And we begin... Part Deux

[The_Global_Warmer]

I haven't read all of these fully but there are plenty more reasons to track snow other than the age/albedo effect of old and new snow.

http://web.mit.edu/j..._SaitoGRL03.pdf

http://journals.amet.../2008JCLI2505.1

http://journals.amet...1175/JCLI4241.1

http://www.nws.noaa....ohen_062211.pdf

All of those papers are about the cooling from the snow albedo affect.

So it is everything. Two falls with identical snow coverage one with mostly deep fresh snow the other with older melted dirty snow would be Warmer and have a different affect on the atmosphere.

If this is not the gist of it then you can tell me what I am missing.

[wxmx]

All of those papers are about the cooling from the snow albedo affect.

So it is everything. Two falls with identical snow coverage one with mostly deep fresh snow the other with older melted dirty snow would be Warmer and have a different affect on the atmosphere.

If this is not the gist of it then you can tell me what I am missing.

For Eurasia in October probably > 95% of the snow is fresh.

[usedtobe]

Understanding the mechanism which the proposed higher snow cover Eurasian anomalies work would help us analyze the real meaning of the current conditions of the NHEM cryosphere.

It is proposed that the greater/lower snowcover anomalies in the Eurasian region promote a higher/lower anomalies in the SLP around the Eurasian region. Looking at the highest snowcover anomalies in this region for October shows that there are higher than normal pressures

Which tend to migrate west and then north, as the Artic Sea freezes.

OTOH, low snowcover anomalies tend to promote lower pressures in E Russia early in the season

And those pressure anomalies usually propagate thru the AO region, which promote a +AO for the winter season

So what's in store for winter 2011-2012. Snow cover anomalies were low for the first 3 weeks of October, with a sudden recovery to above normal the last week of the month, which brought the average to just below normal. SLP anomalies in the month were not good for those looking for high latitude blocking during DJF

But this average tell us little of what really happened.

...during low level anomalies

...and after the sudden increase in snow cover.

I think the coin is still in the air, and we should monitor how the Siberian high behaves for the rest of November, as it is known to promote planetary waves that might disrupt the nightly polar jet and consequent high latitude blocking.

Nice post,

I think monitoring the situation is a good move but there usually is a delay between the anomalous snow cover and the blocking as it takes time to disrupt the polar night jet and then have down-welling then warm the troposphere. At least that is my limited understanding of the process. At any rate, I don't particularly like the October snow cover that Will posted.

[BethesdaWX]

Fresh snow cover reflectsmuch more sun light then melting or older snow. Quiye a bit of the snow cover in Canada is very thin.

Tthis is the only reason to track the snow.

So it would be nice if we had reliable data on this.

Can you explain this hypothesis of yours?

Snowcover is snowcover, old snow and new snow reflect the same amount of shortwave radiation as long as the snowpack is full & clean, dirty snow or patchy snow reflect less shortwave radiation. Think about the "brightness" you see on the snow during a sunny day, 6" of snow vs 3 feet of snow will look the same from space on a bare field. Ever wonder why you can get a sunburn on a snowcovered sky-slope? Additional reflected shortwave radiation is flying back at you.

Snow doesn't cool the temperature because it is "cold", it is because it reflects light in the visible spectrum. That is how clouds cool temperature too, they reflect shortwave radiation. Shortwave radiation is transferred into a longwave form upon interaction with the body of matter (AKA LW = heat). How much shortwave radiation actually gets into the oceans, lower atmosphere, etc, is what determines the global energy budget and as a result the global temperature. Albedo includes cloud cover, snow/ice cover, etc.

And what makes you say the snow in northern canada is "thin"?

[skierinvermont]

Can you explain this hypothesis of yours?

Snowcover is snowcover, old snow and new snow reflect the same amount of shortwave radiation as long as the snowpack is full & clean, dirty snow or patchy snow reflect less shortwave radiation. Think about the "brightness" you see on the snow during a sunny day, 6" of snow vs 3 feet of snow will look the same from space on a bare field. Ever wonder why you can get a sunburn on a snowcovered sky-slope? Additional reflected shortwave radiation is flying back at you.

Snow doesn't cool the temperature because it is "cold", it is because it reflects light in the visible spectrum. That is how clouds cool temperature too, they reflect shortwave radiation. Shortwave radiation is transferred into a longwave form upon interaction with the body of matter (AKA LW = heat). How much shortwave radiation actually gets into the oceans, lower atmosphere, etc, is what determines the global energy budget and as a result the global temperature. Albedo includes cloud cover, snow/ice cover, etc.

And what makes you say the snow in northern canada is "thin"?

I think most people understand the concept of albedo and the difference between SW and LW radiation. What Friv said is correct. Old and/or melting snow has lower albedo than fresh snow.

But what I think Friv is missing is that the areal coverage of snowcover is much more important than the age of the snow since in October pretty much all the snow in Eurasia would qualify as "fresh." November the age might start to matter a little more in terms of albedo.

[beavis1729]

Can you explain this hypothesis of yours?

Snowcover is snowcover, old snow and new snow reflect the same amount of shortwave radiation as long as the snowpack is full & clean, dirty snow or patchy snow reflect less shortwave radiation. Think about the "brightness" you see on the snow during a sunny day, 6" of snow vs 3 feet of snow will look the same from space on a bare field. Ever wonder why you can get a sunburn on a snowcovered sky-slope? Additional reflected shortwave radiation is flying back at you.

Snow doesn't cool the temperature because it is "cold", it is because it reflects light in the visible spectrum. That is how clouds cool temperature too, they reflect shortwave radiation. Shortwave radiation is transferred into a longwave form upon interaction with the body of matter (AKA LW = heat). How much shortwave radiation actually gets into the oceans, lower atmosphere, etc, is what determines the global energy budget and as a result the global temperature. Albedo includes cloud cover, snow/ice cover, etc.

And what makes you say the snow in northern canada is "thin"?

I don't want to speak for friv...but the bold above is exactly the point. "Old" snow is typically not as white as new snow, especially in populated ares. Of course it's probably not as much of an issue in central/northern Canada, as there is not much population there. Then again, even in non-populated areas, the snow can get dirty from wind and dirt settling, as you often see in North Dakota in mid-winter after a few weeks without snow.

In addition, since it's pretty much always snow covered in mid-November in the far north, perhaps it's more interesting to look at how "new" that snow is, if you're trying to find something anomalous about the situation. Plus, how deep is the snowcover?

It's analogous to wondering if International Falls, MN will have a White Christmas. Of course they will...the only questions are: (1) How "fresh" is the snow? (2) How deep is the snowcover?

I believe studies have shown that deeper snow cover reflects radiation more than thinner snowcover, in addition to the fresh vs. dirty snowcover albedo differences.

We may be nibbling around tiny details here...but good discussion nonetheless. The cryosphere is always interesting for a winter weather lover.

[beavis1729]

I think most people understand the concept of albedo and the difference between SW and LW radiation. What Friv said is correct. Old and/or melting snow has lower albedo than fresh snow.

But what I think Friv is missing is that the areal coverage of snowcover is much more important than the age of the snow since in October pretty much all the snow in Eurasia would qualify as "fresh."

Agree.

[BethesdaWX]

I think most people understand the concept of albedo and the difference between SW and LW radiation. What Friv said is correct. Old and/or melting snow has lower albedo than fresh snow.

But what I think Friv is missing is that the areal coverage of snowcover is much more important than the age of the snow since in October pretty much all the snow in Eurasia would qualify as "fresh." November the age might start to matter a little more in terms of albedo.

You and Friv are completely incorrect in both areas in terms of significance, think in terms of "brightness" which is a direct measure of Albedo net value, from space. First, contradictory to Friv's claim, deep snow does not reflect any less SW than "shallow" snow. Imagine my roof from space with snow on it, it will look just as "bright" either way whether or not there is 2 inches or 2 feet on it until the snow melts off the roof...also now, if I have a 1 foot of snow on my roof and over 1 week it melts down to 4", look at it from space, there will be no significant difference in the "brightness" despite it being 1 week old. Maybe a tiny change in the net value but nothing even worth mentioning or "tracking". Friv is wrong.

Out in nature, this is the same exact thing obviously, snow does not get relatively "dirty" after it fell even when laying on the ground for weeks. This notion is silly. Maybe in a city environment there would be enhanced effects due to pollution but even this wouldn't be as significant.

Once the snow melts and bare ground becomes an issue as it thins, then the net value of Albedo over the landmass as a whole decreases unless the snow gets very dirty.

[skierinvermont]

Friv is completely incorrect in both areas, think in terms of "brightness" which is a direct measure of Albedo net value. First, contradictory to Friv's claim, deep snow does not reflect any less SW than "shallow" snow. Imagine my roof from space with 2in vs 2ft on it.....it will look just as "bright" either way until the snow melts off the roof...if I have a 1 foot of snow on my roof and over 1 week it melts down to 4", look at it from space, there will be no significant difference in the brightness despite it being 1 week old. Maybe a tiny change in the net value but nothing even worth mentioning or "tracking". Friv is wrong.

Out in nature, this is the same exact thing obviously, snow does not get relatively "dirty" after it fell even when laying on the ground for weeks. This notion is silly. Maybe in a city environment there would be enhanced effects due to pollution but even this wouldn't be as significant.

You are wrong on both counts. As beavis and I have both explained, snow actually does get dirtier just laying on the ground for a few weeks even in pristine environments because of dust/soot aerosols from the atmosphere. New snow also clings to vegetation more than old snow. And the depth of the snow does matter, probably because deeper snow is more likely to cover up vegetation and rocks.

[BethesdaWX]

You are wrong on both counts. As beavis and I have both explained, snow actually does get dirtier just laying on the ground for a few weeks even in pristine environments because of dust/soot aerosols from the atmosphere. New snow also clings to vegetation more than old snow. And the depth of the snow does matter, probably because deeper snow is more likely to cover up vegetation and rocks.

You obviously did not read anything I wrote because this makes no sense whatsoever. When snow falls, Initially, everything exposed to the Sun's SW radiation gets covered before the wind removes some fo that from tree limbs and it falls to the ground etc, but that process is short and after awhile as long as everything is covered at that high lattitude the value of Albedo does not significantly change, you aren't taking into account the lattiude, amount of daylight, and time-to-dirty before being re-covered, what you are questioning is the net albedo value in it's significance versus available shortwave radiation for snow that:

A) Will not have time to get significantly dirty before being re-covered & expanding in depth through the winter

B ) Is constantly below freezing

C) Is at or over 4" deep with a very low sun angle.

Obviously getting dirty at that lattitude before being re-covered isn't adequate to pose large significance in albedo, obviously it also isn't melting when temps are never over 25 degrees right now, and 3rd with a low sun angle differences in albedo potential mean much less inb total net reflection value, look at "relativity" relative to the value of incoming SW vs the value of Albedo.

This isn't snow in St. Louis MO, or what you say would make sense.

[skierinvermont]

You obviously did not read anything I wrote because this makes no sense whatsoever. When snow falls, Initially, everything exposed to the Sun's SW radiation gets covered before the wind removes some fo that from tree limbs and it falls to the ground, but that process is short and after awhile as long as everything is covered at that higjh lattitude the value of Albedo does not significantly change, you aren't takling into account the lattiude, what you are questioning is the net albedo value in it's significance versus available shortwave radiation for snow that:

A) Will not have time to get significantly dirty before being re-covered & expanding in depth through the winter

B ) Is constantly below freezing

C) Is at or over 4" deep with a very low sun angle.

Obviously getting dirty at that lattitude before being re-covered isn't adequate to pose large significance in albedo, obviously it also isn't melting when temps are never over 25 degrees right now, and 3rd with a low sun angle differences in albedo potential mean much less inb total net reflection value, look at "relativity" relative to the value of incoming SW vs the value of Albedo.

This isn't snow in St. Louis MO, or what you say would make sense.

Read any paper on the subject. Snow age and depth are the two primary variables that effect its albedo. Just as Friv said. This is just basic common knowledge. I am surprised anybody actually questioned him on the subject.

A) It actually doesn't snow that frequently at high latitudes so the snow can get quite dirty. It only takes a short amount of time for soot and dust to begin to build up. Soot concentrations of just .3ppmw can have a significant effect on snow albedo.

C) The snow at high latitudes is often not 4" thick, especially early in fall or winter. Much of these areas are technically deserts.

[BethesdaWX]

Read any paper on the subject. Snow age and depth are the two primary variables that effect its albedo. Just as Friv said.

Yes of course, but that isn't the issue, the net change in albedo at that lattitude is not significant enough over extended timespans to mean anything in terms of temperature or even total net abledo deviation, Friv said that the snow in Northern Canada is "thin" and it means something, only it isn't "thin" relatively and it is newer snow that has been recovered as has the snow in Russia and Eurasia. There will be differences of course but nothing that will show any significant difference in temperature were we to "track" it as Friv suggests.

Thats what I implied in my post and is why I italisized the word "significant".

everything exposed to the Sun's SW radiation gets covered before the wind removes some fo that from tree limbs and it falls to the ground etc, but that process is short

as long as everything is covered at that high lattitude the value of Albedo does not significantly change, you aren't taking into account the lattiude, amount of daylight, and time-to-dirty before being re-covered, what you are questioning is the net albedo value in it's significance versus available shortwave radiation for snow that

Obviously getting dirty at that lattitude before being re-covered isn't adequate to pose large significance in albedo, obviously it also isn't melting when temps are never over 25 degrees right now, and 3rd with a low sun angle differences in albedo potential mean much less inb total net reflection value, look at "relativity" relative to the value of incoming SW vs the value of Albedo.

And yes snowfalls uaually aren't heavy up in the colder high lattitudes since less moisture can sustain, but the snows are "frequent", re-covered frequently at least...and the sun angle is very low which makes relative devation between SW availability and albedo deviation significantly less.

Snow getting dirty at that lattitude is probably the least impactful, snow can be analyzed as a land based version of sea ice.

Look, 8" of snow versus 2" of snow will fall off the trees in almost equal time especially given it's dry. That would be the biggest factor would be green conifer trees over the snowpack. But the depth doesn't matter there neither does the nage because the snow will fall off the trees in equal time usually until it is re-covered.

[skierinvermont]

Yes of course, but that isn't the issue, the net change in albedo at that lattitude is not significant enough over extended timespans to mean anything in terms of temperature or even total net abledo deviation, Friv said that the snow in Northern Canada is "thin" and it means something, only it isn't "thin" relatively and it is newer snow that has been recovered as has the snow in Russia and Eurasia. There will be differences of course but nothing that will show any significant difference in temperature were we to "track" it as Friv suggests.

Thats what I implied in my post and is why I italisized the word "significant".

I like how you went and edited the word 'signficant' into your original post.

Regardless, it is 'signficant' old or shallow snow, which is a widespread phenomenon, can have albedos of .6-.8, much lower than the .9 of deep fresh snow.

[SVT450R]

Doing a quick search i came across this. The albedo of snow typically ranges between 80% (old snow) and 95% (fresh snow). Which to me seem like not much of a difference.

Link

[skierinvermont]

Caught red handed. If you had said this 'new version' originally, I might not have disagreed, or would have disagreed only in terms of the degree of significance. That would depend on how you define 'significance' I guess. Instead you decide to edit your posts after the fact so you can claim to be right. Editing your posts after the fact is pretty low.

Old:

Friv is completely incorrect in both areas, think in terms of "brightness" which is a direct measure of Albedo net value.

New:

You and Friv are completely incorrect in both areas in terms of significance, think in terms of "brightness" which is a direct measure of Albedo net value, from space.

And originally you never mentioned 'significance' at all. You simply said that old 'clean' snow and new snow have the same albedo completely missing the point that old snow is always dirtier than new snow due to soot and dust fallout.

Snowcover is snowcover, old snow and new snow reflect the same amount of shortwave radiation as long as the snowpack is full & clean, dirty snow or patchy snow reflect less shortwave radiation.

[The_Global_Warmer]

http://www.athropolis.com/sun-fr.htm

I would say the claim that the sun angle of the observed area during October does matter.

The topic I brought up is an important part of this process.

The sun never completely sets south of 66N 33 minutes.

That is the circular line on the map.

October snowfall is the main reason to track apparently.

The sun is up 11 hours 12 minutes at 66N on October 1st. And is up 7 hours 34 min on the 31st.

The sun is up 10 hours 22 minutes at 78N on October 1st. it sets on October 26th.

In other words the mainland of Eurasia has sunlight for all of October even if it is much weaker by the end. Which doesn't matter much for the areas by the arctic because they are even warmer in many cases because of the massive arctic sea ice decline and how much heat release is going on there in October.

You can see some big temp variations where snow cover is. it is November 12th not October. Why would the temps vary so much at such high latitudes if there were not many factors involved here.

[Alpha5]

huge gains again in Eurasia

[WidreMann]

You can see some big temp variations where snow cover is. it is November 12th not October. Why would the temps vary so much at such high latitudes if there were not many factors involved here.

Are you really trying to argue that we think there should be uniform temperatures over snowpack? I don't think anyone is proposing that. You are attacking a strawman.

[skierinvermont]

You can see some big temp variations where snow cover is. it is November 12th not October. Why would the temps vary so much at such high latitudes if there were not many factors involved here.

I hope you're not implying it is due to the age/depth of the snow? It's just weather.

[BethesdaWX]

Caught red handed. If you had said this 'new version' originally, I might not have disagreed, or would have disagreed only in terms of the degree of significance. That would depend on how you define 'significance' I guess. Instead you decide to edit your posts after the fact so you can claim to be right. Editing your posts after the fact is pretty low.

Old:

New:

And originally you never mentioned 'significance' at all. You simply said that old 'clean' snow and new snow have the same albedo completely missing the point that old snow is always dirtier than new snow due to soot and dust fallout.

So you affirm that you didn't read the post....I used the word significant 4 times before the edit (which I only did since I knew you'd skip over the post and wanted you to see the word)....Oh and yeah, look at the end of my post that you quoted:

as long as the snowpack is full & clean... dirty snow or patchy snow reflect less shortwave radiation

lol

snow thats been around for a few days will not show any significant deviation in albedo, and there will be NO effect on temperature.

I used the word "significant" 4 freaking freaking times, the edit was to help you since you never read my posts...and if I didn't put "significant" sooner in my paragraph you'd never see it due to your own ignorance.

there will be no significant difference in the "brightness" despite it being 1 week old.

as long as everything is covered at that high lattitude the value of Albedo does not significantly change, you aren't taking into account the lattiude, amount of daylight, and time-to-dirty before being re-covered, what you are questioning is the net albedo value in it's significance versus available shortwave radiation for snow

Obviously getting dirty at that lattitude before being re-covered isn't adequate to pose large significance in albedo, obviously it also isn't melting when temps are never over 25 degrees right now, and 3rd with a low sun angle differences in albedo potential mean much less inb total net reflection value, look at "relativity" relative to the value of incoming SW vs the value of Albedo.

lolz

Your idol Friv was wrong...there is no effect on temperature, no significant effect on albedo, if any at the highest lattitudes.

How soot-covered is the arctic icepack? Snow "getting dirty" is the least of any effect on albedo, and to have a real effect it'd take weeks to months, and even then effect on temps is little to none, and it'd likely be re-covered several times since that snowfall anyway.

[skierinvermont]

I'm not going to engage you on this any longer. What Friv said was correct. Old and/or shallow snow has significantly lower albedo than fresh snow.

Getting back to wxmx's excellent post and Cohen's research. The last two years we have observed spikes in 70hpa temperature in late October/November which if we believe Cohen's research is likely due to the +snow anomalies occurring at that time. This was especially true in late 2009. Below I have listed the 70hpa temperatures for 2008, 2009, 2010 and 2011, along with a timeseries of snow cover for comparison. I think there is a detectable correlation between the high snow cover fall 2009 and 2010 and the 70hpa temps (and subsequent winter blocking DJF '09-'10 and DJ '10-'11). This year, we have yet to witness a late Oct-mid November bump in 70hpa temps as we witnessed in 2009 and 2010. Arguably this is an ominous signal against continued anomalous blocking this winter. The jumps in 70hpa temp in 2009 and 2010 are very noticeable in late oct and november. Especially in 2009 which had record warm 70hpa temps in November.

Those who rely on blocking for snowfall had better start hoping for the latest snow cover anomalies to kick in, or for something else to disrupt the stratosphere later in winter.

[BethesdaWX]

I'm not going to engage you on this any longer. What Friv said was correct. Old and/or shallow snow has significantly lower albedo than fresh snow.

Except it doesn't, did you read the paper linked? I'm guessing not. BTW, regardless the question was in regards to temperature. He was wrong end of disco.

here was the post:

Doing a quick search i came across this. The albedo of snow typically ranges between 80% (old snow) and 95% (fresh snow). Which to me seem like not much of a difference.

Link

And he's right.

The albedo of snow typically ranges between 80% (old

snow) and 95% (fresh snow), whereas most other constituents

of the natural landscape such as earth, grass,

water, forest, and pavement typically range between 5%

and 30%.' Hence it is not surprising at first blush that

snowy landscapes look so white compared with adjacent

trees and buildings or other common snow-free surfaces

with much lower reflectance. Such brightness contrast

effects have been well documented and studied extensively.

2 4 Less well known is that snow also typically appears

much brighter than the sky that illuminates it, even

when the sky and the snow are adjacent. This effect is

particularly apparent during or just after a snowfall, when

the fresh snow on a roof or a mountaintop is set against

the cloudy sky (see Fig. 1). The problem that we address

here is thus the following: How is it possible for the snow

to be brighter than the (overcast) sky that illuminates it?

We show that three factors suffice to account for the major

part of the phenomenon:

1. The law of darkening for the cloud cover.

2. The reflectivity of the snow and the average landscape

albedo.

3. The observer's contrast sensitivity function.

We proceed to discuss these factors in sufficient detail to

calculate radiance profiles along the vertical snowy landscapes

under overcast conditions that can be compared

with actual photometric measurements.

[skierinvermont]

Here is a bump to wxmx's excellent post in case anybody missed it amid all the bickering. Thus far I would say the stratosphere is behaving more like a low snow cover year. And a link to the Cohen work he based it on:

http://www.nws.noaa.gov/ost/climate/STIP/FY11CTBSeminars/jcohen_062211.pdf

Understanding the mechanism which the proposed higher snow cover Eurasian anomalies work would help us analyze the real meaning of the current conditions of the NHEM cryosphere.

It is proposed that the greater/lower snowcover anomalies in the Eurasian region promote a higher/lower anomalies in the SLP around the Eurasian region. Looking at the highest snowcover anomalies in this region for October shows that there are higher than normal pressures

Which tend to migrate west and then north, as the Artic Sea freezes.

OTOH, low snowcover anomalies tend to promote lower pressures in E Russia early in the season

And those pressure anomalies usually propagate thru the AO region, which promote a +AO for the winter season

So what's in store for winter 2011-2012. Snow cover anomalies were low for the first 3 weeks of October, with a sudden recovery to above normal the last week of the month, which brought the average to just below normal. SLP anomalies in the month were not good for those looking for high latitude blocking during DJF

But this average tell us little of what really happened.

...during low level anomalies

...and after the sudden increase in snow cover.

I think the coin is still in the air, and we should monitor how the Siberian high behaves for the rest of November, as it is known to promote planetary waves that might disrupt the nightly polar jet and consequent high latitude blocking.

[Isotherm]

I'm not going to engage you on this any longer. What Friv said was correct. Old and/or shallow snow has significantly lower albedo than fresh snow.

Getting back to wxmx's excellent post and Cohen's research. The last two years we have observed spikes in 70hpa temperature in late October/November which if we believe Cohen's research is likely due to the +snow anomalies occurring at that time. This was especially true in late 2009. Below I have listed the 70hpa temperatures for 2008, 2009, 2010 and 2011, along with a timeseries of snow cover for comparison. I think there is a detectable correlation between the high snow cover fall 2009 and 2010 and the 70hpa temps (and subsequent winter blocking DJF '09-'10 and DJ '10-'11). This year, we have yet to witness a late Oct-mid November bump in 70hpa temps as we witnessed in 2009 and 2010. Arguably this is an ominous signal against continued anomalous blocking this winter. The jumps in 70hpa temp in 2009 and 2010 are very noticeable in late oct and november. Especially in 2009 which had record warm 70hpa temps in November.

Those who rely on blocking for snowfall had better start hoping for the latest snow cover anomalies to kick in, or for something else to disrupt the stratosphere later in winter.

There's more to it than just snow cover = good blocking. I'm of the opinion that the anomalous high latitude blocking of the past two cold seasons was due largely to the stratospheric/tropospheric response to extended low geomagnetic activity. Heading into mid November this year, geomagnetic indicators have fallen off the cliff as K indices and Ap are barely detectable right now. Given that hasn't changed from the last 2 years, I believe it's not a question of if the blocking will occur but when. This year the -NAO should initiate about a month later.

[skierinvermont]

There's more to it than just snow cover = good blocking. I'm of the opinion that the anomalous high latitude blocking of the past two cold seasons was due largely to the stratospheric/tropospheric response to extended low geomagnetic activity. Heading into mid November this year, geomagnetic indicators have fallen off the cliff as K indices and Ap are barely detectable right now. Given that hasn't changed from the last 2 years, I believe it's not a question of if the blocking will occur but when. This year the -NAO should initiate about a month later.

Obviously there's a lot more to it than snow cover. This year should be a good test of which theory is more powerful, although in reality it will just be one more piece of data to add to the pile.

The past two years the high fall snow cover and anomalously warm stratospheric temperatures in November offer a viable alternative explanation to the sun.

This year we have fairly low snow cover and a cold stratosphere thus far, but continued low geomagnetic activity.

I understand that a -QBO and low solar activity or a +QBO + solar flares can create blocking, but I'm not totally convinced that low solar activity alone will create blocking. With the +QBO and snow cover favoring less blocking, it will be interesting to see if we still get blocking perhaps from the continued inactive sun.

[Isotherm]

This year should be a good test of which theory is more powerful, although in reality it will just be one more piece of data to add to the pile.

The past two years the high fall snow cover and anomalously warm stratospheric temperatures in November offer a viable alternative explanation to the sun.

This year we have fairly low snow cover and a cold stratosphere thus far, but continued low geomagnetic activity.

I understand that a -QBO and low solar activity or a +QBO + solar flares can create blocking, but I'm not totally convinced that low solar activity alone will create blocking. With the +QBO and snow cover favoring less blocking, it will be interesting to see if we still get blocking perhaps from the continued inactive sun.

Last winter we had strongly +QBO and a Nina event quite a bit more intense than now, yet we still had blocking comparable to 2009-10 Nino/-QBO year. That's fairly convincing to me but should be interesting as you said, to see how this winter evolves.

[skierinvermont]

Last winter we had strongly +QBO and a Nina event quite a bit more intense than now, yet we still had blocking comparable to 2009-10 Nino/-QBO year. That's fairly convincing to me but should be interesting as you said, to see how this winter evolves.

Yep, 09-10 we had all three factors aligned, snow, -QBO/solar min, solar min.

'10-11 we had 2 factors, snow and the solar min

this year we only have one factor, the solar min (unless the QBO does get negative)

Of course there are other things that affect it too (PDO, AMO, ENSO, luck, etc.) but this will be an interesting test to some degree. I am leaning heavily towards less blocking.

[WidreMann]

Yep, 09-10 we had all three factors aligned, snow, -QBO/solar min, solar min.

'10-11 we had 2 factors, snow and the solar min

this year we only have one factor, the solar min (unless the QBO does get negative)

Of course there are other things that affect it too (PDO, AMO, ENSO, luck, etc.) but this will be an interesting test to some degree. I am leaning heavily towards less blocking.

We're doing better than '10 in terms of snow and have been for a week or so now. We had a crappy time in the middle of October, but then again, '10 had a really crappy time in early-mid November.

[skierinvermont]

We're doing better than '10 in terms of snow and have been for a week or so now. We had a crappy time in the middle of October, but then again, '10 had a really crappy time in early-mid November.

Yes this has not been a 'bad' year for snow... just not as good as 09-10 and 10-11 considering October is the most important. I'm guessing the first week or two of November matters a little bit too considering Cohen just says October is the most important not that nothing else matters. If that's the case we might expect the stratospheric warming to occur a week or two later than it did in 09-10 and 10-11. The reason November probably doesn't matter nearly as much is that all the high latitude areas are already covered with snow, and so any + or - anomalies will occur in the 40-70N latitude where it won't affect the stratospheric vortex. In fact, +snow anomalies in the 40-50+N latitude band might even strengthen the stratospheric vortex by strengthening the N-S temperature gradient (the opposite mechanism whereby +snow anomalies in the 60-90N latitude bands weaken the vortex by weakening the N-S temp gradient).

[BethesdaWX]

Yes this has not been a 'bad' year for snow... just not as good as 09-10 and 10-11 considering October is the most important. I'm guessing the first week or two of November matters a little bit too considering Cohen just says October is the most important not that nothing else matters. If that's the case we might expect the stratospheric warming to occur a week or two later than it did in 09-10 and 10-11. The reason November probably doesn't matter nearly as much is that all the high latitude areas are already covered with snow, and so any + or - anomalies will occur in the 40-70N latitude where it won't affect the stratospheric vortex. In fact, +snow anomalies in the 40-50+N latitude band might even strengthen the stratospheric vortex by strengthening the N-S temperature gradient (the opposite mechanism whereby +snow anomalies in the 60-90N latitude bands weaken the vortex by weakening the N-S temp gradient).

Thats the problem I've had with the snowcover theory, why would this supposed snowcover forcing mechanism just shut off in early november? Do physics change? Both 2009 and 2010 featured well above average snowcover in october yet in november one had the weak -NAO avg (2010) and one had the +NAO avg (2009). Thats why I theorize there is something in the pattern that leads to above average snowcover in the autumn, and that pattern may evolve and/or lead to a -NAO in winter as wavelengths increase given natural flow tendancies. If it were the snowcover, why would october correlate well, yet november not correlate when physics don't change? And why would one month of snowcover deviation affect the blocking for the rest of the winter? That in itself may argue for natural tendancies in the pattern that led to the increased snowcover serving as the culprit for increased blocking rather than a theorized october snowcover correlation with a mechanism in place for 6 weeks only then shutting off somehow. Perhaps it is some connection in the stratosphere.

If it is somehow the snowcover, the only think I can think of would be that the amount of sunlight diminishing in november could mess with something, but what would it be? It just seems iffy to me. And in case I know what you're thinking, the changes in the geomag sun correlating to changes in blocking cannot be placed in the same camp as the snowcover theory because the correlation exists year round with the geomag theory rather than in 6/52 weeks with the snowcover theory.

It'll be interesting to watch thigns unfold.