Welcome, this is the first forecast discussion of the 2017 whitetail deer season. A few states including Wisconsin open their archery season this coming weekend (Sept. 16) so we will discuss the current weather pattern and forecast trends for the coming weekend. This post will give a brief introduction to some of the basics of forecasting, so it will be one of the longer posts you’ll likely see on here.
Unfortunately it looks like it’s going to be a rather warm opening to archery season here in the Midwest. I am sure most of you have been at least passively following along with coverage of hurricane Irma. Hurricane’s have an interesting effect on the overall weather pattern. Hurricane’s are energy powerhouses and when they eventually die off (as Irma is in the process of doing) that energy has to go somewhere. Oftentimes this results in strengthening of the jet stream. We will see this happen with Irma in the coming days, which will result in the midwest and much of the plains seeing very warm temperatures.
Summer weather is usually quiet in most areas for the majority of the season. This is often caused by high pressure. This is more common in the summer because high pressure center’s are generally associated with warmer air, and temperature difference between the equator and Canada is much less than in the winter. Because temperatures are less variable in the summer, there are less high and low pressure systems. High pressure is the result of sinking air in the atmosphere, which doesn’t allow for clouds to develop upward easily or fronts to form. Think of high pressure systems as a cap on the atmosphere. If you think about those sunny, high pressure days on stand that we so often dream about, do you remember seeing an abundance of clouds? Probably not. The high pressure is keeping them at bay. This may sound confusing if you’ve noticed that you often get higher pressure after the passing of a cold front. This is different than an actual high pressure system. The high pressure behind a cold front is due to the cold air behind the front sinking and creating the higher pressure at the surface.
So why does all of this matter? Well first of all I believe that if you have a better understanding of the weather in general you will be able to start to diagnose these things for yourself. The more you learn, the better you will understand your own diagnosis of the current weather, which will ultimately make you a better deer hunter. With that in mind, let’s get into it.
(Image courtesy of Satsquatch.com via GOES-16 Satellite True Color Visible band)
Here’s a view of Hurricane Irma as of 4pm Monday (9/11). The center of the storm is located somewhere over central Georgia. If we look at this same situation on a weather map we can diagnose how it will impact the weekend’s forecast.
The following image is taken from the College of DuPage Numerical Model Analysis website (visit that page here). This is one of a few sites where you can find weather model information. On each of those sites you will find a boat load of different weather models to view. Some are used for long range forecasting while others have very specific applications such as hurricanes or severe thunderstorms. The Global Forecast System (GFS) model is being shown here. It is not by any means the best model out there. Meteorologists love to argue over which one is best. That is not important here because we’re just looking at the big picture and not nitty gritty details.
This is a map of the surface weather conditions. The black lines are lines of constant pressure (isobars) measured in hectopascals or millibars (whichever you prefer; I prefer millibars). Sea-level pressure is 1013 millibars. The colors represent the temperature in Fahrenheit and the black barbs are wind speed and direction. People are often confused by wind barbs, but I have a great analogy for us bowhunters. If you look at the barbs they look sort of like arrows with fletching on one side. The wind is moving the same direction that the arrow is traveling. So at Dallas, TX on this map, the wind is blowing out of the northeast. Below is a graphic to help illustrate this along with a chart of reading wind speed based on the barbs:
Now, if we go back to the previous image, notice the tight grouping of isobars in Georgia. This is the strong low pressure associated with Hurricane Irma, and if we look out to the southeast we can also see the now much stronger Hurricane Jose with a tighter grouping of isobars. If we move this model forward in time two days to a nearly extinct Hurricane Irma:
The area of cooler temperatures over the Tennessee valley and lower Great Lakes is all that’s left of Irma by this time. But notice the very high temperatures across the Great Plains. All of the energy that was held in Hurricane Irma has now been released into the jet stream creating an environment suitable for warmer temperatures in this region. It is a bit complex for why this actually takes place, and it is different for every case. This week it has a lot to do with the Rocky Mountains and how the jet stream has been changed over the top of them. I will not dive into the specifics of this here because it’s about three years worth of a bachelor’s in meteorology to fully understand it. If you want to know more, send me an email and we can discuss it further.
So in general this week is going to be warm over most of the US and in some places downright hot. And this trend is pretty much going to continue into the weekend. Since we are not expecting anything major to happen between now and then, let’s look at Saturday (Sept. 16):
This map shows conditions at 12z (UTC) or 7am on Saturday. We can see that it’s already 78 degrees in parts of Kansas and already in the low 60s in much of the Great Lakes region. Not what you imagine for the best deer hunting, but that’s part of the early season. Winds are out of the south or southeast for most of the midwest and out of the north to northwest in northern plains. As you can imagine, it only gets warmer throughout the day:
This map shows conditions at 21z (UTC) or 4pm on Saturday with most of the eastern half of the country nice and heated up. If we look at the Dakotas region into Montana we can see an area of cooler temperatures with winds coming out of the northwest. This is a fairly strong cold front with around a 20 degree drop in temperature. Unfortunately for me and others in the Great Lakes area, if we jump forward again it doesn’t appear to stay very strong by the time it enters the midwest:
We can still see somewhat of a boundary between warmer and cooler air stretching from Wisconsin to the Oklahoma panhandle, but the front has pretty much stalled by this point and wont bring any drastic changes by the time it pushes through. Not much can be said beyond this point. Any good meteorologist will tell you that a forecast for specific details beyond a few days is nearly a crapshoot. But you can get a ballpark idea of basic information like temperature and overall pattern out to around 120 hours, maybe a bit further. I would even say this last map is a bit of a stretch for reliable information. So keep that in mind next time you see a 10-day forecast on the news. You can get a marginal idea but if they’re giving you specifics about storms or fronts at that range, they’re feeding you bologna.
The long range models show conditions remaining fairly warm for at least the next 7 days. It may be some time before we get a magical cold front to make it really feel like fall. If I go out this weekend, I’ll probably find some water to sit over. Hopefully I’m not carried off by mosquitos.