Dry & Windy For Halloween Weekend

Dry & Windy For Halloween Weekend

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After a very stormy couple of weeks for the Pacific Northwest, the weather is calming down this Friday evening.  It’s always refreshing to see weather geeks get back into “storm mode” each fall, and last week surely didn’t disappoint!  We had multiple atmospheric rivers pummel the West Coast, from Vancouver Island all the way south to San Francisco…where many locations broke their all-time 24-hour rainfall records.

We also had two “bomb cyclones” in the eastern Pacific, a few hundred miles off the Oregon & Washington coasts.  That refers to a very rapidly-developing low pressure center, one that drops more than 24 millibars in 24 hours.  Last Sunday’s bomb cyclone dropped to 942mb, which is nearly a record for our region.  Kudos to fellow WeatherTogether blogger Charlie Phillips, for tweeting the dope imagery on this one!

Our rainfall total at PDX as of last night (Thursday the 28th) was 3.31″, but we had some rain early this morning too.  So our monthly total should end up very close to the October normal of 3.42″, give or take a couple tenths of an inch.

How do I know this?  Well…there won’t be anymore rain this month.  The last two days of October – Halloween Weekend – will be dry across most of the Pacific Northwest.  We have a short-lived ridge of high pressure that will build in over the western part of the North American continent.  For Portland, this means our first “cool” east wind of the season.  By that I mean an east wind that is associated with relatively chilly low-level air in the Columbia Basin to our east.  Today’s WRF-GFS 925mb maps (air temps at circa 2,500 feet elevation), show the cool air to our east tomorrow afternoon at 2pm:

Image credit: UW Atmospheric Science. As we get closer to winter, cool air tends to stagnate in the Columbia Basin. This leads to higher surface pressure and more east wind for the Gorge and Portland.

Note that this is NOT a “cold” east wind with modified arctic air, it’s just cool in the sense that we won’t see much downslope warming off the Cascades to boost temperatures in NW Oregon and SW Washington.  Daytime temps should be very close to end-of-October norms, around 58-60 degrees.  Nights will be cooler than over the past few days, due to the lack of cloud cover and the long nights.

We only are expected to get two dry days before rain returns Monday.  The long-range spaghetti models don’t show any heavy, atmospheric-river-type rain during the first few days of November, just “normal” rainfall with passing fronts.

Credit: WeatherTogether.net/models.

These rain events seem to be associated with cool upper-level troughs, the kind that bring snow to the high Cascades.  Furthermore, the ensemble mean (upper blue line) suggests we stay on the cool side of normal (upper red line) throughout the first two weeks of November, which would mean lots of snow for the mountains.  La Niña should be getting off to a strong start this year – first the October windstorms, and now November snow on the slopes!

One last thing.  Yesterday there was a massive solar flare, with a lot of ionic emissions aimed directly toward Earth.  Late tonight, and especially tomorrow night, there should be excellent Northern Lights (aurora borealis) visible in midlatitude places such as Oregon and Washington!  Just get away from the urban light pollution and look toward the northern horizon.  Here is a link  from Space.com that explains the nitty-gritty of what’s going on.

I will be in northeast Vancouver near Orchards tomorrow evening, signing the lease on a new rental place!  So I should be in a fairly good location to see the lights once the sun goes down.

Be safe this Halloween weekend – and enjoy the sunshine, dry breezes, and auroras!  -Karl

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