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.

This is the current hazard map for the Twin Cities NWS office.

Temperatures are going to warm up for the beginning of next week, and dew points will climb into the 60s, leading to heat indices around 100, leading to an excessive heat watch. Certainly, excessive heat is in the eye of the beholder, much like freeze watches or wind chill advisories. They aren’t going to be issuing these advisories or watches in St. Louis or Dallas, and they don’t continue to issue them if the warning area should have acclimated to a particular temperature by that point in the season. Like, the 3rd day below freezing in a row, the 3rd stretch of 90s in a season, whatever.

So anyways, what I’m trying to say is that these heat indices reflect the fact that Minneapolis is just not used to the 90s, and these warm temperatures this week will be a bizarre aberration –

Whoa, wait. Nope! Temperatures in the Upper Midwest will be very close to normal for this time of year. It will even be a bit cooler than normal just east of town. Admittedly, this is the 6-10 day graphic, and will be valid after the temperatures spike on Monday, but if temperatures cool off this dramatically, and we are getting our first advisory in late July, well, it’s been a cool summer in Minneapolis.