2015-05-03 EVENT: NE/KS/IA/MN/WI

[Royce Sheibal]

Here we are 48 hours away from the 4KM NAM showing up to 3k SB cape and a broken cap from N KS all the way to N WI and no one is talking about it? Might as well make a forecast...

I think the reason why everyone is groaning about Sunday is 1: It's still a little early for this area, 2: Shear is non-existent on GFS and NAM 12z, 3: It's too far north for most of you to care.

So Let's address #2 with the 4KM NAM. Normal NAM agrees somewhat and is predicting some nice 2-3k SB CAPE, as well as a probable broken cap after 21z. But....Normal NAM shows winds from 850 all the way up to 250 just vanishing after the morning convection moves out. The small jet streak is just, POOF, gone. Helicity levels are so low I think I saw some single digits. But take a closer look at 4km NAM and notice the increased helicity in areas of NW WI, NC KS, and just away from the main line in Nebraska. I'm still preaching my love of NAM 4k after it's success in forecasting last June's Nebraska TORs.

So let's refresh:
CAPE: 2-3K, even GFS puts it over 1500
Lift: Not insane but enough (7-8 LI's possible)
Moisture: 60-65 Td at the surface, likely boosted by morning rain
Shear/Helicity: Almost non-existent where the CAPE is, plenty where the CAPE isn't. Storm motions will crawl unless a cold pool forms
Bonus Feature: NW flow aloft might cause a SE storm motion on these pathetic hodographs. Anything moving SE in a typical Midwestern spring day is going to get some decent inflow.

I'm kind of at a loss here guys, what do you think is going to happen? If the shear or cape move 200 miles either way we'll suddenly have EHI's in the 4-8 range instead of 1-2, and we're still 48 hours out so a lot can change. But right now we're starring at a multi-cellular HP poo-storm that eventually cold pools. Sad tornado panda...

 

[Mike Marz]

Well I have had my eye on this day for a little while now. Not because I feel like tornado chances are good, they seem almost non-existant, but because of where I live. Like you said Royce, the shear is complete garbage anywhere that there is good forecast cape. Hopefully some of the stronger 500s can get a bit further south in upcoming model runs. A lot can still change but right now it appears to me that this is a sad setup tornado wise. I may still get out locally in Minnesota and see what is what though. Surprises sometimes do happen. Also, I do think that similar to a lot of previous setups this season, this one will slow down a bit. This could allow things to at least be in better terrain farther west, as opposed to north central Wisconsin.

 

[Jeff Duda]

Decent thermodynamics, but you're dealing with pretty pitiful shear. Definitely only in the multicell range at best, if even that in some areas. It will be hard to get any discrete sustained storms. Probably will just see a line develop along the front with wind gusts being the main threat (perhaps with hail < 2"). Not to mention basically no large-scale support. Couple that with the site downtime lately and I'm not surprised there hasn't been much talk about this event.