Over the past 6 weeks I have been poring over data from a multitude of trusted sources, and have come to a conclusion as to what I think we will be seeing as far as weather is concerned for this coming winter. As many of you know, the National Weather Service issued its outlook on the 16th of this month.
What does this translate to for those of us in Iowa? It means that the climate models (which differ from the short range models we normally refer to such as the GFS, European, and NAM models) are showing an equal amount of variances in temperature anomalies (both warm and cold), which translates to an average winter temperatures.
The second photo shows that the climate models are indicating a variance of less than average precipitation (about 2/3 of what is considered normal). This includes rain and snowfall. This is what they see.
I agree with the temperature outlook, for the most part. I think that the temperatures that we saw for extended periods of time last winter will not make a return this year. I believe that we will see a few stretches of cooler than average, but not the bitter -20° low high temps that set records last year.
The Climate Prediction Center has been calling for an better than average chance for weak El Nino conditions to develop in the early winter, which if it does develop, would explain their precipitation and temperature outlooks. I have looked over some of the different variances and anomalies that go in to their forecasts, and have one minor issue that could be a potential issue for us.
At the heart of this issue is potential precipitation placement. In a typical weak El Nino, the southern tier of the jet stream stays right around the southern plains (also called a Zonal Flow), and has very little vertical movement (also called troughs). This would result in the ability of the storms that do move through to not be able to pull as much moisture from the Gulf of Mexico, which would result in less than normal snowfall and rainfall, as nearly all moisture that we get would be coming from the Gulf of Alaska or the Northern Pacific.
The one variance that I see causing us an issue with this. The placement of the extended pacific Jet Stream has not been as flat, or zonal as it normally would be leading up to an El Nino, resulting in a much longer, and angular, monsoonal flow than normal in Arizona and the southwest during this summer, and a persistent series of tropical storms following along the southern jet. There have been a few hints from model anomaly equations that this could persist through the winter. If this does end up coming to fruition, instead of the precipitation forecast that was released on the 16th by the CPS, we could instead be looking at a normal, to slightly above normal amount of precipitation this winter as storms would be allowed to pull moisture from the Gulf of Mexico. This could also lead to more mixed precipitation, or hybrid type storms, as the temperature gradient would be stronger (temperatures in the 40’s and 50’s ahead of storms, 20°-30° behind, within a 100 mile area).
My overall opinion is that we will have a winter that is either at, or around 5 degrees (on average) below average, and that we will see about 10%-15% more precipitation, mostly in the form of snow, over all of Iowa.
Once again, this is just an outlook, which looks at probabilities of certain types of events, and the general overall view of the atmosphere during a 3 month span. There are many different types of meteorological anomalies that could happen that the models just can’t predict.