8/13/07 NOW: ND / MN / IA / WI

[Justin Turcotte]

Nasty looking sup fully equipped with hook about 60 miles northwest of Grand Forks and moving in my general direction. Some rotation evident on radar but the cell is elevated. Looks like it should pass a bit west of the city based on movement in last few scans. I have to work at 4 but if the storm gets close in the next hour I'll snap some pics. Already looking mighty dark in the forward flank.

Edit 1: Hail covering ground about 45 miles west of Grand Forks. Tor warn issued.

 

[Aaron Kennedy]

Storm quickly went outflow dominant as it approached GFK. Now SE of town, it appears to be a non-player.

 

[John Gnuechtel]

Currently sitting in the Econo Foods parking lot in Hutchinson, MN, watching a whole lot of flat, elongated, elevated convection. Plenty of mammatus...basically no base. The instability is there up high, but the cap still owns all. Will likely continue to hang here until something happens. I'm guessing one of these pancakes is gonna be the start of tonight's MCS show, and any hope of discreet action will evaporate with it.

 

[Justin Turcotte]

Supercell that passed near Grand Forks around 4 pm has regenerated in central MN and looks extremely nasty on radar. Reports of golf ball hail covering ground and 80 mph winds. Brainerd (weekend retreat area for Twin Cities folks) is going to get hammered. Look for car lot hail sales this week.

Edit 1: This thing is making a bee line toward the MSP metro with a 75 dbz core!

Edit 2: Tornadic thunderstorm entering MSP metro at 9pm.

 

[Andrew Pritchard]

As those of you watching spotter network may have seen, I was dumb enough to get in front of that beast. Well, it means as much as business as it's radar signature says it does. Debris was airborn all around me, and was being plastered to my windows by winds I estimated around 80-90 mph while being pummeled by 1" or so hail. Now it's in my way to get home for the nite! Hope people in MSP are aware, because this thing is going to blow some stuff down.

 

[Chad Cowan]

It's quite staggering that a storm can produce golf ball size hail in these temperatures. That is one powerful updraft. Just as I'm typing this that cell went TOR warned, there is an appendage on radar and strong rotation. This is quite strange to be occurring on a bow, but within these enormous helicity values, anything is possible. MSP needs to keep a close eye on this one... anyone know of streaming coverage from the area?

The LLJ has really kicked in and has provided an extremely sheared environment. Here is the profiler data from Wood Lake, MN:
http://www.profiler.noaa.gov/npn/au...000&maxheightagl=-10000&htunits=m&rassunits=c

EDIT: Thanks for the link Justin... video showing wall cloud north of MSP

 

[Justin Turcotte]

I think this station has streaming coverage. My work comp wont do streaming...
http://www.myfoxtwincities.com/myfox/

Upstream storm looks to interact with OFB from the beast. Looks like a narrow area of low MLCIN where something on the surface can't be totally ruled out.

Another update: Golf ball sized hail reported covering ground at 9:40pm by chaser in northern MSP burb.

 

[Jeff Snyder]

Well, the origin bow echo (maybe derecho if it lasts a little while longer) has moved into western Wisconsin, with MPX indicating very strong winds continuing with that complex. I'm sure there's been quite a bit of wind damage with these storms, though the strongest winds managed to avoid much of Twin Cities metro area save for the northcentral and northeastern suburbs.


Meanwhile, another bow is organizing northwest of MSP, intersecting the OFB from the first bow S of St. Cloud. A little while ago, 2.5 degree velocity imagery from MPX indicated a substantial rear-inflow jet just south of St. Cloud. Interestingly, the latest data show what looks to be gravity waves (bores?) ahead of these storms, likely caused, in part, by a stable near-surface layer:

 

[Chad Cowan]

Incredible lightning show on the streaming coverage of the 2nd bow moving through the western and southern burbs of MSP. They have showed some images of hail that appeared to be ~3" from the first line. This is one of the better live severe weather coverage I've seen. It's a breath of fresh air for someone who grew up watching Katie Horner

http://www.myfoxtwincities.com/myfox/

 

[Paul Townsend]

The first line has turned into a beautiful bookend vortex.

 

[Jeff Snyder]

Interesting hearing reports of a house destroyed near New Richmond, WI... It seems like most folks automatically associate high-end damage with tornadoes, but the reporter did a good job of saying that it was probably straight-line wind damage (which can be as significant as weak tornadoes, he noted -- props for not jumping on the 'tornado' bandwagen).

However, I just looked at the MPX data near there, and it actually may have been a tornado. As that part of the bow approached New Richmond, a part accelerated rapidly to the southeast, and an "inflow notch" developed in a similar manner as that which develops north of a hook echo. This area "wrapped up" over the course of the 20 minutes as it progressed south and east of New Richmond, but there were very strong inbound velocities colocated with that inflow notch. Perhaps this was a leading-edge vortex, but those tend to be rather weak and small in my experience. Perhaps the strong surge of outflow created an intense vortex sheet that folded...?

I don't usually include images / graphics in NOW threads, out of consideration for those who are on limited-bandwidth (e.g. cell-phone data) connections. However, I don't think anyone here is chasing this at this time, so I'll put them in here. At any rate, very cool gravity waves continue to eminate from those storms... It's not often that radar captures these as well as MPX is attm.

0258 UTC BR1 and BV1 (the previous 3 scans showed the "notch" better, but I want to show BR from the same time as the BV)... I didn't save the SRV imagery, but the storm motion was nearly perpendicular to the radials at this azimuth, so there was little difference between SRV and BV. In fact, the storm motion used in SRV was a little "away-from-the-radar" here, so the SRV inbound velocities were stronger than shown in the BV image below. The more I examine these data, the more I think that there very well may have been a tornado just south of New Richmond (which is located very near the northernmost purple >65 dBz area):

 

[Kevin Polston]

What's really interesting is how there are two almost identical bows in close proximity with rotating comma heads on the north side of both bows. Shows up pretty good watching the LaCrosse radar. Another interesting thing is most supercell tornado parameters are quite high...but looking at a point forecast sounding for MSP it still showed an appreciable amount of cin...and of course the storms have organized into bows and not discrete cells at this point. All in all....very impressive!