Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Fri Apr 10, 2020 8:26 pm
by TheProfessor
Haven't been able to do an analysis on the mesoscale models yet, but perhaps I'll do one tonight when the WRF models show most of the event.
Anyways this is my early idea of what a potential day 1 risk may look like. It leans heavily on the 15z SREF, though my moderate risk isn't too different than the current one but extends to the west and north a bit.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sat Apr 11, 2020 5:00 am
by cycloneye
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.
..Dean/Broyles.. 04/11/2020
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sat Apr 11, 2020 1:05 pm
by TheProfessor
SPC keeping it a moderate risk, but they introduced a 45% wind threat for parts of Mississippi, Alabama, Tennessee, and extreme eastern Arkansas.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sat Apr 11, 2020 3:08 pm
by Shell Mound
Over the past two runs, the ECMWF has trended toward a shallower trough, weaker wind fields, narrower hodographs, and a less pronounced EML over the warm sector. The threat for a significant tornado outbreak with discrete cells seems to have decreased substantially. A mixed mode with a strong QLCS spin-up or two seems more probable, along with widespread damaging winds, but nothing remotely close to what some people were suggesting, at least as far as strong (or violent) tornadoes are concerned. This is very good news.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sat Apr 11, 2020 4:25 pm
by TheProfessor
Shell Mound wrote:Over the past two runs, the ECMWF has trended toward a shallower trough, weaker wind fields, narrower hodographs, and a less pronounced EML over the warm sector. The threat for a significant tornado outbreak with discrete cells seems to have decreased substantially. A mixed mode with a strong QLCS spin-up or two seems more probable, along with widespread damaging winds, but nothing remotely close to what some people were suggesting, at least as far as strong (or violent) tornadoes are concerned. This is very good news.
When you look at a collection of models the high end parameters are still there. What this system does have is a few legit failure modes that can cap it's potential. One of which are storms not rooting into the boundary layer, another one is messy storm mode and more convection. I think these will be the reason for a busted forecast, not the parameters lining up right now.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
It will be interesting to see if storms have trouble gaining footing in the boundary layer though, it's a legit failure mode. But it does seem suspicious that some of these HRRR storms are producing UH, but they're surviving for long periods. The 0z HRRR also has some hefty storms later in the evening for southern Louisiana and into southern Mississippi and central and southern Alabama, though this looks semi-discrete at best and eventually evolves into a QLCS, even a QLCS could develop strong tornadoes in this atmosphere. Most of this is happening in the enhanced risk area as well so a strong QLCS could verify that risk if it were to occur.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sun Apr 12, 2020 8:42 am
by cycloneye
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0752 AM CDT Sun Apr 12 2020
Valid 121300Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS TODAY INTO TONIGHT FROM THE ARK-LA-MISS EASTWARD INTO AL AND WESTERN GA...
...SUMMARY... An outbreak of severe thunderstorms is likely today into tonight, with the greatest threat expected from Mississippi across Alabama into western Georgia. Strong tornadoes, widespread damaging winds, and large hail are all possible.
...Synopsis... A complex forecast today with multiple scenarios possible across a broad area from the lower MS Valley into the TN/OH Valleys and the Southeast. A midlevel trough near the TX Big Bend this morning will accelerate east-northeastward to the Ark-La-Miss by this evening and the Appalachians by the end of the period, in response to continued amplification of a large-scale trough over the north central CONUS. At the surface, a cyclone will move across OK today and develop eastward to AR by this evening, followed by substantial deepening as the cyclone moves northeastward to the OH Valley/Great Lakes overnight. A moist/unstable warm sector will surge northward across LA/MS/AL/GA today, setting the stage for severe storms with the ejecting shortwave trough and deepening cyclone through tonight. Several scenarios are possible within the overall outlook area, with substantial uncertainty related to early/ongoing convection now in TX.
...Northeast TX to northern MS/AL and TN this afternoon... An ongoing cluster of severe storms continues to move east-northeastward into east central and northeast TX this morning, in association with a lead shortwave trough. All hazards will be possible with this cluster which will include a mixed convective mode of supercells and bowing segments. Low-level moisture will surge northward today across LA/MS/AL in response to the deepening cyclone moving from OK to AR. The main question through mid afternoon will be whether or not surface destabilization will keep pace with the initial cluster. If warming/moistening can occur quickly enough, the chance for surface-based storms on the southern flank will increase. This may occur coincident with an environment characterized by moderate buoyancy (MLCAPE of 1500-2500 J/kg), very strong low-level shear (0-1 km SRH of 400-500 m2/s2) as the low-level jet strengthens over LA/MS, and effective bulk shear in excess of 70 kt. This environment will favor embedded supercells capable of producing strong tornadoes and damaging winds. Again, the main questions in this corridor through this afternoon will be the degree of organization of the late morning-early afternoon convection, and its phasing with the surface warm front.
...MS/AL/GA/Carolinas late this afternoon through tonight... To the south of the initial storm cluster crossing northern MS/AL/TN, a separate pre-frontal band of convection is expected to develop by late afternoon from southern MS into western/central AL. This convection will be well east the synoptic cold front, in an environment with surface-based buoyancy and very strong vertical shear. A broken band with embedded supercells appears likely to persist well into the overnight hours, with an associated threat for strong tornadoes and damaging winds. The pre-frontal convection should reach the western Carolinas by 09-12z.
...Red River Valley this afternoon to the OH Valley overnight... An arc of convection will likely form this afternoon near the surface low in southeast OK, and within the left-exit region of the mid-upper jet. This convection will subsequently spread eastward and northeastward into AR through late afternoon/evening. The northward extent of destabilization in AR/western TN this afternoon/evening will depend largely on the intensity and extent of the early afternoon convection moving from LA into northern MS. Still, steep midlevel lapse rates with the ejecting midlevel wave and strong deep-layer vertical shear will favor fast-moving supercells and line segments capable of producing large hail and damaging winds. Similar to AR this afternoon, the northeast extent of the damaging wind and tornado threat into tonight will depend largely on how widespread/organized the convection is across northern MS/AL this afternoon/evening, and the degree of low-level recovery in the wake of that convection.
..Thompson.. 04/12/2020
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sun Apr 12, 2020 9:15 am
by newtotex
What’s the timing for the warm front moving north? Here in Birmingham it doesn’t feel like “tornado weather.”
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sun Apr 12, 2020 10:47 am
by TheProfessor
URGENT - IMMEDIATE BROADCAST REQUESTED Tornado Watch Number 106 NWS Storm Prediction Center Norman OK 1040 AM CDT Sun Apr 12 2020
The NWS Storm Prediction Center has issued a
* Tornado Watch for portions of Far southeast Arkansas Northeast Louisiana Northern and central Mississippi
* Effective this Sunday morning and evening from 1040 AM until 800 PM CDT.
...THIS IS A PARTICULARLY DANGEROUS SITUATION...
* Primary threats include... Several tornadoes and a few intense tornadoes likely Widespread damaging winds likely with isolated significant gusts to 80 mph possible Scattered large hail and isolated very large hail events to 2 inches in diameter possible
SUMMARY...Intense bowing line with a history of several tornadoes in northwest Louisiana will progress rapidly east-northeast this afternoon. Additional semi-discrete suprecells may develop ahead of the line as well across parts of northern and central Mississippi. Environment is supportive of several tornadoes, some of which will likely be strong in addition to potential widespread damaging winds.
The tornado watch area is approximately along and 85 statute miles north and south of a line from 5 miles north northwest of Monroe LA to 20 miles south of Columbus MS. For a complete depiction of the watch see the associated watch outline update (WOUS64 KWNS WOU6).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Tornado Watch means conditions are favorable for tornadoes and severe thunderstorms in and close to the watch area. Persons in these areas should be on the lookout for threatening weather conditions and listen for later statements and possible warnings.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 105...
AVIATION...Tornadoes and a few severe thunderstorms with hail surface and aloft to 2 inches. Extreme turbulence and surface wind gusts to 70 knots. A few cumulonimbi with maximum tops to 550. Mean storm motion vector 25045.
...Grams
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
Posted: Sun Apr 12, 2020 11:44 am
by cycloneye
The latest.
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Sun Apr 12 2020
Valid 121630Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS NORTHEAST LA...SOUTHEAST AR...MS...AL...WESTERN GA...SOUTHERN MIDDLE TN...
...SUMMARY... An outbreak of severe thunderstorms is likely through tonight, with the greatest threat expected from northeast Louisiana, Mississippi, Alabama, southern Middle Tennessee and western Georgia. Strong tornadoes, widespread damaging winds, and large hail are all possible.
...Synopsis... A complex forecast with multiple scenarios possible across a broad area from the Lower MS Valley into the TN/OH Valleys and the Southeast. A compact shortwave trough over the Edwards Plateau of TX will accelerate east-northeast into the Ark-La-Miss by this evening and towards eastern KY/TN by the end of the period, in response to continued amplification of a large-scale trough over the north-central states.
...Northwest LA to northern AL/middle TN... An ongoing MCS with a history of several confirmed but brief TDSs earlier this morning will continue to move east-northeast along an intensifying baroclinic zone across parts of northern/central MS into northern AL/middle TN. Tornadoes and damaging winds will be likely with this MCS which will include a mixed convective mode of bowing segments and potential supercells developing just ahead of the cluster on its southern flank.
The presence of upper 60s to low 70s surface dew points in much of LA and southern MS will spread north and likely reach northern MS to western AL between 21-00Z. This should overlap strong low-level shear (0-1 km SRH of 400+ m2/s2) as the low-level jet strengthens and shifts northeast. The environment will favor embedded supercells capable of producing strong tornadoes and damaging winds, the most substantial of which may occur from northeast LA through north-central MS into northern AL and southern middle TN. There is still enough uncertainty with regard to convection outpacing stronger surface-based instability (especially with northeast extent), as well as the overall convective mode, to preclude an upgrade to High Risk.
...Southern MS to GA/Carolinas... To the south of the initial MCS crossing northern MS/AL into TN, a separate pre-frontal band of convection is expected to become sustained by early evening from southern MS into central AL. This convection will be well east of the synoptic cold front, in an environment with moderate surface-based buoyancy and very strong vertical shear. A broken band of embedded supercells appears likely to develop through the evening and overnight, with an associated threat for strong tornadoes and damaging winds. The pre-frontal convection should reach the western Carolinas by 09-12z.
...Lower Red River Valley to the OH Valley... An arc of convection will likely form later this afternoon just ahead of the compact shortwave trough and associated surface cyclone in eastern OK to northeast TX, within the left-exit region of the mid-upper jet. This convection will subsequently spread east then northeast across the Mid-South during the late afternoon/evening. The northward extent of destabilization in AR/western TN this afternoon/evening will depend largely on the intensity and extent of the early-day MCS moving from LA into northern MS.
Still, steep midlevel lapse rates with the ejecting mid-level wave and strong deep-layer vertical shear will favor fast-moving supercells and line segments capable of producing large hail and damaging winds. The northeast extent of the damaging wind and tornado threat into tonight will depend largely on how widespread/organized the convection is across northern MS/AL this afternoon/evening, and the degree of low-level recovery in the wake of that convection.
..Grams/Bentley.. 04/12/2020
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE JACKSON MS 428 PM CDT SUN APR 12 2020
..TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA
THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A
* TORNADO WARNING FOR... SOUTHEASTERN JASPER COUNTY IN EAST CENTRAL MISSISSIPPI... JONES COUNTY IN SOUTHEASTERN MISSISSIPPI...
* UNTIL 530 PM CDT.
* AT 428 PM CDT, A CONFIRMED LARGE AND DESTRUCTIVE TORNADO WAS OBSERVED NEAR COLLINS, MOVING NORTHEAST AT 50 MPH.
TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA. THIS IS A PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!
HAZARD...DEADLY TORNADO.
SOURCE...RADAR CONFIRMED TORNADO.
IMPACT...YOU ARE IN A LIFE-THREATENING SITUATION. FLYING DEBRIS MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO HOMES, BUSINESSES, AND VEHICLES IS LIKELY AND COMPLETE DESTRUCTION IS POSSIBLE.
* THE TORNADO WILL BE NEAR... HEBRON AROUND 445 PM CDT. MOSS AROUND 500 PM CDT. SANDERSVILLE AROUND 510 PM CDT. HEIDELBERG AROUND 515 PM CDT. STAFFORD SPRINGS AROUND 520 PM CDT.
OTHER LOCATIONS IMPACTED BY THIS TORNADIC THUNDERSTORM INCLUDE SOSO.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
BULLETIN - EAS ACTIVATION REQUESTED TORNADO WARNING NATIONAL WEATHER SERVICE JACKSON MS 506 PM CDT SUN APR 12 2020
..TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA
THE NATIONAL WEATHER SERVICE IN JACKSON HAS ISSUED A
* TORNADO WARNING FOR... SOUTHEASTERN JASPER COUNTY IN EAST CENTRAL MISSISSIPPI... CLARKE COUNTY IN EAST CENTRAL MISSISSIPPI...
* UNTIL 600 PM CDT.
* AT 506 PM CDT, A CONFIRMED LARGE AND DESTRUCTIVE TORNADO WAS OBSERVED NEAR HEIDELBERG, OR 10 MILES EAST OF STRINGER, MOVING NORTHEAST AT 55 MPH.
TORNADO EMERGENCY FOR LOCATIONS IN THE WARNED AREA. THIS IS A PARTICULARLY DANGEROUS SITUATION. TAKE COVER NOW!
HAZARD...DEADLY TORNADO.
SOURCE...WEATHER SPOTTERS CONFIRMED TORNADO.
IMPACT...YOU ARE IN A LIFE-THREATENING SITUATION. FLYING DEBRIS MAY BE DEADLY TO THOSE CAUGHT WITHOUT SHELTER. MOBILE HOMES WILL BE DESTROYED. CONSIDERABLE DAMAGE TO HOMES, BUSINESSES, AND VEHICLES IS LIKELY AND COMPLETE DESTRUCTION IS POSSIBLE.
* THE TORNADO WILL BE NEAR... VERNON AROUND 510 PM CDT. PAULDING AROUND 515 PM CDT. BARNETT AND GOODWATER AROUND 520 PM CDT. ORANGE AROUND 525 PM CDT. QUITMAN AND STONEWALL AROUND 535 PM CDT. MIDDLETON, SABLE AND SYKES AROUND 545 PM CDT. SNELL AROUND 555 PM CDT.
OTHER LOCATIONS IMPACTED BY THIS TORNADIC THUNDERSTORM INCLUDE PACHUTA.
Re: Potential Severe Weather Outbreak | TX and Southeast | 4/11-4/12, 2020
