I’m not a big fan of giving significant weather events flashy names like “Snowmagedden,” “Frankenstorm,” “Storm of the Century,” etc. But I will jump on the bandwagon and go with “Godzilla El Niño” that the media is currently calling the El Niño that is unfolding as we speak. If you can’t beat them, join them! Plus, it’s kind of catchy. This El Niño will be stronger than many previous El Niño events, including the last strong event in 97/98. Perhaps even “Godzilla-like.”
For those who don’t know what El Niño is, here’s the quick high level definition. El Niño is the warming of ocean surface temperatures off the cost of South America. The greater the warming, the stronger the El Niño will be. This year SST (sea surface temperatures) will be 2 to 3 degrees C above average. That will equate to a strong El Niño peaking late this year in intensity and slowly getting weaker as we head into the spring of 2016.
El Niño impacts the path the polar and sub-tropical jets streams take. In many cases, the southerly jet is active with multiple storm systems that will impact the Southern US this fall and winter. For us here in the Midwest, the impacts are not as easy to pick out because you have to take other considerations into account, such as the SST of the North Pacific, the Pacific Coast, and the North Atlantic, among others. All of these other ocean temperature anomalies will play a role in directing the jet stream.
Here’s what the jet on average looks like in a strong El Nino year:
So what will the Iowa impacts of this strong El Niño be? Will we be warm as the graphic above suggests? I’ll break that down starting with this fall and continue into the coming winter.
Fall 2015
First let’s take a look at what the CFSv2 (Climate Forecasting System) forecast model is calling for in regards to sea surface temperatures as we head into this fall and winter. Here’s the CFSv2 graphic I pulled on August 20th, forecasting SST’s for the month of December:
You can easily see the big slug of warm water off the coast of South America extending out into the Central Pacific. That’s our El Niño. Now notice that we also have above normal SST’s along the west coast of North America. This warm water off the North American coast is expected to continue through this fall and into the winter. What does this mean? Typically when you have a large pool of warm water like this off the west coast it usually means that high pressure will dominate the weather in this area. High pressure will push the polar jet further to the north allowing for warmer than normal temperatures to take place in the west and potentially keep California dryer than it would be in a typical strong El Niño. Now, I do expect Southern California to see storms from the southern branch of the jet stream, but the El Niño will be fighting the warm water off the coast all of this fall and winter. Southern California will see some beneficial rains but Northern California may remain dryer than it normally would in an El Niño Year. We shall see.
When you get high pressure on the west coast and the polar jet climbs into Canada, that jet stream will head back to the south at some point allowing for cold air to spill into the US. In a normal El Nino year, that takes place in New England, but my thoughts are this year that the jet stream will re-enter the US somewhere in the Midwest. Perhaps near Iowa, so that could lead to some interesting results for this coming fall and winter, especially in the temperature department.
Let’s start with this fall first. The Climate Prediction Center (CPC) issued their updated seasonal outlook on August 20th. Here’s what the CPC is calling for the months of September, October, and November:
You can see below normal temperatures are forecast across the Southern Plains, almost into Iowa, with above normal precipitation in the southwestern states extending into Iowa. We’re already seeing this pattern take hold here in August to some extent. Now for a comparison, let’s take a look at the fall of 1957. That year had a rather strong El Niño with a batch of warm water off the west coast. Just like this year. Here’s what the temperatures and precipitation looked like for September to November that year:
The colder than normal temperatures where more widespread across the southwestern half of the US that year. I think this year we’ll see a split between the current CPC prediction and what happened in 1957. As for precipitation, the southeastern US was wet in 1957, and that was for the most part expected. The southwest was near normal and the dry locations in 57 were in parts of New England as well as portions of Oregon and Washington. I think the CPC’s precipitation forecast for this fall will be fairly accurate since we’re already seeing some of this take place.
Early Winter
The Climate Prediction Center is calling for normal to possibly above normal temperatures in Northern Iowa for the beginning of winter with equal chances for above-or-below normal precipitation in Iowa. Let’s take a look at the start of the 57/58 winter to see what it had and if it can be a predictor of the winter to come this year.
November of 1957 into January of 1958 looks very similar to the current CPC predictions for temperature. Precipitation was less in the southwestern US in 57/58. Notice the east coast with above normal precipitation in the first part of the winter of 57/58. That’s our jet stream dipping down across the east bringing multiple storm systems up the east coast. I think we will see that again this coming winter.
Now let’s look ahead to the latter part of winter, January into March. Here’s what the CPC is thinking:
Now let’s look at January to March of 1958 for comparison:
Notice in January to March 1958 the cold weather covered a large portion of the southeastern US into Iowa, and beyond – much more than what the CPC is currently forecasting for this coming winter. This is because with high pressure on the west coast, the trough of low pressure will build further west than what is currently predicted, again thanks to the slug of warm water off the west coast. The precipitation forecast is not too far off from 1958. Iowa I believe will be on the border of normal and dryer than normal precipitation late this coming winter.
So what’s the bottom line for Iowa this fall and winter? I believe we will see a cooler than normal fall across Iowa with slightly above normal precipitation. As we head into the first part of winter, we’ll see warmer than normal temperature with normal precipitation. This always concerns me a little because when it’s above normal in the temperature department in the winter we seem to have better chances for ice storms. We’ll have to wait and see. As we get into the latter part of winter in Iowa, it will likely turn cold with normal to slightly below normal precipitation.
Of course this is August and the fall and winter forecast will change. El Niño will change and the warm pool of water along the Pacific cost will change some, so I’ll be watching how things play out and update the forecast accordingly. Needless to say, however, Godzilla will not plow over Iowa with anything super unusual. Nothing we haven’t seen before and will see again.
As always, get out and enjoy the weather because it’s the only weather we got.