforementioned extreme moisture
and instability transport regime.

PWs of 1.75 to 2 inches are forecast, and with a nose of 1000 to
2000 j/kg of MUCAPE. However, farther down to the southwest over
areas of central/northeast LA and through central MS, there will
be even greater warm-sector instability and deep layer shear that
will be conducive for highly organized and severe-mode convection
that will in itself be capable of producing very heavy rainfall.
Rainfall rates have already been locally observed over 2 inches,
and this potential should continue over the next several hours
with the deeper and more organized convective cores.

The recent runs of the HRRR and the experimental HRRR favor swaths
of as much as 2 to 4 inches of rain, with isolated totals of 5+
inches going through 00Z. Additional heavy rainfall potential will
exist after 00Z over the Mid-South, with an increasing threat also
spreading over the southern Appalachians.

Given the increasingly wet antecedent soil conditions, especially
over the Mid-South, areas of flooding and flash flooding will
remain likely.

Orrison

[yoda]

   URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 109
   NWS Storm Prediction Center Norman OK
   320 PM CDT Sun Apr 12 2020

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     Northern and central Alabama
     Far southern Middle Tennessee

   * Effective this Sunday afternoon and evening from 320 PM until
     1000 PM CDT.

   * Primary threats include...
     Several tornadoes and a couple intense tornadoes likely
     Widespread damaging winds and isolated significant gusts to 80
       mph likely
     Isolated very large hail events to 2 inches in diameter possible

   SUMMARY...Clusters of severe thunderstorms will spread
   east-northeast from Mississippi through this evening. Greatest
   tornado threat will exist across west-central to north-central
   portions of Alabama into early evening.

   The tornado watch area is approximately along and 85 statute miles
   north and south of a line from 45 miles northwest of Tuscaloosa AL
   to 30 miles east northeast of Gadsden AL. For a complete depiction
   of the watch see the associated watch outline u

[McMinnWx]

Heavy rain in Athens. 

[John1122]

Covington MS-Jefferson Davis MS-
421 PM CDT Sun Apr 12 2020

...TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA...

...A TORNADO WARNING REMAINS IN EFFECT UNTIL 445 PM CDT FOR SOUTHERN
COVINGTON AND SOUTHEASTERN JEFFERSON DAVIS COUNTIES...

At 420 PM CDT, a confirmed large and destructive tornado was located
near Melba, or 9 miles southwest of Collins, moving northeast at 55
mph.

TORNADO EMERGENCY for locations in the warned area. This is a
PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!

[Runman292]

Where is the warm front now?

[McMinnWx]

The Laurel, MS tornado looks to be a monster. 

[EastKnox]

26 minutes ago, Runman292 said:

Where is the warm front now?

 

[PowellVolz]

 

I believe there’s 2 WF. The other one is along the Tennessee boarder. The one pictured to the south is holding back the return flow where the big tornados are churning.


.

[McMinnWx]

5 minutes ago, PowellVolz said:

I believe there’s 2 WF. The other one is along the Tennessee boarder. The one pictured to the south is holding back the return flow where the big tornados are churning.


.

Is that other one going to lift this far north? 

[Holston_River_Rambler]

To me it looks like there may be a piece of that airmass beyond the lower warm front that makes it into the southern valley, but it will be close to the time the main front swings through. 

Very heavy rain right now really working over the atmosphere. And that QLCS we were talking about earlier seems to have turned more east, rather than coming up towards Chatt, so some of the convection is perpendicular to the valley now. 

Hard to say with the line back in MS now though. 

[PowellVolz]

Is that other one going to lift this far north? 

I don’t believe it will but it might not matter either way because the atmosphere is not mixed anymore because of all the rain. I think central Ga to SC is the new track.


.

[PowellVolz]

To me it looks like there may be a piece of that airmass beyond the lower warm front that makes it into the southern valley, but it will be close to the time the main front swings through. 
Very heavy rain right now really working over the atmosphere. And that QLCS we were talking about earlier seems to have turned more east, rather than coming up towards Chatt, so some of the convection is perpendicular to the valley now. 
Hard to say with the line back in MS now though. 

I’m not even seeing the pre cold front storms that are supposed to hit after midnight across Tennessee getting going. HRRR had it, lost it and now has it again but I’m not sure it happens now.


.

[Runman292]

1 minute ago, PowellVolz said:

I’m not even seeing the pre cold front storms that are supposed to hit after midnight across Tennessee getting going. HRRR had it, lost it and now has it again but I’m not sure it happens now.


.

The pre cold front storms are entering Arkansas now.

[PowellVolz]

The pre cold front storms are entering Arkansas now.

You are correct. I didn’t look far enough west. My bad.


.

[Holston_River_Rambler]

Absolutely pouring right now. One of the heaviest rains I've ever experienced. Visibility down to >.10 mile with fog. 

[PowellVolz]

This cell south of Chattanooga might lay down a monster


.

[Uncle Nasty]

This is about 20 miles south of us. We are getting pelted with rain and lightning

Sent from my moto z4 using Tapatalk

[PowellVolz]

Most likely a large tornado on the ground moving towards Dalton Ga




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[Holston_River_Rambler]

Bowing storm aiming at Dayton. The northern edge may hit me. 

[Runman292]

Tornado Watch for Southeast TN until 2:00 AM.

[yoda]

Severe Tstorm Watch coming for W TN -- https://www.spc.noaa.gov/products/watch/ww0114.html

URGENT - IMMEDIATE BROADCAST REQUESTED
   Severe Thunderstorm Watch Number 114
   NWS Storm Prediction Center Norman OK
   820 PM CDT Sun Apr 12 2020

   The NWS Storm Prediction Center has issued a

   * Severe Thunderstorm Watch for portions of 
     Eastern Arkansas
     Northeast Louisiana
     Missouri Bootheel
     Northwest Mississippi
     Western Tennessee

   * Effective this Sunday night and Monday morning from 820 PM
     until 100 AM CDT.

   * Primary threats include...
     Scattered damaging wind gusts to 70 mph likely
     Scattered large hail events to 1.5 inches in diameter possible
     A tornado or two possible

   SUMMARY...A fast-moving line of thunderstorms over Arkansas will
   track across the watch area this evening, posing a risk of damaging
   wind gusts and hail.

[PowellVolz]

Bowing storm aiming at Dayton. The northern edge may hit me. 

I’m wondering where the northern most WF is. I hope it didn’t make it across the valley. These storms might rotate more off of it. The line moving off the plateau has breaks and offsets which sometimes indicates mesos imbedded in the line.


.

[yoda]

Tornado Warning Polk County in E TN