Thursday Evening Update: Snow still on Track

December 5, 2013

10pm Thursday…

No changes to our forecast this evening…in fact we’ve now reached the point before a “weather event” where there’s nothing left to do except sit back and see what happens.  Here’s a general look a the areas west of the Cascades where we expect to get a dusting (white)

MarkSnow_PolygonsTotalFcst

and 1″ or more

MarkSnow_PolygonsTotalFcst2

All our models still in agreement on the coverage of snow tomorrow and we won’t get anything new between now and arrival of snow.  Main (or all) action is expected on the central Coast and central/southern Willamette Valley.  Here’s our evening RPM model depiction of snow accumulation…sorry about the hole in the metro area; it’s a combination of most of the moisture staying to our south and strong east wind drying out the lower elevations.

RPM_SNOWACCUM

  • Timing is slowed down a little; it may not start in the valley until 8-10am.  We don’t know exactly when and won’t get any new information before that time except by watching the radar during the post-midnight hours. 
  • Coast should be about to start getting some flurries, radar shows that on the north coast.  It should reach the central coast by 5-6am.
  • Portland metro area won’t get much colder tonight (mid-upper 20s), but wind should be gusting pretty good for the morning commute and beyond.  We haven’t had a windy and cold day like what’s coming Friday in quite a few years.  Sudden those “bitter cold” 36 degree calm days will seem mild!

Stay warm!

I will be sleeping later tonight, like regular people, so no posts until around 9am tomorrow.  During that time, I highly suggest you check for updates on Twitter or Facebook from Brian and Andy.  I’m pretty sure Brian will be storming through social media 3-9am.

Facebook page is http://www.facebook.com/fox12weather 

Twitter is http://twitter.com/fox12weather

And my favorite radar site is here for the Portland radar and here for the Ocean Shores radar

Chief Meteorologist Mark Nelsen


18z Models In…Not Much Change

December 5, 2013

1pm Thursday…

Here’s our latest forecast in a prettier form than the previous post

MarkSnow_TextPanel

And look at this morning’s low temps, the coldest of the season for almost everyone.

PLOT_Lows_Metro

The east wind spots have been colder this season.  The breeze keeps the temperature up, thus the 26 for  a low at Troutdale.

All 18z models (that I use) are in.  This is what I see:

Slightly closer precipitation to the metro area on the 12z ECMWF, but still dry here…it’ll be close!

ecm_12z

18z RPM is almost exactly the same as the 12z RPM at the closest approach to the northern valley, first the 12z, then the 18z:

RPM_12z RPM_18z

But the 18z NAM is definitely a little closer to us.  Compare the two maps:

nam_12z nam_18z

And finally the 18z text output from the RPM.  Check out that cold air!  Notice how it goes perfectly calm Saturday night.  That’s going to be crazy cold for everyone, especially those with snow cover as mentioned on previous posts.

web_RPM_TextPDX_18z

Probably no new posts until this evening so no model info comes out again until after 7pm.  Stay warm as the east wind picks up this evening!

I’ll be watching observations and radar closely as the surface low is now visible on satellite NW of Forks, WA.  So far flurries have spread down almost to Hoquiam.

Chief Meteorologist Mark Nelsen

 


Thursday A.M. Update: Snowstorm For South Valley and Coastline

December 5, 2013

10am Thursday…

A snowstorm is on the way for the central and south Willamette Valley and a good chunk of the Oregon Coast!  I can hear the collective shouts of dismay from Portland area kids, teachers, and weather geeks.  Too bad for us.  Maybe we’ll at least get some flurries…

This morning models have come into agreement with our forecast…always good when that happens!  They are all keeping just about all snowfall well south of the Portland metro area late tonight and Friday morning.  That doesn’t mean we couldn’t get flurries anywhere else, but any “impact snow” (enough to turn roads slick) should stay south of the metro area.

Maybe a slightly later start than previously expected both at the Coast and inland.  Sometime after 3am at the Coast and 6-7am in the valley from Salem south.

  • High clouds thicken up today, as a result our coldest day so far, just creeping a few degrees above freezing
  • Snow will spread onto the beaches (yes, the coastline!) late tonight and inland by sunrise tomorrow.
  • At this point it appears accumulating snow will most likely stay SOUTH of a line from about Seaside to Newberg to Mt. Hood.  Yes, that means just flurries at best for the Portland metro area late tonight and Friday morning.
  • 1-3″  is possible from Tillamook to Newport on the coast, and in the Valley from McMinnville to Salem and south during this time (Friday AM)
  • 2-4″ is possible Albany, Corvallis, and Eugene (south Valley)
  • A dusting to 1″ could make it as far north as Forest Grove and Banks near the Coast Range…maybe
  • Avoid travel south on I-5 all day tomorrow between Salem and Eugene
  • Strong Wind Metro Area Friday:  Gusty east wind pours out of the Gorge tomorrow, bringing a frigid arctic airmass west of the Cascades, the coldest we’ve seen in 4 years.  Between the wind and colder temps, the metro area is going to feel much colder tomorrow than the past few days. We could see 40-50 mph gusts from the east-northeast central and east side of the metro area, and up into parts of Clark County too.  So some power outages are possible during the day.  The wind will dramatically die off Saturay though and be calm by Saturday night.  High temps probably won’t rise above freezing Friday through Sunday; our coldest weekend we’ve seen in a long time…but sunny!

What has changed today?   Not much, you’ll notice the highlights are almost the same as yesterday’s info.  Luckily, our RPM model has finally come into better agreement with all others.  And timing seems to have slowed down a couple of hours too.  Here is the latest snowfall forecast from our RPM model:

RPM_72_SNOW_12z

And the WRF-GFS:

rpm_snowaccum

Are you a casual observer of the weather and don’t spend every waking hour staring at weather maps?  Then keep in mind that you generally shouldn’t read models like this literally.  For example on the lower map don’t assume 3″ of snow is coming for Tillamook and nothing for Pacific City.    Instead note the big picture that then northern extent of the snow is around Astoria and the southern edge is around Newport.

I think it’s interesting to note the placement of heaviest snow in the Willamette Valley is almost exactly the same as what we saw during the “pre-Spring Break” snow in 2012.  The snow begins accumulating somewhere south of Wilsonville and is heaviest in the Albany to Eugene stretch.  It sure won’t feel the same though!  This time it’ll be well below freezing, roads will stay icy, and with a northerly breeze it’ll even be blowing around a bit.

Tomorrow looks very cold across the entire area, even if temps are warmer, it’ll feel as cold as 4 years ago during the 2009 arctic blast due to a strong east wind being pulled out of the Gorge by the surface low tracking down the coastline.

Strong wind may be an issue around metro area tomorrow.  Take a look at the WRF-GFS cross section:

kpdx.th

When I see 50kts getting that close to the surface that’s impressive.  Gusts 40-50 mph look possible not only in the usual east wind spots but also in parts of Clark county and the west hills.  This isn’t a classic downslope wind event; that happens when we have warm air above with an inversion and the flow is capped near the crest of the Cascades.  Still, who wants to lose power on a day the temp has trouble getting above freezing?

That east wind will go calm by Saturday night and Sunday morning as high pressure develops directly overhead.  This, along with the bitterly cold airmass that just moved in, will lead to our coldest nights since 2009.  In the areas with snow cover in the valley, Saturday and Sunday nights will probably be the coldest since the 1998 cold wave.  Lots of single digits south of Salem assuming the snow arrives.

Chief Meteorologist Mark Nelsen