Josh Gebauer

@GumryWX @DualDoppler That is 6 hours of model runs that have not been corrected for nocturnal PBL errors in the EML region. That could be a pretty big deal considering the 12 Z model runs often set the stage for Day 1 risk. Diurnal transition periods are a pretty sensitive time for models.

@DualDoppler Yeah but I mean aside from WMO standards not being met, is this really that huge of a problem if offices shift from 12 to 18Z?

Cutting so many soundings from the EML source region has been disastrous for model data. Forecast verifications have been really bad lately. We really need something to give here…

@sambrandt99 And to be clear, I am not saying the cheat code is definitely happening! I just don't think it can be completely dismissed.

@sambrandt99 Low-level mesocyclones can be primarily driven by ambient very low-level shear (see Coffer et al. 2023), so I don't think that magnitude of baroclinic vertical vorticity is necessarily a given with a strong low-level mesocyclone.

The surface vorticity/3CAPE "cheat code" has a lot of confirmation bias where proponents will ignore null cases. (thread)

@sambrandt99 A cheat code is something that makes the game easier, right? That seems to fit the definition. You really would need values greater than Coriolis though before it could possibly matter.

@sambrandt99 This is probably too strong of a statement. Vorticity of 0.0003 over a 4 km radius area has a circulation of 15, 079 m^2 s^-1. At least theoretically, that can significantly cut down on the amount of vorticity the storm needs generated to produce a tornado.

This suggests that storms might not need to generate their own vertical vorticity to form tornadoes when there are strong coherent structures in the inflow and we would expect those structures to be strongest in the highest shear environments (like the southeast US).

Conceptual models of tornadogenesis have often overlooked the inflow as a source of vertical vorticity, but the inflow is actually not devoid of vertical vorticity. Coherent turbulence found in sheared environments generates vertical vorticity right near the ground in the inflow.

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@jschaut27 If it keeps trending north I do see a small chance that the Pittsburgh area flirts with a change over to sleet/freezing rain, but I don't think that is likely right now.

@jschaut27 I feel pretty good that most of PA will get snow. Only question now is if it is just 6 inches or if it really goes off and the current trend is for it to really go off. The potential is there for a widespread area of over a foot since liquid to snow ratio should be high.

If the warm nose is as strong as what is shown by the ECMWF then I think that it's 2-m temperature over the southern Plains is garbage. I would be willing to bet that the freezing line is closer to Houston than Dallas at 12 Z on Saturday. It's AI companion has the right idea.

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They just completely made up that NWS issued a severe thunderstorm warning. There is no warning.

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Add in the low-level clouds and there is no chance for the temperature to recover in time to meet the high temperature. Models really struggle with this because they can't properly resolve the inversion so the northerly winds in the cold air mass are often underestimated.

Classic conditions for a central Oklahoma high temperature bust. Shallow cold air with high pressure to the northwest. The negatively buoyant air over the sloped terrain enhances the northerly winds in the cold air which causes the it to surge farther south.

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Sigh and I can't write sentences. I meant... so the convective forecast might not be terrible.

Overmixing effects both temperature and moisture. This often means that temperature profile is more favorable than forecast and the dewpoint profile is less. The two errors can offset each other so the forecast convective forecast might not be terrible.

This is a great example of why underdone dewpoints by the HRRR are not always a sign the environment is more favorable than forecast. This HRRR profile has 2616 J/kg of MLCAPE and -99 J/kg MLCIN, the observed profile has 1446 J/kg and -194 J/kg even with a 5 F dewpoint error.