The_Weatherman2 Weather Blog: Next System Bringing More Rain, Winds, and High Mountain Snow

FastCast—Monday, Oct. 24 to Wednesday, Oct. 26:

The next weather system arrives late Sunday night, bringing another round of rain, wind, and mountain snow (above 4,000 feet). Rain will total 0.2-0.4 inches in the lowlands, except for a rain shadow that could decrease totals around Seattle and the Central Kitsap Peninsula, with only 0.1-0.2 inches possible if the rain shadow verifies. With continuous onshore flow on Monday, Convergence Zone bands are possible across the Central Sound. Another element of this system will be winds. Frontal passage will be early Monday morning (3-7 AM). Expect the strongest winds (gusting up to 40-50 mph) on the coast and north of Everett. The interior lowlands will gust up to 25-35 mph, with stronger gusts up to 35-40 mph possible around Olympia and Tacoma. More mountain snow (2-12 inches) is expected above 4,000 feet. Some impacts are possible at Stevens and White Passes, on the North Cascades Highway, and on Chinook and Cayuse Passes. Another weather system will move through on Tuesday, with the same impacts expected, so stay tuned for more information. Wednesday will be a dry day between systems.

———————————————————

Continue reading the full blog below!

The next weather system is heading for Western Washington, bringing more rain, wind, and high mountain snow.

Let’s start with the rain. Below is the HRRR forecast for rain through 12 AM Tuesday.

The HRRR shows 0.2-0.3 inches in the lowlands, with a signal for a Convergence Zone east of Seattle, with up to 0.5 inches possible. The coast and mountains will receive 0.75-2.5 inches, with 0.4-0.9 inches from Mount Vernon northward and Olympia southward.

Now, let’s compare this with the NAM forecast (also through 12 AM Tuesday).

The NAM is quite similar, except with a more pronounced rain shadow effect in the Central Sound and more rain from Everett northward. The mountains and coast still receive around 0.6-2.5 inches.

Frontal passage early Monday morning will bring windy conditions to the area. While some locations will just be breezy, it will be our first decent winds of the season.

Let’s start with the HRRR forecast.

Above is the forecast for 2 AM Monday, showing peak SE winds from Everett northward and on the coast, likely gusting 30-50 mph, strongest on Whidbey and the San Juans and in Whatcom County.

By 7 AM Monday (below), the front will be passing through the lowlands.

The HRRR shows winds gusting 30-40 mph from Everett southward to Olympia.

Now, let’s look at the NAM forecast, starting with 3 AM Monday (below).

This shows peak SE winds ahead of the front, which the NAM has a bit stronger than the HRRR, with gusts of 25-35 mph in the interior and 40-50 mph on the coast and north of Everett (good agreement with the HRRR).

This next frame is the NAM forecast for 4 AM, around the time of frontal passage.

The NAM shows winds gusting 30-40 mph around the interior, and 40-50 mph on the coast and north of Everett.

Regarding winds, the actual wind speeds don’t differ much between the HRRR and NAM. The only difference between the HRRR and NAM is the timing of the frontal passage, so expect the strongest winds around 4-7 AM. These winds are enough to cause slight tree damage and isolated power outages, especially with the leaves still on most trees.

More mountain snow is ahead as well, mainly above 4,000 feet. The NAM forecast is below, showing snow through 12 AM Tuesday.

Expect 2-12 inches above 4,000 feet, most on the mountain peaks.

The HRRR forecast lines up with the NAM.

The HRRR also shows 2-12 inches above 4,000 feet.

With the snow level around 4,000 feet, winter driving conditions are possible at Stevens Pass, White Pass, the North Cascades Highway, and Chinook/Cayuse Passes.

While a wet and active week is expected this week (except Wednesday), the signal for above average precipitation is strong into the beginning of November. The NWS Climate Prediction Center outlook for October 29 to November 2 is below.