5/27/06 FCST: MN/ND/MT

[Glen Romine]

Not saying the wind profile is horrid - but there doesn't appear to be anything that screams tornado. MKX/GRB/LOT all issued TOR's on storms with fairly weak rotation and so far no reports that I can see...
[/b]

As opposed to the 'rock star' environment in North Dakota? I think I'd take the marginal supercell in northern IL over what the envinronment in ND is dishing out right now. If the SPC graphics aren't totally out to lunch, effective shear on the warm side of the boundary in ND is maybe 30 knts, and storms there seem to have the appearance of that type of environment. If you are into parameters, the 6 pm mesoanalysis graphic has a STP of 4 in WI with CIN of -25 or less vs. STP of 2 in ND with CIN of -200. Given the former is also overlayed with 55 knts of effective shear , as well as some convective development in the area, - I don't see any real problem if folks wanted to talk about it. SPC may not be impressed, but maybe the atmosphere will feel differently. Could be, and probably is, that those graphics are out to lunch, but it just seems no worse for discussion.

Glen

 

[Fritz Kruse]

"I noticed nobody is talking about Wisconsin and Minnesota tornado potential today,
but some about Iowa. "

Not saying the wind profile is horrid - but there doesn't appear to be anything that screams tornado. MKX/GRB/LOT all issued TOR's on storms with fairly weak rotation and so far no reports that I can see...
[/b]

I was talking about the tornado potential, not a nowcast. The sfc to mid level shear was
very good with high CAPE. The atmosphere rarely screams tornado, other than the rare
tornado outbreaks, and I was just noting the possibility.

The NWS rarely issues tornado warnings for weak rotation, so I would definately re-think
that one.

 

[rdale]

I watched those storms as they were warned and was very surprised... Rotation was on the order of 30kts, which by any definition is very weak. Not even wind damage was reported from the cells, so my interp stands ;>

What I'm saying is that rotational shear was nothing that would get me excited, speed shear usually doesn't do much for me unless it's extreme and/or combined with a very fat CAPE (which wasn't the case today.)

 

[Fritz Kruse]

I watched those storms as they were warned and was very surprised... Rotation was on the order of 30kts, which by any definition is very weak. Not even wind damage was reported from the cells, so my interp stands ;>

What I'm saying is that rotational shear was nothing that would get me excited, speed shear usually doesn't do much for me unless it's extreme and/or combined with a very fat CAPE (which wasn't the case today.)
[/b]

Not to argue, but rotation at that elevation and distance from the radar would be enough to
suggest stronger rotation toward the ground along with a hook echo. Also what you are
seeing as rotation on secondary sources may not be the same as what the NWS see on the
screen. Plus the NWS can, on the fly, switch the storm motion vector, to see the rotation better
at his screen for better Storm Relative motion and rotation that does not show on your views.

I bet they were using other radars around the area and making a best guess. Point being the NWS
(that I work for) does not normally go with a Tornado warning with only "weak" rotation.

If you want to discuss this further please email me directly.

 

[rdale]

"but rotation at that elevation and distance from the radar would be enough to suggest stronger rotation toward the ground along with a hook echo."

I saw no hook echo, and the storm wasn't that far away from the radar locations.

"Also what you are seeing as rotation on secondary sources"

Not sure I understand what "secondary sources" are - I use Level II data which is the exact same data NWS uses (plus AE allows for volume display which NWS offices do not have ready access to.)

"Plus the NWS can, on the fly, switch the storm motion vector, to see the rotation better"

And so can AE.

"I bet they were using other radars around the area and making a best guess."

And so was I.

"Point being the NWS (that I work for) does not normally go with a Tornado warning with only "weak" rotation."

I think that sort of statement is not valid since many offices have different policies. My interpretation of the data was that rotation was incredibly weak, there were no boundaries anywhere in the vicinity on radar or satellite that could add a "local" rotation factor, and the environment really didn't support tornadoes.

And none were reported in the 3 warnings that I was referring to, not even wind damage ;>

"If you want to discuss this further please email me directly."

That was good - just making sure people are aware that you don't have to be sitting inside a NWS office to be able to analyze radar as good (or better than) a NWS met, since they don't have access to all the tools we do in the private sector.

- Rob

 

[Matthew K. Hartman]

I don't find any of this "on-topic." Let's either get back to the forecast aspect to what's actually going on in ND, MN, or MT. If you want to discuss what's going on in Wisconsin or radar interpretation, either start a new thread, or move this over to the "Weather and Chasing" forum.

...my opinion, anyway.