Question about Thunderstorm Initiation (w/ Atmospheric Sounding)

[Luke Datsko]

On June 14, 2022, an atmospheric sounding on the HRRR model for 21z, F000 near Mansfield, Ohio (in the file I attached) shows a SBCAPE value of 8560 J/kg, and a MLCAPE of 6818 J/kg. I assume that the real CAPE most likely wasn't that high; however, what ended up occurring after this reading was taken was pretty much nothing (except a few cumulus clouds), so I'm struggling to understand why not much happened on this day with such high CAPE values.

I know that in order to initiate thunderstorm growth, there needs to be a source of lift (such as a trough, front, etc.); however, I also know that when the CAPE is high enough it can initiate storm growth on its own (in addition, there was a warm front ahead of the unstable air which could have provided lift). There was also no convective inhibition, and the LFC and LCL were at the same level. If I had to make a ball park guess to why there was no storms it would either be there was an extensive area of large CAPE values on this day (I forgot to take images of this, sorry), or there was an 'upper-level high' preventing storm growth (there were Excessive Heat Warnings for much of the US on this day).

I am mainly just wondering if there is any way to tell from just the Skew-T that there would be no storms occurring. I also attached a satellite image from this day, as well. The sounding was taken from an area just southwest of the band of clouds marking the warm front (near where it says Ohio). Thanks for your help!

 

[Robert van de Velde]

The layer of moisture at the surface is very shallow so the SB parcel trajectory exagerates instability and underestimates the amount of capping. Also it seems that the parcel temperature has virtual temperature correction applied while this is not the case for the environmental temperature, which makes it harder to assess parcel buoyancy.

Maybe the actual moisture was slightly less than forecast and the warm layer at 2 km AGL could have been a bit warmer in reality so that there was actually some capping. But it seems most likely to me that the rising moist air mixes with the dry air at 2 km AGL (reducing buoyancy) and thus making it impossible to push though the warm layer without the help of decent surface convergence (which probably lacks here).

 

[Randy Jennings]

The forecast sounding you posted shows a convective temp of 92 degrees F. The actual high for Mansfield, Ohio on 6/14/22 was only 82. I pulled the closet observed soundings at 0z (3 hrs later) and all where capped. The cloud bands in the satellite pic you show also indicate capping. To me the giveaways that the forecast sounding was fantasy are 1) it missing the actual observed temp by a lot, and 2) a lack of analogs (meaning in real life if just doesn't happen that way often). I should note that there where some svr wind reports near Lake Erie and east of Mansfield near Shreve, OH later that night.

 

[Bob Schafer]

Sorry to pick nits, but surface Td of 82°F and Td's >68 up to 1km AGL is not what I would call shallow moisture.

 

[Jeff Duda]

On June 14, 2022, an atmospheric sounding on the HRRR model for 21z, F000 near Mansfield, Ohio (in the file I attached) shows a SBCAPE value of 8560 J/kg, and a MLCAPE of 6818 J/kg. I assume that the real CAPE most likely wasn't that high

Based on surface obs at that time, it is indeed unlikely that such CAPE was actually present except in isolated pockets (near Columbus, for example, assuming the ob is accurate). However, from the archived mesoanalysis plot, you can see that 5000 J/kg SBCAPE was widespread with pockets of 6000+ J/kg SBCAPE. MLCAPE was about 25% lower, which suggests the lowest 100 mb layer was not perfectly mixed. Also consider that thermodynamic parameters are pretty sensitive to small changes in source parcel parameters (e.g., a temperature or dewpoint offset of 1 or 2 F can result in substantial changes to the composite instability indices).

however, I also know that when the CAPE is high enough it can initiate storm growth on its own

This is not a true statement. The mere presence of CAPE in an air parcel is not sufficient for storm initiation. You are probably conflating the convective temperature notion with CAPE somehow. The idea behind the convective temperature is that it is assumed that the PBL is perfectly mixed at a sufficiently deep layer so that any given buoyant plume within the PBL (which are generated quasi-randomly and in a widespread nature) would have 0 CIN and thus be able to reach its CCL (convective condensation level, which is the LCL for a parcel that has achieved its convective temperature). However, that is where the assumption ends - there is no guarantee of a sustained updraft beyond that point. Entrainment of ambient atmospheric air into a rising parcel is a real thing, and in cases of extreme instability, the degree of cooling with height alone can promote dilution of a saturated parcel with cool air to the point where the parcel trajectory shifts leftward pretty hard, thus reducing the parcel temperature perturbation relative to the environment. Add to that entrainment of air with RH < 100% (check the lowRH and midRH fractions in the sounding) to further dry the parcel and shift the path left more, and it's possible the parcel was sufficiently diluted so as to preclude deep convection from actually materializing.

There was also no convective inhibition, and the LFC and LCL were at the same level

These two are generally equivalent statements.

there was an 'upper-level high' preventing storm growth (there were Excessive Heat Warnings for much of the US on this day)

Indeed, there was an upper level high centered over the Tennessee River valley, and the related large scale subsidence likely further made convective development difficult.

I am mainly just wondering if there is any way to tell from just the Skew-T that there would be no storms occurring.

Even when CAPE > 0, a skew-T diagram cannot tell you whether or not storms will occur (on the other hand, if CAPE = 0 then you know storms cannot occur unless something changes). All the diagram tells you is whether the atmosphere is capable of producing storms (in other words, it's a necessary but not sufficient condition). You cannot deduce sources of lift from a Skew-T, and in summary of my previous discussion, there is no guarantee that storms will form even in the presence of some lift. You need to examine other products to assess whether storms will actually develop.

 

[Robert van de Velde]

Sorry to pick nits, but surface Td of 82°F and Td's >68 up to 1km AGL is not what I would call shallow moisture.

I totally agree with you. Just to clarify, I meant that the surface Td was quite a bit higher than the Td obtained by averaging the amount of moisture in the lowest 50 or 100 hPa of the atmosphere. As noted by Jeff above, a parcel of air rising from the surface will then be diluted on its way upward so that using a SB parcel trajectory will lead to an underestimation of the amount of capping. In that sense I called the SB parcel layer 'shallow'. Nevertheless, there is indeed a lot of moisture up to 1 km AGL.