You are correct. In terms of racing performance for the large majority of runners, the weather can be ideal racing conditions or bad racing conditions. Below is a chart of all the T+Ds (Temperature + Dew Point, like a 80F temp and 50F dew point would be T+D=130) from 6:50am to 11:30am for the Orlando area from Jan 6th to Jan 12th. The 2023 race dates are Jan 5th - 8th.
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I categorized the different weather conditions by how much it would impact the large majority of runner's performances. Based on these different categorizations, you have almost an equal chance of ideal (23%), good (19%), ok (19%), not great (21%), and bad (19%) conditions during the Marathon Weekend races. This year's edition is earlier in January though, and you can see over the last eleven years that the slightly earlier days in January have a higher probability of good days than do the later Jan dates. Despite only being separated by six days.
Just to get a general idea as far as effect on performance, this is the chart I use (this is for a 2:30 HM runner):
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Under different conditions this runner could do:
Ideal - 2:29:54
Good - 2:31:24
OK - 2:32:54
Not Great - 2:34:24
Bad - 2:38:11 (used T+D 152 since that's the highest T+D in Orlando during those dates at 11:30am, but we've seen slightly higher towards the tail end of the marathon)
So an 8-minute swing for someone who is presumed to be heat acclimated. Someone who is less heat acclimated is probably going to see an even slower performance under those conditions.
The crazy part about MW weather is that year to year is hard to predict, but also within a year it's all over the place too. Look at 2015. It was not great, then ideal, ideal, and bad in a span of six days. So you really don't know what you're going to get when it comes to MW. Be prepared for everything, and for it to change quickly. So in preparation for an outfit make it useable at freezing cold and boiling hot (so something that is flexible).