Quincy

FWIW, in regards to tomorrow…

18z NSSL WRF backed off of convective initiation (CI) in Oklahoma tomorrow. Latest 21z SREF also dropped CI probabilities to about 20% along the dryline. 

00z HRRR indicates that most convective inhibition (CINH) is eroded by 22z near the OKC metro area, but no storms initiate. This is thanks to 2m temperatures rising into the mid-80s, atop low to mid-60s dew points. It’s close… modify the forecast soundings for slightly greater boundary layer moisture (HRRR dry bias) and you’d probably get within 1-2F of reaching convective temperatures.

Let’s see how the rest of the 00z suite looks. 

18 minutes ago, CheeselandSkies said:

The bolded was what burned my chase on 5/26/21. I gambled that the CAMS being relatively subdued with convection/UH in west-central/SW KS was a positive thing for chase quality. I ended up on that skeletal LP northwest of Scott City; after it was clear to me it wasn't going to intensify (and in fact was doing the opposite), I broke for additional cells SW of Dodge City which suffered a similar fate by the time I reached them. I don't recall capping really being thought to be a big event-breaker leading up to that day. Was there something else at play?

I remember that day well. There was an intense morning supercell up by I-70 that went nuts and led to some of the best early day elevated supercell structure in recent memory. 

My fate was similar to yours. 

I pulled some obs and data. Most of the activity was confined to near the warm front/thermal gradient. 18z DDC sounding didn’t show much capping at all. At first I thought maybe it had to do with a weakness in the winds around 500mb, but I’m not sure if that was a prominent factor. There were severe storms even farther south in the Texas panhandle, where large scale forcing was weaker and 500mb winds were even less favorable. 
https://www.spc.noaa.gov/exper/archive/event.php?date=20210526

FV3 has an over-convect bias and will almost always initiate in even the more borderline/marginal setups. 

With that said, it does look like a delicate and potentially explosive setup just east of the dryline tomorrow from central Oklahoma into central Kansas.

Most CAMs show little to no convection, which does give more confidence that any development will probably be isolated. Given the orientation of the shortwave and wind fields, shear vectors are perpendicular to the dryline. Thermodynamic profiles are very favorable, with a capping inversion that should prevent convective initiation for most of the afternoon. (Diverging from earlier model runs that were erupting storms by 20-21z)

The NSSL highlights an uncomfortable potential scenario, with one lone supercell forming over central Oklahoma late in the afternoon.

Differing from some previous events, the warm sector looks thick enough to support any sustained storm for several hours, assuming that a storm can initiate.

I still remain skeptical about CI with southward extent across Oklahoma, but it’s still plausible. 

2 hours ago, Chinook said:

Some broad rotation has been in the areas of SW Oklahoma city for a while. I don't believe there have been any reports of tornadoes yet.

Took this photo just a short time before this radar collage. Chased the storm through the south side of OKC. Very rain wrapped, but don’t believe there was a tornado. 

Encountered several supercells in southwestern Kansas early this evening. What a rebound after yesterday’s flop.

Today has some similarities to yesterday. Setup is conditionally favorable for isolated supercells, but CAM support is inconsistent and mixed. Upper level support is weak at best, with neutral or slightly rising height tendencies.

This time, the threat may exist along the dryline in western Oklahoma and a bit farther north into SW/central Kansas, near the warm front and triple point. 

I’ll probably be lured out again, since it’s only a three hour drive, but the odds of seeing a storm are probably in the 20-30% range.

So close, yet so far away today. A few showers initiated, but couldn’t take off. Now wondering if drought conditions on the high plains might be the tipping point to sway more marginal threats (Thursday/Friday) into the “no dice” category. 

Short-term update:

Trends appear to be favoring storm initiation, possibly soon. Satellite imagery shows a growing cumulus field along the dryline in south-central Oklahoma. Not totally surprising with rapid heating and obs of 87/65 at Ardmore and 87/64 at Pauls Valley. 

In general, the more aggressive moisture recovery progs from the 3km NAM are verifying, with a swath of 66-69F dew-points across eastern Oklahoma, immediately ahead of the dryline.

We’re in the nowcast phase, but even the latest SREF featured higher probabilities of convective initiation between 21-00z, compared to earlier runs.

Forecast soundings show very favorable wind profiles for supercells, with NW flow aloft, backing to S near the surface. Mesoanalysis indicates >2000 J/kg MLCAPE with increasing 0-3km instability over the next couple of hours. Forecast hodographs by 23-00z show sickle shaped low level hodographs, which would be very favorable for tornadoes. Even conditionally supportive for a strong tornado.

It’s getting very interesting. I would be shocked if there’s not a mesoscale discussion issued shortly to outline the threat. 

1 hour ago, stormdragonwx said:

Intrigued that the SPC upped the probs slightly for today. Maybe it's because I'm cynical but it feels too cool outside (52 here in Fayetteville, AR at 11:30) and there's too much considerable cloud cover lingering considering its almost noon over much of the highlighted area. We would have to have some rapid clearing and heating to destabilize the area for any supercells to form this afternoon. Even for parts of Eastern Oklahoma where the 5% is. Thoughts?

I’ve felt this way before and was proven wrong when a potent, compact system resulting in rapid thermodynamic recovery across Oklahoma. 

Note 3hr dew-point increases of 4-7 F are common in eastern/central Oklahoma. Mesoanalysis shows convective inhibition eroding and satellite imagery indicates rapid clearing and surface heating east of the dryline. Temperatures have reached the lower 80s already, on the east side of the dryline  

With that said, storm coverage and intensity is still a big question mark, given weak large scale forcing and inconsistent convection allowing model signals. 63-65 F dew-points along/just east of I-35 in north-central Oklahoma catches my attention.

Another nuanced setup in Oklahoma this season… Nearly 50/50 odds, in my mind, of the following solutions today:

1. Attempts at convective initiation end up failing, somewhat similar to last Friday. 

2. One or two sustained storms go up in northeastern Oklahoma and become supercells for a couple of hours.

Watch two areas, near the surface low in far southeastern Kansas, as well as a quasi triple point along the dryline, somewhere near or just southeast of Tulsa. 

Wednesday: Localized early season NW flow setup, focused on northeastern Oklahoma/southeastern Kansas. Would expect at least isolated supercell development near the I-44 corridor. 

Thursday: Another localized threat, in the general vicinity of Kansas. Can’t say I’ve looked at it too closely as there isn’t a strong signal, since heights look to be neutral or slightly rising. 

Friday: A potentially more significant severe thunderstorm threat, centered around Kansas/Nebraska, as a trough swings east out of the Rockies. 

Edit: Added Saturday since SPC has highlighted a 15% risk area including parts of Kansas. 

Still some lingering surface based and mixed layer convective inhibition remaining downstream, but that should mostly be eroded by 4 PM. More than enough CAPE/shear for supercells, as evidenced by two ongoing supercells near Fredericksburg.

Estimating based on that sounding, TTI is approximately 51.5.

Signal for a couple of robust supercells developing over the Texas hill country and dropping toward the San Antonio area this afternoon. Thermodynamic profiles would favor large to very large hail growth. Wind profiles are not particularly favorable for tornadoes, given straight hodographs and minimal low-level SRH. 

Still, the combination of large CAPE and favorable deep layer shear, would expect at least a few significant hail reports near/just north of San Antonio. Will have to watch and see if the metro area is targeted, before storms weaken due to nocturnal stabilization. 

Edit: Austin could possibly be impacted as well, especially if there are any left moving hailers, as storms will tend to drop SE to S with time. 

Analyzing the lower Mississippi Valley portion of the threat area…

Outflow boundary from overnight MCS draped from eastern Arkansas into central Mississippi. Richest low-level moisture is confined to Louisiana, but rapid air mass recovery is underway, thanks to a 50-60 knot low-level jet. 

Still noting some wind field disruption between the two boundaries, where there is some veer-back-veer signals (particularly over southeastern Arkansas. This could result in mixed storm modes with widespread thunderstorm activity developing this afternoon over eastern Arkansas. Even with some wind field issues, most data shows enlarging 0-3km hodographs and supercell wind profiles.

Boundary interaction in this type of setup can be very complex. Do a few storms thread the needle and become intense, long track supercells? Or is it just a blobby mess. I think this is the difference between moderate and high risk  

I believe the most shot for somewhat more isolated supercell activity will be from Far East Texas into Louisiana and possibly southern Arkansas/western Mississippi.

It’s going to be a busy day. 

41 minutes ago, nwohweather said:

What an ominous SPC outlook this morning. Not often they mention a risk of a violent tornado

It’s also Broyles… but the parameter space is pretty volatile looking. Potent shear, rich low-level moisture, a bit of an EML. It’s not perfect, but it definitely has the potential to produce one or two intense supercells. 

Some CAMs, including recent HRRR runs show widespread semi discrete supercells blowing up this afternoon near, along and ahead of the cold front. Only concern there would be cell mergers and interactions, but it does seem ominous with locally backed winds near a residual outflow boundary across the AR/LA border area. Storm mode could get messy, but I’d focus the most intense tornado potential over northern LA, southern AR into western MS.

We could have a localized outbreak on our hands. 

Tang is the man

Impressive, mature bowing MCS slamming Shreveport right now. Numerous circulations noted up and down the bow in northwestern Louisiana.

Will be interesting to see how this system affects the risk tomorrow. Point forecast soundings show a bit of wind field disruption around 700-600mb across southern/eastern Arkansas and vicinity, in the wake of the MCS. It could also leave one or more outflow boundaries as well. 

I think tomorrow is a complex day with higher end potential, at least on a localized level. The only limiting factor may be a tendency for cells along the cold front to cluster/grow upscale. Similar to several events in recent weeks, not a ton of confidence with warm sector supercells. We may have a better idea after watching this MCS evolve through early morning…

Ongoing severe threat with isolated tornadoes across Arkansas… may continue for a few more hours, toward the greater Memphis area. 

Trying to wrap my head around the local threat in Oklahoma tomorrow. Convection seems obvious near the triple point up near Nebraska/Iowa. Confidence is otherwise growing lower of initiation along the dryline in Kansas, but it’s still possible. 

The only models remaining with substantial CI in Oklahoma are the Euro and RGEM. FV3 seems a bit more subdued, although it has a tendency to over convect anyway. A few ARW members hint at very isolated CI as well. HRRR, NSSL WRF and 3km NAM all show nothing, despite a minimally capped environment near peak heating. 

What caught my eye is that the RAP/NAM both show a shortwave crossing across North Texas toward eastern Oklahoma around 21-00z. Given the orientation of the dryline and local climatology, I’d think that at least one storm tries to go up in southwestern/south-central Oklahoma. Not sold on storm intensity or longevity, but it’s a very difficult forecast from a public awareness standpoint. 

Oh yeah, we’ll probably see some strong/severe convection in North Texas toward the Arklatex well. 

SREF odds of convective precip, in vicinity of favorable instability: 

Wednesday is complicated. If early day convection doesn’t lead to a mess, it will be a day to remember. Even if there is ongoing convection (East Texas toward the Arklamiss area), there seems to be good model agreement with a broken line of convection with embedded supercells sweeping across Arkansas and southeastern Missouri in the afternoon. Shear vectors tend to line up more parallel with the boundary there, but some hodograph curvature still supports a tornado risk. 

Even if it evolves as a total mess of convection, I’d be surprised if there isn’t at least 1-2 long-track and/or intense supercells, somewhere in the AR/MO/MS/W TN vicinity, given the degree of shear and moist low-levels; low LCLs.

I think we’re in the midst of one of the more profound multi day early spring stretches, that I can recall, in recent memory. 

I don’t think it’s a slam dunk that there’s initiation up and down the dryline on Tuesday, but I think there’s a strong possibility that the cap is at least locally breached. Any sustained storms that can form will have the potential to produce very large hail and tornadoes.

I can envision a scenario where most areas see nothing, but one or two intense supercells form.

The Euro has been very consistent with convective initiation. The NAM doesn’t convect, but point forecast soundings only show minimal capping. It wouldn’t take much modification at all to break the cap and produce a few intense storms, per NAM progs. 

3 hours ago, Iceresistance said:

Yes, the Pink area matches the SPC's High Risk area, Ventrice's experimental automated forecast uses the colors for the SPC's Convective Outlook. (Thunderstorms, Marginal, Slight, Enhanced, Moderate, & High (Could not find the Pink))

It’s also changed substantially over the past couple of days. I advise extreme caution when looking at severe weather indicies more than 3-4 days out, especially when they’re *probably* based on a deterministic model, rather than ensembles. It’s also kind of silly to show high risk-equivalent graphics for a week out…

A lot can change, but here are my initial thoughts:

Monday looks like limited moisture return, especially with northward extent. I’d imagine the greatest threat remains across East Texas/Louisiana. Remember that we’re early in the season and antecedent dry conditions exist.

Tuesday may have the greatest apparent threat. Dryline could mix slightly farther east than progged, due to ongoing drought conditions. Maybe a more “classic” April event just east of I-35? Parameter space looks volatile, along with deep shear vectors nearly perpendicular to the dryline. Not overhyping yet, but operational models have shown run-to-run signals for at least a couple of days now.

Wednesday diverges in the models, but the threat should shift toward the Mississippi Valley. Wind fields are forecast to become more unidirectional with northward extent, along with less favorable moisture closer to an occluding surface low. Could be yet another threat around AR/LA/MS? Not sold on a farther north threat yet, but it’s still possible. 

Shear vectors look close to parallel to the boundary once again, but those forecast wind fields are nothing to snooze on. I’d expect a similar outcome to the last event, but possibly a bit more widespread in terms of wind damage. Tornado potential, not much confidence beyond the QLCS threat, but it only takes one. (Remember New Orleans…)

At quick glance, it looks similar to last Tuesday’s event. Wind fields support more of a mixed mode/linear event, but that can yield several QLCS tornadoes, along with isolated discrete storms, especially on the southern end of the line and possibly immediately ahead of it. 

Shear vector orientation, virtually uncapped warm sector and a very moist boundary layer = messy and clustered storm mode. A very sloppy evolution so far, but can’t say it’s that far off from what most convection allowing models suggested. 

Any reports from that storm? I chased it from Taylorsville to Decatur before bailing. Couldn’t see anything with the terrain and swarm of chasers. Only caught a few brief glimpses of a scuddy wall cloud. 

Everything is pretty much evolving as expected. The squall line in western Mississippi may be advancing slightly quicker than forecast, but that’s common for these setups.

The wildcard was open warm sector development. It’s underway across southern Mississippi and adjacent Louisiana. A couple of cells near/just west of Hattiesburg appear to be in the process of better organizing. This coincides with cloud breaks and 100+ J/kg 0-3km MLCAPE. I’d keep an eye on that area.