Weather conditions for St. Jude Marathon

Weather conditions for St. Jude Marathon
(Source: WMC Action News 5)
(Source: WMC Action News 5)

MEMPHIS, TN (WMC) - It's almost time for Memphis premier marathon event, the St. Jude Marathon. A big factor in running a race is the weather.

The forecast is fairly typical for this time of year. Temperatures will be in the low to mid-40s with a mainly clear sky and light northeast wind.


10K Race 7:30 a.m.: Clear and cold. 40° Southeast wind 5 mph. 
Full/Half Marathon 8 a.m.: Sunny but chilly. 44° Southeast wind 5 mph.
Kid's Marathon 1:30 p.m.: Sunny and pleasant. 61° South wind 5-10 mph.

But is that good or bad weather for runners? And what is the ideal temperature to run a race?

Simply asking about air temperature is not the right question. Rather, a runner should ask what the ideal "wet bulb temperature" is for a race. The "wet bulb temperature" measures how much water vapor the atmosphere can hold at current weather conditions.

If the air is dry and can hold more water vapor, the wet bulb temperature is low – which makes it easy for sweat to evaporate. If the air is humid and unable to hold more water vapor, the wet bulb temperature is high – which makes it difficult for sweat to evaporate.

Wet bulb temperature is calculated by using the current humidity, air temperature, and pressure of your surroundings.

Ideal racing conditions occur when the "wet bulb temperature" is 46° Fahrenheit or less. At sea level with 50 percent humidity, the ideal air temperature would be no more than 55° Fahrenheit to have the wet bulb temperature be less than the "ideal" temperature of 46° Fahrenheit. At sea level with 90 percent humidity, the ideal air temperature would be no more than 48° Fahrenheit.

SATURDAY MORNING RUNNING CONDITIONS: EXCELLENT! Our forecast calls for low to mid-40s when the races start from 7-8 a.m. Saturday. We will have dry air in place with dewpoints in the 30s which means the humidity will likely be between 50-60 percent in the morning and go down by afternoon. Pressure will be average at about 29.9 inches or mercury. This means the Wet Bulb temperature will range from 37-39°, which is below the ideal of 46°. Once the temperature rises above 55 around 10 -11 a.m., conditions will not be as good as you will sweat more and get tired faster. The good news for this year…no rain or gusty wind!

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