The moderate risk for severe weather that I noted yesterday was downgraded to a slight risk this morning, though there are still a few reports of significant severe weather, namely enormous hail up to 4 inches in diameter in eastern Kentucky. Wind damage has been widespread through the region as well. Take a look at the severe weather that has been observed to this point.

Perception bias leads people to believe that there is some sort of shield that protects them from severe weather (the so-called Arch Effect in St. Louis, for example) but it’s actually a matter of odds. Major cities don’t get hit as often because they don’t take up as much space, so it FEELS like they are safer, though the threat is just as real. Of course (and the day is definitely long from being done) it’s getting harder to believe that West Virginia doesn’t have a dome around it.
(As I say this, there are severe storms east of Lexington, Kentucky with a chance of grazing the state and a line developing from just northwest of Columbus, Ohio to north of Louisville, Kentucky, so the day isn’t over yet, but by golly it looks like West Virginia is going to dodge another bullet.

An active upper level trough is digging it’s way into the Ohio Valley, and the Storm Prediction Center has issued a moderate risk for portions of the Ohio Valley, particularly West Virginia and much of eastern Ohio, primarily because of the threat for significant severe weather (hurricane strength wind, 2 inch hail or tornadoes EF2 or stronger). Before I continue, here is the outlook as the SPC has foreseen.

As you may have noticed, I said the threat for a severe weather outbreak is rare in West Virginia (though not unheard of). Take a look at the following climatology (via the SPC) for this time of year, showing the frequency of severe tornadoes, wind and hail, and note that West Virginia has a lower risk than everywhere around them.

In particular, look at this, the climatology for significant wind this time of year in West Virginia. West Virginia functions as the hole in a donut!

Given that it’s so unusual to see terrible thunderstorms in this part of the world, this moderate risk wasn’t issued lightly. Take care tomorrow in the Mountaineer State!

As Ryan mentioned, we’ve been analyzing the forecast and verification of a system that would affect the Northern Plains over the last couple of days, which was kind of all over the place but eventually honed in on during the morning of the event. The NWS put together a pretty neat graphical overview of the event, as taken from radar images of the storm from start to finish as it went from central North Dakota through northern Minnesota:

As you can see, the main corridor of severe wind reports followed the northern portion of the derecho as it marched though North Dakota. The southern end got a bit more intense as it moved through Minnesota, and as you can tell, the atmosphere was very capped over SD and southern MN. The southern end made very little progression to the south, while there was plenty of activity on the northern end even away from the main line of storms. So while the forecast took a couple of days to really nail down, and was fairly elusive in doing so until the day of, the SPC got it pretty much dead on, and the radar images prove it as well.

Yesterday, I highlighted the lead up to a potentially significant severe weather outbreak in the Dakotas and Minnesota yesterday. It was a little circuitous, and very clear that there wasn’t much confidence or consistency at the SPC for what was going to happen. In the end though, by Monday morning, they had it pretty close to nailed. The thunderstorms developed over North Dakota and congealed into a strong squall line that moved from near Bismarck to Grand Forks and into northern Minnesota. You can see the verification, with storm reports overlaying the convective outlook.

So it took a while, but the forecast eventually ended up pretty close to reality. Of course, I need to remind everyone that we also had this less than 24 hours before the thunderstorms actually erupted:

Next time, I’m sure they will nail something down with a little more lead time.

There is a moderate risk for severe thunderstorms today from the Dakotas to northern Minnesota. How we got to this point is rather circuitous. Let’s take a look at the past 24 hours of SPC outlooks. I don’t think I’ve seen one of these things change so much pre-storm in a very long time. Here is what we started with yesterday morning:

A slight risk, covering most of Minnesota and a lot of the central Dakotas. Furthermore, they had the best threat for severe storms around the North Dakota/South Dakota and Minnesota tri-state.

After a shift change and perhaps the usage of a hallucinogen, Sunday afternoon’s update gave us this moderate risk, with a center about 150 miles to the east-southeast.

And now, thunderstorms were going to be significantly stronger.

Whoa! 45% and hatched, when we only had 30% earlier. And there isn’t much of an overlap, either.

So obviously, something changed, the onus was now on the Twin Cities, St. Cloud and Rochester to be prepared for — Oh, wait. This was the outlook from the overnight.

So we’re back into North Dakota and northern Minnesota, which, initially, wasn’t even in a slight risk for yesterday’s updates. This time, the center shifted about 175 miles to the northwest. Was the threat for significant weather still high? Why yes, yes it was.

Where are we at now with the morning update, you may ask. Pretty similar to the overnight outlook, actually, but greatly elongated.

The only thing is that the threat for strong winds seems to be sneaking back deeper into Minnesota, practically to Wisconsin.

http://www.spc.noaa.gov/products/outlook/day1probotlk_1300_wind.gif?1405956293553

Actually, that’s a pretty significant change, increasing the coverage of significant severe weather like that. There is also a 5% tornado threat now in North Dakota and northwest Minnesota. that really grew over the course of the past two updates.

Expect the afternoon update to push the focus into Iowa.