4/11/2008 DISC: AL/MI

[Dennis Sherrod]

I chased several cells throughout Central and Eastern AL. after leaving Central TN. earlier in the afternoon. As with most all of the other storms throughout the SE, they fizzled out. I was on one Severe Warned TS (just previously Tornado warned) in Eastern AL last night around 8:14 PM getting numerous lightning shots. This storm was kicking out lightning in the clouds literally every 10 - 15 seconds. Very bright, to the point it was lighting up the ground and trees all around.
After downloading, I came across several interesting photos. I would like others opinions on this please. A few people have looked at these and tell me it was a funnel cloud. I say NO, it was only part of the cloud, even though there was distinct lowering of the clouds. The four attached photos are from 8:14:07 through 8:15:27. A duration of 1 minute 20 seconds. Two of the photos are slightly brightened to show the formation better. After this, the formation was gone in the next lightening shots. But all in all, a night chase that was well worth it for the 30 something lightening shots.

 

[Jason Harris]

4/11/08 DISC: MI

1. Here's something, I'm curious about, I'm looking at the tornado watch probability from the other day (http://spc.noaa.gov/products/watch/ww0196_prob.html)
and according to this there was a 60% (mod)chance of 2 or more tornadoes in MI. And there was a 20% (low) "Probability of 1 or more strong (F2-F5) tornadoes."
Why is the prediction center using the F scale and not the EF scale?

2. Was limited Cape, overly fierce upper-level winds, mixing in of dry air, and falling dewpoints the problems that interfered with tornado development in MI on 4-11? And how in the heck did we get that tornado early Wed. morning (1:39 AM EST in Plainwell MI) with no one predicting anything? What was it about the conditions of that particular storm that resulted in producing the EF-1 versus nothing yesterday? Is that being studied?

Thanks for your thoughts in advance.

 

[Rich Thompson]

1. Here's something, I'm curious about, I'm looking at the tornado watch probability from the other day (http://spc.noaa.gov/products/watch/ww0196_prob.html)
and according to this there was a 60% (mod)chance of 2 or more tornadoes in MI. And there was a 20% (low) "Probability of 1 or more strong (F2-F5) tornadoes."
Why is the prediction center using the F scale and not the EF scale?

2. Was limited Cape, overly fierce upper-level winds, mixing in of dry air, and falling dewpoints the problems that interfered with tornado development in MI on 4-11? And how in the heck did we get that tornado early Wed. morning (1:39 AM EST in Plainwell MI) with no one predicting anything? What was it about the conditions of that particular storm that resulted in producing the EF-1 versus nothing yesterday? Is that being studied?

Thanks for your thoughts in advance.

Jason,

1. We need to update the web site. The probabilities were developed a few years before the EF scale, and we just haven't remembered to change that yet.

2. The vertical mixing of dry air was a big problem the afternoon of 4/11 in lower MI. The TOR watch went out before the dewpoints began to fall into the upper 40s to lower 50s. The model forecasts and observations were not particularly suggestive of that drying, and we have no good upstream soundings for the warm sector that morning. The drying reduced the CAPE and what still could have been an interesting scenario along the warm front, given the discrete storms that did form. The wind profiles are a little tougher to diagnose (not bad at DTX at 00z 4/12, but low-level hodograph structure not the greatest), since the best area should have been around 21z toward the Thumb.

Rich T.

 

[rdale]

Kudos to the IWX forecaster, their discussion and our IEM Chat brought up the potential of that drying. Once I saw the 'string bean' appearance of the early cells, I wasn't nearly as enthusiastic. And to make matters worse, cells were running up the exact same line near I-69 out of Indiana so what limited CAPE there was, was getting reused and wasted away.

This was like our fall setups, where we have to balance the CAPE / shear ratio very closely - and this time the shear won out for the most part. At least we got some sevwx - had it been a shower bust that would have stunk

 

[Jason Harris]

Thanks Rich and Rob for your insights from the world of forecasting.
Where does one access this information you mention Rob: "IWX forecaster, their discussion and our IEM Chat"? Is that just for the VIPs of the weather world?

No one picked up the Plainwell tornado part of the question though eh?

 

[rdale]

The actual discussion is at http://www.weather.gov/data/IWX/AFDIWX.20080411172555

The AFD's are openly available, the chatroom is just for media / NWS / Emergency Management agencies. I'll grab some imagery and post a bit more on Plainwell later.

 

[rdale]

I won't have a change to make pics today - but basically that storm picked up some quick rotation off the bat. But happening 1) in the middle of the night 2) our first sevwx of the year and 3) in an environment not conducive to a tornado meant 4) no Tornado Warning. Had that radar image happened on Friday afternoon - a TOR would have been issued.

But the actual touchdown came as the storm was collapsing, so it likely was not a "supercell" tornado but simply a spinup from the outflow at the end of its life.

 

[Jason Harris]

re: Plainwell

Does this mean then if one were spotting that storm the tornado would have likely appeared along the front edge gust front, perhaps under the shelf cloud rather than in the SW quadrant from a wall cloud?

--
Rob writes, "But the actual touchdown came as the storm was collapsing, so it likely was not a "supercell" tornado but simply a spinup from the outflow at the end of its life."

 

[rdale]

Odds are much lower that you'd find a RFD / wall cloud / etc. combo with this event.

 

[Jason Harris]

Rob writes, "Odds are much lower that you'd find a RFD / wall cloud / etc. combo with this event."
--
So, just to be absolutely clear then, that leaves option B that I suggested earlier?

--
"the tornado would have likely appeared along the front edge gust front, perhaps under the shelf cloud"
--

 

[rdale]

Ehhh, I doubt it. What I'm saying is that it likely happened rapidly enough that the classic lowering followed by RFD wrap around clearing out may not have happened.

A gustnado could form with the shelf, but with storm-level rotation in this tornado I don't think that would be the case. But most MI tornadoes that hit like this don't come from any notable features visually, it's more in a low-cloud, full-o-scud soup that makes identification tough.