An Arctic Blast in Mid-November: Much Colder Ahead!

November 7, 2014

Snow & ice in the Gorge less than a week from now…Temperatures colder than an average December day here in Portland with a gusty/cold east wind…Wind gusts around 100mph at Vista House Tuesday or Wednesday.

Yep, it’s all looking quite possible as of Friday evening.

The Big Picture

  • We’re going to make a sudden jump from unusually warm fall weather (think October), to colder than normal winter weather.
  • The transition occurs next Tuesday and Wednesday
  • Strong east wind arrives Tuesday in the Gorge and Portland metro area.  It’ll continue for at least 3-4 days.  Gusts could be in the 40-50 mph range east of I-205.
  • A widespread hard freeze (pipe busting temp) is unlikely west of the Cascades, although widespread frost (25-30 deg temps) IS likely away from the Gorge at that time
  • Moisture returns late Wednesday or early Thursday and it’ll likely be cold enough for snow in the Gorge.  Freezing rain could get as close as Troutdale/Gresham/Camas depending on moisture supply and how cold the airmass is.

So what’s going on?

Models have made a relatively minor change in the general weather pattern that has a huge effect on our local weather.  Does that make sense?  As I mentioned in the previous post we’ll be seeing a ridge of high pressure near us over the next 7-14 days.  In the case of next week, it now appears the ridge is temporarily going to back slightly offshore AND a stronger upper-level high (ridge) is going to develop over eastern Alaska.  gfs_wed When it does that the flow around the high then dives south into the Rockies and Plains.  Cold arctic air surges in below it into the USA Rockies and northern Plains.  The slight shift westward in the entire pattern in models the last day or so means more cold air will make it west of the Rockies.  So Eastern Washington and the northern half of Eastern Oregon will turn very cold.  Take a look at the ECMWF model showing temperatures at 4,000′ or so Wednesday morning (850mb map) ecmwf_850wedam

Temperatures are around -10 celsius over The Dalles (or east side of Mt. Hood).  That would be temperatures in the LOW TEENS at pass elevations…really cold.  Even in mid-winter this would be a decent push of cold air.  But this is forecast to occur on the 12th of November!!!  12z ECMWF (and other models) show around 10-12 millibars easterly pressure gradient through the Gorge.  This is major east wind territory.  The WRF-GFS cross-section is showing 50-60kt wind a couple thousand feet up, once again in the middle of winter even this would be very strong.  It’ll be a 100mph day at Vista House…if not Tuesday for sure Wednesday.  Even Corbett should see gusts 70-80 mph.  Hello Winter!

Expect a widespread strong east wind across the entire metro area both Tuesday and Wednesday and temps will drop both days.  I forecast a high of 46 Wednesday (which could be too high)…that’s going to be a HUGE change from the current calm and 55-60 degree afternoons!

Then it gets even more interesting.  All the models (on days 5 & 6) are showing the classic snow/ice storm scenario for the metro area and Columbia River Gorge.  Moisture arrives from the southwest and rides over the cold air below.  We call this an “undercutting pattern” because moisture is cutting underneath the big upper-level ridge. ecwmf_thurs12zpcp  This time it PROBABLY won’t be cold enough for snow/ice in the metro area, but it looks cold enough for whatever falls to be frozen in the Gorge and Central Oregon.  The east wind will still be raging that day too so if this is correct it’s going to be a really cold and rainy day with freezing rain quite close to the Portland area.  It’s still pretty far out, but as of now all models are showing almost exactly the same thing, which is unusual and lends some confidence to the general sequence of events.  I did not forecast as cold as models are showing.  If you read them literally you would forecast snow/ice for more of the metro area Wednesday night and highs in the mid 30s Thursday!  This is the 7 Day Forecast I came up based on the idea that they are probably sending a little too much cold air over the Rockies/Cascades.

7 Day

I’ve had a little bit of trouble wrapping my meteorological brain around this stuff for about 24 hours.  I think it’s because it seems like warm summery weather “just ended” and I can’t switch into “winter mode” so quickly.

The next thought is…can it really turn this cold this quickly?  It HAS happened in the past, but it’s been very rare.

November 1955 is the gold standard for an early season arctic air event.  That is definitely not on the way.  We haven’t seen anything like it since that time…6 daytime highs at/below 30 degrees in Portland from the 12th-17th!  That was after many highs around 60 for the first ten days of the month.  That freeze caused widespread damage to the nursery & fruit-growing industry since plants weren’t even thinking about winter yet, like this year.  You can see the cold upper-level trough that came out of Alaska and down over us:  nov1955

November 1978 saw a freeze start around the 9th-10th with highs in the lower 40s and lows in the upper teens and 20s.  Neither these events are really similar to what we have (supposedly) coming.  This time its low level cold air coming in and being pulled through the Gorge.  Sitting at 2,000′ in the Cascade foothills or Coast range it’s not a chilly air mass at all.

Since this post is taking so long, the 00z ECMWF just came in exactly the same with precip arrival Wednesday evening ecmwf_wedpm

and 850mb temps the same…around -12c east side of Mt. Hood Wednesday morning.  It’s going to be a historic mid-November arctic blast across the northern half of the USA!


Chief Meteorologist Mark Nelsen