One Last Christmas Break Snow Chance Early Thursday

December 29, 2021

1pm Wednesday…

It’s been a fun ride, if you don’t mind driving in a little snow and/or didn’t need to go anywhere the past week. We’ve seen several little (or big depending on location) snow events. Of course the largest and most widespread was Monday night through Tuesday morning. Officially PDX picked up 2.5″, which now means it’s the snowiest December since 2008 in the metro area. We were overdue for a cold & snowy spell in December, they’ve been very mild lately. Although we still haven’t seen a regionwide outbreak of cold arctic air.

That cold modified arctic airmass has once again surged south and through the Gorge, into northern Oregon. At noon we’re barely above freezing in Portland with a chilly east wind blowing on the east side of town.

That cold east wind isn’t too strong, just about 5 millibars from The Dalles to Portland pressure differential. Weak sauce… right now things look like this as sea level (black lines, not the colors). Cold high pressure sending easterly wind into NW Oregon/SW Washington and a weak area of low pressure forming near Haida Gwaii

That low slides down the coastline, like previous ones have, but this time it goes inland NORTH of us. Looks like this around 10am Thursday. You like my 3rd grade drawing skills?

We get a relatively strong southerly wind later tonight through the first half of Thursday. That means the cold arctic air is replaced by a much milder airmass (temporarily). Snow levels lift up to around 2,000′ or so by midday. All models support the idea of a quick late night warmup from Portland south and all along the coastline. We’re going for a low of 23 in Portland tonight, but that’s before midnight. I expect temperatures to be around 33-34 by 7am across most of the metro area. Precipitation from this system starts as snow which will stick in some spots from the Portland metro area north. South of Portland I think sticking snow is unlikely (including Salem). The cold air sometimes lingers longer than expected in the Longview/Kalama/Woodland/St. Helens areas in this setup. I’ve seen it before. I think that’s where a quick 1-2″ is more likely.

After 10am or so precipitation turns to light showers, mainly rain in the lowest elevations. Most models look something like this

SUMMARY

  • It’s unlikely this will be a significant snow event in the lowest elevations from Portland/Vancouver southward, especially after what we’ve seen the past few days.
  • Sticking snow begins between 5-8am from Portland/Vancouver area north, but for most of us I don’t expect much road accumulation due to rising temps. Snow will still be in the air for a few hours though; it may look quite snowy. I am forecasting NOTHING TO 1″ ACCUMULATION, BEST CHANCE FOR STICKING NORTH OF PORTLAND

METRO AM COMMUTE: Spots of leftover snow/ice on roads from overnight freezing, possibly a few spots of new snow, but not much. Temps rising from 32 around 6am.

METRO PM COMMUTE: Totally clear roads, except leftover snow/ice way up in hills, and possibly northern Clark/Cowlitz counties. Temps in the upper 30s.

COAST/SALEM/ALBANY: Likely clear roads & no snow tomorrow

GORGE: Snowy morning, 1-4″ new snow by midday. I-84 may be icy/snow first half of day

The low pressure system and upper level flow is perfect for heavy snow in Cascades and the Blue Mountains. Tomorrow is not a good day for travelling I-84 east of La Grande or through Cascades passes as you can see in the accumulation graphic above.

Just like Tuesday night and this morning, that chilly arctic air will attempt to surge south by Friday morning. But it won’t be quite as cold. Expect lots of clouds and temperatures only in the mid 30s Friday. New Year’s Eve should be just fine weatherwise, unless we get scattered icy spots on the roads. You can see that chilly high pressure back in control at 10am Friday with more of those nice hand-drawn features. BTW, I think in high school art class I got a C at best…really! Hmmm…

Friday/Saturday will mark the end of the cold northwesterly flow we’ve been in for about two weeks. Here’s the view overhead tomorrow

By Monday, we’ve transitioned back into an active westerly jet stream again with various model solutions for next week. All of them are wet.

Sometimes we get a big snow/ice event at the end of a cold spell. That’s when we get a deep upper-level trough offshore and low level offshore (easterly flow). That’s not happening this time. It’s a relatively quick change to southerly wind Saturday through Monday. When solid precipitation arrives later Sunday and Monday, most likely it’ll be rain. But this means even MORE snow in the Cascades. Snowpack is now well above average in many parts of Oregon. Very good news!

That’s a wrap for 2021. I’ll be off Thursday-Sunday so no blog posts until early next week. Stay safe in your travels.

Chief Meteorologist Mark Nelsen


Quick Moving System Dropping Light Snow Tonight & Cold Weather Continues

December 27, 2021

9pm Monday…

We ended up with 0.7″ snow officially in Portland on Sunday. That was a mix of Sunday morning and again Sunday evening. That brings our winter total to 1.1″

Luckily no freezing rain so far and none in sight!

Today the southern edge of that cold arctic airmass moved through the metro area. That was right around sunrise. A northwest breeze kicked in, bringing the 25-28 degree air south. The high at PDX was right after midnight…34 degrees. It bottomed out at 26, now has risen back to just under freezing for most of us as the thin layer of arctic air mixes in with surrounding air. There’s no fresh supply of cold air coming from the north or east until Wednesday morning. So it’s plenty cold, in fact the 850mb temp of -9.9 degrees at Salem means it’s about 18 degrees at 4,000′ overhead! That’s also the coldest measured over Salem since the arctic outbreak of December 2013.

It’s snowing again tonight! I see a dusting all across the metro area and the boss says he’s got 1/2″ (fresh) in Lake Oswego. Most of the lower elevations west of the Cascades are under a Winter Weather Advisory. Anything over 1″ triggers that advisory. I remember in the 1990s when the criteria was either 2″ or 3″, but then after a few events it became obvious Portland can come to a standstill with 1-2″ snow, so an advisory typically means at least 1″ snow is expected. I think a Trace to 2″ covers it for tonight, although gut feeling says the majority of us get an inch.

I think roads will be mainly fine midday and tomorrow afternoon, assuming we really only do get less than 2″. Side roads in neighborhoods of course could remain snow covered all day

A “BC Slider” (a weak surface low that moves quickly down the Pacific Northwest coastline) is providing lifting, clouds, & light snowfall. The low is well west of Astoria right now

By 4pm tomorrow, the low has weakened and spread out a bit on the southern Oregon coastline. We won’t see much wind from any direction these next 24 hours because it’s so weak.

This light snowfall continues through tomorrow morning with flurries following the rest of the day. Temperatures remain below/near freezing most of the time. All models produce between 1/2″-2″ snowfall, most around 1″. The contour here is the HRRR. The GFS is much wetter/whiter…producing 3-5″ in the Salem/Albany areas by tomorrow evening! That’s due to another weak wave coming down south in the upper atmosphere later tomorrow, prolonging the precipitation. There is a decent “bust potential” in the lowlands with this event…

After the low dies to our south tomorrow evening, a fresh surge of that modified arctic air pours through the Columbia River Gorge. That should bring drier air, sunshine, and high temps only around freezing or so Wednesday. That will be our third day around the freezing mark. A chilly 12 days of Christmas indeed!

I’m watching the next system for Wednesday night & Thursday closely. All models agree that one more little “slider” comes down the coastline, but moves inland across the central part of Washington this time. That gives us a gusty southerly wind for at least a few hours that day. We’ll probably climb into the mid-upper 30s at some point Thursday with the warming onshore wind, but not before somewhere between 1-3″ snow falls.

That’s it for this evening…enjoy the snow! Chief Meteorologist Mark Nelsen


Snow Showers Picking Up In Metro Area: Watch Out For Icy Monday AM Commute!

December 26, 2021

9pm Sunday…

It’s tough to get “sleddable” snow when not much of ANYTHING falls out of the sky. That happened in much of the Portland metro area today. Lots of sunshine, sparse shower action, and very little precipitation. In fact PDX only recorded .05″ yesterday AND today combined! Officially we squeezed out 0.5″ of snow last night and early this morning. The daily total continues through midnight so that could change since we’re seeing plenty of snow showers right now.

I don’t think I saw a report of more than 2″ anywhere in the metro area (so far!) except out in the Hillsboro, Banks, Forest Grove areas. That includes Clark county and the western Gorge too. Most of the showers didn’t do much once they passed over the Coast Range. Of course with some sunbreaks and temperatures above freezing, that little bit of snow melted by early afternoon.

Remember I forecast Trace-3″ in the last few blog posts. Yet there was MORE snow than expected in a few places. Salem, McMinnville, Forest Grove, Longview, Lebanon, Albany. Models had hinted there would be some “training” of those snow showers bands and it did happen. But just in a few spots.

Someone was harassing me on Twitter about the forecast (always wrong, etc…) earlier. How would YOU handle a situation like this when some random spots will get a lot of precip and others will not? On a normal showery weather day hardly anyone would notice if we get 0.45″ vs. 0.15″ rain. The only difference now is that temps are near freezing = snow. Then everyone suddenly cares (for good reason) NWS decided to forecast for those highest numbers and issued a Winter Storm Warning to cover it. I chose to miss those high numbers and focused on what I thought most would get (Trace-3″), hardly mentioning the warning.

This evening the very cold arctic has made it to just north of Longview and east of the Cascades to Arlington.

That “arctic front” is now falling apart and we’ll just see a little filtering of that arctic air down into our area. We won’t be 23 degrees like what Seattle is seeing right now! The surface low and nearly dead arctic front is just south of us tomorrow morning

Snow showers have picked up a bit the last 2 hours and that means we still have a chance for a widespread dusting (likely) or even up to 2″ in the metro area (less likely). Roads are going to be very icy for the Monday morning commute!

The rest of the daylight hours Monday will be uneventful and most frozen roads slowly thaw. Main roads should be fine for the evening commute, just leftover slick spots where more than 2″ snow has fallen.

A “B.C. Slider” will be coming down the coastline tomorrow evening through Tuesday morning. That’s a little wiggle in the cold northerly jet that spins up a surface low pressure system and clouds/snow. A situation like this will be much different than what we are going through right now. This is a general/widespread light snow event. Temperatures will hover near freezing tomorrow night through the morning commute Tuesday. Most likely we pick up 1″ or so snowfall during that time. It’s unlikely we have a frozen mess Tuesday morning, but lots of slushy snow. Still, that’s not fun to drive on either! Then it warms above freezing again Tuesday afternoon for reasonable driving conditions many areas.

After another dry day Wednesday, another “slider” comes down the coastline. But that one is more likely to move inland NORTH of us. That’s important because a southerly breeze warms the lowest levels of the atmosphere quickly in this situation. We may go from snow to rain during that little precip event.

I sure don’t see a “snowstorm” with either of these two systems Tuesday and Thursday, but will be keeping an eye on things…

Enjoy the white start to your Monday!


Snow Showers Pick Up Tonight & Sunday

December 25, 2021

9pm Christmas Day

Merry Christmas!

We expected mixed showers today and that’s what we’ve been seeing. Except there hasn’t been much of ANYTHING in the western valleys. Now we know drier models have been correct…so far. Only .03″ in Portland so far!

Of course if those dry-ish models are correct and we don’t get that many showers tonight/tomorrow, then no sledding for many of us. Right now temperatures are in the low-upper 30s in the metro area, coolest in the higher areas of course

This is a couple degrees warmer than what I expected for 8pm when I last worked Thursday evening. Regardless, the atmosphere overhead continues to cool as cold showers continue to pivot onshore. I see it’s down to -6 (in Celsius ~4,000′ up) over Salem during the afternoon balloon sounding. That’s forecast to go to -9 by daybreak. With temps just a few degrees above freezing, any substantial snow showers will be able to stick tonight through the first few hours of daylight Sunday. In fact, just in the 10 minutes I’ve been typing, the ground at our Seaside camera, including the beach sand, has turned white! We may not see too much sticking midday tomorrow, but then cold enough again tomorrow evening and night.

HIGHLIGHTS

  • ANYONE in the region north of about Florence on the coast and inland can pick up accumulating snow from this point forward.
  • Expect a wide range of accumulation in the lowest elevations. A Trace to 3″ should cover most of us. An outlier 4-5″ could show up somewhere, and up in the higher hills around Portland, Newberg, Amity, Salem I could see 4-6″. It’s possible part of that falls before 10am tomorrow, then a bit more tomorrow evening/night. I know the NWS has a Winter Storm Warning up, but that’s a technicality since any one location needs 4″ or more to qualify as a WSW in the lowlands. These showers will be coming and going…not one big storm that goes on for 12-24 hours.
  • Expect all roads to freeze Sunday night for the Monday morning commute

I still like this graphic, note many main roads may be just fine midday tomorrow

FOR THE WEATHER GEEKS

It’s rare for the lowest elevations to get any significant snowfall when we have a southerly wind going. That was the case today and will still be the case tomorrow, although not as strong. That wind keeps the air mixed up and sure isn’t coming from a colder region = harder to get sticking snowflakes to sea/ground level. That’s why I’m always cautious about using model “snow maps” in these situations. So marginal. Remember some models were showing sticking snow today…at 35-38 degrees. That’s not happening and that’s why we said “mixed showers Christmas Day” for many days leading up to this.

Arctic air pouring out of BC has spun up a surface low that is just west of Forks, WA. Cold arctic air is bottled up north of the red line. Bellingham is 19 with a northeast wind gusting to 40 mph! Of course the cold air over the ocean is picking up moisture, sending a stream of showers inland over southern Washington and Oregon

To get rid of the southerly breeze, it needs to die or go south of us. We will still be in a similar setup tomorrow morning at 10am, with the leftovers of the low somewhere between Olympia and Mt. Adams.

As of midday tomorrow the cold/dry arctic air has NOT arrived, so after getting close to freezing tonight, we rise back up into the mid 30s tomorrow. That’s why I think many roads might be pretty reasonable midday UNLESS some very heavy bands of snow showers develop. Typically I’d say little/no snow with this setup. But 850mb temps are -9 tomorrow, which should just barely overcome the continuing (weak) onshore flow. IF WE DON’T GET HEFTY SHOWERS tonight through tomorrow evening, we’ll get very little snow. It needs to come down at a steady clip if we want to be sledding by Monday morning. By that time (4am Monday), the low has fallen apart and is down off the Oregon coastline

Most of our models are producing somewhere between a Trace and 3″ snow along the I-5 corridor from Longview to Albany, in line with our forecasts. Fresh run of the GRAF model out this evening looks good; now through Monday morning when it dries out

The latest Euro was drier, producing more like a Trace to 2″

The fresh WRF-GFS really tries to enhance the bands of snow coming onshore… 0.5″ up north to (gulp!) 10″ around Salem or Albany areas. Seems unlikely but…we will see!

That’s it for this Christmas Evening, I’ll be on TV at 10pm. I’ll be at work tomorrow and hopefully take a look farther ahead into next week

Chief Meteorologist Mark Nelsen


Lowland “Sleddable” Snow Likely For Many of Us Sunday

December 23, 2021

11pm Thursday…

Merry Christmas everyone! I’ll be off Friday; time to “check out” and hang out with the family. I’m back late Christmas Day. We have a 10pm show and I’ll be there. Plus we do get a nice free meal, I’m really coming in for that…

A very quick post…forecast continues to be the same. Some evening models are a little bet wetter (more white) Saturday night and Sunday. That makes me think many of us will be able to sled on the snow Sunday, or by Monday morning at the latest. Standards for doing so are quite low in our climate…1-2″ will do it. I expect 4-6″ up around 1,000′ or so. This timeline graphic covers the situation well

Enjoy your holiday! Chief Meteorologist Mark Nelsen


Christmas Weekend Snow: Forecast Looking Solid For Now

December 23, 2021

2pm Thursday…

I’ve checked out all the maps/models/soundings/cross-sections today…you know, like normal people do 2 days before Christmas… (insert laughing emoji!)

We’ve gone 13 years without a major snow/ice/cold event during the Christmas-New Year’s week; apparently it’s time. Last time was December 2008 when 10-25″ buried parts of the metro area in the days leading up to Christmas. That’s not going to happen in this case. Far less snow, at least through this weekend.

THE BIG MESSAGE

  • I do not see a “snow storm” between now and Monday when we dry out, BUT anytime after sunset Christmas day you could run into snow on any road ANYWHERE west of the Cascades. That includes the coastline. BE PREPARED IF YOU PLAN ON DRIVING CHRISTMAS DAY OR BEYOND
  • A showery weather pattern, just like today, continues through Sunday, then cold arctic air drifts in from the north and we dry out for at least a few days next week
  • If you live in the hills closer to 1,000′ and above, expect some white on the ground as early as Christmas morning and roads COULD be snowy up there anytime from that point forward
  • Prepare for a hard freeze beginning Monday night for a few days. Teens in outlying areas, even single digits if we get more than 2″ snow on the ground. Cold east wind starts blowing out of the Gorge…brrr!

How much could fall in the lowest elevations?

It’s still 3 days out, but I’m leaning toward a Trace to 2″ for most of us (Saturday night through Sunday night), REALLY TOUGH to forecast since we’re be in a scattered showers pattern and in general precipitation is light during that time. I wouldn’t be surprised to see more than that in a few spots. Could some of us in the lowest elevations see 3-4″ on the ground by Monday morning? Sure! But don’t come complaining to me if you only pick up a dusting or an inch…

I really like the WRF-GFS snowfall depiction, it represents what I’m thinking. 24 hour snowfall ending 4pm Christmas afternoon (Saturday). Hilltop 1-2″, little or nothing below.

The reason we’re not getting much of anything Christmas day is two-fold. First, a mixing southerly breeze continues the entire day. And the atmosphere just isn’t THAT cold during the daytime. A -6 to -7 (Celsius) at 850mb isn’t going to get much sticking snow to the valley floor as long as that wind is blowing. By Sunday, it’s down to a -9, which even with the breeze (lighter) will be enough to bring sticking all the way to sea level. Sunday is just a matter of how much precipitation is still left. We will see.

The WRF-GFS cross section shows the situation well. Time is right to left (Friday – Sunday). “850” is pass elevation around 4,000′. You see the freezing line (drawn in blue) is well above the valley floor through daytime Saturday, then it goes down to the surface Saturday night. See that constant S-SW wind until Sunday morning too (wind barbs in red).

By Sunday evening, the arctic front (leading edge of cold/dry arctic air) is at our doorstep. That drops over us Monday and we’ll have trouble getting above freezing that day. So whatever falls Sunday will be frozen solid Monday morning.

I’m out of time since I’m on TV for all 7 shows this evening. See you on KPTV. Remember you can watch us at www.kptv.com/live


Christmas Weekend Weather & Road Conditions Update

December 22, 2021

8pm Wednesday…

I’ve got a short update to let you know what’s up weather-wise as we head into the busy Christmas Weekend. I’m planning on a longer post early afternoon tomorrow. Just about everything I mentioned yesterday evening is still valid. Here’s what I’m seeing right now:

  • The next 4 days (Thursday through Sunday) we will be in the “showers and sun breaks” weather pattern.  There are no “storms” headed for the lowlands west of the Cascades through Sunday (the 26th).  But the airmass will be cooling each day, and by Christmas Day it’ll be cold enough for sticking snow at night even at the lowest elevations.  During the daylight hours on Christmas Day, we’ll see mixed rain/snow showers, but sun breaks too.  Most or all accumulation of snow that day should be in the higher hills around the metro area and mountains.
  • By Christmas night (Saturday night), there’s a better chance snow showers stick all the way to sea level and I wouldn’t be surprised if many of us wake up to at least some “white” Sunday morning.  More showers follow that day before we dry out a bit Monday.
  • Just about all of our models are saying cold/dry Canadian arctic air gradually works south into the Pacific Northwest Monday through Wednesday next week.  If that’s the case, the lower elevations will freeze up with daytime highs only in the 20s!  Now that WILL be pipe-busting weather. Will it be something we haven’t seen in many years? Or just regular cold? TBD.
  • If you see a snow total forecast or graphic showing “X” inches will fall in Portland in the next week, ignore it. We can’t forecast specific snow totals more than maybe 3 days ahead of time…at best. Especially in a showery pattern like what’s headed our way this weekend. We can say “it looks like many inches”, that’s reasonable. But anything specific 4-6 days ahead of time is silly.

At this point we don’t see a “snow storm” in the Portland metro area through Monday, but multiple chances (in showery form) for sticking snow from Christmas night through Monday.  We’ll be keeping a close eye on the rest of next week though. Some models are trying to produce a “shut Portland down” type snowstorm Monday night & Tuesday. Yes, an “all hands on deck!” sort of event for Portland’s local TV stations. I have vacation scheduled for next week as do lots of other people…we will see.

Wondering about driving in the lowest elevations from Eugene to Longview? Just fine tomorrow, Friday, and daylight hours Christmas Day.

Key point…

YOU SHOULD BE COMFORTABLE DRIVING ON SNOW/ICE BEGINNING SATURDAY EVENING IF YOU PLAN TO HEAD OUT ON THE ROADS IN THE LOWLANDS

I’m not saying that will happen everywhere, but by sunset Saturday it’ll be cold enough for snow showers to drop sticking snow with accumulations anywhere, including the coastline.

Traveling elsewhere? Really tough through the Cascades from tonight through the weekend. I-5 through the Siskiyous could be treacherous at times. The Columbia River Gorge doesn’t look all frozen and messy Saturday, but some snow could accumulate at times Sunday as temps drop.

Coast Range highways will turn snowy for the first time Friday evening and that continues through the weekend, especially overnight hours.

That’s it for now, I’ll take a look at next Monday/Tuesday’s possible snow “event” on tomorrow’s blog post. Plus, we’ll see how cold we’re looking for the last few days of December. I’m on TV right now and will be through 11:30pm tonight. You can always find that at www.kptv.com/live

Chief Meteorologist Mark Nelsen