2016-06-03 EVENT: NE/IA/MN

[RyanConnelly]

Just some quick thoughts on Friday. Mid-level short wave drops in, triggering surface pressure falls and dragging a cold front with it into the northern low plains by Friday afternoon.

Models generally agree on moderate CAPE, with ML values ~2000 J/kg and SB up to 3000 J/kg in places. 0-6 km shear vectors around 40-50 kts support supercells, and their orientation to the cold front should help keep storms in the warm sector discrete for at least a little while, despite the southerly or slightly veered surface flow.

There will be morning elevated WAA crapvection in SD and MN, so right now the best play for tornado potential, imo, is in southwest MN or northwest IA where any potential outflow boundaries from that morning convection intersect the cold front.

Goss was fairly bullish with the Day 3 this morning:
STILL...WITH SLY SURFACE FLOW STRENGTHENING IN CONJUNCTION WITH THE
APPROACHING LOW AND ENHANCED/WLY MID-LEVEL WINDS SPREADING EWD ATOP
THE REGION IN CONJUNCTION WITH THE UPPER SYSTEM...SHEAR SHOULD
BECOME QUITE FAVORABLE FOR SUPERCELLS ACROSS PARTS OF IA/MN/WI
DURING THE AFTERNOON AND INTO THE EVENING. THEREFORE...WILL
INTRODUCE SLIGHT RISK ACROSS PARTS OF THIS AREA...GIVEN THE
APPARENT/EVOLVING RISK FOR HAIL/WIND AND POSSIBLY A COUPLE OF
TORNADOES.

And this may be it for at least a few days, so hopefully we can make something of it!

 

[Mike Marz]

I am definitely worried that early day storms and cloud cover will make this not much of an event, but I will be keeping an eye on it and chasing it regardless.

My play here will likely be the TP/WF, wherever it ends up by the afternoon. I am hopeful the models are currently too fast with this system because at its current pace, some not so friendly Eastern Minnesota or Western Wisconsin terrain is coming into play. I think the best case scenario is that we see the inevitable morning storms and clouds somehow clear the warm sector by noon. If this can happen and the TP/WF can hang back in central MN somewhere and get some insolation, we could be in business. The H5 flow coming through with this system is definitely adequate for supercells and with the helicity provided by the WF, I would not be surprised to see a tornado or two given that storms aren't over-crowded and CAPE is sufficient. Too many storms going up all at once is another issue I can see with this setup.

As of now, my target is St. Cloud, MN by 2pm and crossing my fingers that it is sunny out... Let's see what tonight's 00z NAMs show us.

 

[Royce Sheibal]

Tomorrow just reeks of one of those 'central and W Central Minnesota days' where you get 2-3 nice supercells pushing ESE or SE and straight into the inflow, causing them to go nuts as they tumble downhill. As for a target up north there, I think you want to head further SW for better CAPE recovery after the crapvection. Willmar or Granite Falls area seems to be where the hi-res models are predicting, maybe even further SW than that, as the northerly storms may have nasty mixed models.

That being said, NAM shows best tor risk up in that St Cloud area, but it's nasty VBV soundings just to spite us all. I'd say play the SW side and hope for more LP storms with less VBV. SW Minnesota is like the Dodge City the state.

As for the tail end of the cold front down here in Nebraska, I've still got some hope, as a slight forecast for Day 2 has been known to turn into a High by the end of Day 1 in similar setups. If we can get the front to slow down / wash out a little bit and an MCS leaves a circulation / outflow over the area instead of dumping a cold pool Friday morning, I think the chances for TORs in Nebraska goes way up Friday. Sadly we won't be able to tell if that will happen until Friday morning at about 10am when the models are all done.

I won't be out chasing, but if I did I'd park myself around West Point, NE and then head for the best Td's and moisture convergence, hoping to get an LP spin-up before things line out.

 

[Royce Sheibal]

Latest HRRR models and NAM 4KM are pointing further SW toward the MN/SD border, possibly into NW IA and far NE Neb. SPC ensemble of cape/shear/precip combo gives this area the best chance IMO. NAM is still predicting the remnants moving into NW Wis. to revive and go super, but there is so much crapvection up there I wouldn't put money on it. Best moisture is still over SW MN and SE SD, and if some theta-E convection and moisture convergence can occur ahead of the front I think cape will recover nicely.

This looks like one of those 50/50 Bust or Awesome days. Keep an eye on the tail end of the front, Td's are about 5 degrees above model forecasts in NE Neb / NW IA. Somewhere between Yankton, SD and Storm Lake, IA will things will go surface based. Down the road further I've seen a lot of hail soundings coming out o Nebraska, so yay! GL out there.

Edit: Forgot to mention, the surface low appears to be washing out a bit, and is not longer closed, however the UA vort-max associated has started to deepen and push a little further south into Central NE, and appears to be getting pushed further E instead of NE toward the main target. Perhaps I need to move my target southward further...

 

[Kenny Drake]

This is a classic upper midwest spring-time scenario where the models need to be tossed out, even the short-term. Why? Well it's not exactly known why, but there is strong evidence to suggest that the "Buffalo Ridge" (western MN) combined with the effects of the ice cold Lake Superior water (it's ice cold year round by the way) are the culprit.

Having said that: Throw out the models, throw out the SPC forecasts, throw out the NWS forecasts. The only hope for these scenarios is to wait until day-of and then nowcast. I've been eyeing this day for a while, but due to these reasons you will never see me forecast severe wx in the upper midwest more than a day in advance.

Looking at surface obs, upper air obs, and SPC mesoanalysis the play for storm chasers (if there is any at all with this setup) is going to be down in NW/NC IA where destabilization has already occurred. Today is a pretty classic scenario for the upper midwest where dynamics are too strong for the available thermodynamics (there ain't much north of the MN/IA border). Here is my nowcast'ish forecast:
* The "chaseable" storms will be in SW MN/NW IA stretching east towards SW WI. This is where the thermo energy resides with some juxtaposition of upper air support.
* Anywhere north of this line is going to be crap. Marginal thermodynamics with way too much dynamics = insane amounts of overturning so the result will be any available CAPE slowly erodes with time. You do not want to chase these storms, even if they can muster a landspout or two.
* Further south, the dynamics go away and the thermodynamics go up. Unfortunately there just isn't a good juxtaposition of these features today. Your best hope is going to be where I noted in northern IA, but I expect a quick migration to a linear MCS-type threat.
* SPC should have stuck with their overnight Day 1 with the Slight in IA and Marginal north of the border. I think that is going to verify. A slight risk north of I-90 and west of the MN/WI border is likely not going to verify. I would consider keeping the slight in IA and then maybe a northward push into Central WI where plenty of sunshine is occurring, but I don't know if the upper air support will make it there before diurnal trend kicks in tonight.

I am smack in the middle of the slight risk and I am not even remotely considering chasing today for all of these reasons.

 

[RyanConnelly]

Not sure that the first few counties in SW MN are out of it. It's where better destabilization is occurring right now with elevated convection persisting in northwest Iowa. In NW IA you've got better helicities per mesoanalysis but surface dews are lousy and not advecting in any better. 86/46 at Carroll, IA - the aptly named KCIN.

Meanwhile there seems to be a mesolow up here between roughly Pipestone and Marshall. Evident per slightly max in 0-1 km shear magnitude, and wrapping in of cloud free air on vis sat. Also a CI field going here where the sun is out and CAPEs are up to 1500. And supposedly the region is climatologically favored for tornadoes because of the Buffalo Ridge to the south, which makes sense.

That doesn't mean I have high expectations, but I think I'm content to stay in or near Pipestone than book it south into high LCL Iowa.


Sent from my iPhone using Stormtrack mobile app