Sydney Claridge

That line east of Shreveport may be encountering storm relative helicity of up to 700m^2/s^2 per SPC Mesoanalysis.

I knew southern Tennessee was within the outbreak area on 4/27/2011 (the afternoon and evening storms were especially intense in SE TN), and was aware that the morning convection did result in multiple tornado touchdowns. But notice the relative lack of severe storm reports from western TN up through OH, all areas that were in the Day 2 Moderate risk. It is these areas I was saying had their severe storm potential suppressed (but not completely so, given some wind/isolated tornado reports particularly in KY/OH) by earlier convection. I cited the Day 2 outlook from April 26, 2011 to highlight some of the concerns SPC had then with issuing a Day 2 High Risk.

The CIPS Analogs now place 4/27/2011 as the 3rd best analog. 3/1/2007 (day of the Enterprise tornado) is the 2nd best analog; previous analog runs have consistently placed the 3/1 outbreak near the top. Even as one of the top analogs, it does not mean this this potential tornado outbreak will be like 4/27/11, but the fact that this is showing up so high in the analog list gives us an idea what the worst-case scenario for tomorrow could be. SPC held off on a Day 2 High Risk for 4/27/11 as well, citing concerns about morning convection, although the Day 2 Moderate went all the way up into Ohio (and as we know, that morning convection, although quite severe itself, did seem to suppress severe storms from western TN northwards and kept those northern areas from suffering an outbreak like 4/3/1974). Just because something is the worst-case scenario does not mean it will actually occur. But emergency management, hospitals, and public health authorities need to be ready for that worst-case scenario, especially when the risks for displaced and/or injured people involve more than just losing a home or having injuries treated at a hospital; the ongoing COVID-19 pandemic means that there is very real risk that any displaced and/or injured individuals could catch and/or spread the virus. And as previously mentioned, even sheltering from a tornado in a public shelter could pose some concerns with respect to viral spread. Even if this winds up not being a widespread tornado outbreak, it takes only one tornado going through a highly-populated area (and I mean anything from a moderately-sized city like Meridian MS all the way up to a major metropolitan area like Birmingham) to make these concerns real. While absolutely devastating to the people living there, a tornado strike on a rural area or smaller town should be much more manageable for emergency management, hospitals, and public health authorities, provided that there is adequate hospital coverage and availability (that said, this can be an issue in parts of the South).

Sounds about right. That line near the Mississippi River would probably go linear, but I doubt you could rule out tornadic supercells there either if that 12z NAM run is correct (with higher EHI in that area), and even if linear, QLCS tornadoes and embedded supercells could pose a danger. But the most violent activity would have to be with any supercells ahead of this line.

That would be a very scary situation anywhere from Louisiana to Alabama, but particularly across northern Mississippi, if that run verifies. I still have some questions about the extent of precipitation, but with the level of shear and helicity depicted, any area of warm-sector precipitation could be at risk of turning supercellular and tornadic. This NAM run also shows an area of precipitation ahead of the main line (that is at the western edge of the 70F+ dewpoints) in E Mississippi and SE Louisiana, and I have little doubt that those storms could also turn tornadic. Let's just hope that any tornadoes avoid highly-populated areas. Given the COVID-19 pandemic, people that lose homes will need places to stay in the aftermath of a tornado, so they do not risk contracting COVID-19 (or contribute to its spread if they already have the virus); this is much more manageable if the tornadoes can stick to rural areas and avoid population centers, unfortunately the South is more densely populated than the Plains, so the odds are higher that a population center could get hit. Hospitals are already burdened in some places by COVID-19 (particularly around New Orleans, though the worst of the severe weather should stay north of there), and the U.S. South is at particular risk of people developing serious complications, given that more people living there have preexisting medical conditions such as heart disease and diabetes. Having a major tornado outbreak occur amongst this pandemic is one of my worst fears, especially should at least one of those tornadoes strike a major population center. Needless to say I am hoping that this busts completely, but there could be a tornado outbreak this Sunday.

With the COVID-19 pandemic and all, getting a major tornado outbreak (or just one major tornado striking a populated area) would be horrific, especially once you consider the need for hospital beds for both the injured and COVID-19 patients. It would be much more manageable if the tornadoes stuck to rural areas, but that is never a guarantee; just look at what happened back in 2011. Something like the 2011 Joplin tornado (which destroyed a hospital), if it occurred today, would be a lot worse given the current pandemic. A quiet pattern is a much needed reprieve right now, and hopefully we don't have to worry too much about severe thunderstorms and tornadoes until COVID-19 quiets down somewhat. But you never know, especially considering that we are now in the most active time of year for severe thunderstorms and tornadoes (April/May/June).

12z HRRR lends some credibility to ILN's discussion from yesterday, as it depicts the initiation of scattered cells in NW Ohio around 18z (with motions to the SE), and some of this activity could move across the northern part of ILN's area of responsibility (Dayton and Columbus areas mainly). If taken verbatim the risk would be higher in Columbus (storms in metro area) than Dayton, but you should never take a model run verbatim. South of I-70 the 12z HRRR seems to depict greater mixing with larger T/Td spreads (upper 70s/lower 80s with mid-to-upper 50s dewpoints). Along and north of I-70 the T/Td spreads (lower 70s with lower-to-mid 60s dewpoints) suggest isolated tornadoes are a possibility with any supercells given lower LCLs and sufficient EHI. As with respect to other models, 12z NAM3k and NAM still struggle to initiate storms, however. 12z HRW WRF-ARW shows cellular activity in NE OH (lower dewpoints however); 12z HRW NMMB has higher dewpoints and cellular activity in N/NE OH (and ramps things up a little in the MO/IL border region later on, though highest EHI values depicted are in OH); 12z HRW WRF-NSSL tries to send up cells in E OH but they struggle to get strong. The new Day 2 SPC convective outlook seems to think that morning convection in Ohio will cause subsidence in its wake, which may cast doubt on cellular storms in the Ohio vicinity starting around 18z as depicted by the HRRR. The Slight risk now extends from the Ohio Valley to the Southeast (Carolinas) and Mid-Atlantic (VA) coast. There is also a broad 2% tornado risk shaded across this area (although it would not surprise me to see upgrades in a few areas, especially if that early-afternoon cellular storm mode in OH verifies, and maybe further west in IL/IN too, since some of the models show higher parameters over there too).

This isn't my subforum, but I was wondering some things about the severe potential for Tuesday 4/7. The NAM3k runs (12z and 06z) seem to be ramping up parameters for tornadoes in the eastern parts of the Day 3 Slight risk area (Ohio in particular), although they are not initiating convection. Plain NAM (12z run) may be trying to pop something in central Ohio with some good CAPE/helicity overlap; I'm taking this with a grain of salt though. I know tornadoes are less likely in northwest-flow regimes even with favorable parameters, but seeing relatively-high 0-3 km EHI values on model runs (GFS shows somewhat-elevated EHI slightly further west too) does catch my eye. I would post the imagery but my Internet connection has been painfully slow with the COVID-19 situation and all. I also recall back on March 28th, models (NAM-based, RAP, and HRRR mainly) were showing elevated EHI near the OH/PA/WV border region, and some of that verified with severe thunderstorm reports (and a tornado warning) around Pittsburgh that day, well east of what was expected to be the "main" outbreak in IA/IL (which as we know largely busted). I was wondering if this might be a similar situation where much of the main action occurs further west, but with a few storms possibly going severe further east.

Turns out today will be defined by a southward-surging cold front and then chilly temperatures. Temperatures around Oklahoma City and north-northwestwards are below freezing this morning (and there is even some elevated instability above that cold layer too). Except for southern Texas, forget any potential for severe, aside from perhaps elevated hail producers in some areas of central Texas. Later on, there may possibly be some cells initiating near the Serranias del Burro of northern Mexico and then moving into southern Texas. Should be a quick chilly spell this weekend before warm and humid air begins to surge northwards on Sunday and (especially) Monday. Enjoy it if you like cold weather as this could easily be the last time we see temperatures like these until next fall.

I am starting to wonder about this rainy pattern currently present across the north-central Texas region. With all this moisture in place, and with the region being within an active pattern for precipitation, sooner or later I would not be surprised to see a major severe weather event unfold (I'm not saying that will happen, though). At the moment cool temperatures are dominant, but next week looks as if conditions could get quite warm and humid, possibly setting the stage for severe weather. Additionally, late this week, SPC discussion suggests the possibility of some severe weather in TX on Friday (4/3). Longer-range models (GFS and Euro) suggest that there could be a storm system early next week, with possibly another system around the middle of next week. While less pertinent to this region, the early-week system may also get pretty strong as it moves up towards the Great Lakes at mid-week (if GFS/Euro are correct, especially GFS, and that might mean severe storms in the IA/IL region that was largely spared from having a tornado outbreak last week).

Laredo got well into the triple-digits today for their high temperature today (3/26). And I believe my location (Fort Worth, TX) got to 90 yesterday, although temperatures were cooler today. What is interesting is that I am seeing what could be convection trying to go up over north-central Texas, both on satellite imagery and outside my window. I know there is a cool down coming, but it seems that summer wants to try and appear early. If heat like this tries to show up again in April (we will likely see this again by the end of May), I am wondering about the effects on the severe storm season; for Texas that would probably mean more capping and a stronger EML, but elsewhere (further north and further east) that might mean more severe storms. For instance, I know the EML is modeled to move north-east over Missouri and Illinois for their severe storm event on Saturday.

This same 18z NAM run also ramps up tornado parameters along the warm front in eastern Ohio at the same time as well, as per this forecast sounding. The NAM does not initiate precipitation in this area though, so it seems the threat there would be much more conditional if this run verifies. Forecast parameters are lower in the area between E OH and IL. Lapse rates on the 18z NAM run are also pretty high, with Plains-like 7.5-8.5 values from Illinois over into Ohio.

I'm surprised that SPC still has a "potential too low" in their Day 4-8 outlook. There seems to be a pretty good chance that there will be severe thunderstorms later this week, particularly in the Texas/Oklahoma region, based on various model runs.

I believe the lapse rates were pretty high with this severe weather event. That could have compensated for the lower temperatures and dewpoints somewhat. This also seems to be the first really bad tornado this year. It’s only been a few months since we had a tornado go through north Dallas on October 20th, so it has not been too long since we last had a tornado go through a densely populated urban area. Unfortunately this time around people lost their lives (unlike in Dallas, despite that being one of the costliest US tornadoes monetarily, and that tornado was probably weaker than what moved through Nashville), and the late-night timing could not be worse.

If we are going to see above-normal temperatures and precipitation at the beginning of March, perhaps the severe storm season could start to ramp up. GFS and Euro are both depicting a storm system for the Southern Plains for early next week (around March 2nd), with what seems to be sufficient moisture return across Texas into southern Oklahoma. We are still a ways out, so any model data should be taken with a grain of salt, but the modeled pattern caught my eye (with multiple low-pressure systems moving out of the Rockies on the GFS, and a big storm on the Euro). I'm a little concerned about the late-week storm (that should impact the Great Lakes with snow) scouring the Gulf of Mexico of moisture, though water temperatures are above average across much of the GoM.

Need to watch that storm NW of San Antonio for hail potential. It’s just behind the front so I would expect it to stay elevated (and SPC agrees), though the surface warm sector is fairly close.

Storm initiation looks to have started just east of Wichita Falls. Looks to be on the front itself.

Had a dusting of snow up near Texas Motor Speedway earlier today.

GFS seems quite the outlier right now, depicting a major snowstorm over the north Texas area (especially just west of DFW) on Wednesday. Most other models (NAM, Euro, etc.) are further north.

Maybe an early start to the spring severe season is in order? Not going to comment on summer at this time. GFS gives some threat across the SPC-delineated regions for Friday and Saturday though the Euro runs look more amped (bringing a fairly-humid warm sector as far north as the Ohio Valley next weekend); if those Euro runs verify then a stronger storm system would track from central Texas to the Midwest-Great Lakes region. EDIT: The only cold I see for DFW is way out in GFS fantasy land. I guess we know how that tends to go.

I'll guess 1250 total tornadoes, first high risk April 1st.

I know we are only in a marginal risk zone, but the storm parameters over the DFW area look somewhat interesting right now. Temperatures in the lower 70s (in places) with upper 60s dew points, in conjunction with some high helicity values (ESRH in the 300-500+ m2/s2 range), could produce some potentially severe storms if we can get storm initiation, though veer-back-veer seems to be an issue based on the change in wind directions between the 700mb and 500mb levels (based on the available SPC mesoanalysis data at the time of this post).

The GFS-based models (GFS and GFS-FV3) are placing the warm front with the Saturday system just south of DFW on the 0z runs. Those models do seem to have moved the front's location slightly further north with each of the last few runs. The 0z runs puts DFW in the upper-50s for dewpoints with mid-to-upper 60s dewpoints just to the south and SE. It will be interesting to see how far north the warm front can come, as well as what the NAM has to say about it as it comes into range.

Me too. GFS is showing a pattern suggestive of cold waves in the Northern and Central Plains (along with surging cold fronts) but I'm not counting on that to translate into the Southern Plains as I've always noticed a cold bias with the GFS in the longer ranges.

And we're down to a Slight Risk now. According to the reports so far the Moderate Risk seems like a bust, aside from the Columbus tornado. (there's not many severe reports in the former MDT zone)