It was a cold call. On the third floor of a 1950s-style school building in Union, NJ, a lab technician in Kean University’s meteorology department answered the phone call of a physician from New York.

The lab tech carefully took down the medical doctor’s information and professional request.

The call came from Dr. Stuart Weiss, the NYC marathon’s new chief physician. He needed a weather forecast for race day at multiple locations along the race’s route, so he could more accurately position medical teams where they would be needed most.

You see, the year before Dr. Weiss was hired, two of the nearly 38k finishers suffered cardiac arrests. Those two runners didn’t survive. I would later find out how the minute details of a weather forecast can quite actually be a matter of life and death. 

I was driving home on the lower level of the GWB when I got the call. It was Will, a university lab tech, who thought that my experience would be best suited to give this unique type of weather forecast for the race.

At the time, I was forecasting for the five boroughs and had a unique understanding of New York City’s many microclimates. Will passed along Dr. Weiss’ info and I returned the call later that day. 

During the call, Dr. Weiss explained his goal of zero deaths (no pressure!) and that positioning his medical teams would be based on my forecast more than 10 days in advance of the race.

Remember, back in 2008, weather forecasting skill (the level of accuracy) beyond five days wasn’t incredibly high. Most local TV stations only provided a 5-day forecast. Some outlets were bold enough to offer a 7-day forecast.

A 10-day forecast only existed on some websites, and even those were mostly a guess beyond day 7. He wanted the weather MORE than 10 days out? Impossible!

This forecast that I was tasked to create more than a week in advance would be distributed to the hundreds of race managers, planners, volunteers, and staff. My forecast would be actionable: meaning that logistics would change, based on the future state of the atmosphere.

This gave a new definition to high pressure.

When Dr. Weiss and I met in person in his midtown office, he pointed out a map of Central Park, between Sheep Meadow and Strawberry Fields.  That was the part of the race known as the “walk off”.

If you’ve ever run the NYC marathon, you know that after crossing the finish line, there are race medals, photo walls for official pictures, and goodie bags lined up, along with a vast team of medics ready to help the injured.

This route stretches on for a half mile before reaching the family reunion area. After I was brought onto the marathon team for weather support, I suggested to add a weather station right next to the runners.

The weather variable that Dr. Weiss needed at the “walk off” was a very particular one: the wet bulb globe temperature (WBGT) in order to prevent mass casualties.

I never knew that a few degrees difference of a not-often-measured weather variable could predict either a safe and healthy outcome for the runners or predict a surge of casualties overwhelming the medical teams, possibly resulting in death.

In meteorology, wet bulb is the measure of evaporation rate of moisture into the air. The term is coined as a result of a thermometer’s round bulb (the part containing the liquid) remaining wet, allowing a colder measurement on the thermometer.

The difference between wet bulb and dry bulb (an ordinary thermometer) gives us dew point and humidity measurements. An example of wet bulb in action is when you exit a pool on a dry, breezy day.

Your skin feels very cold due to the pool water evaporating into the surrounding dry air very quickly. The same effect happens to sweaty runners in cold, dry air.

The “globe” part of wet bulb has additional implications. Primarily used in the military as a measure of heat stress, strenuous activity in direct sun can cause a body to overheat, even when the ambient temperature and humidity is comfortable.

A copper sphere, painted black and resembling a globe, is placed in the direct sun to measure the solar irradiance. The strong influence of solar radiation, which is not accounted for in ordinary temperature measurements, can similarly cause runners to overheat.

It still surprises me when I explain to people that ordinary temperatures (either reported in a weather forecast, or delivered to your digital device) are measured in the shade.

While early November in New York isn’t known for its hot and humid days, the dry and cold air can cause those marathoners to cool down too quickly. This is where the wet bulb globe is particularly important.

There is a safe zone, when the WBGT is between 45-55 degrees where runners are at their peak. Wind also is calculated in the WBGT formula. Too hot means runners can overheat. Too cold means runners can cramp up.

When hundreds of finishers cramp up at the same time at the “walk off”, the result is not good for the medical staff.

The “walk off” was just one location of many where the marathon staff needed accurate forecast details. Wind gusts at specific locations along the course were another variable that has significant implications.

Beyond a strong headwind that could tire the marathoners at “the wall” along the Upper East Side, wind gusts could be high enough to make official race signage become dangerous. The race course is lined with miles of temporary structures and informational signage.

Gusts of wind greater than 20 mph (which isn’t very much in a city full of skyscrapers) can turn innocent plastic signs into dangerous projectiles and create course hazards on the ground.

What I’ve discussed insofar is the long range forecast aspect that is actionable seven days before the race. We all know that forecasts change, sometimes quickly.

The short range forecasts (within two days) can make or break the original plan as weather patterns change and storms, like hurricanes (looking at you, Sandy), create new long lasting hazards days after the storm. 

Even a small shower, just a day before the race, can create puddles in the mud and grass of Sheep Meadow, where the medical tents and operations center are located.

On race day, you’ll see a broadcast marathon weather forecast that’s generalized from model data or weather stations meant to support climate sites or general aviation.

The marathon operations tent needs wind gusts at specific elevations and wet bulb globe temperature readings along the course. This data could affect the course pace by changing it from a green course to a yellow (caution) course, which is communicated to the runners via flags.

Weather stations positioned across the city, and proprietary weather data procured through NYC’s Emergency Management teams, helpkeep the runners safe.

Race day inside the operations tent has changed dramatically over my 12 year tenure as NYC Marathon Chief Meteorologist. It started with a single laptop and two way radio under a tent with no walls.

Now, with over a dozen screens at my disposal, housed with many city agencies under a semi-permanent structure, weather information flows in from every nook and cranny of the city.

This weather info is relayed in real-time to all the medical tents and staff around the course. Decisions are made on how to pace the course, how to keep the runners safe, and where to designate extra support staff, such as medical personnel, all based on a real-time weather forecast.

The NYC Marathon is a high-energy day for the spectators and runners along the course. It’s a high pressure day for this meteorologist.

While cardiac arrests are a statistical certainty every year for a race with 52,000 runners (and they do occur at most marathons annually), no deaths have been reported since 2008.