Mr. Golf
Member
Do you not have a chart more updated than 12/9?
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Pattern The Great December Dump
- Thread starter Rain Cold
- Start date
pcbjr
Member
Feel like I'm in 1st grade on this one ... 2 Questions: 1) what's better: a + or - AAM, and 2) any links to some basic primers on the AAM?
More food for thought about Jan's prospects after a mild Dec,:
There have been at KATL four MB Jans (all in coldest 1/8) that followed mild Decs: 1884, 1924, 1985, and 2014. So, anything is possible.
Jan of 1985, the 8th coldest Jan/7 colder than normal, followed the 3rd warmest Dec!
Jan of 1940, the coldest Jan on record, followed a near normal Dec.
There have been at KATL four MB Jans (all in coldest 1/8) that followed mild Decs: 1884, 1924, 1985, and 2014. So, anything is possible.
Jan of 1985, the 8th coldest Jan/7 colder than normal, followed the 3rd warmest Dec!
Jan of 1940, the coldest Jan on record, followed a near normal Dec.
I've always understood it as you want a + global aam with the negative values at the pole. If you have the negative values at our latitude that is a sign of strong subtropical ridging and warmth. The last few summers have had big -aam around 30 north and we have responded with big time late season heat ridges
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January 2014 will never show how truly cold it was based on front timing. Clear and far away the coldest month of my lifetime.
I'm no expert, whatsoever, as anything I say here is just passing along info from Maxar. What the met there told me today is that a +AAM is better for the SE because it has some correlation to an El Nino type pattern of colder anomalies (and wet) in the S US and warmer anomalies in the N US. So, for the SE, +AAM is better per them. For many months the N US has been colder anomalywise. Look how cold it has been in the N Plains/upper Midwest for example while much warmer in the SE. That's a typical La Nina pattern. SE cold lovers obviously don't want that. We want the cold to concentrate down here, not up north.
But still, AAM is but one of many factors.
pcbjr
Member
pcbjr
Member
Day 1.5 in 1st grade and I can print my name now ... Thanks Larry and Shane!
Now if I can only learn to read ...
Webberweather53
Meteorologist
The big difference those 2 Januarys have on this year was a major sudden stratospheric warming event occurred in both winters during December that obliterated the polar vortex and led to a very prolonged period of -AO/-NAO.
The few available radiosonde observations available during World War 2 strongly suggested a SSWE occurred in every winter from 1939-40 thru 1941-42 during the rare triple El Nino event of the early 1940s & those SSWEs and the resulting cold from them likely changed the entire course of world history because those were some of the coldest winters of the 20th century in eastern Europe, potentially hindering Hitler's invasion of Russia.
This is a SSWE surface temperature composite via figure 4b from Butler et al (2016), the stippled areas (including right over the SE US) represent "significant" temperature anomalies attributable to SSWEs.
https://www.earth-syst-sci-data.net/9/63/2017/essd-9-63-2017.pdf
if you're a history buff &/or would like to learn more about these stratospheric warming events & the "triple" El Nino that contributed to them and how these forms of climate variability potentially impacted the outcome of World War 2, this paper is a good read!
https://rmets.onlinelibrary.wiley.com/doi/pdf/10.1256/wea.248.04
Mr. Golf
Member
I pray and hope we can get a SSW event that materializes especially if the QBO can reverse easterly before winter is over.
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Webberweather53
Meteorologist
Here's a few places to start w/ AAM, GWO, Mountain Torque, etc:
https://www.netweather.tv/forum/topic/90558-the-fundamentals-of-atmospheric-angular-momentum/
https://www.weather.gov/media/grr/GLOM2015/Presentations/Marino_GWOSevereStorms.pdf
pcbjr
Member
I can read!!!! Thanks, Webb!
Phil
Yeah it's one of those things where broadbrushing can give you a general answer but the specifics of it can make a difference since there is a latitudnal component to it. Now if you want to get really fun you can go down the rabbit hole of the gwo. Personally I love the gwo but I haven't been able to find any updated information on it
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pcbjr
Member
With you ... broad-brushing anything is silly ... but you gotta learn the lingo and basics before tearing the engine down to figure out what the ping is ... as for rabbits ... they're a hard, tiresome chase and even harder to catch ... but ... if you want rabbit stew, you'd better get to chasin' ...
Webberweather53
Meteorologist
Here are some basic definitions you can pull from the first link, I've added some of my own discussion in this first half of this post.
The global wind oscillation (GWO) took me a while to wrap my head around but the GWO at its core just atmospheric angular momentum & the tendency of atmospheric angular momentum, or the rate of change over time thus:
Global Wind Oscillation (GWO) = Atmospheric Angular Momentum (AAM) + Change in Atmospheric Angular Momentum per unit time (t).
The GWO thus encompasses phenomena like Convectively Coupled Kelvin Waves, the MJO, mountain & frictional torques, & even the El Nino Southern Oscillation to some extent. Why? Because all of these significantly impact AAM on timescales of several days to several weeks which is what we're mainly concerned about from a subseasonal standpoint.
Mountain & frictional torques operate on timescales of roughly several days to 2-3 weeks or so and are closely tied to variability in the extratropical storm track. A Rossby Wave (or mid-latitude cyclone or anticyclone) passing over major topographic features like the Rockies or Himalayas is what actually causes mountain torques. The resulting patterns from these mountain torques create Atmospheric Angular Momentum (AAM) anomalies and frictional torques then act to damp or weaken these anomalies.
This post goes very in depth on Atmospheric Angular Momentum & does a better job explaining than I personally would be able to:
https://www.netweather.tv/forum/top...ular-momentum/?do=findComment&comment=3907466
Angular momentum at its most basic level is a combination of the mass or weight of an object, how fast that object is rotating & the distance from its rotational axis.
I.e. Angular momentum = Mass + Rotational Speed + Distance (from axis of rotation).
Once you also consider that the earth system is relatively closed and therefore the total momentum of the earth system is just the summation of the solid earth angular momentum plus atmospheric angular momentum and must always be conserved
Total momentum = AAM + Momentum of Solid Earth
Change in momentum (M) over time (t) w/ change in time represented by "dt"
i.e. (M/dt) >>> AAM/dt + Earth Momentum/dt = 0
Hence, variations in one of these dictate the other. If AAM rises, as is often the case during El Nino events or West Pacific & Western Hemisphere MJO events or as we are going to see over the coming weeks, the earth's solid rotation will slow down in response (actually causes very minute changes to our length of day!) and frictional torques will act to try and weaken these AAM anomalies!
Torque: " "A turning force" that increases the angular momentum of the atmosphere creating a positive torque, one that decreases the angular momentum of the earth is a negative torque."
Mountain torque: "Mountain Torque is a function of pressure and orography and is the ‘turning force’ exerted due to a difference in pressure across any raised surface on the earth, but most significantly, mountains or mountain massifs. Consider a mountain with a high pressure on the west side of a mountain and low pressure on the east. The pressure system will exert an eastward torque that causes the earth to increase it’s rate of rotation, imparting angular momentum from the atmosphere to the solid earth. The opposite case, where there is higher pressure on the east side of the mountain, will slow the earth’s rotation down, reducing the solid earth’s angular momentum, and imparting it to the atmosphere. "
Frictional torque: "The friction torque is the torque that is exerted on the earth’s surface due to the frictional force that occurs because of the wind directly above the Earth’s surface moving relative to the solid earth. If there is an net global westerly surface wind (i.e. a surface wind from the west) the atmosphere will speed the earth’s rotation up, transfer angular momentum to the earth, and thus the atmosphere loses angular momentum. Analogously, if there is a net easterly surface wind (i.e. a surface wind from the east), the atmosphere slows down the rotation of the earth and angular momentum is transferred from the earth to the atmosphere"
Hope this post helps everyone.
Is there a place to get a current phase diagram for the gwo
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Webberweather53
Meteorologist
Unfortunately, none that I am currently aware of. There used to be several places to attain real-time data but they've all either become proprietary or are no longer in service & the researcher at NOAA ESRL who used to provide this data & is among those who discovered the GWO retired several years ago.
pcbjr
Member
I'm gonna figure out some way to get all of this consolidated and in to Wiki ... as a subtopic in models or winter
Any Mods - can you get all of Webb's AAM info, and the materials Larry and Shane have posted, into a new (maybe duplicate) thread called "AAM" - that would be the easiest way to load it all in to Wiki without taking it out of this one altogether? If so, please PM me when it's done, and then folks can add to the specific topic and Wiki will self-update.
Credits and kudos to Webb for providing so much info - do not want it lost in the middle of this thread!
Any Mods - can you get all of Webb's AAM info, and the materials Larry and Shane have posted, into a new (maybe duplicate) thread called "AAM" - that would be the easiest way to load it all in to Wiki without taking it out of this one altogether? If so, please PM me when it's done, and then folks can add to the specific topic and Wiki will self-update.
Credits and kudos to Webb for providing so much info - do not want it lost in the middle of this thread!
tennessee storm
Member
I am seeing a whole lot of panhandle hookers on the gfs model... long range
Anyone got any thoughts on the mjo progression? Gfs is showing a stronger wave getting into p6 the euro just shrivels it away like my yard in July. I have my thoughts but wanted to hear someone else
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tennessee storm
Member
I have my thoughts but doesn’t mean much because I don’t know much. But GFS is always too fast and it’s crappy model too, and I am very concerned that the euro may be closest to being correct! Typing this as I bend over thinking about picking the towel up. Lol. Come mid January and the flip has not occurred and MJO not in 8,1,or 2 I’m picking that towel up fo sho!!!
For the record- I'm kidding about throwing the towel in!
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@Webberweather53 undoubtedly has his own thoughts about this. What I thought I recall him saying in the past is that the GEFS actually tends to do a little better than the EPS when the MJO is where it is now because the EPS tends to dampen the amplitude and move it too fast to the next phases. However, I also recall that the GEFS tends to have too high of an amplitude in phases 6-7. So, I’d educatedly guess it will be somewhere in between the two.
GEFS:
EPS:
Mr. Golf
Member
Its interesting Larry to me that the euro dont have the mjo in phase 6 at the minimum. You or anyone have any ideas?
pcbjr
Member
8 or 2 helps us all; 1 isn't bad for y'all ... I hope if it happens your towel is wet beforehand and frozen solid afterwards ...
Allow me to sum up: The MJO is about to do it's typical thing, surprising everyone yet again by spending considerable time in phase 6. Therefore, join us across the street at Whamby Sads and Suds.
Webberweather53
Meteorologist
Yes, the MJO forecasts from the GEFS when initialized in phase 5 perform better than the EPS although the GEFS is too fast & amplified.
Forecasts with 10 day lead time going into each phase for the ECMWF, JMA, & GFS (NCEP) models look like this:
The gray scale corresponds to root mean squared error with darker dots corresponding to forecasts with 10 days lead time going into that phase having larger error and vis versa (which is different from the above figure where the models are forecasting the MJO from a specific initial phase).
We can clearly see that the GFS model struggles immensely when the MJO is forecast to move into the Maritime Continent (presumably from the COD or the Indian Ocean), whereas the ECMWF struggles more than either the GFS or JMA models when the MJO is forecast to enter the Western Hemisphere (8-1).
MJO predictability is typically on the order of 10-20 days & predictability limit which this paper defines as the model ensemble forecast spread multiplied by the square root of 2 becomes equal to the amplitude of the MJO. The MJO's predictability limit increases slightly when the MJO is being initialized with amplitude outside the COD and is also higher when its initialized over the Maritime Continent.
From Kim et al (2014):
MJO forecast skill in the CFS model increases when a strong MJO event is ongoing & its predictability increases by several days.
The corresponding paper I'm referencing above wrt MJO bias vectors is this one:
https://www.mdpi.com/2073-4433/8/8/150
pcbjr
Member
Wiki is not available (to me or to some others) ... probably has to do with the server issues a few days ago ... hopefully it'll resurrect soon ...
Storm5
Member
all the dogs in the neighborhood started barking simultaneously after this post...
ICON is some hot garbage, you can't get anymore latitudinal winter than this: 
Mr. Golf
Member
Phil, i think the jan-march maps are most important now since we are almost to January.
I think DJF are the best because JAN is in the middle.
Webberweather53
Meteorologist
3 run trend of the EPS valid for New Year's Eve.
Keep a close eye on the strength & position of the ridge in the NE Pacific as we enter early January. Notice how the ridge is gaining latitude & becoming stronger in more recent runs of the EPS. This is something I've anticipated to happen (especially beyond this point in early January) based on the stereotypical, composite pattern response to West Pac tropical forcing, prior experience, & the understanding that individual wave breaks are typically dampened relative to reality at long leads in NWP models. Interested to see if this continues in later forecasts.
From this past Tue:
"I'd anticipate the 500mb pattern to grow more amplified on the models as verification approaches w/ the Alaskan ridge gaining latitude while the tropospheric polar vortex lobe over northern Canada slides southward in later outlooks."
https://southernwx.com/community/threads/the-great-december-dump.650/page-113#post-220236
Keep a close eye on the strength & position of the ridge in the NE Pacific as we enter early January. Notice how the ridge is gaining latitude & becoming stronger in more recent runs of the EPS. This is something I've anticipated to happen (especially beyond this point in early January) based on the stereotypical, composite pattern response to West Pac tropical forcing, prior experience, & the understanding that individual wave breaks are typically dampened relative to reality at long leads in NWP models. Interested to see if this continues in later forecasts.
From this past Tue:
"I'd anticipate the 500mb pattern to grow more amplified on the models as verification approaches w/ the Alaskan ridge gaining latitude while the tropospheric polar vortex lobe over northern Canada slides southward in later outlooks."
https://southernwx.com/community/threads/the-great-december-dump.650/page-113#post-220236
Webberweather53
Meteorologist
While the RMM index shows the MJO entering the west Pacific in early January, it's not that simple:
What we're really about to see are multiple fast moving convectively coupled kelvin waves projecting onto & interfering with low frequency variability associated w/ the +IOD & ENSO. This also means the downstream pattern over North America will differ considerably from the expected response during West Pacific MJO events.
What we're really about to see are multiple fast moving convectively coupled kelvin waves projecting onto & interfering with low frequency variability associated w/ the +IOD & ENSO. This also means the downstream pattern over North America will differ considerably from the expected response during West Pacific MJO events.