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Pattern The Great December Dump

This Indian Ocean standing wave isn't going anywhere anytime soon, it took the most recent bout of subseasonal forcing over the IO over a month to finally give up the ghost for a week or two.
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I could also see how this subseasonal wave hangs around for a similar span of time as the mean meridional circulation becomes enhanced by warming of the polar stratosphere this month.
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Webberweather53 said:
This Indian Ocean standing wave isn't going anywhere anytime soon, it took the most recent bout of subseasonal forcing over the IO over a month to finally give up the ghost for a week or two.
View attachment 26337



I could also see how this subseasonal wave hangs around for a similar span of time as the mean meridional circulation becomes enhanced by warming of the polar stratosphere this month.
View attachment 26339
Click to expand...

It’s like clockwork, makes that January timeframe look better and better everyday.


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NoSnowATL said:
It’s like clockwork, makes that January timeframe look better and better everyday.


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Click to expand...

Yeah this is by far one of the most uncertain variables going forward. I'm always amazed how rapidly the tropical stratosphere responds to polar stratospheric warming (or vis versa). In some sense, it certainly fits with the "action at a distance" paradigm we often see associated w/ electricity, magnetism, or gravity. The implications of an enhanced mean meridional circulation due to the warming of the NH stratosphere favor more convection over the warm pool, especially in mid-late December. Maybe the Maritime Continent will finally wake up.
 
Webberweather53 said:
This Indian Ocean standing wave isn't going anywhere anytime soon, it took the most recent bout of subseasonal forcing over the IO over a month to finally give up the ghost for a week or two.
View attachment 26337



I could also see how this subseasonal wave hangs around for a similar span of time as the mean meridional circulation becomes enhanced by warming of the polar stratosphere this month.
View attachment 26339
Click to expand...
In English please and less than 50 words....go.

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I can see why a -EPO doesn't always mean cold air over the Eastern US. The jet stream dips over the western states while a ridge builds over the Eastern US, that's only if there wasn't a -NAO. Since we're looking at a -EPO and a -NAO, we could see average to below normal temps. across the Nation, including the Southeast. If that blocking doesn't happen over the north Atlantic, the southeastern US would probably experience above normal temps. occasionally cold blasts at times.

Looking at the 12z EPS from today, -EPO is still there as well as the -NAO. This look indicates below normal temps for much of the Nation. Storm tracks would be coming from the south in the southern stream. This is actually exciting! All we need now is a winter storm to track, which I do think there will be a winter storm of some type at some point in early December.

Edit: If any winter storm, I'm still thinking it would be an ice storm due to the upper high down in the Gulf.
ecmwf-ens_z500a_namer_11.png
 
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metwannabe said:
In English please and less than 50 words....go.

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Click to expand...

The downstream wave pattern from west Indian ocean convection favors a SE US ridge in Dec. If we had convection in roughly the same place in late winter (February-March) it would be an entirely different story and cold/stormy weather would be favored instead.

The secondary area of anomalous uplift west of the dateline in the tropical pacific will save us from complete disaster and keep the SE US ridge transient in nature. If it takes roughly as long for the Indian Ocean convection to quiet down as it did in Sep-Oct, we can expect it to emerge from the Indian Ocean and enter the West-central Pacific in early January (ish), which is consistent with my thoughts from earlier this week.

Fwiw, Central Pacific (phase 7) MJO events in January love to deliver winter storms to NC & the fact that we're in an El Nino may boost our chances even further, so this may be something to lookout for &/or forward to down the road.
 
Webberweather53 said:
The downstream wave pattern from west Indian ocean convection favors a SE US ridge in Dec. If we had convection in roughly the same place in late winter (February-March) it would be an entirely different story and cold/stormy weather would be favored instead.

The secondary area of anomalous uplift west of the dateline in the tropical pacific will save us from complete disaster and keep the SE US ridge transient in nature. If it takes roughly as long for the Indian Ocean convection to quiet down as it did in Sep-Oct, we can expect it to emerge from the Indian Ocean and enter the West-central Pacific in early January (ish), which is consistent with my thoughts from earlier this week.

Fwiw, Central Pacific (phase 7) MJO events in January love to deliver winter storms to NC & the fact that we're in an El Nino may boost our chances even further, so this may be something to lookout for &/or forward to down the road.
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CPC seems insistent we are not in an El Niño. Would effects be somewhat different from a typical Niño? Niño 3.4 has recently crept back into Niño range but Niño 1.2 remains cold.
 
CyclonicFury said:
CPC seems insistent we are not in an El Niño. Would effects be somewhat different from a typical Niño? Niño 3.4 has recently crept back into Niño range but Niño 1.2 remains cold.
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Even though our SST’s look a bit different, when comparing the CHI 200, you will notice that the distribution similar to every El Niño we have had so far. Essentially our climate has been so out of whack that those year the pattern is workin the way it’s supposed to.
 
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So says the GFS, the end of the first week in December looks like it might have legs again ?????
 
CyclonicFury said:
CPC seems insistent we are not in an El Niño. Would effects be somewhat different from a typical Niño? Niño 3.4 has recently crept back into Niño range but Niño 1.2 remains cold.
Click to expand...

Our categorical system of defining ENSO assumes that "traditional" El Nino, modoki El Nino, neutral ENSO, & La Nina are easily distinguishable states, when in reality they're arbitrarily defined snapshots or subsets of ENSO along a multidimensional continuum with La Nina and "traditional" El Nino on either end of the spectrum & most easily recognizable as the mean longitude of anomalous convection in the Equatorial Pacific.

This year, the mean longitude of anomalous convection is ~150-160E, that's further west even than modoki NINO but is significantly different from neutral ENSO. Definitely do not get the impression this year is characteristically neutral ENSO because some SSTs are of "x" value in "y" region in the Pacific, the convection & divergent, upper level circulation generated from it is what ultimately matters. You can clearly see this anomalous convection is triggering a persistent downstream wavetrain over the Pacific & North America. If you shifted this convection east or west, the wavetrain would also shift. This is basically how ENSO impacts the mid-latitude circulation to a first order.


OlrPsiWaf_tp200hPa_20191121.gif
 
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