Harsh winter weather has caused the blood supply serving Iowa hospitals to drop to critically low levels, LifeServe Blood Center said today. LifeServe, which is the sole supplier of blood products to more than 100 hospitals in Iowa, Nebraska and South Dakota, said planned blood collections are down by more than 1,000 units due to poor road conditions, severe cold temperatures and power outages that forced cancellations of mobile blood drives and donor center operations. With a second round of winter weather hitting last week, LifeServe's blood supplies have dropped to less than a two-day supply; normally it's a three- to five-day supply.  "We need to immediately increase our supply, especially type O Negative and O Positive blood types," said Stacy Sime, LifeServe's CEO. "We are calling upon the community for help." Donors are urged to schedule appointments or walk-in to donate.  Visit lifeservebloodcenter.org to schedule an appointment or to see upcoming blood drives.