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Rtd208

December 2017 Discussions & Observations Thread

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58 minutes ago, Ralph Wiggum said:

Overnight ensemble means definitely took a step back in the LR. While not a bad look, clearly not the fantasy runs from last couple days. NAO is weaker and block is shifted farther East, ridging out West less extreme, trof out West slower to move due to decrease in ridging over British Columbia. GEPS which had been most aggressive with -NAO loses it completely in the LR and even attempts a shift to a +NAO. Hope these LR teases that are taken away arent a repeat of last year. Again, not a horrible look on the EPS/GEFS at all.....just not the same perfection from past few runs. Didnt expect that look to remain constant for next 10-16 days anyway.

Actually, there was a shift to stronger blocking in the EPO and PNA regions which may turn out to be colder for us. It's a -EPO/+PNA ridge that connects over the top to the -AO block near Greenland.

 

New run features a stronger -EPO/+PNA block 

eps_z500a_nh_252.thumb.png.05a022b4f46d38d5d3e2c3f92cc98447.png

Old run

 

eps_z500a_nh_336.thumb.png.61dda684c5da9d1ed751544a3bf531dc.png

 

 

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Actually, there was a shift to stronger blocking in the EPO and PNA regions which may turn out to be colder for US. It's a -EPO/+PNA ridge that connects over the top to the -AO block near Greenland.

 

New run features a stronger -EPO/+PNA block 

eps_z500a_nh_252.thumb.png.05a022b4f46d38d5d3e2c3f92cc98447.png

 

 

eps_z500a_nh_336.thumb.png.61dda684c5da9d1ed751544a3bf531dc.png

 

 

PAC is really chaotic this year.....massive changes from one run to the next. Look at that deep trof now showing up S of the Aleutian chain pumping the EPO ridge you noted. Wasnt even there before. Im finding it a challenge to trust much of this data past day 7 or so. This early season seems even more prone to major changes than recent years for whatever reason especially upstream in the PAC which obviously yields big changes downstream. Maybe the general fast La Nina flow out there has something to do with this?

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25 minutes ago, bluewave said:

Actually, there was a shift to stronger blocking in the EPO and PNA regions which may turn out to be colder for US. It's a -EPO/+PNA ridge that connects over the top to the -AO block near Greenland.

 

New run features a stronger -EPO/+PNA block 

eps_z500a_nh_252.thumb.png.05a022b4f46d38d5d3e2c3f92cc98447.png

 

 

eps_z500a_nh_336.thumb.png.61dda684c5da9d1ed751544a3bf531dc.png

 

 

 

I would love for there to be an actual SW out in the south west at day 11 under that block 

It would roll through the M/A.

But I agree the models look very good for deeper negative on the east coast in the LR.

That doesn't always mean snow but we scream because these are the sets ups we need for it to snow .

Those things are just uncontrollable.

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9 hours ago, IntenseBlizzard2014 said:

 

It wouldn't have been negative. It would have made things more interesting. Gotta wait for next winter. 

Tropical volcanic eruptions that release sulfate aerosols and reach the stratosphere have immediate effects. You don’t have to wait until the following winter to feel the effects. Research has shown that immediately following an eruption, it works to cool the stratosphere and strengthen the stratospheric polar vortex, causing +AO. The following winter is when it has the -AO effect. The global temp cooling effects are also more pronounced and found to be significantly so when you have an eruption during a La Niña. The global temp cooling effects are not nearly as pronounced during an El Niño 

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1 minute ago, snowman19 said:

Tropical volcanic eruptions that release sulfate aerosols and reach the stratosphere have immediate effects. You don’t have to wait until the following winter to feel the effects. Research has shown that immediately following an eruption, it works to cool the stratosphere and strengthen the stratospheric polar vortex, causing +AO. The following winter is when it has the -AO effect. The global temp cooling effects are also more pronounced and found to be significantly so when you have an eruption during a La Niña. The global temp cooling effects are not nearly as pronounced during an El Niño 

Please post something to back this statement up

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24 minutes ago, Ralph Wiggum said:
52 minutes ago, bluewave said:
Actually, there was a shift to stronger blocking in the EPO and PNA regions which may turn out to be colder for US. It's a -EPO/+PNA ridge that connects over the top to the -AO block near Greenland.

 

New run features a stronger -EPO/+PNA block 


 
 

PAC is really chaotic this year.....massive changes from one run to the next. Look at that deep trof now showing up S of the Aleutian chain pumping the EPO ridge you noted. Wasnt even there before. Im finding it a challenge to trust much of this data past day 7 or so. This early season seems even more prone to major changes than recent years for whatever reason especially upstream in the PAC which obviously yields big changes downstream. Maybe the general fast La Nina flow out there has something to do with this?

The MJO looks like it may be providing an assist for us as the forcing is shifting just west of 180 right before the big pattern change. This is displaced a little further east than is usually the case during a La Nina December.

 

vp_anom_30.5S-5N.thumb.gif.00cb5ae2b32d5ca38e7e2381b16d79c9.gif

 

LAN.gif.e21026b8b31b980a9087aa5a5e56039e.gif

 

 

 

 

 

 

 

 

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1 hour ago, snowman19 said:

Tropical volcanic eruptions that release sulfate aerosols and reach the stratosphere have immediate effects. You don’t have to wait until the following winter to feel the effects. Research has shown that immediately following an eruption, it works to cool the stratosphere and strengthen the stratospheric polar vortex, causing +AO. The following winter is when it has the -AO effect. The global temp cooling effects are also more pronounced and found to be significantly so when you have an eruption during a La Niña. The global temp cooling effects are not nearly as pronounced during an El Niño 

Actually there’s a 2-3 month lag, it’s not immediate

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1 hour ago, snowman19 said:

 

This study discussed boreal winter conditions subsequent to tropical volcanic eruptions preferentially occurring in the spring / summer; there were a couple cases in October, but not nearly as late as current. Further, it is much too early to ascertain VEI or stratospheric aerosol loading. Hypothetically speaking, if this eruption becomes sufficiently strong, the effects would begin manifesting in the AO by mid to late winter. All of those studied eruptions were VEI 4 or greater. We will need to monitor.

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5 hours ago, bluewave said:

Actually, there was a shift to stronger blocking in the EPO and PNA regions which may turn out to be colder for us. It's a -EPO/+PNA ridge that connects over the top to the -AO block near Greenland.

hasn't this happened in recent years with other modeled -nao blocks in the long range?

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31 minutes ago, forkyfork said:

hasn't this happened in recent years with other modeled -nao blocks in the long range?

The EPS did pretty well with the recent -3.5 AO drop. 

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todays ao forecast has two members near -5 while the rest are negative too...no membrs are positive in the forecast period...of course tomorrow will change but it is a great sign at this time...

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most of the big snows around hear were pna driven with help from a negative ao...12/10 had a negative pna leading up to the blizzard...it almost hit neutral before falling off again...the negative ao and nao were the drivers of that storm...

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20 minutes ago, bluewave said:

Check out how strong the combined -EPO/+PNA/-AO block is in around 10 days. We have not seen all 3 indices this strongly impacted by a block at the same time in a while. 

 

eps_z500a_nh_252.thumb.png.bcd546953b2799a10f16a658e37212bf.png

 

 

 

 

 

 

Does the block impact the indices or are the indices causing the block?

Good lord, that is one crazy West Coast ridge!

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Just now, uncle W said:

most of the big snows around hear were pna driven with help from a negative ao...12/10 had a negative pna leading up to the blizzard...it almost hit neutral before falling off again...the negative ao and nao were the drivers of that storm...

EPS has a long-lasting raging +PNA days 5-15.

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3 minutes ago, danstorm said:

Does the block impact the indices or are the indices causing the block?

Good lord, that is one crazy West Coast ridge!

Aren't they different terms for the same thing?

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On November 27, 2017 at 5:50 PM, Snow88 said:

Weeklies look very good moving into December

Very strong +PNA and -NAO

This was the coldest looking weeklies run in years. Triple -EPO/+PNA/-AO block for the entire run. 

 

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8 minutes ago, bluewave said:

This was the best looking weeklies run in years. Triple -EPO/+PNA/-AO block for the entire run. The last time this happened during a La Nina was December 2000 and 1985.

The whole run averaged out for December looks like this

A.png.07fe081f9bea59a771e3d321acec6ea6.png

 

 

Yeh , a month ( if that verifies ) is hard pressed to look / want better.

It doesn't mean snow , but its patterns like that which produce.

But I agree , great run.

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14 minutes ago, Snow88 said:

Ralieghwx  says that the Euro weeklies keeps it cold through mid January.

Wow

Let's get to Christmas 1st

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56 minutes ago, bluewave said:

This was the best looking weeklies run in years. Triple -EPO/+PNA/-AO block for the entire run. The last time this happened during a La Nina was December 2000 and 1985.

The whole run averaged out for December looks like this

A.png.07fe081f9bea59a771e3d321acec6ea6.png

 

 

Ha I thought you'd say December 2010- January 2011, that was the best start to winter I can remember.  December 1995- January 1996 was great too, but we had a big January thaw, but at least winter came back in a big way in February, March and April.

 

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10 hours ago, snowman19 said:

Tropical volcanic eruptions that release sulfate aerosols and reach the stratosphere have immediate effects. You don’t have to wait until the following winter to feel the effects. Research has shown that immediately following an eruption, it works to cool the stratosphere and strengthen the stratospheric polar vortex, causing +AO. The following winter is when it has the -AO effect. The global temp cooling effects are also more pronounced and found to be significantly so when you have an eruption during a La Niña. The global temp cooling effects are not nearly as pronounced during an El Niño 

There was some idea that the February 1983 blizzard was due in part to El Chicon's eruption the year before, though we do get renegade historic snowstorms in February sometimes during big el ninos (or January as was the case a couple of years ago.)

 

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14 minutes ago, bluewave said:

We always run the risk of cold and suppressed in a pattern like this which happened in 1985. Even December 2000 waited to the end of December to deliver. Hopefully, this one is able to produce for us. 

Thats definitely a risks and I expect that it's dry for a time.

But living here It's either the PAC is too fast and we run the risk of wet and warm or the vortex presses so much that impulses just dive to your south.

We are not a snowy climate.

The reason a lot of us look at these high latitude blocking patterns favorably is because you just need 1 vort to hug the barroclinic zone combined  with a relaxation of HP and if a system  slows behind traffic , then it's on.

( clippers aside ).

It's why I hump temps in here , thats because sometimes that's the easier part and we need the set up to produce anything.

Too often what we want just doesn't happen.

Snow / storms will appear and disappear in the guidance and in the end they are just too hard to forecast with any skill from a distance.

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since 1989 every December that was colder than average had above average snowfall...Dec 89 had a pretty good -ao for three weeks but it wasn't nearly as strong as 2000, 2009 and 2010...

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1 hour ago, uncle W said:

since 1989 every December that was colder than average had above average snowfall...Dec 89 had a pretty good -ao for three weeks but it wasn't nearly as strong as 2000, 2009 and 2010...

This is where our warmer climate is actually helping us (right now anyway).  I hesitate to use the 80s as analogs because that was an entirely different climate- and I would take less cold if that means less chances of suppression and more chances of snow.  Borderline cold is all we really need.

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