Severe Weather Threat 4/28-4/30

Clancy said:
More or less it means storms don't form due to a strong cap - at least this is what modelling suggests.
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Not exactly - the linked tweet is saying that the CAMs are likely over-estimating capping and ignoring synoptic lift that should mitigate the capping.

In other words, he's not buying the no convection scenario presented by the CAMs.
 
I understand on one hand the CAMs over-estimating capping for tomorrow, but the other side of me is also just feeling less and less confidence about the 7+ hour drive being worth it, especially if its an overall model agreement and not just a couple.
 
18z NAM backs off on the capping quite a bit, allowing for explosive development ahead of the dryline tomorrow. It's still running but right now, it definitely supports the higher end scenario tomorrow and would be a bona fide tornado outbreak.
 
lake.effect said:
Not exactly - the linked tweet is saying that the CAMs are likely over-estimating capping and ignoring synoptic lift that should mitigate the capping.

In other words, he's not buying the no convection scenario presented by the CAMs.
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I was referring to the significance of convective initiation conceptually, not that it would actually verify.
 
While there's definitely still cause to be cautious about the intensity and coverage of storms tomorrow, I do hope folks in the Twin Cities area will be aware tomorrow, given that they haven't dealt with too many significant events as of late. That's a lot of people under a significant risk for tomorrow. Not sure how seasoned people are with severe weather in general up there, would love to know what anyone on the board from that region is hearing/seeing.
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^yeah Clancy, me too. I have family up there. Gonna be giving them a heads up. The Twin Cities metro is, geographically, pretty huge. The chances of a populated area getting some tornado action tomorrow is quite high.

I don't think the CAMs quite know what to do with this set up. They're acting all kinds of weird. I think it's going to come down to observations tomorrow morning. We'll see what the environment looks like. I'm leaning strongly towards the high-end (outbreak) scenario for several reasons at this time. But we'll see.
 
Clancy said:
While there's definitely still cause to be cautious about the intensity and coverage of storms tomorrow, I do hope folks in the Twin Cities area will be aware tomorrow, given that they haven't dealt with too many significant events as of late. That's a lot of people under a significant risk for tomorrow. Not sure how seasoned people are with severe weather in general up there, would love to know what anyone on the board from that region is hearing/seeing.
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At least here, the local subreddits have posts and discussion, as well as coverage by local news, so that's encouraging. I haven't checked Twin Cities stuff, but if we're discussing it here in local social media, I'm sure they are, too.
 
I still find it hard to trust the CAMS on this one - model guidance agrees the forcing will be impressive. The nose of the 300mb jet is placed nearly ideally relative to the warm sector on Monday afternoon/evening. Considering this will be fast moving, I just really don't see how we don't get at least 1-2 powerful tornadic storms in either IA, MN or WI.

models-2025042718-f030.300wh.conus.gif

Often, models may underestimate surface backing with deepening low pressures like the one tomorrow, and so I wouldn't be surprised for the dryline and any prefrontal confluences to be even slightly more convergent than expected.

Models also struggle to initiate convection in drier mid-level environments (Think 3/14, where a fair few number of CAMS were failing to initiate convection into AR just hours before the event, let alone the day before). I think a NAM or FV3 solution is closer to reality where get at least a few storms.

If the CAMS remain adamant all the way up to tomorrow then we may be able to breathe a sigh of relief regarding any tornado risk - but I still pretty uneasy about the whole setup and believe a higher end scenario is most certainly still on the table.
 
UK_EF4 said:
I still find it hard to trust the CAMS on this one - model guidance agrees the forcing will be impressive. The nose of the 300mb jet is placed nearly ideally relative to the warm sector on Monday afternoon/evening. Considering this will be fast moving, I just really don't see how we don't get at least 1-2 powerful tornadic storms in either IA, MN or WI.

View attachment 40452

Often, models may underestimate surface backing with deepening low pressures like the one tomorrow, and so I wouldn't be surprised for the dryline and any prefrontal confluences to be even slightly more convergent than expected.

Models also struggle to initiate convection in drier mid-level environments (Think 3/14, where a fair few number of CAMS were failing to initiate convection into AR just hours before the event, let alone the day before). I think a NAM or FV3 solution is closer to reality where get at least a few storms.

If the CAMS remain adamant all the way up to tomorrow then we may be able to breathe a sigh of relief regarding any tornado risk - but I still pretty uneasy about the whole setup and believe a higher end scenario is most certainly still on the table.
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One thing that would actually help in convective initiation is if the vorticity maxim of the surface low is slightly further south than modeled.

As that would certainly back surface wind vectors enough to induce enough moisture convergence along the dry-line to allow convection.

Cams like the hrrr are finally beginning to pick up on some spotty convection in confluence bands, although the inversion is still a bit too stout.
 
UK_EF4 said:
I still find it hard to trust the CAMS on this one - model guidance agrees the forcing will be impressive. The nose of the 300mb jet is placed nearly ideally relative to the warm sector on Monday afternoon/evening. Considering this will be fast moving, I just really don't see how we don't get at least 1-2 powerful tornadic storms in either IA, MN or WI.

View attachment 40452

Often, models may underestimate surface backing with deepening low pressures like the one tomorrow, and so I wouldn't be surprised for the dryline and any prefrontal confluences to be even slightly more convergent than expected.

Models also struggle to initiate convection in drier mid-level environments (Think 3/14, where a fair few number of CAMS were failing to initiate convection into AR just hours before the event, let alone the day before). I think a NAM or FV3 solution is closer to reality where get at least a few storms.

If the CAMS remain adamant all the way up to tomorrow then we may be able to breathe a sigh of relief regarding any tornado risk - but I still pretty uneasy about the whole setup and believe a higher end scenario is most certainly still on the table.
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You think anything initaties from central to north central Iowa, eastward?
 
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