Winter 2014-2015 Pattern Discussion Thread I

[Stormsfury]

So, departures through the 15th:

Atlanta: +4.8

Asheville: +3

Charleston: +0.8

Charlotte: +2.5

Columbia: +2.3

GSP: +3.3

Greensboro: +1.5

Raleigh: 0.0

Of those, I would assume CHS and RDU have the best shot at a normal month. Otherwise, we all could end up significantly above normal for the month, probably somewhere around +3, especially if we end up with a post christmas warm shot.

KCHS has had some cold mornings (30+ degree temp spreads day/night) due to excellent radiational cooling on several nights this month). Last Friday, 27 morning low, mid 60's afternoon.

[LithiaWx]

If I remember right mp is currently in his met program. I wouldn't just outright dismiss what he's saying. Maybe you're right webber, maybe not but what he said does seem to have some merit. This doesn't seem like a case of black and white who is right and wrong. Both of you can be correct here.

[burgertime]

If I remember right mp is currently in his met program. I wouldn't just outright dismiss what he's saying. Maybe you're right webber, maybe not but what he said does seem to have some merit. This doesn't seem like a case of black and white who is right and wrong. Both of you can be correct here.

 

The problem is I've never seen anything to prove mp right. I've heard multiple mets talk about how the snowpack helps during a CAD event. In fact I'm pretty sure when NC has a snowpack and HP is in place it significantly cools GA as there is a better cold air transport. At least Webber is giving facts and examples to back up his claims. When has there been a big snow pack and a good HP in place and temps were warmer?  That's what mp needs to show. 

[franklin NCwx]

It's pretty obvious that having snowcover on the ground will keep it colder than bare ground.

[LithiaWx]

It's pretty obvious that having snowcover on the ground will keep it colder than bare ground.

 

Let's say there is no snowcover south of PA.  Do we want snowcover or not over the NE?  Is what mp said just completely wrong?  Does snowcover promote lowering of pressures underneath a high pressure?  I don't see anyone here arguing that air blowing over snowcover doesn't stay colder than air blowing over bare ground.

[SN_Lover]

I really thought some of this was common sense, to some degree, since when does snow cause diabatic heating? I think you have the processes of melting, freezing, & sublimation mixed up, among other things... You do realize if there's a region of high pressure over the northeast & southeastern Canada, there will likely be little-if any clouds in place right, and given other conditions are equal the ambient temperature over a region of snowpack vs w/o will be cooler to begin w/ before the clouds even move in? Snow because of it's color & due to kirchoff's law (poor absorber of a particular radiation band is also a poor emitter) reflects up to 90-95% of incoming solar radiation, cools the surrounding air because less shortwave radiation is absorbed into earth's surface, & more is reflected back out into space. The colder surrounding air due to the snowpack, causes the air to become less buoyant & sink, which leads to a piling up of air in the boundary layer forcing heights to rise, thus enhancing not negating a region of near surface high pressure. Not to mention, despite the fact that the air is a poor conductor of heat, some turbulent mixing is bound to occur between the surface & the lower levels, and this interaction with the underlying snowpack will lead to some cooling of the near surface air. Additionally, any appreciable sunshine that breaks out in the residence period between the formation/laying down of the snow & its application in a cold air damming event, will lead to sublimation of some snow (solid->gas) which further cools the air... His point doesn't have any merit...

I was just confused by what you said before. Dont have to be so condescending. Yes, you are correct about albedo being higher but once sublimation and melting starts clouds form and then diabatic heating starts. There appears to be some clouds that form in the wake of the departing low prior to this weekends storm, this is why the high weakens as this weekends storm forms in the models. I think the main reason the damming isnt so stout is the gradient isnt strong at all due to a positive NAO. Once we get a more negative NAO, we will see more blocking. 

[Webberweather53]

If I remember right mp is currently in his met program. I wouldn't just outright dismiss what he's saying. Maybe you're right webber, maybe not but what he said does seem to have some merit. This doesn't seem like a case of black and white who is right and wrong. Both of you can be correct here.

 

 

 

I was just confused by what you said before. Dont have to be so condescending. Yes, you are correct about albedo being higher but once sublimation and melting starts clouds form and then diabatic heating starts. There appears to be some clouds that form in the wake of the departing low prior to this weekends storm, this is why the high weakens as this weekends storm forms in the models. I think the main reason the damming isnt so stout is the gradient isnt strong at all due to a positive NAO. Once we get a more negative NAO, we will see more blocking. 

 

I try not be condescending, but from a conceptual basis as I posted above, to say that the snowpack would actually somehow hurt CAD makes absolutely no sense whatsoever, independent of other conditions, the snow is a positive feedback on the CAD, no questions asked. Again, note in my comment the statement "given other conditions are approximately equal" I made no reference to the NAO, cloudiness, etc., all that was said air being advected over a snowpack will be colder than bare terrain, there's no "maybe" about that. Sure you can claim *maybe* the NAO or the clouds are the reason for the weakening of the CAD, but in order to go onto claim it is playing a *more* significant role than the snowpack, requires not just mere conjecture, but the presentation of actual evidence as I did using the daily IMS snow record since 1998, which shows we haven't yet observed a CAD event result in wintry weather in central NC when the snowpack was well north of I-80. The evidence I presented also exemplifies when the snowpack was very extensive it was followed by a powerful CAD event, the two are directly correlated to one another...

[SN_Lover]

I try not be condescending, but from a conceptual basis as I posted above, to say that the snowpack would actually somehow hurt CAD makes absolutely no sense whatsoever, independent of other conditions, the snow is a positive feedback on the CAD, no questions asked. Again, note in my comment the statement "given other conditions are approximately equal" I made no reference to the NAO, cloudiness, etc., all that was said air being advected over a snowpack will be colder than bare terrain, there's no "maybe" about that. Sure you can claim *maybe* the NAO or the clouds are the reason for the weakening of the CAD, but in order to go onto claim it is playing a *more* significant role than the snowpack, requires not just mere conjecture, but the presentation of actual evidence as I did using the daily IMS snow record since 1998, which shows we haven't yet observed a CAD event result in wintry weather in central NC when the snowpack was well north of I-80. The evidence I presented also exemplifies when the snowpack was very extensive it was followed by a powerful CAD event, the two are directly correlated to one another...

Yes, snowpack with no clouds whatsoever will cause the pressure to rise. But, snow has to sublimate and melt and that forms clouds. So pressure might rise after a storm passage, but lower again when clouds form. I think you may be putting too much emphasis on diabatic effects and not on the overall pattern, There is differential vorticity advection, thermal advection, and topographic forcing to also consider when determining vertical motion. The NAO effects all of these variables. 

[Webberweather53]

Let's say there is no snowcover south of PA.  Do we want snowcover or not over the NE?  Is what mp said just completely wrong?  Does snowcover promote lowering of pressures underneath a high pressure?  I don't see anyone here arguing that air blowing over snowcover doesn't stay colder than air blowing over bare ground.

 

No, but the temperature of an airmass is related to its pressure... In an isolated parcel, a warmer airmass will exert more pressure, however, since we're talking about the planetary boundary layer only, w/ an impenetrable surface (the ground) underneath, this argument doesn't have much basis here, and because temperature is generally a measure of the average movement of the particles in a specified volume of air, the slower moving particles in a colder air mass are allowed to pass closer to one another. Thus you can pack more air into the same amount of space (increasing the density of the air), which makes the air within that same specific volume above the surface heavier, hence the pressures at the surface rise...

[franklin NCwx]

Let's say there is no snowcover south of PA. Do we want snowcover or not over the NE? Is what mp said just completely wrong? Does snowcover promote lowering of pressures underneath a high pressure? I don't see anyone here arguing that air blowing over snowcover doesn't stay colder than air blowing over bare ground.

no it does not promote lowering pressure over the snowpack. Snowpack can help setup A baroclonic zone at the edge of it.

You guys do want snowpack to your northeast for cad. I want snowpack to my northwest over the plains.

[Webberweather53]

Yes, snowpack with no clouds whatsoever will cause the pressure to rise. But, snow has to sublimate and melt and that forms clouds. So pressure might rise after a storm passage, but lower again when clouds form. I think you may be putting too much emphasis on diabatic effects and not on the overall pattern, There is differential vorticity advection, thermal advection, and topographic forcing to also consider when determining vertical motion. The NAO effects all of these variables. 

 

 

Again, the entire focus of my post was aimed towards the diabatic effects of snow, I made no reference to the other conditions because I was purposely trying to isolate this variable, & if you're going to claim that effects of diabatic heating from clouds is more significant than the snowpack then supply the actual evidence that shows this is the case.. It seems to me you're suggesting that sublimation and melting of snow always forms clouds? Not necessarily, that's dependent upon the saturation vapor pressure of the ambient air, and it's common for these cooling processes to occur w/o any cloud formation, thus the net effect of the snowpack as a whole is cooling, not diabatic "heating" as you stated earlier, which enhances CAD...

[burgertime]

Again, the entire focus of my post was aimed towards the diabatic effects of snow, I made no reference to the other conditions because I was purposely trying to isolate this variable, & if you're going to claim that effects of diabatic heating from clouds is more significant than the snowpack then supply the actual evidence that shows this is the case.. It seems to me you're suggesting that sublimation and melting of snow always forms clouds? Not necessarily, that's dependent upon the saturation vapor pressure of the ambient air, and it's common for these cooling processes to occur w/o any cloud formation, thus the net effect of the snowpack as a whole is cooling, not diabatic "heating" as you stated earlier, which enhances CAD...

 

I think it's pretty clear he screwed up. Not sure why he is still trying to argue this. I would just let this one die man. 

[SN_Lover]

Again, the entire focus of my post was aimed towards the diabatic effects of snow, I made no reference to the other conditions because I was purposely trying to isolate this variable, & if you're going to claim that effects of diabatic heating from clouds is more significant than the snowpack then supply the actual evidence that shows this is the case.. It seems to me you're suggesting that sublimation and melting of snow always forms clouds? Not necessarily, that's dependent upon the saturation vapor pressure of the ambient air, and it's common for these cooling processes to occur w/o any cloud formation, thus the net effect of the snowpack as a whole is cooling, not diabatic "heating" as you stated earlier, which enhances CAD...

All im gonna say is that int his case, the clouds in the NE will lower the pressure of the high. The upper level pattern is screwing the CAD up the most IMO. I look as snow being a product of the weather, not weather being a product of the snow. Snow in my eyes is only one of many variables. 

[franklin NCwx]

I think webbers original point was that there looks to be multiple storms coming across the country. Each time one comes across it drops snow on its nW side, then the following one even farther south. At least that is what I took away from his original post.

[Webberweather53]

All im gonna say is that int his case, the clouds in the NE will lower the pressure of the high. The upper level pattern is screwing the CAD up the most IMO. I look as snow being a product of the weather, not weather being a product of the snow. Snow in my eyes is only one of many variables. 

 

That's fine, but you don't suppose those clouds actually aren't originating from the snowpack but from another source? 

I suggest next time before arriving at such claims, to present at least some shred of physical evidence why this is true & a case study certainly wouldn't hurt. It's a chicken or egg argument in reality that all draws back to the sun, and you are entitled to think that snow is the product of the ongoing pattern and I agree to an extent, but I would suggest going through Cohen's work on the SAI/SCE, which on a larger scale is applicable to my argument, before claiming it is solely as a product of the pattern, and it should be common sense that the snowpack also provides a positive feedback, inducing pattern persistence that is particularly crucial to getting wintry weather in the southern tier... In terms of claiming snow as a reflection of the pattern, the same can certainly be said about the NAO that you've touted, but for the sake of this discussion I'll refrain for now....

[Shawn]

Here's how it works for the most part guys.  CAD is better with snow pack from the air's source region.

[SN_Lover]

I think webbers original point was that there looks to be multiple storms coming across the country. Each time one comes across it drops snow on its nW side, then the following one even farther south. At least that is what I took away from his original post.

Oh okay. I thought he meant the NE side. If he meant the plains,then he was right. I think that's where the confusion might have stemmed from. 

[buckeyefan1]

That's fine, but you don't suppose those clouds actually aren't originating from the snowpack but from another source? 

I suggest next time before arriving at such claims, to present at least some shred of physical evidence why this is true & a case study certainly wouldn't hurt. It's a chicken or egg argument in reality that all draws back to the sun, and you are entitled to think that snow is the product of the ongoing pattern and I agree to an extent, but I would suggest going through Cohen's work on the SAI/SCE, which on a larger scale is applicable to my argument, before claiming it is solely as a product of the pattern, and it should be common sense that the snowpack also provides a positive feedback, inducing pattern persistence that is particularly crucial to getting wintry weather in the southern tier... In terms of claiming snow as a reflection of the pattern, the same can certainly be said about the NAO that you've touted, but for the sake of this discussion I'll refrain for now....

The bolded is exactly what it is. Keep the discussion on topic folks. 

[Webberweather53]

Oh okay. I thought he meant the NE side. If he meant the plains,then he was right. I think that's where the confusion might have stemmed from. 

 

I was referring to area to our north & northeast, the source region for the air that's associated w/ CAD... It's still not a bad idea to have a deep snowpack over the plains, but the naturally drier air over the plains, & especially on the lee side of the Rockies under the periodic surges in the Chinook makes the snowpack there relatively more transient & volatile in nature than their neighbors further to the east (like the Great Lakes for example) located closer to the axis of the Canadian Shield...

[SN_Lover]

I was referring to area to our north & northeast, the source region for the air that's associated w/ CAD... It's still not a bad idea to have a deep snowpack over the plains, but the naturally drier air over the plains, & especially on the lee side of the Rockies under the periodic surges in the Chinook makes the snowpack there relatively more transient & volatile in nature than their neighbors further to the east (like the Great Lakes for example) located closer to the axis of the Canadian Shield...

One thing i will agree on with you is that more snow in the plains will cool the air more. I'm just gonna agree to disagree on the NE part.   

[buckeyefan1]

One thing i will agree on with you is that more snow in the plains will cool the air more. I'm just gonna agree to disagree on the NE part.   

fwiw......I agree with your bolded. While it's nice to have a snowpack and it does help, it is not a necessity. 

 

 

NOW.........if there is anything further to say on this subject, take it to the banter thread before timeouts are issued   

[packbacker]

Webber - you buying this? Or is GFS rushing things?

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014121618&var=TMP&lev=1mb&hour=384

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014121618&var=HGT&lev=10mb&hour=336

[Heisy]

Patience my friends, we're seeing a step down process right now. I think come the first week of January we'll all be happy. Need to endure a few cutters to help jump start the pattern to a colder one. 

[Webberweather53]

Webber - you buying this? Or is GFS rushing things?

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014121618&var=TMP&lev=1mb&hour=384

http://www.instantweathermaps.com/GFS-php/showmap-strat.php?run=2014121618&var=HGT&lev=10mb&hour=336

 

 

It may be a tad fast, but we are going to see the mean tropical forcing once again shift back towards the Pacific sector in a few weeks or so, which will eventually induce an extension of the Pacific Jet & a re-invigoration of the Aleutian Low (remember MJO that phases 6-8 (Pacific) tend to be followed by warming in the polar stratosphere & there's even a lower frequency signal that exists in the PDO for stratospheric warming) that could viably crank up another surge in heat eddy flux on that disrupts the polar vortex... (irregardless of interference from the Walker Cell which could viably reduce the MJO's amplitude once again, but since we have such a long lead time with an elusive pre-condition such as is the case w/ Equatorial Waves, there's a considerably amount of uncertainty at hand) & HM concurs...

 

From a conversation on twitter that transpired several hours ago...

HM:

"Deciding on how much I want to hype Jan threat window #ku?"

Me:

"Hopefully w/ the return of MJO/CCKW forcing into the Pacific maybe we can take another shot at a SSWE... thoughts?"

HM:

"yeah I'm starting to think the whole thing goes down like a normal Nino now....slower. No doubt that's the beginning tho xmas"

[WidreMann]

Patience my friends, we're seeing a step down process right now. I think come the first week of January we'll all be happy. Need to endure a few cutters to help jump start the pattern to a colder one.

"Step down" is code for "not gonna happen".

[WidreMann]

CFS continues to show warm January, with a trend away from a slightly cool east coast. The weeklies are also warmer for the east. Trend is not encouraging.

[CaryWx]

"Step down" is code for "not gonna happen".

 

I disagree.  Look at the current snow pack.  It is an odd bird indeed that gives any decent winter weather in these parts with bare ground up into and including nearly the whole LP of Michigan and most of Wisconsin.  Betting that changes in 7 days time.

 

[Webberweather53]

I disagree.  Look at the current snow pack.  It is an odd bird indeed that gives any decent winter weather in these parts with bare ground up into and including nearly the whole LP of Michigan and most of Wisconsin.  Betting that changes in 7 days time.

 

 

 

Agreed, although have seen wintry wx here in central NC when the snowpack looked worse than this, but my post was intentionally just geared to Miller B storms only, a Miller A, Canadian Clipper, or powerful upper level low (as was observed in Columbia on Nov 1st for example but this is an extreme case) is at times sufficient to drop some snow here in NC because unlike in CAD events, we're not trying to drive the antecedent cold air into submission...

 

December 2000 is a nice case study of a Miller A still leading to snow in spite of the dismal snowpack

 

 

 

Dec 18-19 2009 also was a Miller A... extent of the snowpack to our north was a little ways north of I-80...

[Brick Tamland]

18z PARA with that insane phased super storm for around Christmas. By the way 18z GFS in the LR says pattern change begins at 240. Major cold in the west moving east. By 288 winter is arriving in the SE.

 

 

CFS continues to show warm January, with a trend away from a slightly cool east coast. The weeklies are also warmer for the east. Trend is not encouraging.

It's like two different worlds.

If we don't end up having a good winter, though, the mets are going to have to go back and figure out why everything they thought they knew about what gives us a good winter was wrong. There has been so much consensus for a good winter based on the evidence and signs we have now compared to the the good winters of the past. If it doesn't happen a lot of mets are going to be second guessing everything they thought gave us a good winter.

[Cold Rain]

CFS continues to show warm January, with a trend away from a slightly cool east coast. The weeklies are also warmer for the east. Trend is not encouraging.

This is concerning....unless one wants to just summarily discard the CFS. You could have discarded it for November. But the cold pattern got a huge boost from the super typhoon. And it was right about the warm December, though maybe not to the magnitude it was showing.

The last couple of runs of the Weeklies also don't sound as good as they did two weeks or so ago. I'm only judging that based on what I have interpreted other peoples' interpretations to be.

You also have the EPS dumping the cold more west.

All of that vs the GFS and CMC ensembles and analogs and SAI expectations. Right now, it still feels like the balance of power is tipped toward cold coming sooner rather than later. But if we get to mid January and we're still stepping down or laying the groundwork or setting the table, then we'll know next time which data to throw out and which to weight more heavily.