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Old 10-11-2016, 05:46 PM
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Default Big first storm

Typhoon Songda’s Leftovers: Stormy PacNW Ahead!
Posted by Mark Nelsen
11am Monday…

In the fall it is not unusual for tropical cyclones (referred to as typhoons) in the western Pacific to get caught up in the jet stream as they die. Then the leftovers end up somewhere along the west coast of the USA. They don’t survive the move over cold water, but their remains can help new storms develop much farther east. They more or less transfer heat & moisture from the tropics into the mid-latitudes…where we live. That’s going to happen later this week and it’s part of the reason Thursday through early next week is looking like the stormiest mid-October period we’ve seen in almost a decade. I recall a strong storm in mid-October 2007, but none since that time. October typically has quite benign weather until the last week when rainy weather kicks in. This year that rainy season has started early!

The Next 3 Days

They look great! We have leftover areas of fog & low clouds today, but sunshine will gradually break out. Tuesday looks incredible with bright sunshine and cloudless skies under a dry easterly wind. This should be a great photo-op day with the blue, sun, & changing fall leaves.

Thursday through Early Next Week

A mid-winter strength Pacific jet stream sets up over the entire north Pacific ocean. Check out one model forecast of wind speeds up at jet-cruising altitude:

jetstream_sat

jetstream_wide

That would be quite a tailwind flying from Japan to Portland if one followed the jet!

Note that as the strong jet arrives on the West Coast, it makes a slight curve to the left. It’s a long story, but there is lots of lifting high up in the atmosphere in that spot (called the “left-exit region”) in the jet. Powerful surface low pressure systems can spin-up in that spot and Thursday through Sunday it is quite close to our coastline. This is the pattern than CAN produce big windstorms for us.

The gold standard of models, the ECMWF on last night’s run showed 3 deep lows that come relatively close to the West Coast. Thursday night, Saturday morning/midday, & Monday. All three will produce a round of wind and rain for our region. This isn’t really an atmospheric river setup, but a series of separate storms that are all warm and very wet. Regardless, it’s going to be mid-winter type wet. Take a look at the ECMWF rain forecast for Salem:

ecmwf_ensemble_rain_sle

The bottom shows accumulation of rain from the operational model in blue…somewhere between 5-6″ by Monday afternoon! The group of 51 ensembles averaged together are just under 5″. The colored lines above each represent one of the 51 ensemble members. Excellent agreement with very wet weather…a soaker! Note it tapers off dramatically after Monday/Tuesday next week. I mentioned in the 12 Day Trend last night at 10pm that the weather turns more reasonable after about 6 days of this crazy stuff.

The morning GFS shows the soaking as well, but for now not as extreme.

gfs_7day_precip

Looks like around 3″ in most of the valley. You can ignore the bullseye over Portland, the model is pushing the south Cascades rain in Washington out over the lowlands. That doesn’t happen. Even with this “lighter” 3″ of rain, that’s more than we typically get in an entire October!

As for wind, lots more uncertainty on where the strongest wind is headed as Typhoon Songda as it dies east of Japan and follows the jet stream. If you are thinking this is similar to the Columbus Day Storm…it is somewhat, although the track was farther south in 1962.

gefs_wp23_2016101006

Songda’s remains turn into a deep low pressure center that ends up somewhere between Vancouver Island and Haida Gwaii according to both the GFS and GEM models this morning. The overnight ECMWF was farther south with a 968mb low into central Vancouver Island.

ecmwf_satmidday

That’s a big windstorm for the coastline but too far north and west for a windstorm in the valleys. It’s interesting to note that 6 out of 51 ensemble members have some sort of devastatingly deep low pressure center much closer to us for a big windstorm inland. Yes, I counted…but that also means 45 out of 51 did not. There was even one member that had a 945mb low center hitting Vancouver Island.

So we’ll keep a close on it all week as we get closer to see exactly where the deep low pressure systems are going to spin-up. Otherwise enjoy these 3 dry days because we have a huge soaking ahead!

Chief Meteorologist Mark Nelsen
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