PNW December 2022 - Part II

[Skagit Weather]

NWS just tweeted out their thoughts for the upcoming week. I think it's quite well done at least in their emphasis on the uncertainty of the forecast.

[SilverFallsAndrew]

Honestly I am not on board with the Gfs, however completely disregarding is a bit of a wishccast. 

[Skagit Weather]

And here's their snowfall forecast for Sunday night. I was hoping to see a little bit higher totals up here based on what looked like somewhat promising models, but seems like a good graphic to at least get people's attention that there may be snow.

[Snownerd3000]

Area Forecast Discussion
National Weather Service Seattle WA
325 PM PST Fri Dec 16 2022

.SYNOPSIS...An upper level ridge will shift further offshore
today. Meanwhile, an upper level trough spanning across British
Columbia will bring colder temperatures and a chance for wintry
precipitation in the lowlands this weekend. This trend will
continue into the first half of next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...The upper level ridge
located in the NE Pacific will gradually flatten into Saturday,
but, will generally provide cool conditions for the remainder of
the day. Conditions will be mostly dry tonight, with low
temperatures ranging in the mid to upper 20s. Expect increasing
cloud cover ahead of our frontal boundary late tonight into
Saturday morning.

A frontal boundary will slide southward from the British Columbia
early Saturday morning, with precipitation starting along the
coast and portions of the northern interior, and will spread
southward through our CWA. Precipitation will start off as rain
in the lowlands and snow showers within the mountains, but as the
evening progresses, lowland rain will start to transition into a
rain/snow mix into the first half of Sunday as colder air filters
in.

As this frontal boundary continues to slide south, a surface high
located over northern B.C will help Fraser Outflow winds set up
over Western Whatcom County and the San Juans Sunday afternoon and
filter colder air into these regions. Snow levels will start to
decrease and reach levels near the surface, prompting the
rain/snow mix to transition fully to snow by Sunday night.

On top of snow showers Sunday night, some of the hi-resolution
models are focusing in on a Puget Sound Convergence Zone over
northern King and Snohomish County, due to the arctic front. The
potential definitely exists for higher snowfall amounts within the
PSCZ, so cannot rule out more than an inch or two in those
locations.

There is better agreement that this time frame (Saturday
into Monday morning) that snow showers within the lowlands are
to be expected, but accumulations will not be significant (less
than an inch) across most locations, the exception being areas
across Western Whatcom County, the Northern Olympic Peninsula, and
areas within the Puget Sound Convergence Zone. Snow showers will
likely linger throughout Sunday night and into early Monday
morning.

Relatively, Monday looks to be a tad drier with high temperatures
hovering in the low to mid 30s as the cold air mass hovers over
Western Washington. It will feel chilly, with morning lows in the
mid to upper 20s. Cooler in locations up north, especially up
near Bellingham, where lows could be in the teens.

.LONG TERM /TUESDAY THROUGH FRIDAY/...The latest trends continue
to highlight the uncertainty in the long term forecast,
especially Tuesday into Thursday. Models are picking up on
shortwave to pulse through Tuesday morning, where precipitation
type will be tricky. The general trend of ensemble models is to
slide the bulk of the trough east quicker as a ridge builds
offshore, which would limit the duration of the arctic air and
introduce warmer temperatures through the region. The challenge
with this is with the cold temps already in place for a longer
duration, it is likely for the cooler temperatures to stay around
and create an overrunning event.

Compared to previous model runs, this disturbance on Tuesday
seems to be tracking faster, which can definitely help with
lowland snow potential. NBM precipitation guidance has shifted
away with a 50-50 split in snow vs. rain, and has trended more
towards a 70-30 split throughout the interior, favoring the
precipitation type more as snow than rain during this period.
Snowfall probabilities through the NBM have tinkered, reinforcing
the degree of uncertainty with this forecast. Right now, there is
a 50-60% chance of 1" or more Olympia northward into Wednesday.
Again, have to express the uncertainty of this time period.
Multiple outcomes are possible, and it is mainly dependent on the
temperature profile and how fast these disturbances track through.
This time frame will continued to be monitored over the next
couple of days as we get new guidance.

The active pattern still continues Wednesday into Friday, as a
warm front lifts north through our region, raising snow levels.
This is depicted in the ensemble clusters, as deep troughing is
over the Great Lakes and ridging more focused in on the West
Coast. The organization of this system is somewhat messy as
ensemble guidance is not particularly agreeing with each other,
but have kept rain in the grids for this time period as we will
continue to stay wet.

[TT-SEA]

4 minutes ago, Perturbed Member said:

Really pleased to see this feature continue to show up. The arctic front reaches NW OR and then you get some kind of deformation over the same area as the low approaches. 18z ICON and RGEM continue to have it. 

 

It was there on the 12z GEM and Euro too but the euro had the low a good bit further north. 

 

 

I think the GFS is entirely on its own and it will completely cave tonight and start to look more like these models. Cold air penetrates further south, limited to no cyclogenesis up north by BC. There will still be uncertainty over where that low goes on Tuesday. The ICON and GEM have a better track for NW OR but the Euro takes it further north and gives snow to western WA and snow to ZR for PDX. 

I'm sure we will see lots of waffling around on the models on exactly how this low tracks. 

Also add that the last 3 runs of the ECMWF have moved that band significantly southward... one more shift south and its in Portland.   

[Snownerd3000]

1 minute ago, Skagit Weather said:

And here's their snowfall forecast for Sunday night. I was hoping to see a little bit higher totals up here based on what looked like somewhat promising models, but seems like a good graphic to at least get people's attention that there may be snow.

I'm in the PINK

[thickhog]

5 minutes ago, Skagit Weather said:

NWS just tweeted out their thoughts for the upcoming week. I think it's quite well done at least in their emphasis on the uncertainty of the forecast.

Great job communicating the uncertainty

[Meatyorologist]

5 minutes ago, Snownerd3000 said:

Area Forecast Discussion
National Weather Service Seattle WA
325 PM PST Fri Dec 16 2022

.SYNOPSIS...An upper level ridge will shift further offshore
today. Meanwhile, an upper level trough spanning across British
Columbia will bring colder temperatures and a chance for wintry
precipitation in the lowlands this weekend. This trend will
continue into the first half of next week.

&&

.SHORT TERM /TONIGHT THROUGH MONDAY/...The upper level ridge
located in the NE Pacific will gradually flatten into Saturday,
but, will generally provide cool conditions for the remainder of
the day. Conditions will be mostly dry tonight, with low
temperatures ranging in the mid to upper 20s. Expect increasing
cloud cover ahead of our frontal boundary late tonight into
Saturday morning.

A frontal boundary will slide southward from the British Columbia
early Saturday morning, with precipitation starting along the
coast and portions of the northern interior, and will spread
southward through our CWA. Precipitation will start off as rain
in the lowlands and snow showers within the mountains, but as the
evening progresses, lowland rain will start to transition into a
rain/snow mix into the first half of Sunday as colder air filters
in.

As this frontal boundary continues to slide south, a surface high
located over northern B.C will help Fraser Outflow winds set up
over Western Whatcom County and the San Juans Sunday afternoon and
filter colder air into these regions. Snow levels will start to
decrease and reach levels near the surface, prompting the
rain/snow mix to transition fully to snow by Sunday night.

On top of snow showers Sunday night, some of the hi-resolution
models are focusing in on a Puget Sound Convergence Zone over
northern King and Snohomish County, due to the arctic front. The
potential definitely exists for higher snowfall amounts within the
PSCZ, so cannot rule out more than an inch or two in those
locations.

There is better agreement that this time frame (Saturday
into Monday morning) that snow showers within the lowlands are
to be expected, but accumulations will not be significant (less
than an inch) across most locations, the exception being areas
across Western Whatcom County, the Northern Olympic Peninsula, and
areas within the Puget Sound Convergence Zone. Snow showers will
likely linger throughout Sunday night and into early Monday
morning.

Relatively, Monday looks to be a tad drier with high temperatures
hovering in the low to mid 30s as the cold air mass hovers over
Western Washington. It will feel chilly, with morning lows in the
mid to upper 20s. Cooler in locations up north, especially up
near Bellingham, where lows could be in the teens.

.LONG TERM /TUESDAY THROUGH FRIDAY/...The latest trends continue
to highlight the uncertainty in the long term forecast,
especially Tuesday into Thursday. Models are picking up on
shortwave to pulse through Tuesday morning, where precipitation
type will be tricky. The general trend of ensemble models is to
slide the bulk of the trough east quicker as a ridge builds
offshore, which would limit the duration of the arctic air and
introduce warmer temperatures through the region. The challenge
with this is with the cold temps already in place for a longer
duration, it is likely for the cooler temperatures to stay around
and create an overrunning event.

Compared to previous model runs, this disturbance on Tuesday
seems to be tracking faster, which can definitely help with
lowland snow potential. NBM precipitation guidance has shifted
away with a 50-50 split in snow vs. rain, and has trended more
towards a 70-30 split throughout the interior, favoring the
precipitation type more as snow than rain during this period.
Snowfall probabilities through the NBM have tinkered, reinforcing
the degree of uncertainty with this forecast. Right now, there is
a 50-60% chance of 1" or more Olympia northward into Wednesday.
Again, have to express the uncertainty of this time period.
Multiple outcomes are possible, and it is mainly dependent on the
temperature profile and how fast these disturbances track through.
This time frame will continued to be monitored over the next
couple of days as we get new guidance.

The active pattern still continues Wednesday into Friday, as a
warm front lifts north through our region, raising snow levels.
This is depicted in the ensemble clusters, as deep troughing is
over the Great Lakes and ridging more focused in on the West
Coast. The organization of this system is somewhat messy as
ensemble guidance is not particularly agreeing with each other,
but have kept rain in the grids for this time period as we will
continue to stay wet.

Very reasonable.

[Meatyorologist]

18z Euro should be rolling out now. Anyone got a sneak peek?

[lowlandsnow]

2 minutes ago, Meatyorologist said:

18z Euro should be rolling out now. Anyone got a sneak peek?

[snow_wizard]

13 minutes ago, Skagit Weather said:

NWS just tweeted out their thoughts for the upcoming week. I think it's quite well done at least in their emphasis on the uncertainty of the forecast.

Pretty much nothing left to actually be confident of.

[lowlandsnow]

4 minutes ago, Meatyorologist said:

18z Euro should be rolling out now. Anyone got a sneak peek?

[Joshua Lake Oswego]

26 minutes ago, Brennan said:

I seem to remember something like this happening in recent years, where we were all shocked at how well the GFS did in comparison to the EURO and others... Can't remember when, but within the last 5 years. I tend to think the GFS will be right as well... Hoping for a blend between the EURO and GFS. 

The GFS nailed the ''impossible'' heatwave of June, 2021 well in advance of other models.

When the GFS is stubborn as heck, it is usually correct.

[awright-31]

4 minutes ago, Meatyorologist said:

18z Euro should be rolling out now. Anyone got a sneak peek?

 

[MossMan]

Just scrolled past this while on the Good old FB…

[snow_wizard]

1 minute ago, lowlandsnow said:

Gorgeous block!  This thing is looking better all the time.

[Cloud]

[Meatyorologist]

Just now, lowlandsnow said:

How does it compare to its 12z run? Looks better than its 06z run at least.

[snow_wizard]

Just now, Joshua Lake Oswego said:

The GFS nailed the ''impossible'' heatwave of June, 2021 well in advance of other models.

When the GFS is stubborn as heck, it is usually correct.

In this case it's totally on its own.  Pretty unlikely it will verify.

[Meatyorologist]

1 minute ago, Cloud said:

Looks almost identical to its 12z run, sans some minor wobbling. Euro is ROCK SOLID.

[snow_wizard]

1 minute ago, Meatyorologist said:

How does it compare to its 12z run? Looks better than its 06z run at least.

It won't let you compare 18z to 12z.

[lowlandsnow]

1 minute ago, Meatyorologist said:

How does it compare to its 12z run? Looks better than its 06z run at least.

Pretty much the same maybe slightly better

 

[WeatherGeek2022]

3 minutes ago, awright-31 said:

 

love to see that bomb low come back into the equation.

[lowlandsnow]

1 minute ago, snow_wizard said:

It won't let you compare 18z to 12z.

Just realized that 

[Meatyorologist]

1 minute ago, snow_wizard said:

It won't let you compare 18z to 12z.

That is lame-o!

[runninthruda206]

4 minutes ago, awright-31 said:

 

Omg

[snow_wizard]

Very pretty ECMWF run so far.  The block looks slightly beefier in the mid section.

[TT-SEA]

Total snow through 10 a.m. Monday... a little less overall than the 12Z run.

[snow_wizard]

2 minutes ago, lowlandsnow said:

Pretty much the same maybe slightly better

 

That is 6z to 18z comparison.

[TT-SEA]

It appears this run might shift the Tuesday system south a little more.   But will only go out through Tuesday morning.  

[lowlandsnow]

1 minute ago, snow_wizard said:

That is 6z to 18z comparison.

Thought I was comparing 12z to 18z 

[Cloud]

Pivotal is slow updating so have to check back. Day 2.5. Holding its ground

[snow_wizard]

The second cold shot is going to happen on this run.  No question.

[Meatyorologist]

1 minute ago, Cloud said:

Pivotal is slow updating so have to check back. Day 2.5. Holding its ground

North American view? Upstream stuff is hidden.

[snow_wizard]

1 minute ago, TT-SEA said:

It appears this run might shift the Tuesday system south a little more.   But will only go out through Tuesday morning.  

I'm sold on the cold being extended now like the 12z was showing.  Snow is always the tricky thing, but it will be hard to avoid something around Tuesday.

[lowlandsnow]

Cold air farther south

[TacomaWx]

The event starts in 48 hours roughly folks. Definitely potential for lots of places in western WA to get snow Sunday and Monday…which has been slightly overlooked with all the attention on the event Tuesday. It looks hit or miss outside of the favored areas but things are going to get interesting soon. 

[snow_wizard]

Just now, Meatyorologist said:

North American view? Upstream stuff is hidden.

It's locked on now.  Nothing more than slight wobbles.

[Cloud]

1 minute ago, Meatyorologist said:

North American view? Upstream stuff is hidden.

 

[Prairiedog]

31 minutes ago, snow_wizard said:

Everything is against the GFS right now.  It didn't used to be like this.

Seems like the last 5-6 years I've seen this happen in similar events.   I agree, its on it's own.  I don't pretend to know what it sees vs the EURO.  We'll see but when we get close and the two don't agree and neither blink, it seems the GFS figures it out and the EURO doesn't. This will be a good case study.  I'm a biology guy not an atmospheric science student.  I certainly don't know anything about how these models are programmed.  I would love to have the ability to "see" what each model sees vs what they don't or don't take into account.  I guess in a way we do when we look at the model runs but it goes beyond that for me.  Way above my pay grade.