FAIRBANKS - Meteorologists described Monday's widespread rainfall as an "extraordinary event," and it's not over yet.
Three-tenths of an inch of rain had fallen at Fairbanks International Airport by 3 p.m. Monday and forecasters at the National Weather Service said more than an inch of rain could fall by the time it stops Wednesday.
"We haven't ever seen anything like this in the Interior," hydrologist Ed Plumb at the National Weather Service in Fairbanks said Monday as the rain continued to fall.
The service issued a winter storm warning that remains in effect through 6 p.m. today.
The rain will compact and melt the snowpack and it is possible that runoff from rain and melting snow will cause ponding of water on roadways and other poor drainage areas, as well as localized flooding, the service advised in a statement Monday.
"The water is not going to have anywhere to go," Plumb said.
Significant overflow is also expected on lakes and rivers. Some small streams and creeks may experience elevated water levels.
"We're not expecting water to run out of the rivers and cause ice jams," Plumb said.
An extremely warm and moist air mass moving around a large high pressure system over the North Pacific pumped warm, moist air into the Interior and much of the rest of the state early Monday morning, resulting in widespread rain from Anchorage to Barrow, said meteorologist Brad Sipperley.
"It started raining at 5:30 a.m. and it's been raining ever since," he said. "We've had freezing rain from Anchorage to Barrow."
The heaviest rain fell in the central Interior. In the Yukon River village of Galena, about 270 miles west of Fairbanks, six-tenths of an inch of rain fell from 6 p.m. Sunday to 10 a.m. Monday, Sipperley said.
Rain was expected to continue most of Monday and much of today before cooler air begins moving into the area, Sipperley said.
"We could surpass the record (winter) rainfall we had in 1937," Plumb said, referring to the 0.99 inches of rain that fell on Jan. 20, 1937.
Rain during the winter in Fairbanks is unusual and rainfall amounts over one-quarter of an inch between mid-November and early April are extremely rare, according to the weather service.
The last time that happened in Fairbanks was February 2003, when 0.29 inches of rain fell between Feb. 8-10.
It marked only the second time in more than 100 years that measurable rainfall was recorded in Fairbanks in the second half of November, according to weather service records. The only other November rainfall on record was Nov. 24, 1936, when 0.42 inches of rain fell.
"It is quite the blast of warm, moist air," Sipperley said.
The air broke down a high-pressure ridge that was centered over the Interior, Sipperley said. He called it a "tropical moisture train."
"There's a large trough of low pressure aloft that came over from Siberia," he said. "It's pushing on top of the ridge and flattening it out. As it flattens out the top of the ridge it allows that moisture and warm air in the door.
"We're receiving every bit of moisture and warm air that is available," Sipperley said.
Freezing levels were all the way up to 6,000 feet, Sipperley said. Temperatures are expected in the low 30s today and most of Wednesday in Fairbanks. Rain is forecast through 9 a.m. Wednesday.
"Colder air doesn't start pushing into here until Wednesday night," Sipperley said.