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Pattern Jammin January 2023

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GFS wants pretty significant severe mid week next week


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The period with highest potential IMO is after this squeeze play occurs between the western ridging and Greenland ridging, which forces the TPV lobe down into Hudson Bay, shown here on the EPS for Jan 23-29....which pushes both cold air and the storm track to the south

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The Euro Control Run that @Robert West posted with the deep south snow does this beautifully here Jan 25-30

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Prior to the TPV dropping south, I think any wave that amplifies enough to generate a storm is going to cut too much to our NW.

Now, it's certainly possible that the squeeze play isn't as sharp as shown on the EPS, and the TPV doesn't drop south as much, and we end up with a continued Ohio Valley or Iowa Tarheel storm track during this preferred timeframe.


Lastly, I wanted to bring up a comparison between this January and last January. With respect to the Pac Jet and the overall pattern, there are some key similarities and differences between the 2. Last Jan, the Pac Jet over-extended in early Jan (mild period), then retracted in mid Jan, then extended again to a good location in mid-late Jan (cold period). Sound familiar? We are seeing a very similar evolution this January with the exceptions being: 1) the Pac Jet extension in early Jan this year was even stronger (Super El Nino like), and 2) as we go into late Jan this year, we are going to see the MJO / tropical forcing become active in the Indian Ocean...that was not the case last year whereby the -VP signal of the MJO was moving out into the Pacific during mid to late Jan.

So, last year's tropical forcing supported maintenance of a nicely extended Pac Jet that produced the necessary western ridging that led to the cold and wintry period in mid-late Jan. In contrast, we are likely to see a quick retraction of the Pac Jet as we go into late Jan which would affect things into early Feb

On the positive side, we should have increased support for a period of Greenland ridging in late Jan compared to last year based on the forecasted Scandi ridging that will want to retrograde to the west given the overall weakness in jet momentum in the pattern during that timeframe.
 
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griteater said:
Trend loops of the EPS for Jan 27 and Jan 29. Improvement shown over Iceland / Greenland and with the TPV dropping south in Canada

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Hence why blocking is often associated with the action of “squashing” the SER as seen by the trend loops. Hopefully we can maintain this look for the late January period
 
Webberweather53 said:
Much like I did around this time in December (linked below), here's my general sentiment on the rest of meteorological winter.

Again, looking at the big, general picture, don't worry about any details this far out. Only concerned about the planetary-continental scale wave pattern evolution & tropical-extratropical subseasonal coupling processes, not individual storms, not rain/snow p-type maps, etc.

From a tropical forcing perspective & using weekly model forecasts + Nina climatology & analogs as a basic guide line (not actual forecast), this is what things generally look like to me. Tropical forcing will be very dominant over the next several weeks as the MJO &/or Kelvin Waves in the E Hem superposes onto La Nina (gets an assist from the SSWE in the form of an enhanced Brewer Dobson Circulation & we begin to approach the annual peak in MJO amplitude in Feb-Mar).

The big -EAMT event we saw this past week set this pattern evolution into motion and the Pacific jet retraction will get handed off & further reinforced by the MJO as we enter February, leading to a prolonged period of -PNA/SE ridge pattern in the first half-2/3rds of February.

Thus, I think we'll probably go from this central-western weighted trough & southern Canada vortex late month w/ occasional bouts of cold + an outside chance of a CAD event, to a more traditional -PNA in the first week of February that probably shuts down any real chance we have wintry weather, unless we see the 50-50 low go completely crazy like a few EPS & GEFS runs have hinted at.

Thereafter, as we get into the 2nd week of February, I suspect the SE US ridge will actually amplify + flex up the East Coast as the -PNA retreats further into western Canada, yielding a potentially very/unusually mild pattern for much of the E US (not just the SE US this time). I think this pattern will try to persist into at least the 3rd week of February (Feb 14-21), even as the MJO (or whatever comes of subseasonal tropical forcing) enters the West Pacific but by then, I believe we'll see the large-scale puzzle pieces begin to start shuffle around, eventually yielding a potential +EAMT &/or MJO-induced Pacific jet extension sometime around Feb 20th or so.

Eventually, I think that coupled with rapidly shortening jet wavelengths will cause a lot of reshuffling of the circulation pattern over the N Pacific + N America, allowing us to shake off this -PNA/SE ridge pattern sometime around the last week of February & transition to a favorable look for cold/snow right at the tail end of February &/or early March, a time of the winter where we tend to see the most big dog winter storms per capita.

Given that we're not only in a La Nina but would be closing in on a time of the year where the MJO tends to be the most amplified (& therefore slow), plus potential interaction with a SSWE &/or ENSO, there's a risk this overall timeline on the back end of February gets pushed back some closer to early March, but not favoring that scenario for now.

I think these RMM regression maps from Paul Roundy get the general idea generally right here.

Late January: (Very) marginal pattern for cold/snow w/ mean trough centered to our west w/ trough south of Greenland. Slight chance of a CAD event.
Early-mid February: Transition to a more canonical La Nina -PNA/SE ridge pattern w/ the SE ridge flexing up the East Coast, & getting warmer (anomaly wise) as time progresses during this period.
Late February: +EAMT &/or MJO-induced jet extension flips the Pacific pattern, pattern reshuffles over N America in response to that & seasonal changes to the jet stream. Favorable pattern for cold/snow tries to return during the last week of Feb or so.
Early March: A favorable pattern for cold/snow seems most likely to return during this time period. Fighting against increasingly unfavorable climo as early March turns into mid-March. Suspect after our "false spring" in early-mid February, actual spring may get put on hold for a bit this year once we flip the calendar to March.

https://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html




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Here are the JMA MJO composite OLRa & VP200a for each MJO as a rough reference guide to compare w/ against the extended GEFS above.

https://ds.data.jma.go.jp/tcc/tcc/products/clisys/mjo/composite.html

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Today’s Euro weeklies look very similar to the animation I showed earlier this morning from Paul Roundy’s site.

Also notice the Aleutian trough returning ~Feb 20.

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Webberweather53 said:
Big signal for a SSWE on today’s Euro weeklies.

This kind of thing can make a difference later in February and March when we probably get rid of the SE ridge

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Just out of curiosity, is that what happened in 2009. We had those two storms that year on 1/20 and 2/3 respectively and then got very mild for several weeks, then had that winter storm on 3/1-2 followed by a couple days of 25-30 degree below average temperatures
 
Chazwin said:
Just out of curiosity, is that what happened in 2009. We had those two storms that year on 1/20 and 2/3 respectively and then got very mild for several weeks, then had that winter storm on 3/1-2 followed by a couple days of 25-30 degree below average temperatures
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Yes, that's actually what happened. I think if we get a SSWE here, it makes -NAO/-AO on the RMM regression composites much more likely in late Feb-early March.
 
Chazwin said:
Just out of curiosity, is that what happened in 2009. We had those two storms that year on 1/20 and 2/3 respectively and then got very mild for several weeks, then had that winter storm on 3/1-2 followed by a couple days of 25-30 degree below average temperatures
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Looks like a SSWE in late January.
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Stevo24 said:
What exactly is a SSWE and how does it affect us?
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Basically, if the stratosphere splits or stretches due to sudden warming and couples with the troposphere, it can send down some colder sourced air to the lower heights. However, even if that happens, there's no guarantee that we'll have much impact, especially during a La Nina. And, this process would take about 3-4 weeks to impact us. However, I wouldn't mind having a SSWE in the cards late Feb/Mar as the Pacific circles out of the warm phases.
 
Webberweather53 said:
Yes, that's actually what happened. I think if we get a SSWE here, it makes -NAO/-AO on the RMM regression composites much more likely in late Feb-early March.
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Thank you. As I’ve been reading your posts about how you think these next few weeks might go, that February to early March keeps coming up in my head. Ironically enough that was also a time period in which a LaNina was breaking down and of course about to head towards an El Niño… something that I’ve read may happening now as this La Niña continues to break down.
 
Ollie Williams said:
Basically, if the stratosphere splits or stretches due to sudden warming and couples with the troposphere, it can send down some colder sourced air to the lower heights. However, even if that happens, there's no guarantee that we'll have much impact, especially during a La Nina. And, this process would take about 3-4 weeks to impact us. However, I wouldn't mind having an SSWE card in late Feb/Mar as the Pacific circles out of the warm phases.
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If this week's -NAO continues to trend a lot stronger than forecast like it has the last day or two, we could see more rapid coupling/downward propagation of zonal wind + temperature anomalies into the troposphere/lower stratosphere.

Aside from making late Jan's pattern better, getting more -NAO the next 2-3 weeks could also pay dividends down the road. This -NAO showing up on the models now is something to keep an eye on, even if you're looking a month or more down the road.
 
Ollie Williams said:
Basically, if the stratosphere splits or stretches due to sudden warming and couples with the troposphere, it can send down some colder sourced air to the lower heights. However, even if that happens, there's no guarantee that we'll have much impact, especially during a La Nina. And, this process would take about 3-4 weeks to impact us. However, I wouldn't mind having a SSWE in the cards late Feb/Mar as the Pacific circles out of the warm phases.
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The highlighted is what killed us in Feb / Mar 2018. The SSW occurred on Feb 12, 2018. A nice, west-based NAO developed right at the beginning of March. Northern NC and VA got hit multiple times that March even though the Pacific pattern was poor as the MJO was running thru the warm phases (3-4-5-6). It would likely be the opposite this time if one were to occur in early Feb, as the MJO should be in the colder phases in late Feb into early March

MJO in late Feb and March 2018...


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griteater said:
The highlighted is what killed us in Feb / Mar 2018. The SSW occurred on Feb 12, 2018. A nice, west-based NAO developed right at the beginning of March. Northern NC and VA got hit multiple times that March even though the Pacific pattern was poor as the MJO was running thru the warm phases (3-4-5-6). It would likely be the opposite this time if one were to occur in early Feb, as the MJO should be in the colder phases in late Feb into early March

MJO in late Feb and March 2018...


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So if I’m understanding correctly the SSW coupled with cold MJO phases could make it very cold late Feb and into March?
 
LukeBarrette said:
So if I’m understanding correctly the SSW coupled with cold MJO phases could make it very cold late Feb and into March?
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Ifs and buts and candy and nuts. A lot of people hate to even discuss SSWs. In fairness, a lot has to happen to get SSWs to affect the pattern like we want it. First, you need the actual SSW to occur. Right now, it's still way out in time in the modeling, but the pattern precursors for SSWs are present over the next 10 days (Bering Sea and Greenland troughing / Urals and Scandi ridging) and the 10mb zonal wind forecasts in the polar cap show significant weakening upcoming. But if one occurs, the weakness in the zonal winds needs to downwell from the stratosphere into the troposphere (if the AO/NAO are already negative when the SSW is occurring as Webb mentioned, then you wouldn't really need to have it downwell, as there would already be weakness in the troposphere). But the SSW gives you the best chance at seeing a more robust, extended period of -AO/-NAO (no guarantees of course). The MJO cold phases is just that...a better shot at western ridging when the MJO is in the cold phases. So, yes, these 2 could both act to encourage a colder pattern for us in late Feb / early March if the stars align
 
Assuming that the expected SSW occurs, is it unheard of for it to propagate down much quicker than the usual +-30 days? Say something like 10-20 days?
 
Wild Weather Monger said:
Assuming that the expected SSW occurs, is it unheard of for it to propagate down much quicker than the usual +-30 days? Say something like 10-20 days?
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The SSW in the 20-21 winter occurred on Jan 4, 2021. This is a good example of the troposphere already being in a -NAM phase (i.e. -AO) when the SSW occurred, so the effects of the SSW were very quick...essentially just acting to continue to foster the -AO / -NAO environment.

The NAM (Northern Annular Mode) is essentially the AO, but it includes both the troposphere and stratosphere. The warm colors here (negative values) indicate the occurrence of -NAM

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Webberweather53 said:
Big signal for a SSWE on today’s Euro weeklies.

This kind of thing can make a difference later in February and March when we probably get rid of the SE ridge

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I finally found the paper I read the other day that talks about S2S ECMWF model biases during weak vortex/SSWEs & how the model tends to underestimate the U wind response at short lead times prior to SSWEs.

Seems more likely than not we're at least going to see a "weak vortex" event (where the zonal wind at 10hpa & 60N is < 5ms-1 vs < 0ms-1 for a full fledged major sudden stratospheric warming event).

https://wcd.copernicus.org/articles/4/81/2023/
 
griteater said:
The SSW in the 20-21 winter occurred on Jan 4, 2021. This is a good example of the troposphere already being in a -NAM phase (i.e. -AO) when the SSW occurred, so the effects of the SSW were very quick...essentially just acting to continue to foster the -AO / -NAO environment.

The NAM (Northern Annular Mode) is essentially the AO, but it includes both the troposphere and stratosphere. The warm colors here (negative values) indicate the occurrence of -NAM

kE0XHjS.png
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Yeah just another reason why we gotta watch how the -NAO evolves in week 2 on the models.
 
Also, just to reinforce @griteater's post

This is from White et al (2018):

"The Downward Influence of Sudden Stratospheric Warmings: Association With Tropospheric Precursors"
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7440399/

"Further, Black and McDaniel (2004) observed that the determination of the DW (downward) propagation of a SSW depended on the pre-existing tropospheric state; in the case of NDW (non downward) -propagating events, the troposphere was already in a positive northern annular mode (NAM or +NAO)-like state that acted to mask the DW (downward) stratospheric influence. In the case of DW (downward)-propagating (stratospheric warming) events, the troposphere was already in a negative NAM (or -NAO)-like state, although slightly out of phase, latitudinally, with the canonical NAM."

I.e. getting a -NAO near the onset of a sudden stratospheric warming event (SSWE) is a critical factor in determining whether the SSWE actually impacts the troposphere.

Hence, trends like this matter a lot, not just for guiding the chances of us seeing a winter storm in late January, but also in this situation, seemingly small errors like this in week 2 forecast could actually have the potential impact the overall pattern at least through March. This -NAO in the extended range could be a wildcard/throw a wrench at things if it goes unchecked & we trend even more to it the next several days.

Interesting times ahead



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