December 2020 Weather Observations for the PNW

[snow_wizard]

FWIW the latest GFS extended ensemble shows PNA going decently minus mid January.  That's true for the mean and control both.

[snow_wizard]

2 minutes ago, DJ Droppin said:

It just seems to keep getting pushed back. A week ago the SSWE was supposed to begin at Day 6.

It basically begins right away on the latest runs.

[umadbro]

1 hour ago, Deweydog said:

 

 

[Jesse]

12 minutes ago, Omegaraptor said:

The only two are Feb and March I’m pretty sure.

That’s the few.

[umadbro]

No idea why that post wanted to include an empty Dewey quote.

[Gradient Keeper]

Just now, snow_wizard said:

It basically begins right away on the latest runs.

Ahhh. Okay. I misread it.

[Gradient Keeper]

Day 5

[snow_wizard]

10 minutes ago, Phil said:

If that doesn't provide a kick in the arse nothing will.

[Gradient Keeper]

00z GFS SSWE begins Day 2 - 2.5. You'd think models fairly soon are going to reflect this with dramatic changes.

[snow_wizard]

4 minutes ago, DJ Droppin said:

Ahhh. Okay. I misread it.

The really good news is the ECMWF shows the SSW being well along about half way through the recent runs and it only goes 10 days out.  This should be it.

[Gradient Keeper]

Day 6

[Deweydog]

8 minutes ago, DJ Droppin said:

Ahhh. Okay. I misread it.

I think it’d be beneficial to have a forum Zoom class on SSW’s of varying grades and how to interpret them at various stages.  I know I don’t know enough to be dangerous.

[Phil]

17 minutes ago, DJ Droppin said:

It just seems to keep getting pushed back. A week ago the SSWE was supposed to begin at Day 6.

It was never projected to start D6.

At least if you’re referring to the SSW (wind reversal) itself.

[Gradient Keeper]

1 minute ago, Deweydog said:

I think it’d be beneficial to have a forum Zoom class on SSW’s of varying grades and how to interpret them at various stages.  I know I don’t know enough to be dangerous.

A pretty swell idea.

[Deweydog]

One thing to at least consider about a “top tier” warming event is just how disruptive it can be, both positively and negatively.  An open spigot to the promised land of ice and snow is never a bad thing, but the last major event absolutely railroaded ENSO climo two years ago...

[Phil]

7 minutes ago, DJ Droppin said:

00z GFS SSWE begins Day 2 - 2.5. You'd think models fairly soon are going to reflect this with dramatic changes.

In 2019, the models didn’t shift abruptly until 10 days *after* the wind reversal.

IIRC, in Feb 2018 it was ~ 2-3 days from the wind reversal.

Either way it’s not a timeframe you’d expect good model performance.

[Gradient Keeper]

Day 7

[SouthHillFrosty]

7 minutes ago, Deweydog said:

I think it’d be beneficial to have a forum Zoom class on SSW’s of varying grades and how to interpret them at various stages.  I know I don’t know enough to be dangerous.

I am actually down for a zoom call on SSW and  @Phil could be the teacher if he was up for it

[Gradient Keeper]

1 minute ago, Phil said:

In 2019, the models didn’t shift abruptly until 10 days *after* the wind reversal.

IIRC, in Feb 2018 it was ~ 2-3 days from the wind reversal.

Either way it’s not a timeframe you’d expect good model performance.

Ahhh, so rather boring and pointless model riding for another 20 days. I can't wait.

[snow_wizard]

1 minute ago, Deweydog said:

One thing to at least consider about a “top tier” warming event is just how disruptive it can be, both positively and negatively.  An open spigot to the promised land of ice and snow is never a bad thing, but the last major event absolutely railroaded ENSO climo two years ago...

Good point.  At this point it will be a welcome reshuffling of the deck that at least gives us a shot at something great.  Let's hope it doesn't backfire.  At least the present background state (ENSO and QBO) favors a cold West, but nothing is  guaranteed.

[AbbyJr]

I realize this is the control run and will most likely change, but its honestly one of the possible pattern progressions after the SSW. Essentially, the polar vortex is annihilated allowing that offshore ridge to develop into a strong GOA block forcing the cold down south. This run also shows it within the time frame where I predict we will see some arctic air at the very least if not lock into a cold and snowy pattern.

 

 

[snow_wizard]

1 minute ago, DJ Droppin said:

Ahhh, so rather boring and pointless model riding for another 20 days. I can't wait.

At least we are getting little cold interludes now.  Could be much worse.

[AbbyJr]

5 minutes ago, Phil said:

In 2019, the models didn’t shift abruptly until 10 days *after* the wind reversal.

IIRC, in Feb 2018 it was ~ 2-3 days from the wind reversal.

Either way it’s not a timeframe you’d expect good model performance.

Is the wind reversal the result of a completed SSW or something that occurs after the SSW completes?

[Gradient Keeper]

Day 8

[Phil]

1 minute ago, Deweydog said:

One thing to at least consider about a “top tier” warming event is just how disruptive it can be, both positively and negatively.  An open spigot to the promised land of ice and snow is never a bad thing, but the last major event absolutely railroaded ENSO climo two years ago...

You make a really good point here. The structural dynamics are unique to each event, and the end result is a dependent variable of sorts..IE: via tropical forcing(s), seasonality, in-situ AAM modes/deposition + QBO (dynamics along zero wind line), etc.

In this case I suspect a favorable outcome is more likely given where the system state is now, and the time of year. But it doesn’t really tip its hand until a few days out if u really think about it.

Right now we still don’t know which daughter vortice will be dominant. The ECMWF/EPS and GFS/GEFS are diametrically opposed in that regard, despite the fact both are projecting a major SSW.

[snow_wizard]

1 minute ago, AbbyJr said:

I realize this is the control run and will most likely change, but its honestly one of the possible pattern progressions after the SSW. Essentially, the polar vortex is annihilated allowing that offshore ridge to develop into a strong GOA block forcing the cold down south. This run also shows it within the time frame where I predict we will see some arctic air at the very least if not lock into a cold and snowy pattern.

 

 

The mean on that model is ok too for the second half of January.  In my book a cold second half of Jan would be a HUGE win.  Historically that period delivers the goods big time when it gets cold.

[AbbyJr]

1 minute ago, snow_wizard said:

The mean on that model is ok too for the second half of January.  In my book a cold second half of Jan would be a HUGE win.  Historically that period delivers the goods big time when it gets cold.

January 1954, C'MON!!! 

[Phil]

4 minutes ago, AbbyJr said:

Is the wind reversal the result of a completed SSW or something that occurs after the SSW completes?

To meet definition of SSW there must be a reversal of zonal winds to easterly in bulk @ 60N/10mb. At least that’s the standard definition.

Of course, like everything else we ascribe strict threshold-based definitions to, the reality is more muddled.

[Brian_in_Leavenworth]

2 minutes ago, Phil said:

You make a really good point here. The structural dynamics are unique to each event, and the end result is a dependent variable of sorts..IE: via tropical forcing(s), seasonality, in-situ AAM modes/deposition + QBO (dynamics along zero wind line), etc.

In this case I suspect a favorable outcome is more likely given where the system state is now, and the time of year. But it doesn’t really tip its hand until a few days out if u really think about it.

Right now we still don’t know which daughter vortice will be dominant. The ECMWF/EPS and GFS/GEFS are diametrically opposed in that regard, despite the fact both are projecting a major SSW.

A lot of us are under the impression, right or wrong, that where the SSW occurs makes a big difference as to where the cold goes, and that explains Feb. 2019 during a Nino.  What do you think?

[Rubus Leucodermis]

42˚F and rain. The warm-up is underway.

[AbbyJr]

1 minute ago, Phil said:

To meet definition of SSW there must be a reversal of zonal winds to easterly one bulk @ 60N/10mb. At least that’s the standard definition.

Of course, like everything else we ascribe strict threshold-based definitions to, the reality is more muddled.

Thanks Phil. 

[Gradient Keeper]

Day 9'er

[Deweydog]

12 minutes ago, snow_wizard said:

Good point.  At this point it will be a welcome reshuffling of the deck that at least gives us a shot at something great.  Let's hope it doesn't backfire.  At least the present background state (ENSO and QBO) favors a cold West, but nothing is  guaranteed.

I like surprises, and there are a lot of people around the world that probably like cold and snow.  

[Phil]

6 minutes ago, Brian_in_Leavenworth said:

A lot of us are under the impression, right or wrong, that where the SSW occurs makes a big difference as to where the cold goes, and that explains Feb. 2019 during a Nino.  What do you think?

It can, and often does. However, the exact time of year and in-situ tropical low pass regime often matters just as much, sometimes more.

Once the event gets closer, it’s easier to extrapolate some of the elements. But the SSW itself can also reshuffle the low pass tropical forcing, ignite the MJO, etc.

IIRC, in 1987/88, a SSW torpedoed El Niño in its tracks by setting off one of the stronger MJO events of the decade into destructive interference at a vulnerable point in the OKW cycle. I’m not 100% sure if that’s the correct year but that is the sum of it.

 

[Gradient Keeper]

00z ECMWF 10 Day Rainfall, Snowfall totals

[Phil]

Think of it this way..the “warming” component in the SSW is a result of subsidence/compressional heating.

If air is sinking somewhere, it’s rising somewhere else. In this case, it is rising in the tropical stratosphere while sinking at the pole. This acts to reduce static stability in the tropics and ignite deep convection..and for whatever reason, this often culminates in the inception of an MJO event. Which is where the time of year/in-situ modes of AAM transfer come into play.

I probably oversimplified it, but I believe that’s the gist of it.

[Gradient Keeper]

EURO was a far better Nina run than the GFS, especially for northern CA, Sierras.

[Brian_in_Leavenworth]

3 minutes ago, Phil said:

Think of it this way..the “warming” component in the SSW is a result of subsidence/compressional heating.

If air is sinking somewhere, it’s rising somewhere else. In this case, it is rising in the tropical stratosphere while sinking at the pole. This acts to reduce static stability in the tropics and ignite deep convection..and for whatever reason, this often culminates in the inception of an MJO event. Which is where the time of year/in-situ modes of AAM transfer come into play.

I probably oversimplified it, but I believe that’s the gist of it.

Thanks, I actually understood that.  Sort of a domino effect.  But not knowing which direction the Dominos end up falling until they start to fall

 

[Phil]

ECMWF vs GFS D10.

Notice how GFS wants to finish with a much stronger Eurasian daughter vortex vs the ECMWF...which is both more aggressive with the event and sooner to split it vs GFS.

How exactly that unfolds could, in theory, make a difference. One of the many “dominoes” @Brian_in_Leavenworth mentioned.

[Brian_in_Leavenworth]

47 minutes ago, AbbyJr said:

I realize this is the control run and will most likely change, but its honestly one of the possible pattern progressions after the SSW. Essentially, the polar vortex is annihilated allowing that offshore ridge to develop into a strong GOA block forcing the cold down south. This run also shows it within the time frame where I predict we will see some arctic air at the very least if not lock into a cold and snowy pattern.

 

 

The GEFS ensemble mean was very similar.  Started around the 20th or so.