Much of Southcentral Alaska has been placed under a weekend flood watch Friday, as forecasters predict a tropical weather front with warm winds moving into the area and changing snow into rain -- a combination expected to drastically increase avalanche danger.
A flurry of National Weather Service bulletins issued Friday call for a flood watch in the region, including Anchorage, the Mat-Su Valley, the western Kenai Peninsula and Prince William Sound. The watch is expected to remain in effect until Monday morning.
“A shift in the weather pattern will bring a strong weather front into Southcentral Alaska this weekend,” NWS forecasters wrote in a special weather statement. “The front should move into the Cook Inlet and Susitna Valley region during the morning on Saturday and push eastward over Prince William Sound and the Copper River basin by Saturday evening. This front has a tropical connection with it and therefore will bring in unseasonably warm air to the area.”
The weather statement describes precipitation in Anchorage taking shifting forms during rising temperatures over the weekend, with Saturday snow becoming rain by Sunday.
“The Anchorage area is expected to have some light snow on Saturday that will begin to mix with freezing rain late in the afternoon,” forecasters wrote. “The freezing rain will turn to straight rain as temperatures warm through the night Saturday night and rise above freezing. Rain will then persist into Monday morning with the heaviest rain Sunday night.”
Channel 2 chief meteorologist Jackie Purcell says the weekend’s warm weather is the product of warm “Pineapple Express” storm systems being drawn north by southerly winds in the upper atmosphere north of Hawaii -- which the NWS referred to as an “atmospheric river” in a graphic posted on its Facebook page Friday.
“It’s not uncommon for us to get a midwinter meltdown in the month of January,” Purcell said.
The NWS says river ice may become unsafe over the weekend due to the likelihood of significant overflow, and urges people to avoid river travel.
In a Friday update posted on its website, the Chugach National Forest Avalanche Information Center calls avalanche danger going into the weekend considerable above the treeline and moderate below it. Even before the storm’s arrival, the center has recently warned of avalanche risks in the region from snowfall and temperature changes.
“Natural avalanches are possible and human triggered avalanches are likely on slopes steeper than 35 degrees,” center officials wrote in the update. “Any avalanche triggered has the potential to be very large and dangerous.”
According to Purcell the storm systems will pass to the south and east by Tuesday, but will affect Southcentral communities until then.
“It’s all combining to make a wet and windy and warm, warm weekend,” Purcell said.
Contact Chris Klint