FastCast—Wednesday, Nov. 2 to Saturday, Nov. 5:
November, statistically shown to be the stormiest month of the year in the Pacific Northwest, will live up to its reputation this year, as an active beginning of the month is expected. Showers will move through the lowlands at times from Tuesday night to Wednesday evening, bringing 0.1-0.4 inches of rain, most south of Everett. Temperatures will be on the cool side, with highs in the mid to upper 40s and chilly morning lows in the mid 30s to low 40s. A significant storm will approach on Friday, with strong winds and an atmospheric river. Expect 1-3 inches of rain across the lowlands by Saturday night. Winds will peak on Friday afternoon into the evening, with gusts of 35-45 mph across the lowlands. Higher gusts of 50-55 mph are expected along the Strait of Juan de Fuca and from the Everett area northward. Tree damage and localized power outages are expected. River flooding is possible as well, especially on the Snoqualmie River system and the Skokomish River near Hood Canal. Prior to the atmospheric river, the snow level will be around 1,500 feet, bringing snow showers to all the passes. The atmospheric river will raise the snow level to 6,500 feet from late Thursday to late Friday (contributing to river flooding). Then, in the wake of the atmospheric river, the snow level will plummet to 1,500 to 2,000 feet, with the potential for heavy snow at all the passes on Saturday. Stay tuned, as very active weather is expected.
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Continue reading the full blog below!
A lot of active weather is ahead to begin November! This blog will break it all down.
We’re starting below with the HRRR forecast for rain through 5 PM Thursday.
This forecast shows 0.1-0.4 inches of rain, mainly from Everett southward. Most of this rain will fall on Tuesday night and Wednesday. Some areas, particularly from Tacoma south and west and on the northern Olympic Peninsula (a rare area for lots of rain) will receive over 0.5 inches.
It will also be on the chilly side. The European model forecast for Thursday morning lows is below.
The European model is calling for widespread lows in the mid to upper 30s. Outlying areas will likely drop into the low 30s, with the first frost possible. Eastern Washington will drop into the upper 20s to low 30s, and in the mountains, it will be in the low 20s. In addition to this, high temperatures will only be in the 40s for most of the area.
However, the chilly and showery pattern will radically change on Friday, as a strong atmospheric river and associated windstorm hit the region.
Below is the UW forecast for 2 PM Friday, showing the strong atmospheric river aimed directly at Western Washington.
Notice that this is a much larger and stronger atmospheric river than the previous one on Sunday and Monday. Integrated water vapor transport (amount of water vapor moving through the atmosphere, called IVT) is the value used by meteorologists to determine the strength of atmospheric rivers. The previous atmospheric river had IVT values of 500-800, while this upcoming one has values of 1000-1200!
As expected, this atmospheric river will bring significant rainfall to the area. Below is the European model forecast showing total rain through 11 PM Saturday.
Note: This includes rain from Tuesday to Thursday, so for total atmospheric river rainfall, subtract 0.2-0.5 inches for the lowlands.
This atmospheric river will bring 1-2 inches of rain to the interior lowlands and 2-3 inches for the foothills and areas from Olympia southward and Everett northward. There will be a rain shadow (due to westerly flow) from Seattle to Everett, with totals there of 1-1.5 inches.
The mountains and coast will be drenched with 3-6 inches of rain (snow over 6,500 feet). Eastern Washington will also get in on the rain, with 0.75-1.75 inches expected!
As expected, this atmospheric river and high snow levels will bring river flooding, especially since rivers have risen after the previous atmospheric river. Stay tuned for more information about river flooding later this week.
This storm will also bring the strongest winds of the season on Friday. The forecast below from the European model shows winds on Friday afternoon.
Peak winds in the lowlands will gust up to 40-45 mph, especially near the water. The coast will reach 40-50 mph, along with Eastern Washington.
As we go into Friday night, a strong westerly wind surge is expected along the Strait of Juan de Fuca, with strong westerlies reaching the Everett area as well. This is clearly shown on the European model forecast for Friday night’s peak gusts.
Winds will gust up to 50-55 mph along the Strait and in the North Sound, especially in areas from Port Angeles to Everett, including all of Whidbey Island. As it gets dark on Friday, winds will still be gusting 35-40 mph for the rest of Western Washington, and 45-55 mph in Eastern Washington.
One more weather impact for this significant storm will be mountain snow. In the wake of the atmospheric river, snow levels will crash from 6,500 feet to around 1,500-2,000 feet. Snow will be falling at all the passes by Saturday morning. Below is the European model forecast for snow through 11 PM Saturday.
The post-atmospheric river snow will be significant in some areas. Expect 6-12 inches at Snoqualmie Pass by Saturday night, and 8-18 inches at Stevens and White Passes. Snow accumulations are also possible for lower elevations of Eastern Washington, with 1-4 inches in areas like Leavenworth, Spokane, and NE WA.
As we enter next week, a shift to a much colder pattern, with significant mountain snow, a SLIGHT potential for lowland snow, and potentially record-breaking cold temperatures is becoming increasingly likely in extended forecasts. However, that’s a topic for a later blog.
Stay up-to-date on the active weather on the blog and on Twitter (top right of blog site).
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