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January Medium/Long Range Discussion


nj2va

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10 minutes ago, cbmclean said:

I need some weenie education.

So in the figure above I see the 540 dm geopotential height line almost completely in Canada.  I know that the 540 dm 1000 - 500 thickness line is generally considered the "baseline" rain snow line.

So I do not understand why the geopotential height is ever very different from the 1000 - 500 thickness.  Isn't 1000 hPa basically the surface?  So wouldn't the thickness between 1000 hPa and 500 hPA be about the same as the height of the 500 hPa geopotential surface?  I am obviously missing something but I am not sure what. 

They are mostly separate. Heights are based on pressure in the column and thickness is based on temperature (and density) in the column. The 540 line is generally found where the surface is at freezing. Not exact but close. Its not correlated with the 540 height isobar.

It's better practice tonuse soundings or look at temps at various levels instead of using thickness.

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5 minutes ago, Bob Chill said:

No, it really wouldn't.  Good enough for an op beyond the range we should be looking at [but we can't help it because we have problems... serious problems]

I’m happy we’re tracking something within 200 hours that’s not a 384H pattern change.  Even if we fail next weekend (which is the likelier outcome at this point), it doesn’t sting as much considering all signs are pointing to multiple chances after that.  Who’s starting the thread for it? :ducks:

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4 minutes ago, Snowstorm5921 said:

Lol.  GFS looks awful past day 10 again.  Yay

1.  The guidance didn't have the trough and threat day 7 a couple days ago either 

2.  The true flip in the Pacific pattern isn't established until day 13/14. There probably will be a mild period ~day 9-13.  That's not a new revelation. Still looks like towards the 20th things should improve

3.  What is your deal seriously?  

And you still never answered my question regarding persistence in banter. 

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1 minute ago, Ji said:
6 minutes ago, psuhoffman said:
Yea this looks awful.
IMG_8207.thumb.PNG.9b321ebfffd491600c4b8879641967fa.PNG
IMG_8208.thumb.PNG.518aad08484306375e53b2550dfa121d.PNG
Did you take model reading lessons from Chuck?

Lol good luck with that Miller b bro

That was a weird hybrid with an anomalous south h5 cutoff low pass. Kinda like the second feb 2010 storm or the march 2013 storm. Yea I know that one sucked but because of boundary temps. A month earlier and that was a 10" snow. Those have a slightly better chance then a pure miller b where the upper low develops and cuts off later. But this doesn't matter it's all fiction. I was just pointing out he said the gfs looked awful past day 10 when in reality it's a pretty good look there. 

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10 minutes ago, Bob Chill said:

They are mostly separate. Heights are based on pressure in the column and thickness is based on temperature (and density) in the column. The 540 line is generally found where the surface is at freezing. Not exact but close. Its not correlated with the 540 height isobar.

It's better practice tonuse soundings or look at temps at various levels instead of using thickness.

But I just don't understand.

From the definitions (simplified, as I as I understand them)

500 hPa geopotential height  =  the height at which the atmospheric pressure is 500 hPa

1000 to 500 hPa thickness =  the height difference between the 1000 hPa level and the 500 hPa level

Since sea level pressure is about 1000 hPa, I would think that the height at which atmospheric pressure is 500 hPa should be about the same as the height between the 1000 hPa level and the 500 hPa level.

For example the pressure at RDU is about 1015 hPa.  Let's say my 1000 hPa height is 11 dm, and my 500 hPa height is say 560 dm.  So my 1000 - 500 thickness is 560-11 or 549 dm.  So yeah, the 1000 - 500 thickness is a little less than the 500 hPa height, because 100 hPa is a little up in the air from the surface.  But why don't 1000 - 500 thickness basically follow 500 hPa heights, just with a little negative offset?

 

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We need to take advantage of these threats before the real pattern change. A good winter snows in marginal situations....we got a bonus week next week when it was suppose to be an epic torch. If we get to jan 20 still shutout it will be a disaster imo

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Just now, Ji said:

We need to take advantage of these threats before the real pattern change. A good winter snows in marginal situations....we got a bonus week next week when it was suppose to be an epic torch. If we get to jan 20 still shutout it will be a disaster imo

Why do you like drawing lines in the sand for Mother Nature?  

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20 minutes ago, cbmclean said:

But I just don't understand.

From the definitions (simplified, as I as I understand them)

500 hPa geopotential height  =  the height at which the atmospheric pressure is 500 hPa

1000 to 500 hPa thickness =  the height difference between the 1000 hPa level and the 500 hPa level

Since sea level pressure is about 1000 hPa, I would think that the height at which atmospheric pressure is 500 hPa should be about the same as the height between the 1000 hPa level and the 500 hPa level.

For example the pressure at RDU is about 1015 hPa.  Let's say my 1000 hPa height is 11 dm, and my 500 hPa height is say 560 dm.  So my 1000 - 500 thickness is 560-11 or 549 dm.  So yeah, the 1000 - 500 thickness is a little less than the 500 hPa height, because 100 hPa is a little up in the air from the surface.  But why don't 1000 - 500 thickness basically follow 500 hPa heights, just with a little negative offset?

 

Check this link out. Answers every question you have

https://www.weather.gov/source/zhu/ZHU_Training_Page/Miscellaneous/Heights_Thicknesses/thickness_temperature.htm

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