Space City Weather long-range forecast for the Houston Marathon

Apologies if you could not care less about the marathon, which will take place on Sunday, Jan. 20, in downtown Houston and nearby roadways. However, for the tens of thousands of people who have trained over the last four months (yours truly, included) the weather for that morning is of profound importance. Anything too warm—for me that’s above 55 degrees—and it’s going to be a long, long day. After today’s post, I’ll append a short marathon outlook at the bottom of the daily updates.

Before jumping into the forecast, let me set some expectations. Until about 10 days before the race, we can’t have much confidence in the forecast. We can set some constraints, but not much more than that. From 7 to 10 days we can glean some better insight from the ensemble models, and then about a week out we can begin to have some confidence in the overall forecast. Alright, enough caveats!

For this week, we’re going to see a front later on Tuesday, and then another one in the Friday-Saturday timeframe (that one may yield 0.5 to 1.0 inch of rain). After this front, the first half of next week (Jan. 13 to 15) looks fairly cool, with highs in the 50s perhaps. Monday or Tuesday of next week would be ideal to run the marathon on. After this, it looks like we’ll see a warm-up by the middle of next week, with highs in the 70s perhaps.

The key question, of course, is whether another front makes it through between next Wednesday and next Saturday. (Absent a front, weather for the marathon could be really ugly in terms of heat and humidity). At this point there is no clear signal, and frankly there are conflicting messages coming from the global models. (All model forecasts are from 12z Monday, and came out at noon or shortly thereafter).

First up is a product of the North American Ensemble Forecast System, which is produced by the U.S. and Canadian government weather services. This provides a probability distribution for the forecast:

This is a pretty good forecast for runners, as the most probable range of low temperatures on Sunday, January 20th at sunrise, when the marathon begins, is in the 30s. Highs would be in the mid- to upper 60s. My guess is that this will end up being too cold (in terms of lows).

Next up is the U.S. Global Forecast System model’s ensemble forecast. Again, we’re looking at a range for high and low temperatures on January 20.

This is a rather busy chart, but in summary it shows a range of low temperatures on Jan. 20 from the mid-30s to the low-50s, with daytime highs ranging from 45 to 65 degrees. This feels a little more realistic to me, because as of right now I’m not seeing too much in the overall pattern to bring the kind of Arctic air that could drive overnight lows into the 30s.

Finally, there’s the output from the European model. The “operational” run of this model shows a low temperature on the 20th of 45 degrees, with a high of 60 degrees. But what concerns me is that, in looking at a number of the ensembles, there is a fair amount of support for “warmer than normal” temperatures on Sunday, January 20, during the morning hours. This is a warning to me that the forecast for the Houston Marathon is very far from locked down, with the biggest question being whether we get a cold front during the second half of next week. We probably will, but who knows?