Forecasting “green up”

Green up is that period in time when the landscape first turns green in the spring. In Anchorage and in Fairbanks, this can happen quickly. It often feels like green up occurs in the space of a day.

For the first time, Rick Thoman, Climate Science and Services Manager for the Alaska Region, is attempting forecast when green up will occur in Fairbanks.

“Right now we've got a fifty-percent chance green up will occur in Fairbanks between May 7th and 10th,” says Thoman. “And that's almost exactly normal.”

The question is — why is green up something you want to forecast?

Green up affects allergies, fire weather and some niche industries.

“Many people have pretty significant allergies to birch and aspen,” says Thoman. “The birch pollen explodes a couple of days after green up.”

Thoman also says that as soon as the leaves come out, they draw water out of the ground and release it into the air. Assuming other conditions remain the same, Thoman says, “the low level humidities go way up within a couple of days of green up, so that can have a significant impact on things like fire weather.”

And industries like birch syrup producers may find this information helpful. Once green up occurs, the sap from birch trees is no longer good for syrup. Dulce Ben-East with Kahilta Birchworks says as of Friday, they hadn't seen any green.

“Our average season is 21 days, so we're hoping to get that this year,” says Ben-East. “Signs look good so I don't see any greening up just yet. I'm thinking we'll get close to our 21 days if not getting it.”

Data for green up in Fairbanks has been kept since the 1970s. It was started by forest ecologists with the University of Alaska Fairbanks and taken over by the weather service in the late 1990s.