January Medium/Long Range Disco Thread

[WinterWxLuvr]

Talk of temps, or lack thereof.... it just snowed about 5” in Knoxville Tn. I say that because if you get on the correct side of these lows it’s plenty cold enough for snow. Fact is we aren’t going to get snow with lows in Missouri or lows that run the apps along cold fronts. Forever it seemed  we had a storm track from about Mississippi to North Carolina and up the coast. We get that again and it won’t matter about temp anomalies most times. And we are just getting to the best temps of the season for about the next 8 weeks. We get the ridge off the east coast dampened and we will be ok.

[WinterWxLuvr]

17 minutes ago, cbmclean said:

OK, so atmospheric physics questions: how is it physically possible for a region to have a sustained period of below normal 500 MB heights yet also have above normal temps over the same period?

As I have mentioned elsewhere I do not have a strong background in meteorology or any serious model chops but I have read a fair bit and have seen it stated over and over in explanations that the geopotential height can be considered as a proxy for the average temperature for the parcel of air between the surface and the height level.  So cooler parcels mean lower heights, and vice versa.  How can we have low geopotential heights for a long period of time yet have warm temperatures in that parcel of air?

That’s the thing though, there really hasn’t been any sustained period of below normal heights east of the Mississippi. We’ve had a glancing blow or two but it has mostly been above normal. Just loop the latest GFS and you’ll see that the heights are sustained above normal for the east almost the entire run. Only the latter stages of that run do we see any below normal heights.

[WxUSAF]

4 minutes ago, WinterWxLuvr said:

Talk of temps, or lack thereof.... it just snowed about 5” in Knoxville Tn. I say that because if you get on the correct side of these lows it’s plenty cold enough for snow. Fact is we aren’t going to get snow with lows in Missouri or lows that run the apps along cold fronts. Forever it seemed  we had a storm track from about Mississippi to North Carolina and up the coast. We get that again and it won’t matter about temp anomalies most times. And we are just getting to the best temps of the season for about the next 8 weeks. We get the ridge off the east coast dampened and we will be ok.

Next ~2 weeks aside (and there's still a chance of some frozen precip on Sunday/Monday), I think there are definitely more signs to be positive beyond that then negative.  Doesn't mean this will end up being a memorable winter, but I don't see any signs that it's a repeat of last year/11-12/01-02/etc.  

[cbmclean]

4 minutes ago, WinterWxLuvr said:

That’s the thing though, there really hasn’t been any sustained period of below normal heights east of the Mississippi. We’ve had a glancing blow or two but it has mostly been above normal. Just loop the latest GFS and you’ll see that the heights are sustained above normal for the east almost the entire run. Only the latter stages of that run do we see any below normal heights.

Well, I was referring to the discussion we were having about the disconnect between the advertised H5 pattern shown for days 15 -22 on the latest Euro weeklies versus the advertised 2m temp anomalies for the same time.  So according to that model we will have a 7 day period with an negative average 500 MB anomaly yet we will simultaneously have a positive 2 m temp anomaly.  How is that physically possible? 

[psuhoffman]

21 minutes ago, WxUSAF said:

I think it's probably a situation where both are somewhat correct.  In a smoothed ensemble mean, you often don't see sharp ridges or troughs due to orientation, timing, and other differences between each member.  So even if all the members have a nice NAO ridge around a given time +/-, when you average them all together, it may just look like what you see in the long range ensemble mean or weeklies product.  

As @Ji said earlier, we actually haven't had a true NAO ridge yet.  That can has definitely been kicked a bit, although it does seem like a real one will develop as we start January.

We had a nice AO block in Dec though but it was centered northwest of a true NAO block.  I respect Tombo and others who are saying it’s just higher heights but I respectfully disagree with that take. First of all it’s impossible to see the ridge in the height lines past 12 days or so due to timing and location differences between members. One might have the block centered over Greenland. Another Baffin. Another Hudson Bay. The ridge meanders around. Those differences smooth it out. Then you add in the outlier members and seeing a ridge signature at that range is not happening. But at the same time those kinds of + anomalies would be unlikely without a ridge somewhere. If it was weak + heights maybe. But to get those kinds of positives at those ranges given the smoothing and outliers would be almost impossible without a ridge somewhere on most members.  Also we wouldn’t get lower heights across the CONUS with that pac if there wasnt true blocking. Add in the fact that the control has a true block and when I look at most operationals and individual members they do have blocking the evidence suggests that’s not it.  I respect their hypothesis but I don’t see evidence of that. 
 

I think the simplest answer is the best. The pac is less then ideal. We begin the period with all of N AM torched. Despite a really good h5 look it thinks we never recover in that regard. History says domestic cold should work in that look. But the eps weekly members obviously think it’s just not going to be cold enough to keep storms from cutting.  I think it’s wrong. I’ve seen it run too warm at range. We’ll see 

[WxUSAF]

11 minutes ago, losetoa6 said:

Many if not Most places just nw of i95 probably already equaled or surpassed last years snow totals and it's only December. Last year is already in the rear window 

Alot of 1-4" seasonal totals max last year near the big cities?

I’m 0.1” short of last winter 

Yeah, I think BWI was like 1.5” last winter and DCA was under 1”?

[Ralph Wiggum]

14 minutes ago, cbmclean said:

Well, I was referring to the discussion we were having about the disconnect between the advertised H5 pattern shown for days 15 -22 on the latest Euro weeklies versus the advertised 2m temp anomalies for the same time.  So according to that model we will have a 7 day period with an negative average 500 MB anomaly yet we will simultaneously have a positive 2 m temp anomaly.  How is that physically possible? 

Torch for a few days as the ridge wobbles around like a rubber band? All the cold air is locked up in Siberia. So a few days near 60 ahead of a cold front followed by N temps behind can yield well AN for the period.  I dunno....thats my simplistic take. 

[cbmclean]

12 minutes ago, psuhoffman said:

But the eps weekly members obviously think it’s just not going to be cold enough to keep storms from cutting.

Is there a "positive feedback loop" for cutters and warmth?  If a storm cuts and pulls up a lot of warmth, does it tend to act to reinforce the baroclinic gradient being too far west for our liking?

[WxUSAF]

22 minutes ago, psuhoffman said:

I think the simplest answer is the best. The pac is less then ideal. We begin the period with all of N AM torched. Despite a really good h5 look it thinks we never recover in that regard. History says domestic cold should work in that look. But the eps weekly members obviously think it’s just not going to be cold enough to keep storms from cutting.  I think it’s wrong. I’ve seen it run too warm at range. We’ll see 

If you assume the GEFS is a similar evolution, and it looks to be, then you can see the end of the 18z GEFS has 850mb cold anomalies filling back in over the CONUS. 2m temps lag a bit, but generally the same idea. Once you cut off the PAC firehose and get some meridional flow from Canada, you’ll get BN temps eventually with that H5. 

[Ralph Wiggum]

Just now, cbmclean said:

Is there a "positive feedback loop" for cutters and warmth?  If a storm cuts and pulls up a lot of warmth, does it tend to act to reinforce the baroclinic gradient being too far west for our liking?

Fancy way of saying atmospheric memory ie repeating patterns/storm tracks.

[WxUSAF]

2 minutes ago, cbmclean said:

Is there a "positive feedback loop" for cutters and warmth?  If a storm cuts and pulls up a lot of warmth, does it tend to act to reinforce the baroclinic gradient being too far west for our liking?

More the opposite. Often a series of cutters “carves” the baroclinic zone eastward progressively. That’s why follow up waves work for us sometimes. 

1 minute ago, losetoa6 said:

.1" ...that's nothing.  You'll get that Friday morning or Sunday. 

I’ll hold you to that 

[cbmclean]

1 minute ago, Ralph Wiggum said:

Torch for a few days as the ridge wobbles around like a rubber band? All the cold air is locked up in Siberia. So a few days near 60 ahead of a cold front followed by N temps behind can yield well AN for the period.  I dunno....thats my take. 

I want to make it clear that I don't think I'm smarter than the physics of the model.  I'm just perplexed by the complexity of the relationship between 500 mb anomalies and temperature anomalies.  The simplistic relationship that is taught to newbies is that low geopotential heights generally equate to low temps.  Obviously it must be more complex than that.  

[Eskimo Joe]

5 hours ago, CAPE said:

The new edition of the Euro weeklies think the west based -NAO is gonna be around awhile.

Key difference with Euro weeklies now is that it's NW flow across all of Canada which rapidly builds snow cover and solidifies a cP airmass for us. If this holds, it significantly increases the likelihood of below normal temps and at least embedded clippers.

[87storms]

29 minutes ago, cbmclean said:

Well, I was referring to the discussion we were having about the disconnect between the advertised H5 pattern shown for days 15 -22 on the latest Euro weeklies versus the advertised 2m temp anomalies for the same time.  So according to that model we will have a 7 day period with an negative average 500 MB anomaly yet we will simultaneously have a positive 2 m temp anomaly.  How is that physically possible? 

I think a lot of it has to do with how the atmosphere is an open container (a lot of variables). For example, how high pressure generally brings warmth in the summer versus cold in the winter due to variations in the amount of daylight/net temp loss at night  under fair skies etc. Pressure and temp isn’t a direct relationship in that regard, sort of how cad can form even with a bad surface low track. We just need a colder pool of air to tap into at this point...I think.

[Ralph Wiggum]

11 minutes ago, cbmclean said:

I want to make it clear that I don't think I'm smarter than the physics of the model.  I'm just perplexed by the complexity of the relationship between 500 mb anomalies and temperature anomalies.  The simplistic relationship that is taught to newbies is that low geopotential heights generally equate to low temps.  Obviously it must be more complex than that.  

If you are referring to geopotential heights, then do a loop of them on the conus from 18z. The 540 line spends most of the 384 hrs north of the Canadian border. So I dont think you are seeing a negative correlation between those heights lines and 2m temps. The PV (lowest heights) is on the other side of the hemisphere for the most part. I just picked this map to illustrate my point:

We are going to need pac help to get the lower heights and PV into Canada and the US....period. BUT marginal temps can still work during prime climo so keep that in mind.

Eta: even with the -NAO, we are going to be spending alot of time near avg to AN temps. There just isn't a pac catalyst to get an arctic outbreak down here...yet.

[psuhoffman]

12 minutes ago, WxUSAF said:

If you assume the GEFS is a similar evolution, and it looks to be, then you can see the end of the 18z GEFS has 850mb cold anomalies filling back in over the CONUS. 2m temps lag a bit, but generally the same idea. Once you cut off the PAC firehose and get some meridional flow from Canada, you’ll get BN temps eventually with that H5. 

Agree

[nj2va]

30 minutes ago, losetoa6 said:

Many if not Most places just nw of i95 probably already equaled or surpassed last years snow totals and it's only December. Last year is already in the rear window 

Alot of 1-4" seasonal totals max last year near the big cities?

Already over two thirds of last season’s total in McHenry (~40-42” this year when we had 60” last winter) - it’s been a good winter here so far especially considering 99% of that fell in December.

At home, I’m not sure I hit 1” last winter...I’m already halfway there this season.  

[cbmclean]

1 minute ago, 87storms said:

I think a lot of it has to do with how the atmosphere is an open container (a lot of variables). For example, how high pressure generally brings warmth in the summer versus cold in the winter due to variations in the amount of daylight/net temp loss at night  under fair skies etc. Pressure and temp isn’t a direct relationship in that regard, sort of how cad can form even with a bad surface low track. We just need a colder pool of air to tap into at this point. I could be wrong, but I’ve thinking about this similar topic before.

Thanks for the input.  I have been very frustrated by the lack of available information about the more complex relationship between geopotential height anomalies and temp anomalies.  All the information online is just "areas under negative gph anomalies tend to be cool, areas under positive gph anomalies tend to be warm" and leave it at that.  Obviously the crux of the matter is in the "tends" part.  it's obviously not a 1-to-1 relationship.  But what is the actual relationship? 

[cbmclean]

3 minutes ago, Ralph Wiggum said:

If you are referring to geopotential heights, then do a loop of them on the conus from 18z. The 540 line spends most of the 384 hrs north of the Canadian border. So I dont think you are seeing a negative correlation between those heights lines and 2m temps. The PV (lowest heights) is on the other side of the hemisphere for the most part. I just picked this map to illustrate my point:

We are going to need pac help to get the lower heights and PV into Canada and the US....period. BUT marginal temps can still work during prime climo so keep that in mind.

That makes perfect sense, but the plots posted by PSU showed the Euro depicting a negative average 500 MB anomaly in the eastern conus while simultaneously having a positive 2m temp anomaly.  I am specifically referring just to those two plots.  Anyway I realize its probably related to factors well beyond my knowledge at this time.  And I am hoping it doesn't come true.

[Huffwx]

31 minutes ago, psuhoffman said:

We had a nice AO block in Dec though but it was centered northwest of a true NAO block.  I respect Tombo and others who are saying it’s just higher heights but I respectfully disagree with that take. First of all it’s impossible to see the ridge in the height lines past 12 days or so due to timing and location differences between members. One might have the block centered over Greenland. Another Baffin. Another Hudson Bay. The ridge meanders around. Those differences smooth it out. Then you add in the outlier members and seeing a ridge signature at that range is not happening. But at the same time those kinds of + anomalies would be unlikely without a ridge somewhere. If it was weak + heights maybe. But to get those kinds of positives at those ranges given the smoothing and outliers would be almost impossible without a ridge somewhere on most members.  Also we wouldn’t get lower heights across the CONUS with that pac if there wasnt true blocking. Add in the fact that the control has a true block and when I look at most operationals and individual members they do have blocking the evidence suggests that’s not it.  I respect their hypothesis but I don’t see evidence of that. 
 

I think the simplest answer is the best. The pac is less then ideal. We begin the period with all of N AM torched. Despite a really good h5 look it thinks we never recover in that regard. History says domestic cold should work in that look. But the eps weekly members obviously think it’s just not going to be cold enough to keep storms from cutting.  I think it’s wrong. I’ve seen it run too warm at range. We’ll see 

Ji showed a graph where the NAO wasn't negative.  I said a few times heights were higher Azorors were high as well and that is how they measure ( or use to)

 

A lot of gray on on the calculations  but agree base is warmer and PAC isn't helping. 

 

In early 02, we had blocking and it got colder as heights lowered. Had a suppressed storm Richmond to RDU.. maybe 12 at RDU again.

 

 

[WinterWxLuvr]

32 minutes ago, cbmclean said:

Well, I was referring to the discussion we were having about the disconnect between the advertised H5 pattern shown for days 15 -22 on the latest Euro weeklies versus the advertised 2m temp anomalies for the same time.  So according to that model we will have a 7 day period with an negative average 500 MB anomaly yet we will simultaneously have a positive 2 m temp anomaly.  How is that physically possible? 

I understand but you also have to consider that that is an ens mean. And the “below” normal heights it is showing in our area are barely below normal. Also there is  it a one to one correlation. Normal heights doesn’t translate into exactly normal temps. Also in that mean you could have some really warm temps in areas that are not that far above normal heights. There’s a lot of reasons that a mean area of slightly below normal heights might go hand in hand with above normal temps. You would really need to look at each member to get an idea of why that map showed what it did.

[WinterWxLuvr]

4 minutes ago, cbmclean said:

Thanks for the input.  I have been very frustrated by the lack of available information about the more complex relationship between geopotential height anomalies and temp anomalies.  All the information online is just "areas under negative gph anomalies tend to be cool, areas under positive gph anomalies tend to be warm" and leave it at that.  Obviously the crux of the matter is in the "tends" part.  it's obviously not a 1-to-1 relationship.  But what is the actual relationship? 

That relationship is only a general guideline and if I’m not mistaken acts slightly differently in winter and summer. 

[nj2va]

7 minutes ago, Ralph Wiggum said:

If you are referring to geopotential heights, then do a loop of them on the conus from 18z. The 540 line spends most of the 384 hrs north of the Canadian border. So I dont think you are seeing a negative correlation between those heights lines and 2m temps. The PV (lowest heights) is on the other side of the hemisphere for the most part. I just picked this map to illustrate my point:

We are going to need pac help to get the lower heights and PV into Canada and the US....period. BUT marginal temps can still work during prime climo so keep that in mind.

Eta: even with the -NAO, we are going to be spending alot of time near avg to AN temps. There just isn't a pac catalyst to get an arctic outbreak down here...yet.

Yes, we’re getting into the heart of climo so marginal/slightly below can work.  We don’t need 2,234,423 things to line up in our favor in January (just 2,234,422 ). Sometimes I think people obsess over the temp anomaly maps...give me a good H5 setup and I’ll let the chips fall.  

[87storms]

5 minutes ago, cbmclean said:

Thanks for the input.  I have been very frustrated by the lack of available information about the more complex relationship between geopotential height anomalies and temp anomalies.  All the information online is just "areas under negative gph anomalies tend to be cool, areas under positive gph anomalies tend to be warm" and leave it at that.  Obviously the crux of the matter is in the "tends" part.  it's obviously not a 1-to-1 relationship.  But what is the actual relationship? 

I think it’s a mixed bag which is why there’s so many equations that go into these models to begin with. It makes sense that the pacific pattern is not helping by mucking with the amount of cold air that can stay locked into the conus, one of the reasons why the high pressure systems aren’t bringing or maintain frigid cold here yet. But you’re questions are valid. I’d be interested in what others have to say on it.

[cbmclean]

3 minutes ago, WinterWxLuvr said:

That relationship is only a general guideline and if I’m not mistaken acts slightly differently in winter and summer. 

That's actually the part of meteorology that really interests me.  I find cyclogensis, precipitation, winds speeds, only mildly interesting, but I am fascinated by temperature.  Unfortunately there just isn't a whole lot of easily available information out there beyond the simplistic guidelines we have just been discussing.  I need to find a text book on "Atmospheric temperature patterns and 500 MB analysis".

[North Balti Zen]

56 minutes ago, WxUSAF said:

I’m 0.1” short of last winter 

Yeah, I think BWI was like 1.5” last winter and DCA was under 1”?

The futility thread will have this.

[GEOS5ftw]

47 minutes ago, cbmclean said:

That's actually the part of meteorology that really interests me.  I find cyclogensis, precipitation, winds speeds, only mildly interesting, but I am fascinated by temperature.  Unfortunately there just isn't a whole lot of easily available information out there beyond the simplistic guidelines we have just been discussing.  I need to find a text book on "Atmospheric temperature patterns and 500 MB analysis".

Since I don't think it has been answered yet, the 500mb height is a function of the surface pressure and thickness (which is proportional to temperature averaged over the layer). So, BN heights can be the result of BN temperatures from the sfc to 500mb, BN surface pressure, or some combination. When the 500mb height is BN but sfc is AN, that tells me the sfc pressures are low and/or the sfc temp is higher than would be expected for a given thickness. This makes sense since Pacific maritime air masses have steeper lapse rates (warm sfc, cold aloft) than continental/arctic origin air (cold sfc, cold aloft). Think about it - air coming from the Pacific more or less assumes the SST after many days. There isn't enough time when these travel over North America to cool radiatively at the sfc. Also, the latent heat added from orographic precip over the Rockies actually results in a warming of these air masses (chinook effect). Contrast that with Arctic air masses - the cooling is strongest at the surface (surface radiates heat much more effectively than atmosphere), so these tend to have a strong inversion. Further, when you get an EPO ridge the cold air doesn't have to cross the Rockies, it comes down the eastern slope from the north so no latent heat gets added (not that there would be much considering how dry these air masses are).

Models are really good at moving air around - I'm not sure how well they represent the radiative heating/cooling though. It's pretty complex and depends on the surface properties, water vapor, etc. I remember reading a paper about the formation of deep cold air masses, and the authors found that you get "diamond dust" ice crystals - basically very light snow w/o clouds - forming below -40C (or something really cold), and these radiate heat more effectively than the air itself. At really long lead times if these processes are not represented properly it could result in a odd looking temperature for a given flow pattern. There are modeling experts on this forum who know way more than me (I'm from more of a radar/remote sensing background) , so I'm happy to be corrected.

[Maestrobjwa]

32 minutes ago, GEOS5ftw said:

Since I don't think it has been answered yet, the 500mb height is a function of the surface pressure and thickness (which is proportional to temperature averaged over the layer). So, BN heights can be the result of BN temperatures from the sfc to 500mb, BN surface pressure, or some combination. When the 500mb height is BN but sfc is AN, that tells me the sfc pressures are low and/or the sfc temp is higher than would be expected for a given thickness. This makes sense since Pacific maritime air masses have steeper lapse rates (warm sfc, cold aloft) than continental/arctic origin air (cold sfc, cold aloft). Think about it - air coming from the Pacific more or less assumes the SST after many days. There isn't enough time when these travel over North America to cool radiatively at the sfc. Also, the latent heat added from orographic precip over the Rockies actually results in a warming of these air masses (chinook effect). Contrast that with Arctic air masses - the cooling is strongest at the surface (surface radiates heat much more effectively than atmosphere), so these tend to have a strong inversion. Further, when you get an EPO ridge the cold air doesn't have to cross the Rockies, it comes down the eastern slope from the north so no latent heat gets added (not that there would be much considering how dry these air masses are).

Models are really good at moving air around - I'm not sure how well they represent the radiative heating/cooling though. It's pretty complex and depends on the surface properties, water vapor, etc. I remember reading a paper about the formation of deep cold air masses, and the authors found that you get "diamond dust" ice crystals - basically very light snow w/o clouds - forming below -40C (or something really cold), and these radiate heat more effectively than the air itself. At really long lead times if these processes are not represented properly it could result in a odd looking temperature for a given flow pattern. There are modeling experts on this forum who know way more than me (I'm from more of a radar/remote sensing background) , so I'm happy to be corrected.

Well I've certainly learned something this evening...especially the part about the Chinook effect...and why an EPO ridge is helpful (though I still need clarity on exactly what it is). Thanks for breaking that down! 

[cbmclean]

36 minutes ago, GEOS5ftw said:

Since I don't think it has been answered yet, the 500mb height is a function of the surface pressure and thickness (which is proportional to temperature averaged over the layer). So, BN heights can be the result of BN temperatures from the sfc to 500mb, BN surface pressure, or some combination. When the 500mb height is BN but sfc is AN, that tells me the sfc pressures are low and/or the sfc temp is higher than would be expected for a given thickness. This makes sense since Pacific maritime air masses have steeper lapse rates (warm sfc, cold aloft) than continental/arctic origin air (cold sfc, cold aloft). Think about it - air coming from the Pacific more or less assumes the SST after many days. There isn't enough time when these travel over North America to cool radiatively at the sfc. Also, the latent heat added from orographic precip over the Rockies actually results in a warming of these air masses (chinook effect). Contrast that with Arctic air masses - the cooling is strongest at the surface (surface radiates heat much more effectively than atmosphere), so these tend to have a strong inversion. Further, when you get an EPO ridge the cold air doesn't have to cross the Rockies, it comes down the eastern slope from the north so no latent heat gets added (not that there would be much considering how dry these air masses are).

Models are really good at moving air around - I'm not sure how well they represent the radiative heating/cooling though. It's pretty complex and depends on the surface properties, water vapor, etc. I remember reading a paper about the formation of deep cold air masses, and the authors found that you get "diamond dust" ice crystals - basically very light snow w/o clouds - forming below -40C (or something really cold), and these radiate heat more effectively than the air itself. At really long lead times if these processes are not represented properly it could result in a odd looking temperature for a given flow pattern. There are modeling experts on this forum who know way more than me (I'm from more of a radar/remote sensing background) , so I'm happy to be corrected.

Thank you very much, GEOS5ftw, this is exactly the additional details that I have been looking for.  I am intensely interested in learning more about this.  If I was looking to invest some hobby money into technician literature about this topic, is there a term for this sub-specialty of meteorology?  I don't mean modeling.  I mean understanding why air masses obtain the temperature characteristics that they do, and how the get moved to different locations.  For example, what made the Feb 1899 airmass so cold in its source region, and how did it get unleashed into the lower 48 with so little attenuation?

[cbmclean]

5 minutes ago, Maestrobjwa said:

and why an EPO ridge is helpful (though I still need clarity on exactly what it is)

I stole this graphic from the post that PSU made to start off the snow climo thread last year.  He has marked the EPO domain.  An EPO ridge is just AN 500 MB heights in the EPO region.