Not long after southerly winds moved smoke from the destroyed World Trade Center Towers, two young highly specialized Air Force meteorologists were directed to plan a mission to collect atmospheric data in support of the first U.S. raid into Afghanistan.

In October 2001, the duo began their reconnaissance from a secret vantage point in the remote mountains of South Asia. They collected the data and dispatched a transmission via secure text to the task force commander.

In response, the commanding general launched the first operation of the war, and leveraged the first of what would become tens of thousands of weather forecasts in support of operations to topple the Taliban, rout al-Qaida, kill Osama bin Laden, cultivate an Afghan national security force, establish and protect an infant democracy and repel the Islamic State. In recent weeks, forecasts also supported the withdrawal from Afghanistan, including of all forces and diplomats, and ultimately the last U.S. soldier.

When weather insights were properly integrated from the onset, missions could be executed with tremendous precision. But not every mission could wait for the perfect conditions. Countless missions were launched based on real-time intelligence with only very brief windows of opportunity.

The commanders relied on weather forecasters to provide the best-available information on the skies and the seas, taking into account all air and ground components, originations, routes and return times. The goal? To provide the greatest possible advantage over the enemy.

Each day provided its own set of forecast challenges. Early on, the absence of real-time weather observations and credible computer models made prediction difficult.

Enterprising young officers dispatched remote weather sensors from low-flying helicopters, transmitting their observations via satellite communication. But sustaining the stream of observations was hard. There could never be enough sensors to get a perfect picture of weather changes from valley to valley.

Forecast uncertainty in Afghanistan was primarily tied to its complicated terrain. The Hindu Kush mountain range fans out from the northeast of the country, ridges and valleys running in multiple directions. The fault lines running east-west created a ridgeline the often locks in stratus clouds and fog sweeping down from Central Asia. South of the ridgeline, the city of Herat would be sunny and hot. North of the ridge, the city of Bala Murghab would be gray and chilly with little visibility for aircraft takeoffs and landings.

Mountains would capture cloud moisture from passing storm systems; mornings would look crystal clear, and by noon the sun-warmed peaks would be socked in with clouds obscuring helicopter transit routes. The ascending elevation and narrowing channels on the highway from Kandahar to Qalat would create tens of meandering dust devils and sand-sky brownouts in the summer but induce whiteout blizzards come winter. Ghazni and Wardak provinces could be covered in feet of snow overnight.

In addition to their forecasting responsibilities, it was common for staff meteorologists to fulfill additional roles, including guard duty, assisting medical teams caring for the wounded or providing humanitarian support to the Afghan families near the base. Most deployed meteorologists experienced inbound rockets and mortar fire.

One forward-deployed weather observer reported a temperature of 136 degrees during a firefight while on patrol, the result of both hot weather and heat from rifle barrels amid the fighting. Such observations were critical to casualty and medical evacuation operations. As weather differed from one valley to the next, such “ground truth” assisted planning for flight routes and travel times.

A soldier once recalled awaiting medevac and watched a helicopter “find the one gap between the storms our weather guy said would be there.”

One heroic Air Force weather officer was posthumously awarded the Silver Star for gallantry during a “green on blue” active shooter incident. Two specialized weather observers received Purple Hearts for wounds sustained repelling attacks from insurgents. One weather observer was awarded a Bronze Star with Valor for leading a light infantry unit to safety following an intense firefight.

The diversity of weather forecasters and observers who served in Afghanistan and supported operations was vibrant. And many are likely to ponder which forecasts they got right, and which ones they missed, reflecting on predictions that aided mission accomplishment and how they felt when weather put their comrades in harm’s way.

Many may remember just how much the fighting seasons were dependent on the weather; the dust hanging in the sky for weeks over Kandahar; the full moon illuminating the Panjshir Valley, and oppressive humidity embracing Asadabad, Jalalabad and Torkham Valley.

Some may smile remembering the millions of moths and bugs attracted to runway lights and how they would vanish once the winds rose above 18 knots. One meteorologist recalls a sudden cloudburst that coincided with the celebrations of Eid al-Fitr, allowing people to use a rising Pech River to deliver ample fresh firewood to joy-filled families in the adjoining valleys.

Many still serving may quietly wonder if they’ll ever have to forecast the weather in Afghanistan again.

Jonathan D. Sawtelle is an active duty Air Force officer who served four tours in Afghanistan, from 2006 to 2011. He holds a bachelor’s degree in atmospheric sciences from the University of North Dakota.