December 2016 Observations and Model Discussion for the Pacific Northwest

[snow_wizard]

Still looks like a reasonably solid cold shot coming up. Too bad the models can't nail down the moisture for Sunday night through Tuesday morning a bit better.

[Gradient Keeper]

Areas close to the gorge could see some decent (sh*tty) icing.

I'm well east of I-205 and often I'm in the sh**tty zone.

[IbrChris]

Still deciding when I'll head east through the Gorge next week...but it looks like if I'm not on the road by Wed afternoon the next window looks to be Friday sometime. Wed night-Thu night looks pretty gnarly.

[snow_wizard]

Day 3 looks promising. Arctic trough digging further offshore

 

That cluster of positive anomaly centers is insane!

 

The 534 line is way further west than the GFS.

[Deweydog]

I'm well east of I-205 and often I'm in the sh**tty zone.

You can have it.

[Gradient Keeper]

That cluster of positive anomaly centers is insane!

 

The 534 line is way further west than the GFS.

Yeah the block is actually trying to hold further west.

[SilverFallsAndrew]

My brother lives in The Dalles now... He should see some good action. 

[BLI snowman]

The soundings from like 3 or 4 of the last WRF runs in a row have shown this snow profile sounding for PDX though. Some on here don't buy it. What do you think?

If that energy drops off the coast a bit more like tonight's runs (sans the NAM) are showing, then I think the modeled precipitation would do the trick. Pretty good odds of a widespread 1-3" type of event.

 

I tend to think that the 11th hour trends towards mitigating airmasses and pushing lows northward may kill those odds, though.

[Gradient Keeper]

Forecast Trend from past 2 days of ECMWF runs. Much like the GFS trend I posted earlier note the south-southwestward progression of colder air. The arctic trough is digging just a tad more each run. Let's keep this going!!!!

http://imgur.com/cxLG7OX

[snow_wizard]

00z is the third run in a row where the operational is on the warmer side of the mean. 

 

Nice to see the overall cooling the longer range. No above normal temps.

[IbrChris]

00z is the third run in a row where the operational is on the warmer side of the mean. 

 

Has to do with the slightly worse resolution of the ensembles vs the operational...in the nearer term the ensemble plume correlates better so it looks like the operational is an outlier when in fact the operational at a higher resolution has a better handle on terrain. At 850 mb there's still plenty of terrain influence.

[Kayla]

500 mb thickness down to 520-522 during the precip is encouraging...however in a situation like this with steepening lapse rates as the 500 mb cold pool swings through the region the 500 mb thickness has a weaker correlation with snow at the surface compared to situations where the lower levels are more stable. Surface temps/dewpoints still seem a bit too warm on Monday on the 00z GFS.

 

One reason I say 925 mb temp/850 mb thickness is superior.

 

850 mb thickness

00z NAM: ~1298 (precip mostly over by hour 48 or 00z Monday)

00z GFS: 1293 (hour 54), 1290 (hour 60)

 

925 mb temp

00z NAM: -1.5c (hour 48)

00z GFS: -1.4c (hour 54), -2.2c (hour 60)

 

GFS at face value suggests snow basically to sea-level...the questions then become 1) is it bringing the cold air in too quickly, 2) is it too aggressive with the precip. NAM is about as cold for hour 54/60 but dry with just a few isolated showers around.

 

If the GFS is an accurate depiction snow may be a real concern for much of the metro area, but just some very minute differences in the profile of the lower levels (850-925 mb) and the temporal extent/intensity of the precip would be the difference between 1-2" and zero. 

 

Looking at the 00z NAM and GFS I feel like the odds of accumulation above about 500-700' is pretty good (80%+) provided the precip sticks around through hour 54-60 and I'd give a roughly 30-40% chance of measurable accumulation downtown.

 

Great input on your thoughts on this, thank you.

[IbrChris]

Great input on your thoughts on this, thank you.

I guess everyone was put off by my perceived "Negative Nancy" persona yesterday, but I wasn't trying to drag people down...I guess I should have said something similar to tonight versus blurbs that come across as simple naysaying.

 

Maybe miniscule improvement on the 00z tonight vs 24h ago...or maybe I'm just choosing to see it a bit more optimistically.

[Poulsbo Snowman]

'm not off put by anyone who wear the green.

[Timmy]

Has to do with the slightly worse resolution of the ensembles vs the operational...in the nearer term the ensemble plume correlates better so it looks like the operational is an outlier when in fact the operational at a higher resolution has a better handle on terrain. At 850 mb there's still plenty of terrain influence.

The term "outlier" is used too loosely anyway here. When in actuality it refers to irrelevant data outside the standard deviation that would increase as we get further out in time. So to say something is an outlier when it is 2 degrees off the mean a week away is false. Likewise something 1 degree off 3 days away would not be an outlier either.

[snow_wizard]

No question the ECMWF hold onto much stronger blocking over the Aleutians and Bering Sea in the longer range than the GFS.

[Kayla]

Looks like the column (by a smidgen) stays below freezing as the precip arrives early Thursday morning per the Euro.

[Kayla]

I guess everyone was put off by my perceived "Negative Nancy" persona yesterday, but I wasn't trying to drag people down...I guess I should have said something similar to tonight versus blurbs that come across as simple naysaying.

 

Maybe miniscule improvement on the 00z tonight vs 24h ago...or maybe I'm just choosing to see it a bit more optimistically.

 

Yeah have to hand it to the super computers. They've shown amazing consistency in the short to medium range.

[Heavy Snow]

The updated run of the 00z KING EURO is still showing a significant overrunning event for PDX on Thursday. From the maps I see, it looks like PDX only gets to 31 on Thursday with widespread 0.5"-2" of snow and some ice!

[Gradient Keeper]

Day 7 ..... Look what King EURO is trying to do this run...

 

http://maps1.pivotalweather.com/maps/models/ecmwf/2016120300/168/500h_anom.na.png

[HighlandExperience]

00z Euro shows about an inch for most of the I-5 corridor in Western WA through Tuesday morning. That's about it.

 

I think it's safe to say the models still have no handle on precip for Monday/Tuesday morning. Hopefully by 00z runs tomorrow we will have a better idea.

I'd take an inch for our first warning shot.

[IbrChris]

The term "outlier" is used too loosely anyway here. When in actuality it refers to irrelevant data outside the standard deviation that would increase as we get further out in time. So to say something is an outlier when it is 2 degrees off the mean a week away is false. Likewise something 1 degree off 3 days away would not be an outlier either.

When looking at the spread at a particular hour (in this case within the first 5 days) and the ensemble member spread is very small, yes the operational would be rightly termed an "outlier" at least at first glance given the fact the standard deviation in the ensemble is very small and the operational is 2+ standard deviations from the mean.

 

But my point was actually that the operational isn't an outlier, the discrepancy has to do with poorer resolution on the ensembles. We really should run them at a higher resolution inside day 7 IMO.

[Gradient Keeper]

Day 8 ....... Just got mildly interesting

 

http://maps1.pivotalweather.com/maps/models/ecmwf/2016120300/192/500h_anom.na.png

[Timmy]

When looking at the spread at a particular hour (in this case within the first 5 days) and the ensemble member spread is very small, yes the operational would be rightly termed an "outlier" at least at first glance given the fact the standard deviation in the ensemble is very small and the operational is 2+ standard deviations from the mean.

 

But my point was actually that the operational isn't an outlier, the discrepancy has to do with poorer resolution on the ensembles. We really should run them at a higher resolution inside day 7 IMO.

Sure I get that, I was more pointing out the term being loosely used after day 6-7 to point out ensemble members that aren't really outliers.

[luvssnow_spokane]

[snow_wizard]

Is the King Euro a new model I didn't know about?

[HighlandExperience]

[Gradient Keeper]

Day 9  Entirely different 500mb progression after day 6 compared to previous runs

 

http://maps1.pivotalweather.com/maps/models/ecmwf/2016120300/216/500h_anom.na.png

[Heavy Snow]

As of right now for PDX, I think the Thursday over-running event will mirror the January 3 2016 event earlier this year with the possibility of something even bigger. Some light snow accumulations to start (0.5" to 2", up to 3" in isolated spots) followed by some ice with highs at or below freezing. Areas on the East side will thaw out later than the West side. That's my forecast right now if I had to make one.

[Gradient Keeper]

Ahhhh. Close...... sorta ..... but not really..... Better luck next run

 

http://www.tropicaltidbits.com/analysis/models/ecmwf/2016120300/ecmwf_T850_nwus_11.png

[luvssnow_spokane]

[Perturbed Member]

I guess everyone was put off by my perceived "Negative Nancy" persona yesterday, but I wasn't trying to drag people down...I guess I should have said something similar to tonight versus blurbs that come across as simple naysaying.

 

Maybe miniscule improvement on the 00z tonight vs 24h ago...or maybe I'm just choosing to see it a bit more optimistically.

 

I appreciate your relatively objective analysis of the models. It helps keep the expectations here in check.

[luvssnow_spokane]

I appreciate your relatively objective analysis of the models. It helps keep the expectations here in check.

Ditto! Thank you!!

[Bryant]

Has to do with the slightly worse resolution of the ensembles vs the operational...in the nearer term the ensemble plume correlates better so it looks like the operational is an outlier when in fact the operational at a higher resolution has a better handle on terrain. At 850 mb there's still plenty of terrain influence.

 

Was talking to bainbridgekid about this earlier. As the time frame in question nears, the ensemble will often give false hope of being colder, when in reality the operational has a much better idea in general 

[Bryant]

00z Euro shows about an inch for most of the I-5 corridor in Western WA through Tuesday morning. That's about it.

 

I think it's safe to say the models still have no handle on precip for Monday/Tuesday morning. Hopefully by 00z runs tomorrow we will have a better idea.

 

I know I ask you this all the time, but can you post up the Washington Euro snowfall map? For the Mon-Tue time frame

[IbrChris]

Tweaking the consensus forecast output...classic box plot with whiskers (max/min values)

 

3Q = 3rd Quartile (50th-75th percentile), warmer than the median

2Q = 2nd Quartile (25th-50th percentile), colder than the median

[Gradient Keeper]

6z Pacific Surface Analysis

This is a possible game changer. The NWS/NCEP forecasters now forecast over the next 24 hours for the Kona Low to dissipate. I have yet to see any model guidance suggest this, but the forecaster must be seeing something. Now obviously if that were to occur it could change things quite a bit and possibly result in colder model runs soon. Understand that I am not saying that's what we'll see. I do use the PSA tool often and it is quite regularly very accurate, but it's not always gospel either. I have looked at the latest surface observations from buoys and other stations north of Hawaii and any pressure falls are largely negligible. If that continues there may be some validity to this new forecast of dissipation. Let's hope so. 6z GFS is about to run in 13 minutes and I wouldn't expect to see it to initialize the Kona Low, then dissipate it 18-36 hour later, but we'll just have to see.

 

http://i.imgur.com/TMOd8t2.jpg

[Gradient Keeper]

6z GFS
Begins in.... 6 minutes

I wouldn't expect any changes as models and ensembles are very much in agreement. Let's see if there is any change to how the Kona Low is handled. Let's dig that arctic trough!!!!

Feel free to play along (You may need to refresh pages)
Northwest view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=nwus&pkg=mslp_pcpn_frzn&runtime=2016112912&fh=0&xpos=0&ypos=197
North America view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=namer&pkg=z500_mslp&runtime=2016112912&fh=0&xpos=0&ypos=197
North Pacific view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=npac&pkg=z500_mslp&runtime=2016112912&fh=0&xpos=0&ypos=197
Alaska view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=ak&pkg=T850&runtime=2016112912&fh=0&xpos=0&ypos=197
 

[Phil]

Well, the ECMWF/EPS actually (mostly) caved to the GEFS/GFS in the extended range. Don't see that too often.

[Perturbed Member]

6z GFS

Begins in.... 6 minutes

 

I wouldn't expect any changes as models and ensembles are very much in agreement. Let's see if there is any change to how the Kona Low is handled. Let's dig that arctic trough!!!!

 

Feel free to play along (You may need to refresh pages)

Northwest view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=nwus&pkg=mslp_pcpn_frzn&runtime=2016112912&fh=0&xpos=0&ypos=197

North America view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=namer&pkg=z500_mslp&runtime=2016112912&fh=0&xpos=0&ypos=197

North Pacific view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=npac&pkg=z500_mslp&runtime=2016112912&fh=0&xpos=0&ypos=197

Alaska view - http://www.tropicaltidbits.com/analysis/models/?model=gfs&region=ak&pkg=T850&runtime=2016112912&fh=0&xpos=0&ypos=197

 

 

What are your thoughts as far as snowfall in PDX on Monday?