December 2020 Weather Observations for the PNW

[Esquimalt]

4 minutes ago, hawkstwelve said:

12z EPS members show the following chances for snow...

KBLI: 84% (Avg: 1 inch)

KPAE: 84% (Avg: 1.25 inch)

KSEA: 76% (Avg: .5 inch)

KPLU: 96% (Avg: 2 inch)

KOLM: 16% (Avg: .1 inch)

What does it say for Esquimalt?   

[VancouverIslandSouth]

13 minutes ago, Esquimalt said:

RGEM also a touch north.  I'm not worried yet, but will wait till the GFS and euro to cast my judgement. 

These things always seem to take a last minute jog north, although most models have moved toward what the GFS has been showing. It's usually best to be just to the north of where the best activity is shown.

[Esquimalt]

Just now, VancouverIslandSouth said:

These things always seem to take a last minute jog north, although most models have moved toward what the GFS has been showing. It's usually best to be just to the north of where the best activity is shown.

Yeah I think we’re in a pretty good spot here in Vic. Environment Canada doesn’t seem to think so but honestly their endorsement could be the kiss of death lol

[SilverFallsAndrew]

Norte 

[wxmet]

A notch or two north doesn’t matter as much as how much cold air filters in behind the system once it passes.

[GHweatherChris]

[bainbridgekid]

Definitely a last minute slight North trend.

May not make a huge difference though because it's only in the backwash behind the low that has the chance of snow.

 

[wxmet]

Heavy snow for the central Sound

 

[bainbridgekid]

Beauty.

 

[VancouverIslandSouth]

Just now, bainbridgekid said:

Definitely a last minute slight North trend.

May not make a huge difference though because it's only in the backwash behind the low that has the chance of snow.

 

Yeah, it matters more up here than it does down there. The backwash will cover a much larger geographic area and it would take a very large jump north to miss out on that.

[wxmet]

The 0C isotherm is closer to the surface in this N-S cross section. Should bode well in terms of accumulation if you've got a couple hundred feet of elevation.

 

[El_Nina]

Really monumental rain today as we approach 3 inches towards the end. Reminds me a little bit of December 2015. 

[Esquimalt]

Beauty of a c-zone signature on the HDRPS this afternoon

[Christensen87]

When would NWS post a WWA or even a WSW? 

[TT-SEA]

19 minutes ago, El_Nina said:

Really monumental rain today as we approach 3 inches towards the end. Reminds me a little bit of December 2015. 

And its been dry here all day... win-win!

[wxmet]

1 minute ago, Christensen87 said:

When would NWS post a WWA or even a WSW? 

During the event 

[Winterdog]

2 hours ago, MossMan said:

If the 18zzzz’s still have me in the blue I am going to go ahead and stage my plow and get the snow shovel out of the shed.

 

Currently drizzling and 46. 
.02” so far on the day. 

You had better get to staging that thing.  18Z has you and I both in the pinkish 6"+ area.   I'd hate for that low to go much farther north though since the area of backwash snow will shrink for us.

[wxmet]

There is talk about how this event looks very similar to the December 1974 event which led me to read about it in a paper by Ferber et al in 1993. Some of the highlights include significant snowfall that occurred where strong diabatic cooling occurred due to melting. Precip fell as rain where it was light and snow where precipitation was heavy. Temperatures were in the low to mid 30s across the Puget Sound. 850s were only marginal for snow. Nearly 10 inches of snow fell in Seattle.

[Meatyorologist]

1 minute ago, wxmet said:

There is talk about how this event looks very similar to the December 1974 event which led me to read about it in a paper by Ferber et al in 1993. Some of the highlights include significant snowfall that occurred where strong adiabatic cooling due occurred due to melting. Precip fell as rain where it was light and snow where precipitation was heavy. Temperatures where in the low to mid 30s across the Puget Sound. 850s were only marginal for snow. Nearly 10 inches of snow fell in Seattle.

Some very intriguing similarities. I'm a little bit more excited for this now that we're within 24 hours.

[Deweydog]

10 minutes ago, Christensen87 said:

When would NWS post a WWA or even a WSW? 

Monday night.

[Timmy]

20 minutes ago, wxmet said:

There is talk about how this event looks very similar to the December 1974 event which led me to read about it in a paper by Ferber et al in 1993. Some of the highlights include significant snowfall that occurred where strong diabatic cooling occurred due to melting. Precip fell as rain where it was light and snow where precipitation was heavy. Temperatures were in the low to mid 30s across the Puget Sound. 850s were only marginal for snow. Nearly 10 inches of snow fell in Seattle.

Sounds like jan 2010(11?) here.  I don’t think it ever dropped below 33 and we had about a foot of snow in scappoose.

[TheNewCulverJosh]

4 minutes ago, Timmy said:

Sounds like jan 2010(11?) here.  I don’t think it ever dropped below 33 and we had about a foot of snow in scappoose.

I remember that event.....I wasn't there but my brother was.  35-39 degree rain in PDX metro that just wouldn't change over.

[MossMan]

1 hour ago, wxmet said:

Heavy snow for the central Sound

 

Rain for me. 

[SilverFallsAndrew]

8 minutes ago, Timmy said:

Sounds like jan 2010(11?) here.  I don’t think it ever dropped below 33 and we had about a foot of snow in scappoose.

12

[Hawksfan2008]

Must be a lot of debate happening at NWS Seattle. I'm in North Bend and they still have no mention of snow in the forecast. 

[wxmet]

1 minute ago, MossMan said:

Rain for me. 

"Precip fell as rain where it was light and snow where precipitation was heavy"

[SilverFallsAndrew]

Not a great GFS run but not a torch. Just can’t get legit cold to dig toward the pnw this year. 

[MossMan]

31 minutes ago, Acer said:

You had better get to staging that thing.  18Z has you and I both in the pinkish 6"+ area.   I'd hate for that low to go much farther north though since the area of backwash snow will shrink for us.

It does? I need to take a look! 
Anyway the damage is done, equipment is staged, and my wife just found out. 

[Jesse]

It has almost stopped raining here :0

Just shy of 2” in the last 24 hours. Also at my current low for the day at 48 degrees. Should get warmer and wetter again this evening as the next wave moves in.

[Deweydog]

12 minutes ago, MossMan said:

It does? I need to take a look! 
Anyway the damage is done, equipment is staged, and my wife just found out. 

[snow_wizard]

13 minutes ago, SilverFallsAndrew said:

Not a great GFS run but not a torch. Just can’t get legit cold to dig toward the pnw this year. 

It actually has a number of chilly interludes though.  All in all the Pacific looks to be slowing down with above normal heights showing up a good part of the time.

[El_Nina]

5 minutes ago, Jesse said:

It has almost stopped raining here :0

Just shy of 2” in the last 24 hours. Also at my current low for the day at 48 degrees. Should get warmer and wetter again this evening as the next wave moves in.

All done here with 2.83" since 11pm. 

[bainbridgekid]

Can somebody post the zoomed in snow map from the 18z?

[snow_wizard]

We shall soon see if the 18z ECMWF gets back to showing more snow or not.  The 18z GFS was pretty impressive for this area.

[SouthHillFrosty]

2 minutes ago, snow_wizard said:

We shall soon see if the 18z ECMWF gets back to showing more snow or not.  The 18z GFS was pretty impressive for this area.

Can you post it pls

[snow_wizard]

4 minutes ago, bainbridgekid said:

Can somebody post the zoomed in snow map from the 18z?

Here it is.

 

[AbbyJr]

2 hours ago, Phil said:

Lol, well it’s moving up in timing. It’s just more of the event has entered the picture.

The blocky, highly meridional pattern you mention is directly associated with the tropical forcing/poleward EP flux vectors behind the SSW, so I don’t think you can really separate them.

I view the SSW is sort of an inflection point, or fork in the road, where its occurrence (or lack thereof) can/will have significant impacts for months afterwards following the same trigger. For instance, had the SSW in January 2019 failed, February 2019 outcome likely would have been very different..probably would’ve been an ordinary, canonical niño February. Deposition of momentum/Dt would have been radically different.  

 

How long after a SSW event does it normally take the models to pick up on it's effects?

[wxmet]

NWS:

In regards to the snow potential along the Puget Sound and into
the Cascade Foothills, there is considerable uncertainty. Overall,
the primary concern is the fact that this setup doesn`t suggest
much wintry precipitation in the area, not to mention the lack of
cold air in place with temperatures today through tonight in the
40s to low 50s. Possibly the biggest piece of the puzzle for snow
potential in the Puget Sound will be the extent dynamic cooling
during the heaviest precipitation on Monday afternoon. HRRR, 3K
NAM, and other hires models have a changeover to a brief heavy
thump of snow Monday afternoon across areas of the Puget Sound as
cold air filters in. If this does occur, the primary concerns in
regards to impacts would most likely be a quick reduction in
visibility with a heavy, wet rain/snow mix. The current thinking
regarding any accumulations would be trace amounts on grassy
surfaces (at best) near the water, with less than an inch for the
Cascade Foothills (or snow levels above 700-1000 feet). Timing of
this would be focused on 10AM-2PM north of King County, mainly
late afternoon into the evening south of this area. However, it is
also possible guidance is overdoing the extent of cooling and a
cold rain will be the main focus for most of the area on Monday.
Of course, it is also possible, albeit not expected, that the snow
event plays out as shown on shorter range guidance. The current
thinking though is that significant accumulations aren`t expected
for the Puget Sound area at this time, though monitor the
forecasts through tonight.

 

[snow_wizard]

The sudden temperature plunge the models are showing for King and Pierce Counties tomorrow afternoon makes a lot of sense when you consider there will be cold air dammed up along the north slopes of the Olympics that will plunge down in the backwash behind the low.  There will likely be convergence involved also.

[Jesse]

18 hours ago, BLI snowman said:

Wonder whatever happened to Farmboy?

Took of one Tesla's experimental rockets to Mercury when he realized this planet is 70% water and only has an average surface temp of 57F