Your comprehensive race day forecasting
You know, I JUST ran the Twin Cities Marathon, and this weather forecast is causing me to reconsider taking a break. The weather is just too perfect in Grand Rapids, and fairly close in Detroit. So here's what's happening. Detroit is going to be 33 degrees at the start. It wouldn't be a bad idea to wear tights if you have sore knees or ankles in cold weather, but after mile 2 you should be able to heat up. Temps will warm to just below 39 degrees 3 hours later, and the lower 40s closer to 5 hours in. If you're going for sub 3, this is your day. While the lower 40s are ideal, you'll have full sunshine. The only minor problem will be the wind, which will affect you on the bridge (cross) and portions of Belle Isle. Otherwise you will have a tail on most of the course. Check back on Saturday night for mile-by-mile weather.
In Grand Rapids, the weather will be mostly the same, but maybe warmer by a degree or two at the start and finish, so 35 at the start, and 43 at the finish line for those running at 3 hours. Later times will warm by a degree. You'll have light west winds at around 3 to 5 mph, so that will not be a factor until the last 3 miles, and only as a cross wind. In other words, if you're in excellent shape, this has an excellent chance of being a PR race. More to come on Saturday! First and foremost, congratulations to all runners who happened to run Twin Cities and Chicago. Chicago had more rain than I expected but overall, both races had excellent running conditions. Okay, onto the two biggest Michigan fall marathons, Detroit and Chicago!
Let's look at Detroit first. The course itself is set up in a strange fashion, not north/south/east/west, and that's because of Detroit position on the Detroit river, placing the course in a mostly ENE to WSW position, out and back. Wind and temperature won't make much of a difference from miles 7 to 8 under the tunnel, but when there's wind, it will affect you most of all on the bridge and on Belle Isle, miles 19 to 23, approximately. https://www.freepmarathon.com/wp-content/uploads/2016/07/MarathonMap-Final-9-27-18.pdf So setting up for race day, forecast models are predicting winds out of the NW from 5 to 10mph. This will affect you most of all from 22 to 23, so once you turn left from 23, you're going to be mostly in the clear with the exception of a cross wind. In fact, there will be cross winds throughout most of the race. Some will push you along, like when you're in Canada, and some will be slightly a headwind, such as the final 23 to 26.2. Temperature look ideal in the mid to upper 40s, with partly cloud skies. Now only Grand Rapids. The strength, and maybe weakness of this race is that there's never a lot of wind. That's because for most of the miles, you're running in the trees. Grand Rapids is mostly a northeast to southeast to northeast course (http://grandrapidsmarathon.com/wp-content/uploads/2016/10/Course-Map.png) so on a colder day, you will find some headwinds in the final 3 miles when you're out in the middle of a meadow and heading into the city. While that's not great for post-wall running, the good news is that a north wind will help keep temperatures low. I'm looking at the lower to middle 40s with NNW winds at 5 to 10 mph. I might actually run this race, so say hi to your favorite weather man if you see me on the course! Look here for any updates to the forecast - if things don't change, this is your final forecast! I can't remember a Chicago marathon that was under 60 degrees, and this one will be no exception. Right now the forecast models are showing mid 60s for most of the race, high humidity and scattered showers and thunderstorms. If you haven't started acclimating, now is the time. And by acclimating, I mean making yourself sweat. Run with extra clothes, a jacket, tights, hang out in warm clothes all day, spend time in a sauna - anything to initiate the sweat response (but please drink adequate fluids). Here's why. 60 degrees in Chicago, with full sun and humidity could feel like it is in the 70s, even with an occasional northeast wind . There's a cold front near Chicago right now, but it's stalling for the weekend.
So here is my race day forecast for runners between 2:30 and 4 hours. With the exception of the wind, if you're running between 4 and 7 hours, expect it to max out at around 65 degrees with NE winds at 10 MPH max, everything else below should be accurate. Miles 0-7.5 - Mostly cloudy with scattered showers, some potential rain on the course. Winds will be from the northeast off the lake, but it will still be humid and mild. I'd wear as little as possible, and maybe a hat if you have glasses. 61 degrees. Miles 7.5 - 12.75 - You'll have either no wind here (from the buildings) or a slight tailwind. Mostly shady here, but still humid. 63 degrees. Still some showers at this point, but not anything major. Miles 12.75 - 15 - The course heads west here, and it's more open, so you may feel a bit of a tailwind. Don't blow it though. 65 degrees here. Miles 15-23 - A few twists and turns here. You'll have a slight tail from 15 to 19, and a slight headwind from 19 to 21. To 23 you should have a bit of a tailwind and a cross. It's wide open out here and close to the highway. 65, but will feel like 75 degrees with the road and humidity. Miles 23-26.2 - This is mostly a straight shot north, with little cover from the wind, so find someone to work with and block it out if you can. 65, but will feel like 70 with some help from Lake Michigan. I'll post another forecast on Saturday night if this should change - otherwise, this is your final sendoff. Good luck runners! |
Chris Rozoff and Jesse Sweeney, content contributors.Chris is the expert meteorologist and MVP. Jesse is someone who watched the weather channel a lot as a child and breaks it down for the masses. Chris runs ultras. Jesse runs road and ultras. Archives
April 2019
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