The pattern has flipped around across the hemisphere with mid-latitude amplification flattening out with the NAO/AO going positive but as a result, rather than dealing with unseasonable cold and snow, the storm train off the Pacific has cranked into high gear for the Pacific Northwest following a record dry spell. If you live in the Pacific Northwest, you don’t need me to tell you your getting pounded by wind, flooding rains and heavy mountain snows. This will continue through much of the upcoming week as a powerhouse Pacific jet roars in with a parade of strong storms.

The upper winds have increased dramatically with this pattern reversal and so has the distribution of precipitation or in some cases the lack of.
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Why the sudden increase in PNW storminess? With the retreat of arctic air and loss of blocking, jet stream winds have increased, meaning air piles up at an increased rate when there are ripples or kinks in the upper level flow. This ‘piling’ up of air forms storms and with the jet now ‘zonal’, it sends one storm after the other directly into the West Coast.

While there has already been a heck of a lot of rain over the past 36 hours up and down the I-5 corridor between Portland and Seattle, expect plenty more inches to add to the already impressive 1-3″ and of course this raises the concern for flooding. Check out the above 5-day QPF chart for precipitation. Yes, your reading it right.. 10″ or more of rain is expected in places and to be honest I recon some may see over a foot of rain between now and Friday.

Check out the GFS 850 temps/mslp chart (above) for 12 hours from now. Notice the elongated low pressure trough stretching from the south coast of Alaska all the way to the WA coast with 3 individual low pressure centres and all at 980 mb. All this energy will continue to pile strong winds and copious amounts of moisture onshore and up against the mountains. Orographic influence will bring enhanced rains to western upslopes. The Olympic and Cascade mountains can expect 6-18″, locally 24″ over the next 24-36 hours and 24-36″ (locally higher) over the next 3-5 days.

The below chart looks out to Wednesday and you can still see storminess attacking the Pacific Northwest.

While there is plenty of weather to contend with throughout the PNW extending down the California coast and raising the risk of heavy and prolonged spells of rain through San Francisco and even LA and San Diego, high pressure dominates the Plains and Heartland all the way to the East Coast.

The strong west winds of Pacific origin will keep the entire country mild over the next week. The combination of ridging and strong, downsloping winds which will blow over and down the east face of the Rockies will heat the air as flow descends, dries out and compresses. The ‘Chinook’ effect should warm temperatures throughput the western High Plains into the 70s and for some spots including southwestern South Dakota and western Nebraska, we may even see 80s.

I expect highs to reach the mid and upper 60s throughout the Plains, extending into the Lower Midwest. Both Minneapolis and Chicago will warm into the 60s and if it tops 60 in Chicago on Thanksgiving day, it would be the warmest in 14 years.

These highs btw would be 10 to nearly 30 above normal for the time of year!

Here’s a look at the ECMWF upper chart and 850 temps for this week.

Monday

Wednesday

Friday

 

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