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DanLarsen34

March 17-18 Severe Weather Event

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34 minutes ago, magpiemaniac said:

The next update should come out at 0730 UTC or 2:30 AM CDT.

I would be a little surprised to see this go moderate at the next update. I think it gets upgraded at some point but it may not happen before day 1 outlooks come out tomorrow night or Wednesday morning. Cams look a little messy 

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47 minutes ago, magpiemaniac said:

The next update should come out at 0730 UTC or 2:30 AM CDT.

Thats the Day 3 OTLK time.

Day 2 OTLK will be at 2 AM EDT/1 AM CDT

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Here are some of my ideas based off the 00z models. Initially, you would think the mid-day threat with the cold front/ almost-dryline situation in AR/LA would be the most impressive. But then I was thinking that the continuation of the convection into the night, may bring many more tornado threats.  Late night severe threats are always worse from a human standpoint, as people are sleeping.

KFv3AAf.jpg

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SPC AC 160608

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0108 AM CDT Tue Mar 16 2021

   Valid 171200Z - 181200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FROM
   EAST-CENTRAL ARKANSAS AND SOUTHWESTERN TENNESSEE INTO NORTHERN AND
   EASTERN MISSISSIPPI AND MUCH OF ARKANSAS...

   ...SUMMARY...
   A broad area of substantial severe weather potential -- including
   risk for large hail, damaging winds, and several strong tornadoes --
   is anticipated Wednesday from  the Arkansas/Louisiana vicinity
   eastward across the central Gulf Coast states/southern Appalachians.

   ...Synopsis...
   A compact/vigorous upper low initially over the Oklahoma area is
   forecast to move steadily eastward through the period, spreading
   strong flow aloft and a broad zone of enhanced ascent across the
   south-central and into the southeastern CONUS.  This low will reach
   the Ozarks overnight, flanked by ridging across the Rockies, and
   along the East Coast.

   At the surface, a 998 mb low is progged to advance eastward along a
   similar track, crossing northern Oklahoma/southern Kansas through
   the day, and then the Ozarks overnight.  A trailing cold front will
   shift from eastern portions of the southern Plains and across
   Arkansas/Louisiana through the afternoon, and then across the
   Tennessee Valely and central Gulf Coast states through the end of
   the period.  Meanwhile, a warm front extending eastward from the low
   across northern Arkansas/southern Missouri and then
   east-southeastward across the Tennessee Valley into Georgia will
   linger in place on its eastern fringe, but will lift slowly
   northward in advance of the progressing low.  These two fronts will
   outline a broad/moist warm sector, which will gradually destabilize
   through the day supporting a widespread/potentially significant
   severe weather event.

   ...Southern MO/AR/LA vicinity east to the TN valley/western GA...
   Scattered showers and thunderstorms are forecast to be ongoing ahead
   of the cold front from eastern Oklahoma/western Arkansas southward
   into east Texas, and east-southeastward along the warm front across
   the Tennessee Valley area to the southern Appalachians.

   As the synoptic system advances, convection over the central Gulf
   Coast region/Southeast should remain generally north of the warm
   front, while some decrease in pre-cold-frontal convection is also
   expected through the morning.  This should permit some heating of
   the moist (generally mid 60s dewpoints) warm-sector boundary layer,
   pushing mixed-layer CAPE values into the 1000 to 2000 J/kg range by
   early afternoon.

   New storm development is expected to occur from the southwestern
   Missouri vicinity southward across the Arklatex region by early
   afternoon.  Strong shear -- including veering of the wind field with
   height from southerly to southwesterly -- will support ready
   evolution of rotating updrafts, with some long-lived storms likely
   evolving with time.  Along with large hail potential, locally
   damaging winds will be possible, along with a steadily increasing
   tornado risk through the afternoon.  As storms move into central and
   eastern Arkansas, at least a few intense supercells are expected,
   within the broader area of storms.  Potential for a couple of
   significant tornadoes is apparent, with this risk spreading into
   southwestern Tennessee and northern Mississippi with either
   pre-cold-frontal storms moving eastward into the region, or with
   other cells developing in a zone of increasing low-level warm
   advection in the warm sector/near the warm front.  

   During the evening and into the overnight hours, substantial
   strengthening of the low-level southerlies across the central Gulf
   Coast region is expected.  While some diurnal decrease in
   instability is expected, this should be more than offset by the
   increasing low-level and deep-layer shear.  As such, risk for
   additional/significant tornadoes is anticipated to last through the
   overnight hours, focused particularly across much of Alabama.  Hail
   and relatively widespread damaging winds will also be possible
   across this same region.

   ..Goss.. 03/16/2021

   CLICK TO GET WUUS02 PTSDY2 PRODUCT

   NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 1730Z
   CURRENT UTC TIME: 0633Z (1:33AM), RELOAD THIS PAGE TO UPDATE THE TIME

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Next two days have all the makings of a significant outbreak. Serious speed shear, great lapse rates, low LCL and solid instability in this moist air mass is going to help storms have enough spin not to get messy convectively in my opinion. Wouldn’t be shocked to see a few long trackers through MS/AL.

 

The QLCS threat is interesting tomorrow night as well with the jet strengthening in the overnight hours to offset the loss of heating. Will probably see some off the charts EHI’s tomorrow night.

 

Thursday seems complicated with this dang wedge front just lingering, could limit the northern extent of the outbreak a bit east of the mountains. Regardless, Thursday has the ability to be potent, especially into SC/GA. May go out and chase that day but also have a new truck so no hail haha.

 

I want to say kudos to the SPC for going Moderate here and maybe High. Whenever there is a solid threat of long track tornadoes you have to make that call. Atmospheric profiles are far too good for a couple wedges and that’s going to be the real danger

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4 minutes ago, nwohweather said:

Orangeburg would not be a bad place at all to sit out and watch this thing.

Newton Grove in NC is a nice go to as well.

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The 3K NAM doesn't show anything severe over central NC before 8PM.  (that's when it currently ends).  At 8PM, a line of storms is popping over the mountains
GFS much quicker...    Timing still up in the air.

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New 1730z OTLK Day 2 remains MOD... large area of hatched sig wind on 1730z OTLK introduced as well as larger hail hatching since 30% contour was increased in size by a large amount

Also MOD/ENH risk added back west and southwestward into NE LA and central into E AR

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Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1231 PM CDT Tue Mar 16 2021

   Valid 171200Z - 181200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
   ARKANSAS...NORTHEAST LOUISIANA...SOUTHWEST TENNESSEE AND MUCH OF
   MISSISSIPPI AND ALABAMA...

   ...SUMMARY...
   A regional outbreak of severe storms is expected Wednesday into
   Wednesday night across portions of the lower Mississippi Valley into
   Alabama. Widespread severe storms capable of producing tornadoes
   (several of which may be intense), very large hail and intense
   damaging wind gusts are expected. More than one round of severe
   storms are possible across parts of Mississippi into Alabama during
   the afternoon into the overnight hours.

   ...Synopsis...

   A compact and intense upper low over the southern Plains will eject
   eastward to the Ozark Plateau/lower MS Valley on Wednesday. A
   surface low centered over northeast OK will develop east/northeast
   in tandem with the upper system. At the beginning of the period, a
   cold front will extend southward from the low across eastern OK into
   eastern TX before arcing southwest into south TX. A warm front
   draped northwest to southeast from near the MO/AR border into
   northern AL will gradually lift northward through the period. There
   is some uncertainty in how far north this boundary will lift across
   northern GA/eastern TN given strong cold air damming across the
   Carolinas until very late in the period. The cold front should push
   eastward to Middle TN/central AL and the western FL Panhandle.
   Across the broad warm sector, dewpoints in the mid/upper 60s are
   expected beneath steepening lapse rates and intense vertical shear,
   resulting in an environment capable of supporting a widespread
   severe weather outbreak. 

   ...Southern Plains to the Mid-MS Valley...

   Convection will be ongoing Wednesday morning near the surface low,
   southward along the cold front, and eastward along the northward
   retreating warm front from central AR into northern MS/AL. Any
   convection north of the warm front will be elevated and pose a
   threat mainly for large hail. However, shear profiles will improve
   through the morning and surface-based storms near the triple point
   and along the warm front are possible and will increase the risk for
   damaging gusts and a few tornadoes. Further south along the cold
   front across eastern OK into eastern TX, convection will move into
   an increasing unstable and moist environment. A line of supercells
   and line segments is expected to develop as convection moves into AR
   and approaches the Sabine Valley. All severe hazards are expected
   with this activity from Wednesday morning into the afternoon. 

   ...Lower MS Valley into AL/GA...

   Multiple rounds of intense, severe convection will be possible,
   mainly across MS/AL on Wednesday afternoon into the overnight hours.
   Convection will intensify along the eastward progressing cold front
   across central and eastern AR/LA during the late morning/afternoon
   as it encounters effective shear greater than 60 kt, MLCAPE around
   1500-2500 J/kg and midlevel lapse rates around 7-8 C/km. Fast storm
   motion, with 925-700 mb flow greater than 40 kt will support
   widespread damaging gusts with some gusts greater than 65 kt
   expected. Large hail (some greater than 2 inch in diameter,
   especially from the AR/MO border into northern LA, southwest TN and
   northern/central MS) is also expected with this activity.

   Further east across northeast LA into MS and AL a more concerning
   scenario appears possible. Most forecast guidance agrees that a
   round of afternoon thunderstorms are expected. This activity is
   expected to develop in weaker ascent, driven by heating and low
   level warm advection. Strong 0-3 km shear near 30-40 kt will already
   be in place with enlarged low level hodographs evident. Given weaker
   forcing, this activity will have an opportunity to remain more
   discrete and any cell will quickly become a supercell capable of
   producing strong tornadoes. As a 40-50 kt low level jet increases
   around 00-03z, intense supercells are expected to advance eastward
   along with the cold front across MS and into AL overnight. This will
   bring a second round of significant severe storms capable of intense
   tornadoes, large hail and intense damaging winds across much of
   MS/AL. If these trends are maintained, an upgrade to a High risk
   could be necessary with the initial Day 1 Convective Outlook at 06z
   tonight.

   ..Leitman.. 03/16/2021
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CIPS seems to be thinking the best analog is April 15th, 2011. That event spoofed a lot of forecasters, so I can see why the SPC would be bullish on this event to be on the safe side in the event we get another scenario like that.

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8 minutes ago, SmokeEater said:

This is NOT 4/27/11, but man the memories of tracking that day are coming back.


 

"this is not going to be April 3-4 1974"  everyone was saying that morning

point being every outbreak is unique and even if another  4/27/11 was perfectly  modeled  the day before no one would claim "This will be 4/27/11 all over again"

 

of course all the stars have align perfectly and the odds are it won't 

I suspect the slower trend will continue ..

 

even though now this may start in the central western forum (OK/TX) it may be a good idea to make this the main thread for the event?

 

 

 

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6 minutes ago, Bob's Burgers said:

CIPS seems to be thinking the best analog is April 15th, 2011. That event spoofed a lot of forecasters, so I can see why the SPC would be bullish on this event to be on the safe side in the event we get another scenario like that.

some background on that event

https://en.wikipedia.org/wiki/Tornado_outbreak_of_April_14–16,_2011

 

 

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Comparisons to the infamous Carolina Outbreak are interesting for sure. Comparing anything to April 27th is a bit of a reach because the LLJ was absurd during the midday hours leading to some of the largest helicity numbers I've ever seen before, heck it was visually obvious with condensation still spinning off the funnel on many of the tornadoes. Also this low looks to deepen to 995-997 MB while that day had a 980 MB monster low which is why you saw not only great supercell development, but LP supercells compared to what is usually seen in the South.

One thing to keep in mind is that tomorrow's outbreak could transform into multiple lines and put down a nice boundary for a Carolina event on Thursday. 

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This is only anecdotal, but one thing I've learned over the last decade is that I need to pay attention to even the "marginal" hatches. I've actually logged the 5 most destructive thunderstorms that have hit my location - these are storms that have damaged or impacted my property in some way (severe/moderate i.e trees down, power line on the ground, home damage etc.). 

4 of those storms occured under "marginal" threat hatches for my area, 2 of which accompanied cells that had tornado warning criteria at some point (either before, during or after impacting my property).

I've learned to keep an eye on anything within those risk hatches regardless of risk percentages. I will certainly be watching this closely.

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3 minutes ago, Bevo said:

I've learned to keep an eye on anything within those risk hatches regardless of risk percentages. I will certainly be watching this closely.

100% on this. I remember the Dallas tornado of 2019 quite vividly. We were in a slight contour, 5% tor risk, non-sign (albeit just barely outside the higher risk zones) and still had an EF3 plow through the northern suburbs just a few miles south of where I live. Its a reminder that, while this day could underperform (and that's a fairly reasonable bet given all that needs to go "right"), it could very well overperform as well! 

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