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Friday, July 30th, 3:50 P.M. 

Happy Friday!

Clouds and a smoky haze kept today a bit cooler than expected, but it was still very warm with highs making it into the mid 90s around the metro area. We are seeing some showers on the radar, but most of the rain is very light and evaporating before it hits the ground. A chance of thunderstorms or light showers will linger tonight, especially over the Cascades.

Saturday brings more high clouds and a smoky haze above with highs in the low 90s. Expect that smoke to stick around on Sunday, but it should have little to no impact on our air quality.

After a couple more 90 degree days on Monday and Tuesday, things cool off midweek. Thursday and Friday bring our first decent chance of showers in over a month and a half!

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So far this week has turned out about as expected. I made these points on Sunday (bold is what happened)

  1. Temperatures finally cool down to, and then below normal for late October this week. That’s going to be quite a change! In fact by next weekend it’ll be jacket/sweater weather (WE HAVE COOLED AND THIS WEEKEND LOOKS COLDER)
  2. First snow is likely in the Cascade Passes either Wednesday (less likely) or Friday night (more likely) (SNOW IN THE AIR YESTERDAY; AN INCH OR TWO STILL POSSIBLE LATE FRIDAY NIGHT)
  3. First frost is likely in outlying areas Thursday and/or Friday mornings (JUST HAPPENED THIS MORNING!)
  4. I don’t see a rainy weather pattern for the next 7-9 days, just some showers at times (ONLY .01″ SO FAR THIS WEEK, & ONLY A FEW LIGHT SHOWERS EXPECTED THE NEXT 7 DAYS)
  5. There is a small chance some lower elevations in the Gorge and eastern Oregon get a very rare October snow dusting late this week. (MOST OF THIS WON’T HAPPEN, MODELS BACKED OFF ON COLD A BIT AND MOISTURE TOO)

Today was the coolest day so far this fall…only 57 degrees in Portland. Not exactly a “chilly” day, but we get used to all the warm weather so far this month

Of course what was most noticeable was the morning chill and frosty areas. About 1/2 of the metro area saw a first frost today

Here in Portland we had an early frost last year, but most years we don’t see it until sometime in November

Right now a warm-ish area of upper-level high pressure is centered south and west of us. A cool upper-level trough moved through yesterday (remember a few showers?); that’s why we’ve turned cooler.

But look up to the north right where British Columbia, Yukon, & NW Territories meet. A pocket of cooler air is about to surge south. By midday Saturday it is swinging through the northern Rockies and Intermountain region

That’s chilly air for this early in the season. Ahead of it a Pacific frontal system brings us light showers tomorrow. Then cold air pours in behind during the day on Saturday. By that time most of the moisture for producing snow to lower elevations east of the Cascades is gone. That’s why I don’t expect any significant snow in the Oregon Cascades or most of Eastern Oregon. Notice the ECMWF snow forecast is quite “dry”.

You’ll need to be in the Blue or Wallowa mountains to get more than 1-2″ snow this weekend. Even there models have really backed off, because that upper-level system is shunted a bit farther east. By Monday, the warmer upper-level ridge is popping back up over us…lots more dry weather ahead!

What we WILL get over the weekend will be an increasingly strong easterly wind. This will be the strongest event since the Labor Day East Wind Storm. Models are consistently showing a 16-20 millibar gradient from Spokane down to North Bend (OR) by Sunday morning. The WRF-GFS tends to overplay the low level cold, but you get the idea. Lots of isobars = a very windy day Sunday for ALL areas west of the Cascades, not just near the Gorge. Here’s the WRF forecast for 5am Sunday…brrr! It may be tough to get above 50 degrees Sunday. Combine that with wind and it’ll feel more like late November or early December; for one day

The cross-section gives 50-55 knot wind (circled) Saturday night through early Sunday between 2000′-4,000′ over the Portland area. That’s not ridiculously strong like what we experienced Labor Day evening. But it’s strong enough to give us gusts 35-45 mph Saturday night through Sunday. Even though dewpoints will be plunging Saturday night, all that wind will keep us well above freezing. Sunday night should be a different story as the wind dies down. Very dry air, calming wind, low humidity…much of the urban area away from the Gorge will see a killing frost (down to 30 or so).

Much of next week will be dry. The ECMWF 15 day ensemble run from this morning…each horizontal line is one ensemble member. Time goes from now on left side to 15 days out on the right side. Highlighted is next work week.

So, much like last year it appears we’ll be seeing a slow start to the rainy season. Maybe a dry Halloween? We’ll see, that’s still 9 days out.

Enjoy the sunshine! After tomorrow’s showers…

Chief Meteorologist Mark Nelsen

Residents are digging out of record-breaking snowfall in Newfoundland, Canada

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A resident struggles through the snow in St. John's, Newfoundland.

Residents are digging out of record-breaking snowfall in Newfoundland, Canada

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A record-breaking snowfall in Newfoundland, Canada, has left residents with the enormous task of digging themselves out of piles and piles of snow.

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7pm Thursday…

Get ready for a real taste of October weather this weekend!  Luckily that does NOT mean a ton of rain.  Let’s just say it’ll feel a bit more “refreshing”.

Summary

  • Nothing dramatic is expected (weather-wise) below 4,000′ over the next few days
  • Cooler showers arrive Friday afternoon in NW Oregon and SW Washington.  Then expect light showers off/on Saturday.  Sunday might be dry west of the Cascades.  There will be plenty of sunshine between showers the next few days, not gloomy at all.
  • Coastal weather looks great!  Not many showers Saturday OR Sunday.
  • Temperatures drop well below normal for late September, but frost is unlikely for 90% of us west of the Cascades
  • Light snow is possible down to around 4,000′ or maybe a bit below both Saturday and Sunday mornings.  Trace-2″ at Government Camp, but possibly 6-10″ up at Timberline Lodge by Sunday afternoon when things dry out
  • Passes should remain clear, although a brief morning dusting or icy spot is possible both Saturday and Sunday mornings.

This weather pattern has been forecast quite well by our weather models.  For the past week they’ve been showing a cold pool of air dropping south through western North America.  Sure enough, this evening a cold “upper-level trough” is right over Juneau, AK

500vor.12.0000

By Friday afternoon it is right over Washington, this IS our “arctic outbreak” pattern in winter.

500vor.36.0000

Then by Saturday afternoon it’s over NE Oregon.  A large upper-level ridge has developed in the eastern Pacific and cold northerly flow extends from the Yukon down to California!

500vor.60.0000

We get a surge of showers ahead of it Friday afternoon and evening, then the majority of shower action Saturday evening and beyond moves south and east of us.  At the same time high pressure at the surface turns our wind flow “offshore” late Saturday.  That gives us an easterly wind Sunday and Monday, drying things out with plenty of clearing.

The WRF-GFS (from UW) cross section over Portland shows the big cool down in the airmass overhead.  Time goes from right to left, starting with this morning and ending on the left side with Sunday afternoon.    I’ve drawn the zero degree line (celsius) in blue.  The 850 horizontal line is around 4,000′.  You see it goes from around 50 degrees (F) at that elevation today to about 32 degrees late tomorrow night.  It remains within 5-10 degrees of that freezing mark through at least Monday morning.

cross-section

That means it’s reasonable to say anything above that 4,000′ elevation will fall as snow beginning sometime after sunset Friday.  Models are showing plenty of mountain precipitation tomorrow night through Sunday morning.  I see the 18z ECMWF is giving the higher parts of Mt. Hood 6-10″+.  That seems reasonable.  Same thing in the central Cascades of Oregon and at least 2-6″ in higher parts of Eastern Oregon too.

web_ECMWF_snowaccum_hourly

Our RPM model thinks there will be spots over 10″ up around Timberline and higher.  Seems reasonable and goes with the Euro forecast

RPM Snow Accumulation Mt Hood Zoom In

There are even hints that at least a dusting could fall down to Sisters, Bend, and Redmond by Sunday morning with a cold northerly wind blowing moisture “upslope” into that area.  This is a classic hallmark of an “arctic blast” in that area.  Northerly flow moves uphill from the Columbia River into Central Oregon, clouds form, and snow is squeezed out when the air rises.  We don’t get many situations with flow from that direction but it’ll probably happen over the weekend.

The big snow/cold event will be to our north and east.  Look at all the Winter Storm Watches and Warnings across Washington, Idaho, & Montana.  Some spots in the Rockies could see 3-4 feet of snow!  Very early, even for that area.

Winter Weather Advisory 2017

So how “cold” will we get in the lowlands west of the Cascades?  For most of us Sunday will probably be the coolest day.  Even with abundant sunshine we’ll barely make it to 60…maybe only upper 50s

Forecast Max Temperature NWS NDFD Grids

If you’re a gardener like me you might be worried about frost.  I think that’s unlikely for most of us west of the Cascades.  Maybe either Monday or Tuesday morning around Tillamook, Vernonia, Banks, Battle Ground.  Just the very coldest outlying areas.  The rest of us remain above 35 degrees.  Your warm weather veggies won’t like it, but it’ll sure give them the hint the “end is near” for this growing season.

Forecast Min Temperature NWS NDFD Grids

What you’ll notice most Saturday through early next week will be the refreshing air and bright sunshine and of course much cooler mornings.

Enjoy your weekend!  Chief Meteorologist Mark Nelsen