Models Coming Together = Forecast Snow Totals

February 4, 2017

11pm Saturday…

Now that we are within 18-24 hours of our snow (or no snow for some) event, the general plan is coming together nicely.  This evening it was time to put some numbers on the table and put a forecast plan together.  Let’s hope the actual weather decides to stick to that plan this time!  I’m sure there’s going to be some wrinkle at the last moment…there always is.

TRENDS I’M SEEING THIS EVENING

  • The stationary front is situated slightly farther north and the surface low pressure system that moves across the Northwest is progged by all models farther north than morning runs, and this has been the trend for at least 24 hours now.
  • This means the snow/rain line is farther north = light snow totals from the metro area south into the Willamette Valley.
  • If this is correct, Super Bowl travel plans within the metro area may be just fine with a wet snow/rain mix falling all the way through the evening.
  • The possibility exists that there will be little to no snow on the ground in the metro area by Monday AM.  I give that about a 30% chance, thus the TRACE-3″ forecast
  • Areas farther north really get dumped on…Longview to Olympia could be big winners with that elusive one foot of snow in that area.

FORECASTS I USED ON-AIR TONIGHT

markheadlines_coldwx

 

marksnow_portlandoutlookpercentages2

 

Note there is a good chance Astoria/Tillamook get far more snow than Salem?  That’s because the heavy snow falls just north of the front and specifically just north/northwest of a low pressure center as it moves onshore.  If you are south of the low pressure area, than at least part of the next 36 hours you’ll see rain.  In fact the evening run of the trusty ECMWF did exactly that, changing snow to rain in the metro area tomorrow evening even in the hills.  If that model is correct we’ll see almost nothing (snow) out of this in the lowest elevations around the metro area.

WHAT COULD GO WRONG WITH THE FORECAST?

Here’s the most obvious wrinkle.  If the front decides to sit about 70 miles farther south than expected and the low tracks inland well to our south, Portland gets a huge snowstorm from tomorrow midday through Monday AM.  But as I mentioned, the trend is the opposite direction.

FOR TOMORROW:

Be aware that between 8am and 1pm there’s a decent chance we switch to lots of snow mixed in or even all snow in the metro area.  But with temps above freezing I think a large area of sticking snow on roads is unlikely.  Of course it’ll be close and roads WILL turn snowy high up in the hills.  Factor that into your Super Bowl travel plans.

I’ll be here at work from Noon-11pm; likely doing some live Facebook videos during the afternoon while we are not on the air.  You can find those on my feed MARK NELSEN page over on the right.

Chief Meteorologist Mark Nelsen

 


Super Bowl Sunday Super Sized Snow For Some Of Us

February 4, 2017

Some nice alliteration in that title eh?  Ridiculous I know, but I couldn’t stop myself on this Saturday morning at 11am.

Luckily we avoided an ice storm for MOST of the metro area yesterday and most of the forecast in the end worked out just fine.  Tons of ice for the morning commute and then by the afternoon most areas were clear except right around/in the Gorge and up in the higher hills.  Of course the cold air lingered longer than expected right along the Columbia River…PDX Airport ended up with .30″ ice and poor Troutdale had .81″ once it was done just before sunrise.  That’s the 4th ice storm along the Columbia River this winter!

Let’s add it up: We’ve had 2 snow/ice events in December, 3 in January, and now 1 in February.  That’s a total of 6 times we’ve dealt with ice and/or snow (or a combo) so far this winter right here in the city.  We haven’t seen a winter like this in the 26 years I’ve been forecasting in Portland.  That doesn’t count 2-3 other wet snow events in the higher hills too.

Tomorrow through Monday morning will likely be #7.  This time you can forget freezing rain, it’s all about 32-33 degree snow under a calm wind.

What’s the plan?

It’s going to  rain a LOT Sunday and Sunday night west of the Cascades where most of us live as a stationary front sits along a line from near Newport to The Dalles.  Subtropical moisture will be riding up along that front = juicy with lots of precipitation.

Check out model forecasts of total precipitation the next few days, most of it is done by Monday morning:

rpm_rain_nworegon

A huge soaker right?  In fact there could even be some localized flooding with this kind if rain intensity.  During the daytime Sunday that front is hung up somewhere across the NW corner of Oregon.  The location is slightly different on each of our models; here’s the ECMWF temperature plot at 4pm (middle of Super Bowl):

ecmwf_temps_4pmsunday

50s in the southern Willamette Valley, but cold enough for a very heavy/wet snow from the Portland metro area north! Is this rare?  Yes, the last time I’ve seen a situation like this was March 21st, 2012, the “Spring Break Surprise”.  Actually it was a couple of days before spring break started, but close enough for a clever name.  Nice pic…

capture

That was a big snowstorm in the central/south Willamette Valley and is now known as the latest snowfall ever at PDX Airport.  You can see looking at that map how a very slight movement north or south will make a HUGE difference in snowfall totals (and who gets a heavy cold rain instead) for the daylight hours Sunday.  Now Sunday evening and night the whole front shifts south as a cold front, which means probably ALL of us in the western valleys get at least some snow.  The big question is who gets pounded with a heavy wet snow and who gets just heavy rain tomorrow during the day.  The short answer is:  We don’t know for sure yet, but north of Portland is looking like the surest bet for daytime snow at this moment.  In this pattern the coastline can get the heavy snow too since there is no warming onshore wind.


SUMMARY

All areas west of the Cascades in the lowest elevations (including the coastline) see steady rain to start Sunday morning

Many areas from Portland/Tillamook north (including Astoria & Longview) may switch over to a heavy/wet 32/33 degree snowfall the rest of the day with many inches possible

The Portland metro area MAY see a switch over to snow during the day; best chance for that will be as you go up in elevation into the hills.  We’ll know more after evening models come in.

South of the metro area a switch to snow is less likely during the daylight hours, but still a possibility

All areas at the lowest elevations along I-5 from Olympia to Albany will likely see at least some snow on the ground by late Sunday night and for the Monday AM commute since we’ll all cool close to 32 degrees

There is a high potential for a heavy/wet snow storm anywhere above 1,000′ in SW Washington and NW Oregon.  There will be locations that see 10-20″!

There is a decent potential that some location somewhere along the I-5 corridor at the valley floor (somewhere between Albany & Olympia) and some city along the coast north of Pacific City will see a foot of snow on the ground by Monday morning.  We just don’t know exactly where at this point.  


Due to the potential that just about any area could see the big snow, the NWS has issued a Winter Storm Watch for all of us westside.  That doesn’t mean everyone is going to get heavy snow, but it’s just a “hey, keep an eye on the forecast” type of watch.

Because of the possibility we could have some sort of historic heavy wet snowstorm in the lowlands, I’ll be working tonight on the 10pm newscast.  Of course I’ll be in tomorrow as well.

Stay tuned because it’s going to be a wild ride for some of us the next 48 hours!

My guess is that you’ve seen different maps on social media floating around showing snow totals from models.  I’ve included a bunch here.  They are all different because each model has a slightly different location for the front, a low passing by to the south Sunday evening, and physics. They each calculate snow in a different way too.  You get the idea…someone is going to get nailed by a big dumping of snow!  By the way, the Cascades have several feet coming too.

ecmwf_snow_monday10am nam_wrf_4km nam_wrf_3km_parallel wrf_snow_mondayam rpm_snow_12z

 

Chief Meteorologist Mark Nelsen