December/January Medium/Long Range Discussion

[psuhoffman]

23 minutes ago, Mdecoy said:

Thanks PSU. I don't deny that late Nov and early December was a great pattern that broke the wrong way for us. It is why I was so disappointed. I was told, calm down its only December 8th, but the truth is, snow is so rare here, that any missed opportunity, is a huge missed opportunity. They simply don't come around often (outside of the 1 in 30 year winter).

I guess I am just projecting the last few years of "its only 2 weeks away" followed by it never coming, onto this year, and its wrong for me to do that,..................................... I hope. But I can sit here now and remember 12/27/2017, when we were sitting in the tundra and no precip, that the date of 20 Jan was identified as when things would reset. It is just flashbacks that have no scientific basis. So I apologize.

Hopefully we get something out of this year.

fair enough...and I remember a few people rooting on the pattern change in January the last 2 years because they were tired of the "cold dry" pattern.  I was NOT one of them.  I remember saying "be careful what you wish for" because in a nina cold/wet is just not on the table and I would have rather stuck with the cold dry pattern and just hoped that eventually we would luck into one of those waves or a nice clipper or something.  Sure enough the pattern flip meant 8 weeks of warm and mostly a shutout pattern.  This isn't the same thing. 

[psuhoffman]

2 minutes ago, Ralph Wiggum said:

So if they/we are having an anomalous string of 'bad luck' does that not raise a 'red flag'? Not trying to be philosophical  but they do go hand-in-hand no?

Are we?  We had 3 straight years of above average snowfall from 2014 to 2016.  That is pretty rare actually.  Since then we had one really awful year, and one year that was actually only a little below a median winter even though people acted like it was god awful (probably because it was mediocre following a god awful winter and we got spoiled).  But where is the perception we are having bad luck?  Or did you just mean this winter so far?

[LP08]

Euro looks to be onboard for the wave riding the boundary through 168.....

[psuhoffman]

36 minutes ago, Bob Chill said:

12z GEFS has a dozen variations of the wave working for our general area. The "new twist" compared to the previous bunch of runs is potential for NC or SVA. It's not an insignificant shift but I'll reserve any optimism until it's under 5 days and still shows promise. Thread the needles don't model well in the med/long range.  

I see the potential for another miss to the south and if Richmond and NC are sitting above climo while we are still waiting in a week its going to get UGLY in here lol

[psuhoffman]

Just now, LP08 said:

Euro looks to be onboard for the wave riding the boundary through 168.....

It was a close miss last night but everyone was to gloom and doom for me to bother mentioning it. 

[LP08]

Just now, psuhoffman said:

It was a close miss last night but everyone was to gloom and doom for me to bother mentioning it. 

Temps are quite iffy and its in and out pretty quick...But at least there is some digital snow for those that need their fix.

[psuhoffman]

@frd

great stuff as usual.  My only skepticism regarding this strat stuff...and why I think sometimes some of the strat experts put too much into it, the seasonal guidance was forecasting the SAME general pattern from back in September/October, a LONG time before they started picking up on the SSW potential.  And most of the winter outlooks that forecasted the cold/snow look the second half did not rely on ssw to get it.  And most of the analogs that turned snowy also did not include a SSW.  I think 1966 did, but most of the others did not.  So if the seasonal guidance was already showing a -NAO and eastern US trough before seeing a SSW, and the analogs indicate that is what is likely even without an ssw...why are some acting like this SSW needs to save us and putting so much emphasis on the SSW regarding our prospects for cold?  Don't imply this means I don't think ssw's have significant impacts on our weather.  They do.  The one last year definitely impacted our cold/snowy March pattern.  And this has the potential to help for sure.  But despite what Chuck thinks, an SSW is not the only way to get blocking or a trough in the east during winter. 

[psuhoffman]

5 minutes ago, LP08 said:

Temps are quite iffy and its in and out pretty quick...But at least there is some digital snow for those that need their fix.

That's 99% of our threats lol

[Ralph Wiggum]

7 minutes ago, psuhoffman said:

Are we?  We had 3 straight years of above average snowfall from 2014 to 2016.  That is pretty rare actually.  Since then we had one really awful year, and one year that was actually only a little below a median winter even though people acted like it was god awful (probably because it was mediocre following a god awful winter and we got spoiled).  But where is the perception we are having bad luck?  Or did you just mean this winter so far?

Was referencing your post irt Logan and them only having .2" this season so far which you asked if it was bad luck.

[psuhoffman]

Just now, Ralph Wiggum said:

Was referencing your post irt Logan and them only having .2" this season so far which you asked if it was bad luck.

Ok...fair question.  I think its too small a sample size to know.  But history suggest Boston wasn't getting big storms early in most nino years...but they were getting nickel and dime stuff from clippers and such...this year that kind of thing has been absent in general, even during the cold period it was big storms or bust.  Boston had a couple close misses also so them sitting with nothing vs a couple inches so far is probably bad luck. 

[Maestrobjwa]

8 minutes ago, psuhoffman said:

I see the potential for another miss to the south and if Richmond and NC are sitting above climo while we are still waiting in a week its going to get UGLY in here lol

For me, if that scenario were to verify...it would still be better than last year's classic "snowhole"...This time, we wouldn't be suffering alone...the whole northeast would be singin' the blues, lol Misery loves company! 

[Ralph Wiggum]

7 minutes ago, psuhoffman said:

Ok...fair question.  I think its too small a sample size to know.  But history suggest Boston wasn't getting big storms early in most nino years...but they were getting nickel and dime stuff from clippers and such...this year that kind of thing has been absent in general, even during the cold period it was big storms or bust.  Boston had a couple close misses also so them sitting with nothing vs a couple inches so far is probably bad luck. 

Well most of us know and are aware things can turn on a dime much like the NYE/NYD looks we have and are seeing. I have confidence and believe it or not I am optimistic even tho it doesnt appear that way. Just bored right now like most. No reason at this point to 'cancel winter'. I don't see a complete fail this year. I think at absolute worst we get a 10-14 day window of really legit opportunities but I have faith in your forecasting skills based on experience and well as all of the dissecting you have done recently and over the years. It's still very early. At least some ops had digital flakes to hold us over for the time being.

[BTRWx's Thanks Giving]

2 hours ago, frd said:

 

A great read and overview.

Interesting reference to the CFS below. it is the CFS versus the Pioneer, Euro and the Ukmet seasonals.

from 

https://simonleewx.com/2018/12/27/not-all-ssws-were-created-equal/amp/?__twitter_impression=true

Not all SSWs were created equal

 Simon Lee

3 hours ago

Non-downward propagating SSWs? 

Major stratospheric sudden warming events (SSWs) attract widespread attention because they are now known to have significant impacts on the tropospheric circulation (e.g. Baldwin and Dunkerton 2001, hereafter BD01). Anomalies in the stratospheric circulation (often expressed as the Northern Annual Mode (NAM) index, or polar cap geopotential height anomalies) propagate downwards through the stratosphere into the troposphere, rather like “dripping paint” (such as BD01 Fig. 2). A major SSW is associated with the development of a negative NAM in the stratosphere; the “typical” response is the development of a negative NAM (or the associated NAO/AO) in the troposphere ~10-14 days after the central date of the SSW (when the 10 hPa 60N zonal-mean zonal wind becomes easterly) which can persist for several months.

However, not all SSWs were created equal – and some SSWs do not strongly couple to the tropospheric circulation. A recent study by Karphechko et al. (2017) classified major SSWs as “downward propagating” (dSSW) or otherwise (nSSW) based on the 1000 hPa NAM index following the event, and found 43% were nSSW – i.e., not followed by a strong and persistently negative surface NAM. This is not a small fraction of SSWs, and the atmospheric evolution following the two types was found to be significantly different. 

Our perception of SSWs in recent years has been highly influenced by a relatively unusual clustering of vortex-split, downward-propagating events (Jan 2009, Feb 2010, Jan 2013 and Feb 2018) which all had similar tropospheric impacts (all 4 of those events were followed by an outbreak of snow/cold in the UK, for example). The most recent nSSW occurred in Feb 2008. Thus, the announcement of a major SSW – particularly on social media – has become synonymous with a specific weather pattern.

In the nSSW cases considered by Karpechko et al., the composite (their Fig. 1c) actually shows intermittently positive NAM in the troposphere following the SSW – with the sign of the NAM opposing between the lower stratosphere and the troposphere for ~40 days following the central date. This is very different to the picture of dripping -NAM anomalies into the troposphere that BD01 made famous (which is consistent with Karpechko et al.’s dSSW).

Composites of all major SSWs are influenced by the higher frequency of dSSW and the stronger circulation anomalies induced, but this work suggests we need to be wary of these stratospheric events which don’t strongly influence what happens beneath. However, forecast models often struggle to predict the downward propagation – so forecasting these events is troublesome. It also presents a communication problem, which current forecasts (see below!) suggest we may be about to run into: a major SSW could mean a significant reversal of the normal tropospheric circulation (with the potential for “Beast from the East”-type events in the UK), or it could mean very little (e.g. January 2002 following the non-downward propagating Dec 2001 SSW). Predicting these differences, and understanding the mechanisms involved, is an area of active research – and something I hope to address in my PhD work.

Do current forecasts suggest nSSW or dSSW?

As I write this, we’re in a tentative stage – the main stratospheric heat flux event has occurred, and the 60N zonal-mean zonal wind has reversed to easterlies in the upper stratosphere. However, at 10 hPa we’re still decelerating – with the event expected to become ‘major’ around Jan 1 (Fig. 1 & 2) if current forecasts are correct (inter-model agreement has substantially increased now the upper-stratospheric reversal is in the observations).  The event looks very likely to be first driven by a wave-1 displacement of the vortex towards Eurasia, with an increasing likelihoodo of a vortex split (wave-2) to then occur, with the dominant daughetr vortex over Eurasia and a smaller vortex over N America (interestingly, this is opposite to what happened in Feb 2018). However, agreement on the split evolution remains lower than the displacement.

Figure 1: Forecasts of the 10 hPa 60N zonal-mean zonal wind from 00Z December 27th. There is a good agreement between the GFS and its ensemble of a major SSW occurring around Jan 1st.

Figure 2: ECMWF operational forecast from 12Z December 26th for 12Z January 1st showing a major SSW. Source: http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/. 

So, predicting the tropospheric impacts is a challenge when the stratospheric forecasts don’t agree! The spread in the GEFS forecasts beyond 10 days is very large – with some members showing a quick return to stratospheric westerlies whilst others flirt with record-strong easterlies. There’s even some indication of bifurcation in the ensemble at longer ranges (perhaps relating to whether or not a split occurs), which may render the ensemble mean of less use.

Despite the uncertainty, one aspect that has been relatively persistent is the absence of a signal for downward propagation in the deterministic GFS (Fig. 3) and the longer-range models such as CFSv2 (Fig. 4). Comparing Fig. 3 here with the nSSW composite in the Karpechko paper is striking – there are many similarities, including the weak -NAM before the main event and the ~day 10 tropospheric +NAM development. On its own, this screams nSSW – but of course is just a single deterministic forecast from one model.

Fi

 

 

 

The CFSv2 initially trended strongly towards a -NAO for January 2019 as the SSW signal grew – but this has since decayed and transitioned more towards an Atlantic ridge pattern (Fig. 4). The model clearly picked up on a major SSW occurring – but, like all forecast systems this time, has struggled to predict the type of SSW. There is currently no indication (Fig. 5) from the CFSv2 forecasts of a widespread hemispheric cold outbreak (a “warm Arctic-cold continents” pattern).

Figure 4: CFSv2 forecasts from Dec 1 – Dec 27 for January 2019 700 hPa geopotential height anomalies. Note the initial trend away from a +NAO towards a strong -NAO, before trending towards an “Atlantic ridge” pattern.

Figure 5: CFSv2 2m tempertaure anomaly forecast for January 2019 from an ensemble of forecasts launched between Dec 16-25. Base period 1999-2010. Source: http://origin.cpc.ncep.noaa.gov/products/people/wwang/cfsv2fcst/. 

My advice would be not to hold your breath for a “Beast from the East 2019 Edition”. But as predictability typically increases once a major SSW has occurred, we should gain a much better picture in the first few days of 2019.

Takeaway message: the impacts of SSWs are more complex than whether it is a displacement or a split, and the mere reversal of the 10 hPa 60N zonal wind doesn’t mean you’ll be shovelling snow 2 weeks later.

References

Baldwin, M. P., and T. Dunkerton, 2001: Stratospheric Harbingers of Anomalous Weather Regimes. Science, 294, 581-584, https://doi.org/10.1126/science.1063315.

Karpechko, A. Y., P. Hitchcock, D. H. W. Peters, and A. Schneidereit, 2017: Predictability of downward propagation of major sudden stratospheric warmings. Quart. J. Roy. Meteor. Soc., 143, 1459-1470, https://doi.org/10.1002/qj.3017.

Categories: Communication, Stratosphere, SSW

 

 

 

I kind of want to believe that ssws are a secondary indicator to other pattern recognition signs.  The MJO still has a few weeks.

[frd]

13 minutes ago, psuhoffman said:

@frd

great stuff as usual.  My only skepticism regarding this strat stuff...and why I think sometimes some of the strat experts put too much into it, the seasonal guidance was forecasting the SAME general pattern from back in September/October, a LONG time before they started picking up on the SSW potential.  And most of the winter outlooks that forecasted the cold/snow look the second half did not rely on ssw to get it.  And most of the analogs that turned snowy also did not include a SSW.  I think 1966 did, but most of the others did not.  So if the seasonal guidance was already showing a -NAO and eastern US trough before seeing a SSW, and the analogs indicate that is what is likely even without an ssw...why are some acting like this SSW needs to save us and putting so much emphasis on the SSW regarding our prospects for cold?  Don't imply this means I don't think ssw's have significant impacts on our weather.  They do.  The one last year definitely impacted our cold/snowy March pattern.  And this has the potential to help for sure.  But despite what Chuck thinks, an SSW is not the only way to get blocking or a trough in the east during winter. 

Agree on all points.  I think that if the strat event's final outcome is one that has an impact it would only act to possible enhance or possibly lenghten a favorable period. I view a non event or a negative impact as the least possible outcome. 

The ultimate outcome is unknown. Some models take the response and get it to to troposphere, others do not.

it is possible we might know a lot more by early next week. 

 

 

[psuhoffman]

10 minutes ago, frd said:

Agree on all points.  I think that if the strat event's final outcome is one that has an impact it would only act to possible enhance or possibly lenghten a favorable period. I view a non event or a negative impact as the least possible outcome. 

The ultimate outcome is unknown. Some models take the response and get it to to troposphere, others do not.

it is possible we might know a lot more by early next week. 

 

 

2 weeks

[frd]

@poolz1

Wonder the track record of the GOES- 5 ?

it takes it down so there are sensible impacts somewhere ( have to pin that down too )

 

and from the Euro

FYI. euro from today is not there , I have to track that down 

 

 

[luckyamaha]

2 weeks

Seems like we are going to push it or every week by two weeks for a better outcome until it's mid March and then is over. Let's all go to the Panic room

Sent from my SM-N960U using Tapatalk

[Maestrobjwa]

22 minutes ago, frd said:

Agree on all points.  I think that if the strat event's final outcome is one that has an impact it would only act to possible enhance or possibly lenghten a favorable period. I view a non event or a negative impact as the least possible outcome. 

The ultimate outcome is unknown. Some models take the response and get it to to troposphere, others do not.

it is possible we might know a lot more by early next week. 

 

 

Man I hope so...I'm just tired of all the speculation about this SSW without knowing anything! Just want it to hurry up and happen already so we can see where we're at...geez, lol

[frd]

3 minutes ago, Maestrobjwa said:

Man I hope so...I'm just tired of all the speculation about this SSW without knowing anything! Just want it to hurry up and happen already so we can see where we're at...geez, lol

You know Jan. was always a transition month. It is tough, but we will get there. 

[Bob Chill]

2 minutes ago, Maestrobjwa said:

Man I hope so...I'm just tired of all the speculation about this SSW without knowing anything! Just want it to hurry up and happen already...geez, lol

The best advice I can give you about SSWs is to pretty much discount them completely until effects are measurably happening in the troposphere. It's a neat phenomenon and has at times assisted in unleashing winter wx in the mid latitudes but the unpredictable nature of the correlation between the strat and trop makes it bad practice to set expectations based on the existence or lack of SSWs. 

[Maestrobjwa]

1 minute ago, Bob Chill said:

The best advice I can give you about SSWs is to pretty much discount them completely until effects are measurably happening in the troposphere. It's a neat phenomenon and has at times assisted in unleashing winter wx in the mid latitudes but the unpredictable nature of the correlation between the strat and trop makes it bad practice to set expectations based on the existence or lack of SSWs. 

I gotcha...I mean, seeing as I don't know much about it, I haven't set any expectations on it at all...(other than just hoping it doesn't serve as a negative if it happens at all, of course, lol). But I take it all the speculation so far is as good as a random guess?

[Bob Chill]

Just now, Maestrobjwa said:

I gotcha...I mean, seeing as I don't know much about it, I haven't set any expectations on it at all...(other than just hoping it doesn't serve as a negative if it happens at all, of course, lol). But I take it all the speculation so far is as good as a random guess?

The discussion about what is going on with the strat PV is very valid. It's the first time in a while where it's been weak and battered this early in the season. The disruption and split has been well modeled and like I said before, it's very interesting. Where it gets very muddy is how it will impact global weather patterns. I wasn't implying that we should discount the fact that there is significant disruption/warming going on as we speak because that's very real. Just don't expect it to change anything in regards to sensible wx until it's actually happening (no signs of that anywhere yet). 

[LP08]

For some good news..12z EPS looks much better than 0z through 222.  PV in NE Canada, -NAO, +PNA, -EPO with the Aleutian Trough.  I'd imagine the there will be some good looks in the individuals with that look.

 

240 below.

[psuhoffman]

10 minutes ago, LP08 said:

For some good news..12z EPS looks much better than 0z through 222.  PV in NE Canada, -NAO, +PNA, -EPO with the Aleutian Trough.  I'd imagine the there will be some good looks in the individuals with that look.

 

240 below.

The nao tanking (now in only a few days) has been trending stronger. The EPS has also been delaying its breakdown. Perhaps the transient window ends up longer than thought.   The guidance really becomes jumpy and unclear beyond day 10. Even in the generalities. Hopefully soon they start converging on the changes we want in the high latitudes. 

[LP08]

Just now, psuhoffman said:

The nao tanking (now in only a few days) has been trending stronger. The EPS has also been delaying its breakdown. Perhaps the transient window ends up longer than thought.   The guidance really becomes jumpy and unclear beyond day 10. Even in the generalities. Hopefully soon they start converging on the changes we want in the high latitudes. 

That was what caught my eye as well.  It helps keep the PV planted in Northern Canada.  Also looks like some support for the follow up idea as well around Jan 3rd-5th.  I haven't look at the members just the 24hr precip maps.

[Bob Chill]

Just now, LP08 said:

That was what caught my eye as well.  It helps keep the PV planted in Northern Canada.  Also looks like some support for the follow up idea as well around Jan 3rd-5th.  I haven't look at the members just the 24hr precip maps.

Ens members look better than the previous 2-3 EPS runs. A lot of spread but not as dire as recent runs have shown. 

Interestingly, the control run has the follow up wave and it's pretty strong. Runs to the west but still hits western zones pretty good. Considering the best op looks we're getting is a glancing blow to the SE, seeing the control run a fairly strong low to our west is telling in how little confidence we can have in how things transpire next week. 

[nj2va]

Uptick in snowfall means on the 12z EPS vs earlier runs.  0.5” through 360 for DC at 00z vs 2”+ at 12z.  It’d be nice to see purples over DC...hopefully in 2 weeks.

[psuhoffman]

If you want me to be critical one thing I don't like is how the PV is just sitting over the pole and seems stuck there off to day 15 on the euro guidance. Gefs breaks it down faster. That's really interfering in our ability to get blocking to lock in. Need that to move to get either cross polar flow and or permanent ridging up top to establish. 

[psuhoffman]

Definitely nice pacific pattern moving into mid January. Now just get the other side right. 

[frd]

29 minutes ago, psuhoffman said:

If you want me to be critical one thing I don't like is how the PV is just sitting over the pole and seems stuck there off to day 15 on the euro guidance. Gefs breaks it down faster. That's really interfering in our ability to get blocking to lock in. Need that to move to get either cross polar flow and or permanent ridging up top to establish. 

Hmm, that is a bit odd. Not really sure why that look is there given the weakened state of the PV and recent heat fluxes. 

maybe related to the SWW event 

I think the -NAO is from the Atlantic side wave breaking but the North pole blues is really is odd.