High Risk, Bust or Brilliant?

There seems to be a lot of discussion generated by the issuance of a high risk outlook for a chunk of the Southeast US by the Storm Prediction Center Thursday and Friday. And there seems to be two opinions - you think was a bust or you think it was not a bust. So here's a few thoughts on it.

It is interesting to note that to the best of my knowledge, SPC had never issued a high risk outlook for Day 2 before Thursday. So their forecast was a historic first!

At this writing, there were 691 reports of severe weather yesterday including 48 tornado reports, 141 wind reports, and 502 hail reports. Those 502 hail reports included 26 with 2+ inch hail size. I think people can agree that this was a significant event.

So before going on, let's take a look at the definition of a high risk. This definition is cut and pasted verbatim just as it appears on the SPC web site from Section 3 of their Frequently Asked Questions page:
The HIGH risk area almost always means a major severe weather outbreak is expected, with great coverage of severe weather and enhanced likelihood of extreme severe (i.e., violent tornadoes or extreme convective wind events over a large area). Within a high risk area, expect at least 20 tornadoes with at least 2 of them rated F3+, or an extreme derecho causing 50+ widespread wind events (50+) with numerous higher end wind (80+ mph) and structural damage reports.

Trying to be as objective as I can, it seems to me that the established criteria was met. I would qualify the events of yesterday as a major severe weather outbreak with great coverage of severe weather. I'm fairly confident from the video I have seen that we will see at least one tornado rated an F3 - the one that struck Gallatin, TN. There could be others because all of the video I've seen was from Gallatin, so I simply cannot say about any of the other tornadoes that occurred in Tennessee.

I expect that of the 48 tornado reports, some of which are different reports from different locations along the same tornado path, the final number will be around 30. That certainly qualifies as the expection from a high risk area. I would also opine that the people in Tennessee would call their weather yesterday extreme.

There definitely were structural damage reports. This was not a derecho event, so that qualification does not apply to yesterday.

I said I wanted to be objective, so I have to note that the high risk area, and I'm using the 1300Z outlook from April 7, 2006, came close to Gallatin, TN, but did not include that location. My opinion is that if you think that negates all the other factors, then you may be a perfectionist. After all, the high risk area was surrounded by a moderate risk area and the high risk area was very close to the Gallatin, TN, area.

Finally, I tried an experiment to overlay the 1300Z, April 7, 2006, outlook with the storm reports. Here is the map which I think shows a high degree of correlation between the definition and what occurred.

SPC has excellent expertise in severe weather forecasting. They do nothing else but focus on severe weather. They are not perfect as no meteorologist is. We all have our share of forecasts that go awry. And when/if they bust, I will be right there to take them to task. But I do not believe that they should take any heat on this one. Their high risk outlooks on Day 1 and Day 2 were on target.

Be sure to scroll down to see the graphic.

-Brian-

Overlay of the 13Z Day 1 Outlook, April 7, 2006, and the SPC Storm Reports.