DIANE SAWYER (ABC NEWS)(VO): And now, we want to examine more about the long-term effects of this record heat, stretching across two-thirds of the country, temperatures as much as 35 degrees above normal. And ABC's Sam Champion is going to explain what this heat wave means for health.
SAM CHAMPION (ABC NEWS)(VO): Again today, stunningly high temperatures across the country.
SAM CHAMPION : Sioux City, Iowa, a record high near 80 degrees. In Kansas City, another broken record, the mercury climbing to over 80. And the thermometer topped 80 in Pierre, South Dakota. South Dakota. But Americans seem to be welcoming the warmth.
PEDESTRIAN (MALE): March, I never expected anything like this. So just get out and enjoy it.
SAM CHAMPION : This unusually warm spell is caused by the jet stream stuck to the north of the nation, keeping the cold, arctic air out of reach. This warmth is expected to last for the next few weeks. But it's confusing Mother Nature and concerning farmers tonight, especially those with fields of winter wheat and orchards of apples, who worry that their crops would be damaged if we get a late frost now. "World News" watchers are curious, too, documenting many early blooms, azaleas in Louisiana in January, sunflowers in February and in Wisconsin, crocuses growing in ground that's normally frozen in March.
SAM CHAMPION: From all over the country, people are tweeting us pictures of their early blooming trees like this magnolia in southern Illinois. Here in the northeast, it's the juniper, the box elder and the maple that are throwing their pollen out early.
SAM CHAMPION: You can't see it. But we're getting readings two to four weeks earlier than normal.
SAM CHAMPION (ABC NEWS)(OC): And that's a real problem for the 30% of adults and 40% of children that suffer from seasonal allergies.
SAM CHAMPION (ABC NEWS)(VO): Sandra Holmes of Atlanta is already suffering mightily from seasonal allergies that she says have arrived a full month early.
SANDRA HOLMES (ALLERGY SUFFERER): You're so stuffed up you can't breathe, so you never really get any rest. I'm tired all of the time.
SAM CHAMPION: And along with all the other concerns, there is the looming spring storm season for 2012. Long-range forecasters are expecting a warmer than normal spring to continue this trend. We've already seen severe storms in February. And the peak of the tornado season, Diane, isn't usually until May.
DIANE SAWYER: Sam Champion, out in his white coat, in this time of year. Thank you so much, Sam.