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Things got interesting over parts of the area late Wednesday night and Thursday morning as an intense thunderstorm complex that formed in Minnesota and Wisconsin brought much needed rain to parts of the region. This was not predicted by the high-res models but it was something I was concerned about. Storms as strong as Wednesday night's develop their own cold pool as rain cooled air is drawn to the surface through the downdrafts. As it reaches the ground it's forced out ahead of the complex. From here the cool pool encounters the unstable air to the south where the storms ingest the fuel and regenerate and sustain themselves. This process can go on for hours as the storm complex builds southeast in the NW flow aloft. It's a classic summertime set-up on the ring of fire. In last night's case the models saw the potential and SPC even issued a moderate risk for severe weather to our northeast.

They even put out a PDS thunderstorm watch. The PDS standing for particularly dangerous situation. Geographically the models were on target with the severe weather threat and the situation was well forecast.

Just look at all the severe weather reports form the event.

However, in my area it was supposed to be a quiet night. The hi-res convective allowing models below showed this for precipitation Wednesday night. Essentially no storms and thus nothing was indicated in my area.


The NAM 3K

Yet, by midnight (less than 3 hours after the rain forecasts you see above came down), storms were already approaching my northern counties. Here's what actually happened through 9:00 AM Thursday in terms of rain. 2.5 inches in 3 hours was measured in Camanche near Clinton.

So why the bust in the models. My feeling is that they did not foresee the strength of the storms up north which grew rapidly in intensity allowing a more substantial cool pool to develop. The process happens so fast and is so complex we just don't have the capability to model it. That is why I always talk about mesoscale impacts, especially when it involves thunderstorms. Just because a model says no rain doesn't mean a cool pool or outflow boundary can't pop up. They do and they can really create havoc with a forecast.

I could see trouble last night and in my post which I completed about 1:00 AM. I anticipated a model bust and wrote this paragraph to that effect: prospects Thursday night are mainly over the northeast half as a cold pool from intense storms in Wisconsin backs into that area. By daybreak Thursday some robust storms may occur in that area. As I write this most of the hi-res guidance keeps the activity just out of my region, more in SW Wisconsin and NC Illinois. I seriously doubt that and think the storms and convective debris will make it further into my area by daybreak Thursday. I have no idea how far the penetration will be but I could certainly see some gusty winds and downpours, especially north of a line from Manchester to about the Quad Cities (Clinton more likely) and Princeton, Illinois by Thursday morning.

That was a pretty good call and you didn't have to be a meteorologist to make it. By observing the intensity of the radar returns, the size of the storm complex, and its movement, and observing the mesoscale environment, many of you could make that call. The biggest hindrance for many professionals is that they see the model says no and they are afraid to buck it and take a stand. I'm way past that stage. Anything I can use to get an edge I will. There is nothing more satisfying to me than beating the models or picking the right trend when there is model diversity, that's what makes forecasting fun. I'm not always right but I so enjoy challenge.

The next order of business are rain chances Saturday. A convective complex is expected to form along a stationary front aligned NW to SE over northern Missouri. Showers and storms over western Iowa Friday night will track southeast towards my area Saturday. At this point, there is pretty good agreement that the SW 1/3 of my area stands to see some rain. My NW counties which really need it appear to be on the outside looking in once again. Saturday will be a much better day there.

Some models are also indicating a chance of some additional showers and storms is spots Saturday night as another cool front digs in from the north. The GFS is most bullish on that particular scenario. I'll be able to firm that up later Friday.

Meantime here are several rain forecasts for the Saturday event. Since we are still 36 hours out some adjustments are still possible. Personally, I like the placement of the GFS which is further SW on the heavy rain band than the other models. That would mean far less rain in my SW counties.


The 3K NAM

The 12k NAM


With the rain threat gone by Sunday, we then enter into a period of very pleasant mid summer temperatures. Highs much of the next 10 days are expected to remain in the upper 70s to mid 80s. The EURO ensemble shows this for readings through August 13th. We can say bye-bye to the muggies for quite awhile.

One last thing to mention. Air quality is expected to be poor Friday as a fairly thick layer of smoke from western forest fires drifts across the region. You can see the milky tinge of the smoke plume on the hi-res satellite from Thursday evening.

An air quality advisory is in effect for my counties in Iowa where conditions are expected to be the worst.

That's all for this edition. Happy Friday one and all. Roll weather...TS


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