As the roar reached a deafening pitch and winds howled, Futrell, 29, clambered into a walk-in freezer in a desperate attempt to find shelter.
It was a final and tragically futile act of maternal love; she was found dead clutching her infant, the youngest of 24 victims of the twister.
The fate of these two mothers showed the capriciousness of nature on a day when split seconds made the difference between life and death. If Futrell had reached the clinic, as more than 200 other residents did, she would have lived to tell Case about the day the tornado struck.
Surveying the shredded shell of the medical centre - the two-floor structure torn apart as if a bomb had struck - it is hard to believe that there were no casualties inside.
Yet the accounts of those within who rode it out make the story of survival all the more extraordinary.
They describe people lifted off their feet and carried tumbling down hallways by screaming gusts; the thump of cars smashing into the building; shards of doorways, picture frames and tiles turned into projectiles and hurtling past them; the air choked with dust; and that all-encompassing noise: a jet engine meeting a freight train.
That nobody suffered more than cuts and bruises is down to a combination of detailed planning, calm heads, quick thinking, selfless bravery and plain luck.
At the medical centre, the emergency alert was sounded about 3pm.
Dr Stephanie Barnhart, 34, the doctor in charge of the emergency room, and her team then learnt they were directly in its path. Until a few minutes earlier, it had been a quiet day, but two new patients - a woman suffering a seizure, a girl with an asthma attack - had just arrived for treatment alongside two already in the clinic.
The medical staff knew their drill and moved with their patients into a designated safe area, a room in the middle of the ground floor. There they gathered mattresses and pillows for protection and explained to the patients how to brace low to the ground.
As they waited, they watched the ominous pictures on the television until the power suddenly cut out, leaving them in darkness, the air sticky, a roar approaching them. "We could hear it and we knew that it was coming for us," Barnhart said.
Outside, Nick Stremble, the emergency department manager, and his colleagues were making sure that patients and staff were taking refuge in inner rooms and corridors and decided to evacuate the upper floor.
As emergency sirens wailed across the town, he headed back downstairs, only to discover an influx of locals streaming through the clinic's front doors seeking shelter.
The new arrivals added to the pressure on space and most were shepherded into the cafeteria, others spilling into corridors.
Stremble raced upstairs to do a final check.
It was then that he looked inside the labour room and was stunned to find four nursing staff around a woman in the final stages of delivery.
"She was in active labour and the nurses said the baby was in possible distress so we decided that it was too risky to move her. We moved her into a surgical suite with back-up power and the nurses all volunteered to stay with her."
Back on the ground floor, he wedged his back against the building's front doors in an attempt to hold them shut. "The doors blew inwards and I was wedged between the doors and the wall.
"The wind and debris surged down the hallway and carried people tumbling and falling into a pile at the end of the corridor.
"In the other direction, I saw a car flying through the air and hitting a pillar by the entrance. The noise was incredible. There was so much stuff flying through the air. And then it just ended."
In his now all too familiar role as the nation's consoler-in-chief following its latest tragedy, President Barack Obama will arrive for a memorial service for the victims today.
