Warm front coming in, creating a stir up with air masses

Weather

PORTLAND, Ore. (KOIN) – It has generally been cold in the Pacific Northwest going back to Christmas weekend. We’ve had a handful of days where temperatures didn’t warm up outside of the mid-30s, with a deep pool of cold air for the mountains to reap the benefit of buckets of snow.

We have a warm front and a mild air mass starting to move in our direction to wrap up the week. This is going to increase the temperatures around the valley and will increase the snow levels, most likely above the passes, by Thursday.

With that in mind, we have to transition from the cold to the warmer air mass and that will happen Wednesday. We should start the morning around Portland with just a few isolated showers. Those showers will turn more into light rain later in the day.

Showers start to increase late morning, turning more steady by the evening. At this time, temperatures start warming to the south. Eventually, the warm air is expected to transition late Wednesday into Thursday morning. This is going to stir up some issues for the Columbia River Gorge as warm air moves in over the top of the cold snowy surface. We will have an update on that later Wednesday.

Rain gear will be useful today around Portland, especially for the second part of the day. Rain totals through the day are ranging from a quarter-inch of rain to three-quarters of an inch. Higher totals to the north, likely less to the south (south of Marion county).

We will also see a moment where the wind starts to pick up Wednesday. You can swipe through the graphics below to get an idea of the wind gust for your neighborhood. It should increase later at night as the southerly wind starts to ramp up. Weather models have an east wind pulling into Portland until late. This will keep us cooler until the southerly flow takes over. That is expected closer to midnight, which is why the clash of air masses will be important to follow for areas of the Gorge.

Check out the temperature charts for the morning, afternoon, and late hours. Most should begin the day in the lower 40s, holding in the lower to mid-40s by afternoon and evening.

We will in fact be warmer overnight, compared to what we have going on earlier in the day because of that warmer air. If you check out the temperature futurecast for 11 p.m. Wednesday, you will notice the temperatures rushing to the lower 50s.

Big flooding potential Thursday and Friday across western Oregon and Washington due to heavy rain and snowmelt. The next atmospheric river will bring in tons of moisture and warm air Wednesday night, boosting snow levels to 7,000′ by midnight.

The warming will also induce snowmelt in the Cascades, which may cause rock and landslides and rivers to rise these next few days. A Flood Watch is in place across NW Oregon tomorrow and Friday. The Pudding River in Aurora is one to watch for minor flooding. Urban flooding is also possible around the metro area.

Icing in Central Gorge

Another issue will be the freezing rain set up in the central Gorge and upper Hood River Valley. An east wind will pick up this afternoon and cause surface temps to drop near freezing. As warm air arrives, it is likely we’ll see freezing rain develop. Ice accumulations around 0.25″-0.5″ are possible in spots. The window for freezing rain is anywhere from 10 p.m. to 4 a.m. Expect hazardous travel in the Gorge.

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