Hooray! We’re now within 10 days of the marathon so we can at least start to begin to look at global model forecast outputs and not laugh outright. Right now the main difficulty for the marathon forecast is timing the arrival and strength of a cold front before race day.
Here’s how each of the global models handle the front, along with conditions at 7 a.m. Sunday morning:
Canadian forecast model: Front arrives late on Friday, Jan. 15th. By Sunday morning it is cold, with temperatures in the low- to mid-30s. No rain. Sunny with moderate winds.
European forecast model: Front arrives on Saturday, Jan 16th. By Sunday morning temperatures are in the mid- to upper-30s. No rain. Sunny with moderate winds.
GFS forecast model: The front is much less pronounced. By Sunday morning temperatures are in the upper 40s. Sunny with moderate winds.
Looking at the ensembles for the European model, about 80 percent of the members show colder-than-normal temperatures for the morning of the marathon. Just 1 out of the 50 model runs show temperatures 6 Fahrenheit degrees, or more, warmer than normal. This can give us pretty good confidence in at least seasonable, if not cooler than normal, weather for the marathon.
With 10 days to go the precise timing of the front remains a real challenge. For example, if it is slower then conditions on the morning of the race could be warmer (worst case scenario is probably about 55 degrees). A frontal passage during the race would also bring rain. But right now that seems less likely than an earlier passage.
