December 2016 Observations and Model Discussion for the Pacific Northwest

[Gradient Keeper]

We aren't going to have much in the way of Gorge help on Monday morning...the mid-week transition event is almost a week away, a lot WILL change. Due to pretty respectable WAA even if Portland surface temp is around freezing thanks to the Gorge outflow we are still looking at rain or ZR, not snow. The 925 mb 0c line is already basically to Portland by 6z Thu on tonight's GFS as well as the 12z Euro...typical warm tongue is around 900 mb suggesting at least south and west of downtown there's a good likelihood of rain even as early as late Wed evening. It only gets warmer from there.

00z WRF wants to give us snow.

 

http://www.atmos.washington.edu/mm5rt/data/2016120200/images_d2/kpdx.90.0000.snd.gif

[bainbridgekid]

We aren't going to have much in the way of Gorge help on Monday morning...the mid-week transition event is almost a week away, a lot WILL change. Due to pretty respectable WAA even if Portland surface temp is around freezing thanks to the Gorge outflow we are still looking at rain or ZR, not snow. The 925 mb 0c line is already basically to Portland by 6z Thu on tonight's GFS as well as the 12z Euro...typical warm tongue is around 900 mb suggesting at least south and west of downtown there's a good likelihood of rain even as early as late Wed evening. It only gets warmer from there.

Gorge outflow will be totally irrelevant on Monday.

 

Flow will be weak onshore and there won't any cold air over there anyway.

 

I think it will be tough to see sticking snow at sea level due to likely weak Southerly winds, but the airmass looks cold enough and there looks to be enough moisture for things to likely be a bit better than you are talking about.

 

You are definitely right about the transition event being totally up in the air at this point though.

[MossMan]

http://cliffmass.blogspot.ca/2016/12/significant-coldsnow-event-next-week.html?m=1

[Bryant]

Looks like a decent shot at some snow showers on Monday morning ahead of the switch to NE winds. QPF amounts probably 0.25" or less.

The models are all handling the amount of precip differently. GFS much better scenario for whatcom county compared to the GEM which leaves everyone up north dry

[Gradient Keeper]

WRF also gives PDX a legit modified blast

 

http://www.atmos.washington.edu/mm5rt/data/2016120200/images_d2/kpdx.132.0000.snd.gif

[Perturbed Member]

00z WRF wants to give us snow.

 

http://www.atmos.washington.edu/mm5rt/data/2016120200/images_d2/kpdx.90.0000.snd.gif

 

He feels those soundings are too unrealistic. 

[snow_wizard]

I understand not wanting to get your hopes up, but being this pessimistic despite some pretty solid model trends in our favor doesn't really accomplish anything. 

 

 

I have to agree.  It would be a huge model fail if we see little or no snow.

[Deweydog]

Marginal setup with southerly flow in the valley...I like the optimism.

 

I'm not going to belabour my opinion, it's simply my opinion. Fine if you agree, fine if you don't.

 

Even assuming we get sticking snow you would probably need to halve the 10:1 ratio the WRF snowfall maps utilize...it's going to be pretty wet slop in the 5-7:1 range best case scenario.

 

I will say if you want snow below 1000' Clark County up around Battle Ground might be the best spot.

The winds are definitely the biggest question in my mind as far as widespread 200' accumulations go. 200 being a fairly arbitrary number at this point...

[Perturbed Member]

We aren't going to have much in the way of Gorge help on Monday morning...the mid-week transition event is almost a week away, a lot WILL change. Due to pretty respectable WAA even if Portland surface temp is around freezing thanks to the Gorge outflow we are still looking at rain or ZR, not snow. The 925 mb 0c line is already basically to Portland by 6z Thu on tonight's GFS as well as the 12z Euro...typical warm tongue is around 900 mb suggesting at least south and west of downtown there's a good likelihood of rain even as early as late Wed evening. It only gets warmer from there.

 

I feel that Monday morning is doable even though it is borderline, I think the biggest risk is the precip shows up later than modeled when it will be a bit too warm.

[Deweydog]

I feel that Monday morning is doable even though it is borderline, I think the biggest risk is the precip shows up later than modeled when it will be a bit too warm.

Timing isn't that big of a deal. If the dynamics are right, the column will cool.

[HighlandExperience]

[Kayla]

I could see you getting 3-6" easily Monday morning and perhaps another inch or two before a transition to rain sometime late Wednesday/Wed night.

 

Looking at the 00z GFS forecast soundings for PDX Monday morning (T/Td):

 

Hour 87 (15z Dec 5): 36/30 (dry layer below about 950 mb), maybe flurries.

Hour 90 (18z Dec 5): 35/33, rain or mix

Hour 93 (21z Dec 5): 37/36, rain

 

All those numbers are higher than the sounding I see for PDX...

 

The sounding at hour 90 gives PDX 32/31

[SilverFallsAndrew]

I always liked Sam Bond's Garage while I lived in Eugene. I wasn't there in March 2012 (barely missed by a few months) but March 2012 was still pretty interesting in PDX. It was so humid and insanely wet.

 

March 2012 has been my favorite month at my present location. Honorable mention go to January 2012, December 2013, Dec. 2012, and May 2013. 

[chopper 918]

The winds are definitely the biggest question in my mind as far as widespread 200' accumulations go. 200 being a fairly arbitrary number at this point...

 

This is going to be a deal where you see a few splats on the windshield and wet ground below about 500', then maybe some wet sticking slushy champagne powder above.

[snow_wizard]

Call me crazy, but I still see a legit snow threat for Seattle Sunday morning.  This run is actually the fastest yet for bringing the 925s below zero.  Precip is still going at that time.

[Perturbed Member]

Timing isn't that big of a deal. If the dynamics are right, the column will cool.

 

Even if the temps at 4AM start at 37-38 as you predict?

[IbrChris]

Gorge outflow will be totally irrelevant on Monday.

 

Flow will be weak onshore and there won't any cold air over there anyway.

 

I think it will be tough to see sticking snow at sea level due to likely weak Southerly winds, but the airmass looks cold enough and there looks to be enough moisture for things to likely be a bit better than you are talking about.

 

You are definitely right about the transition event being totally up in the air at this point though.

There's a 5 kt easterly drift along the river if you buy the 00z UW WRF.

 

I mean, sure it could end up being a nice 1-3" snowfall in the PDX metro on Monday morning, I just wouldn't forecast that outcome at this point. The more likely scenario is an inch or two atop Council Crest and Mt Scott with a positive splat test or even very wet snow in the air across most other parts of the metro.

[luminen]

March 2012 has been my favorite month at my present location. Honorable mention go to January 2012, December 2013, Dec. 2012, and May 2013. 

 

How was your area in September 2013? That was really good for Eugene-Corvallis.

[bainbridgekid]

http://cliffmass.blogspot.ca/2016/12/significant-coldsnow-event-next-week.html?m=1

More bullish than I would have expected from him.

[snow_wizard]

Hope we don't get dry shafted.

 

The dry area the WFR has been showing on Monday is a bit mysterious.  No down sloping, no blocking from the Olympics at the 850mb or 700mb levels.

[SilverFallsAndrew]

How was your area in September 2013? That was really good for Eugene-Corvallis.

 

That was a pretty insane month. About 13.5" of precip. Broke the previous September record by about 6". My power was out a total of 3-4 days late in the month.

[HighlandExperience]

Call me crazy, but I still see a legit snow threat for Seattle Sunday morning.  This run is actually the fastest yet for bringing the 925s below zero.  Precip is still going at that time.

 

That would be pretty awesome if we could get a nice dusting before the main event later in the week. I am pretty excited about the transition event for the Seattle area. 

[IbrChris]

All those numbers are higher than the sounding I see for PDX...

 

The sounding at hour 90 gives PDX 32/31

WRF seems to have a cool bias on its' soundings a lot of the time. Try the actual GFS, then look at the surface winds, 925 mb temp, modeled precip etc.

[Kayla]

Marginal setup with southerly flow in the valley...I like the optimism.

 

I'm not going to belabour my opinion, it's simply my opinion. Fine if you agree, fine if you don't.

 

Even assuming we get sticking snow you would probably need to halve the 10:1 ratio the WRF snowfall maps utilize...it's going to be pretty wet slop in the 5-7:1 range best case scenario.

 

I will say if you want snow below 1000' Clark County up around Battle Ground might be the best spot.

 

Right... The point being the models do not show a southerly flow for PDX Monday morning. Are southerly winds possible, most definitely! But right now the models say things relax a bit during those hours which could throw a wrench into this theory.

[HighlandExperience]

The dry area the WFR has been showing on Monday is a bit mysterious.  No down sloping, no blocking from the Olympics at the 850mb or 700mb levels.

 

I think the WRF is programmed to assume there is no snow over Puyallup. Pretty much every run shows that dry spot whenever it snows 

[Deweydog]

Even if the temps at 4AM start at 37-38 as you predict?

Yes. This kind of setup depends on heavy precip in cold advection with light or calm winds. Once the column cools to at or near 32 it theoretically remains there until the precip lightens. Valley locations will not be at or below freezing at onset.

[Heavy Snow]

That was January 11, 2000. Portland area got a widespread wet 2-3" out of that, does seem like a good comparison.

 

Thanks, yeah that rings a bell! I remember the flakes were huge and there was little to no wind. 

[IbrChris]

Timing isn't that big of a deal. If the dynamics are right, the column will cool.

Right. In this scenario (Monday morning) you're probably not going to see evaporative cooling do the trick as the surface will have a fairly small dewpoint depression (~2c) before the precip starts...what could deliver is CAA...however during the precip the CAA seems fairly weak/even neutral in the lowest couple thousand feet.

[BLI snowman]

WRF seems to have a cool bias on it's soundings a lot of the time. Try the actual GFS, then look at the surface winds, 925 mb temp, modeled precip etc.

 

Meteostar also shows during freezing temps during precip onset on Wednesday in its output,with the column below freezing at 850mb and 925mb.... at face value clearly a 1-2" snowfall on the GFS for Portland.

[Front Ranger]

Followed by a January 1993 repeat for all of December and a December 1992 repeat for all of January.

 

And then a Feb 1993 redux for February.

[snow_wizard]

I think you're overestimating the effect of the ground temps.

 

Maybe if you're talking about the roads, but 32-33 degree snow will stick to grass almost regardless of the ground temps going into it.

 

Plus Sunday looks pretty chilly so it's not like the the ground will be 50 degrees or something.

 

Well yeah...it's going to freeze Sunday night.  I've never bought the warm ground thing anyway (except in some cases).  I've seen it go from torching to sticking snow in a matter of a few hours a number of times.

[Brennan]

per "event" or storm total?

Both. I have my hunch but I want to see what some others think.. models don't seem to catch on to tendencies up here.

[snow_wizard]

That would be pretty awesome if we could get a nice dusting before the main event later in the week. I am pretty excited about the transition event for the Seattle area. 

 

Don't rule out Monday.  I'm betting that dry area being shown will disappear.

[Deweydog]

Right. In this scenario (Monday morning) you're probably not going to see evaporative cooling do the trick as the surface will have a fairly small dewpoint depression (~2c) before the precip starts...what could deliver is CAA...however during the precip the CAA seems fairly weak/even neutral in the lowest couple thousand feet.

It's a tough call, no doubt. It is a little concerning the sounding has things right about freezing at onset. That just isn't gonna happen.

[Gradient Keeper]

Day 2 block bit stronger than previous run

 

 

http://maps1.pivotalweather.com/maps/models/ecmwf/2016120200/048/500h_anom.na.png

[ShawniganLake]

Both. I have my hunch but I want to see what some others think.. models don't seem to catch on to tendencies up here.

1.5" Monday. 3" with the transition event

[snow_wizard]

What do you think about the chances of a CZ setting up?

 

Not much.  The low will be tracking a bit to the west of us.  I suppose there could be one early Sunday.

[Deweydog]

Block is most definitely more masculine, meatier and malcontent.

[SilverFallsAndrew]

Well yeah...it's going to freeze Sunday night.  I've never bought the warm ground thing anyway (except in some cases).  I've seen it go from torching to sticking snow in a matter of a few hours a number of times.

 

Yeah 2/19/93 was a seminal moment in my young life. 13" that day in Silverton. Another big event 2 years later in February. How was I to know it would then be 19 more years until another major February snow event. 

[BLI snowman]

It's a tough call, no doubt. It is a little concerning the sounding has things right about freezing at onset. That just isn't gonna happen.

 

It's really just dependent on precip rates IMO. If we manage to see >0.30" or so of precip on Monday, then I'm confident that some accumulating snowfall will be included in that (assuming things don't trend dramatically warmer with the airmass itself).