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Bob Chill

Winter 2017-18 Disco

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55 minutes ago, Cobalt said:

Looking much better compared to last year

 

 

One of the things I have liked seeing this fall is the snow cover building in Canada. Think we will have plenty of cold nearby this winter to tap into if we can just get the trough/ridging placement through the CONUS to cooperate.

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Canada is typically cold in Nina’s. Which is why we can get some cold shots, even if things end up warm in the balance.

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3 hours ago, WxUSAF said:

Canada is typically cold in Nina’s. Which is why we can get some cold shots, even if things end up warm in the balance.

True, but I still like to see a good snow pack. Helps to create a deep dense layer of cold that isn't easily scoured out nor do you have the temp issues at mid-levels that quite often occurs with shallow cold. And it seems in recent years it has been a fight to get decent snow pack in Canada.

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36 minutes ago, showmethesnow said:

True, but I still like to see a good snow pack. Helps to create a deep dense layer of cold that isn't easily scoured out nor do you have the temp issues at mid-levels that quite often occurs with shallow cold. And it seems in recent years it has been a fight to get decent snow pack in Canada.

Oh I don't disagree.  Certainly better than the alternative.  I particularly hope the snow pack builds up in Ontario and Quebec.  

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I got 12" last year, so I will gladly take 18-30"

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If we can get started by Thanksgiving, those numbers could be blown out of the water.  I’ll certainly take 20, but 12. Meh. Anyway, looking forward to our first big GFS happy hour runs followed by a good NAMing. :)

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2 hours ago, showmethesnow said:

Talking snow I hope. ;)

RR liking this cracked me up more. But yes. Obviously. 

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2 hours ago, RIC_WX said:

1984-5 and 2005-6 are the analogs mentioned, but the subjective forecast clearly supports the 1984-5 analog in terms of pattern progression.

The 84-85 analog showed up a long time ago when looking at enso conditions that were forecast.  Interesting that it's still there.

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8 minutes ago, WinterWxLuvr said:

The 84-85 analog showed up a long time ago when looking at enso conditions that were forecast.  Interesting that it's still there.

2005 flipped on a dime in December, from historically cold the first 23 days or so to uninhibited warmth beginning around the holidays into early / mid January.  Winter didn't really return until February, and even then it was never quite the same.  Pretty sure 1984-5 was the same play, but in reverse.  

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29 minutes ago, RIC_WX said:

2005 flipped on a dime in December, from historically cold the first 23 days or so to uninhibited warmth beginning around the holidays into early / mid January.  Winter didn't really return until February, and even then it was never quite the same.  Pretty sure 1984-5 was the same play, but in reverse.  

Yeah, my memories of the last half of winter in 1985 are good ones.  The cold outbreak was incredible 

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23 minutes ago, StormchaserChuck said:

Models have gravitated toward more -PNA in the medium range. Negative AO/NAO doesn't really show up until after day 10. If verified good, but there can be a lot of changes. Kind of a 5/10 signal on models today wrt Winter

What kind of pattern does a -PNA -AO -NAO usually yield for us?  The +PNA -AO/NAO is great but sometimes just gives us dry and cold unless something can dig and turn negative. 

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1 hour ago, BristowWx said:

What kind of pattern does a -PNA -AO -NAO usually yield for us?  The +PNA -AO/NAO is great but sometimes just gives us dry and cold unless something can dig and turn negative. 

a pattern full of bowling balls, clippers, and the occsionally well timed SWFE.

:P

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2 hours ago, BristowWx said:

What kind of pattern does a -PNA -AO -NAO usually yield for us?  The +PNA -AO/NAO is great but sometimes just gives us dry and cold unless something can dig and turn negative. 

The 60's were loaded with them. Generally speaking, HL blocking and a -PNA is a wintry pattern for the bulk of the conus except for the far SW. It's not a clean pattern for our region but further north loves it. The majority of the years with a -ao/-pna combo reached climo snow in the MA. The short story is a -pna isn't nearly as big of a deal with a -ao winter as it is with a +ao one. That combo is a death knell. 

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The 60's were loaded with them. Generally speaking, HL blocking and a -PNA is a wintry pattern for the bulk of the conus except for the far SW. It's not a clean pattern for our region but further north loves it. The majority of the years with a -ao/-pna combo reached climo snow in the MA. The short story is a -pna isn't nearly as big of a deal with a -ao winter as it is with a +ao one. That combo is a death knell. 


How about a +EPO, -PNA,-AO,-NAO


Sent from my iPhone using Tapatalk

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35 minutes ago, Philadelphia Snow said:


How about a +EPO, -PNA,-AO,-NAO


Sent from my iPhone using Tapatalk

Generally speaking, a numerical +epo will coincide with a -pna because of domain space overlap more often than not but certainly not always. Depends on the location of the +EPO trough axis though. If we have a big GOA vortex then the only thing a -AO/NAO will displace is Pac maritime air. If the +EPO trough is centered more over land like AK then it's different because cold air can still build in Canada. 

I'm not big on using numerical indices for sensible wx. Best to use the h5 height panels because they tell the real story versus numerical stuff. The answer to your question is sometimes it can suck and sometimes it can be serviceable. 

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This panel shows a +EPO and neutralish PNA. You can see the trough is centered more over AK than digging deep over the Epac:

 

gfs-ens_z500a_nhem_41.png

 

 

This height pattern supports BN temps in our region because the -AO/NAO is displacing continental air southeastward. The 250mb jet pattern shows why:

 

gfs-ens_uv250_nhem_41.png

 

 

A different version of a +EPO/-PNA/-AO/-NAO that royally screws us is what we saw in the second half of Dec 2012. The deep trough in the east pac flooded NA with maritime air so the only thing the -AO/NAO did was displace the AN temps southward:

iKC4RiP.jpg

 

 

Numerical indices don't tell the full story of what is going on. Feature placement inside of the numerical calculation can cause vastly different outcomes with what appears to be the same setup numerically. 

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If we pull out only months with a -NAO/-PNA during a nina it shows a muddy result.  

Those months are

Dec 1970, 2010

Jan 1971

Feb 1955, 1956, 1965

Mar 1955, 1965, 1975

The temperature are skewed cold in the Dec and Jan analogs and warm in the Feb and Mar ones FWIW

Snowfall is pretty average with the following totals at DCA in order by the months in that list

5.2, 2.1, 4.8, 4.2, T, 1.9, T, 5.4, 0.3

So not awful given climo but no big hitters either.  

I also parsed the data for a -NAO and a neutral PNA and the results were only slightly more favorable but also note there were only 5 examples of such an outcome so the correlation may not be significant.

One other problem with this is the values are for the entire month.  We would really need to look at weekly data and see when the periods of NAO and PNA overlapped.  But the general idea is ok but not great for snowfall.  Of course the data sets are so small that I am not sure how valuable they are.  

 

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6 hours ago, BristowWx said:

What kind of pattern does a -PNA -AO -NAO usually yield for us?  The +PNA -AO/NAO is great but sometimes just gives us dry and cold unless something can dig and turn negative. 

Negative NAO is number 1 for snow. With -PNA, when it's cold its dry and warms up only to rain. A lot of signals pointing toward -NAO right now but with a pretty good La Nina developing, we need at this time of the year different Pacific pattern. Could be the difference between mediocre years and 95-96. The attention given to models right now is because there is about a 65-35 ratio between November repeating for the Winter (maybe higher in established ENSO), Pacific-wise. What we want is for ridging to break through Alaska and even the Gulf of Alaska/west coast.

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1 hour ago, StormchaserChuck said:

Negative NAO is number 1 for snow. With -PNA, when it's cold its dry and warms up only to rain. A lot of signals pointing toward -NAO right now but with a pretty good La Nina developing, we need at this time of the year different Pacific pattern. Could be the difference between mediocre years and 95-96. The attention given to models right now is because there is about a 65-35 ratio between November repeating for the Winter (maybe higher in established ENSO), Pacific-wise. What we want is for ridging to break through Alaska and even the Gulf of Alaska/west coast.

Chuck, Wes and others like myself have sliced and diced snowfall data every which way from Sunday over the last 5-7 years or so. For the MA region, our #1 is decisively a -AO. The NAO phase change from neg to pos is a common feature for big storms but our "tell" for favorable conditions seems to point more towards the AO than the NAO. Of course it gets muddy because the two indices share space and bigger storms usually need cooperation from all 3 (ao/nao/pna). But the biggest correlation for snow in general around these parts is the AO.

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13 minutes ago, Bob Chill said:

Chuck, Wes and others like myself have sliced and diced snowfall data every which way from Sunday over the last 5-7 years or so. For the MA region, our #1 is decisively a -AO. The NAO phase change from neg to pos is a common feature for big storms but our "tell" for favorable conditions seems to point more towards the AO than the NAO. Of course it gets muddy because the two indices share space and bigger storms usually need cooperation from all 3 (ao/nao/pna). But the biggest correlation for snow in general around these parts is the AO.

Yep

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