The active weather continues across the Northwest as a new storm moves in this weekend. A very potent upper-level disturbance will drop southward from the Gulf of Alaska, into the Northwest, and eventually into the Southwest US during the start of next week. It is this disturbance that will bring a widespread snow to the intermountain West, a region that has been experience snowfall deficits so far this winter.
On Friday, rain showers will begin to sneak in ahead of the main disturbance into the Washington and Oregon coast while snow falls in portions of the Cascades, mainly in Washington state. A heavy snow is also expected to fall in portions of the northern Rocky Mountains in northern Idaho and western Montana. It’s not until Friday night when the activity will begin to ramp up as our upper-level disturbance takes a southward plunge into the Northwest US. Most of the activity will be confined to Washington Friday night with a widespread rain at the coast and snow developing in the mountains. Spotty snow showers will also continue in portions of Idaho and Montana.
The main event will be on Saturday as tons of moisture stream into the Northwest. A widespread rain is forecast to fall throughout the day, especially in the morning, on the windward side of the Cascades while the Cascade Mountains itself experiences a heavy snow. Again, the heaviest of snow and the most activity will be found in Washington. Also the northeastern corner of the state will experience snow on Saturday. In addition, a moderate to heavy snow will slide into the northern Rockies with snowfall rates up to two inches per hour. The snow will continue Saturday night across portions of the Northwest, although it will become a bit more scattered with snow showers in the northern Rockies. Spotty snow showers are even possible near the Northwest coast, so a city like Seattle will cool down and may experience a brief snow squal.
The activity will become widespread again on Sunday, although snowfall intensities will be lighter than they were on Saturday. Snow showers are forecast for most of the Northwest region, and this snow will fall as far south as the northern Sierra Nevada Mountains and into northern Nevada and Utah. Also the coastal range of Oregon and California will experience a light snow throughout the day. To the east, a separate disturbance will lead to a brief swath of light snow from the Northern Plains into the Upper Midwest, but this will be more of a nuisance snow instead of a significant snowstorm. Overnight Sunday, the activity will wane again as the energy associated with this disturbance moves into the Southwest US. This will allow for snow to fall further south and east. Therefore Sunday night, snow showers are forecast across the northern Rockies, the coastal range of Oregon and California, and into the Sierra, which is desperate for snow. As the surface low moves into the central Rockies, snow will develop again in portions of the Northern Plains into the Upper Midwest.
Then on Monday, snow will continue as times in the Northern Tier of the US. Meanwhile to the West, snow is expected to fall across much of the Rockies and back into the coastal range and the Sierra Nevada. Snow will also work into the northern mountains of Arizona as moisture works into the region with cold, freezing air aloft. Overnight Monday, our storm will begin to wind down as the upper-level disturbance just sits over the Southwest and weakens. A light to moderate snow is still expected, however, from the Four Corners States in the higher elevations through the central Rockies and into the Northern Plains and Upper Midwest.
As we get into Tuesday, the snow activity will shut off as the day progresses with all the snow expected to end from the Midwest through Southwest. Meanwhile across the Central US from the Ohio Valley through the Southern Plains, a flood threat will begin to kick in as deep, tropical moisture streams in between a gradient of a trough over the West and a ridge over the East.