PORTLAND, Ore. — A new weather system will bring more winter weather to the Portland metro area this week. The Willamette Valley is expected to see a dry Tuesday morning that will develop into freezing rain in the early to mid-afternoon.
"Out of all the wintry precipitation types, freezing rain is the worst because it gets everywhere and it's a skating rink. It's a literal skating rink," said KGW meteorologist Chris McGinness.
The National Weather Service upgraded a Winter Storm Watch to an Ice Storm Warning for much of the Willamette Valley, parts of the northern and central Oregon coast (except for the immediate coastal areas), and southwest Washington. It will be in effect starting at 2 p.m. in the Portland area.
The south end of the Willamette Valley will likely start seeing freezing rain first, according to McGinness, and then the impacted area will spread northward throughout the afternoon to hit Salem and the Portland metro area and finally north Clark County and the Columbia River Gorge.
The front end of the freezing rain wave will likely enter Wilsonville at about 2 p.m., according to KGW meteorologist Rod Hill, and then spread to the rest of the metro area shortly thereafter.
Conditions will quickly become icy, and Hill cautioned people in the Portland area to try to be off roads before it begins. Ice accumulations could reach an inch in some places, potentially causing trees to fall and power outages. Most of the metro area can expect an average of 0.22 to 0.37 inches of ice, McGinness said, but that could still be enough to start bringing down tree limbs on power lines — and it's easily enough to make the roads dangerous.
"The second you get freezing rain, it gets bad in a hurry," Hill said. "Much more quickly, in my opinion, than a snow storm where you watch it stack up and you go 'well, it's getting deep, things are getting bad.' No, this will get bad really quickly."
He cautioned Portlanders not to relax just because Tuesday began with sunny skies in the morning. Temperatures are indeed warming up at higher altitudes over the valley, but ground temperatures remain stubbornly in the low 20s, which creates perfect conditions for freezing rain as the band of moisture works its way up the valley.
"Here's the problem," Hill said. "Cold arctic air is still in place. All of our modeling suggests that this is a solid warming aloft, which means all raindrops until the moisture strikes and makes impact with surfaces, then it glazes into a sheet of ice."
Hill expects freezing rain to continue to fall into early Wednesday morning for much of the north valley, but temperatures will rise rapidly over the course of the day, getting up to well above freezing.
Even though the ice storm warning lifts at 4 a.m. Wednesday in Portland, Hill cautioned that the area could still see freezing rain as late as 9 a.m., especially in the eastern part of the metro area, where east winds in the Gorge are likely to make Wednesday's warming more gradual. There could be a point Wednesday morning where Portland remains under a sheet of ice even though places to both the north and south like Longview and Salem have all thawed out.
"Tomorrow morning, maybe you're driving your car, at your place it's great, and then you come into the city center of Portland and you're like 'whoa, it's still freezing rain and ice here,'" Hill said.
Portland will eventually catch up with the rest of the region and thaw out by the afternoon, and the rest of the week is set to bring rainy weather and low temperatures staying above the 40 degrees.
VIDEO PLAYLIST: KGW Weather