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mattie g

October/November 2019 Mid/Long Range

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I like where the advertised pattern is heading in general towards the end of the month. It will become a bit milder for a time. Guidance indicates continued disruptions of the SPV, with some warming and height rises. Just need to keep the SPV on the weak side- a SSWE is not required for a good response in the HL troposphere to allow cold air delivery into the midlatitudes. Looking at the teleconnections on the EPS, AO stays slightly negative, NAO trends negative, and this is clearly seen at h5 on both the EPS and GEFS in the LR with heights building across Greenland into Baffin. We shall see if it materializes. The PNA trends neutral, and WPO/EPO positive. So it looks like while we lose the big coupled blocking ridge out west, we will see improvement in the NA, hopefully in the form of a legit -NAO (blocking ridge) towards the end of the month. I don't think the PAC is going to turn hostile- this looks to be more of a relaxation. Ofc time will tell, lol.

 

nao.thumb.png.358d55f38d8468456c259da1b15c7dc4.png

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1 minute ago, showmethesnow said:

Fringed. :(

That's alright. I will gladly give up these nickle/dimers to you snow starved shore men just as long as I get in on the death bands from all the N'easters we are going to get this year. :D

I would be surprised to see anything on the ground. Have seen this hundreds of times on guidance, and it almost never materializes. Cold chasing rain. Seeing some flakes fly would be a win.

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1 hour ago, C.A.P.E. said:

I would be surprised to see anything on the ground. Have seen this hundreds of times on guidance, and it almost never materializes. Cold chasing rain. Seeing some flakes fly would be a win.

I'm definitely not expecting to see anything on the ground, or maybe even anything elevated. I'd just like to see significant accumulations on the map because it assures we will see a period of snow falling from the sky.

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@showmethesnow

I see your concern about the lower heights near Bering Strait/Chukchi, but I am not too worried at this point as there is still some ridging over western Canada, and it seems this may be part of a pattern relax/reload. Now if we see those heights persist and lower, and we end up with a blue ball migrating towards the GOA, then there might be a problem. Looking at the strat panels on the Euro, the PV gets elongated but there is still a piece on our side. Verbatim on the EPS, surface temps are average to slightly above from the 20th to the 25th in the east, but if the developments in the NA are real, and the EPAC doesn't further deteriorate, we should see lower heights develop in the eastern US on future ens runs in response.

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11 minutes ago, osfan24 said:

I'm definitely not expecting to see anything on the ground, or maybe even anything elevated. I'd just like to see significant accumulations on the map because it assures we will see a period of snow falling from the sky.

Yeah that's a good way to look at it. My forecast has rain ending as snow, little or no accumulation.

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Whether right or wrong the ensembles are advertising a mostly CONUS wide warm up as we head into the extended and somewhat beyond.

Below we have the EPS (GEFS has some slight differences but generally has the same idea). What will induce this warm up is the PV that has generally been located around the Hudson Bay region will migrate westward towards Alaska/NE Russia. This effectively cuts off cross polar flow which has been sending and will send much colder air relative to norms into our region. With the withdrawal of the pv in central/eastern Canada we are also seeing the amplified troughing in the mid-west/east flattening as well. Part of the reason we were seeing good ridging in the west was due to the backing of the flow that was being induce but the amplified troughing in the east. Take that strong troughing out and we lose that backing and so correspondingly we see the western ridging breakdown as the PAC flow overwhelms it as seen below. Now we do still see an extreme northern based +PNA but it does us little good. What is happening is that the PAC Flow is overwhelming the CONUS effectively putting up a wall against the N Stream which is flowing around the extreme northern ridging.

 

EPS500s.gif.977080b3360cc04d8aa1a5d6ac0e66ee.gif

 

Now below we have the response in temps to this setup. Notice we have basically warmth through the whole of N America at the end of the extended (We do see below norm temps in the SW which are the product of weakness/troughing we see in that region.). As we can see, the N Stream is flowing off the N PAC around the troughing setup by the PV. With coming off the PAC these temps are moderated somewhat so they are showing as warm anomalies through Canada but they would be more then sufficient for our needs if they decided to give us a visit. Unfortunately there is no vehicle to deliver them. The extreme N based ridging comes no where near to providing the oomph to bust through the PAC flow that has setup through the CONUS. And the eastern trough that could have served us as well? That has become muted as well with the pv withdrawal. So the core of the colder air is basically locked up into Canada.  Now as far as our region what we could probably expect with this setup is longer periods of warmth with brief intrusions of seasonal to slightly below temps as cold fronts would slide down into the Mid-west and slide eastward as they work around the very weak troughing we see through the region. The cold provided would most likely not be sufficient for our needs (snow) as we are still very early in the season. Now this doesn't take into account an extreme event that can manufacture its own cold (Bombing low, Bowling bowl across the south). So there is always that.

 

EPS850temps.gif.ea0b7f3e7705270f3e0b760cc11af811.gif

Now I know there are some in here who will panic. I wouldn't. This will more then likely be a somewhat brief warmup (2 weeks maybe 3) as there are already signs of this look breaking down at the end of the extended. And we couldn't have asked for better timing as well as this early in the season we struggle mightily anyway (better then handicapping the temps during the heart of winter). This will also be a good test to see if the period we have seen recently is actually the base state (+PNA, -EPO, eastern troughing) that we can expect through the CONUS for at least the first half of winter, which in my mind would be a winner. And some of what I am seeing suggests to me that the models may in fact be beginning the process of reverting to this. 

There are actually quite a few things I like seeing even while we may be experiencing this relax. The stratpv is actually getting hammered. This pretty much coincides with the CFS projections that it has had for several weeks and what the GEFS has been advertising recently. Also we are seeing quite a disconnect from the 10mb pv down to the 500mb one. Another sign that the pv is under extreme duress. Still want to see a few more days of runs but the evolution I believe we are over/around the pole beyond the extended is one that will actually feature some great blocking (think big red ball) with a correspondingly strong -AO. As far as the NAO domain I am starting to lean fairly strongly on that becoming a player as well (I favor an eastern based one at this time). Let's see what the next week or so of runs give us and whether the current projections are somewhat accurate. If they are, we could be setting up for a very favorable look come mid-December.

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4 minutes ago, showmethesnow said:

This will more then likely be a somewhat brief warmup (2 weeks maybe 3) as there are already signs of this look breaking down at the end of the extended.

Good writeup. Maybe we’ll be able to spend turkey day outside and not be cold the whole time.

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2 hours ago, C.A.P.E. said:

I would be surprised to see anything on the ground. Have seen this hundreds of times on guidance, and it almost never materializes. Cold chasing rain. Seeing some flakes fly would be a win.

To say I am less then enthused about the prospects at this time, especially west of the bay would be an understatement. As the snow maps suggest I believe the best chances for anything of substance will be confined to the eastern/southern portions of MD and NE Va as we do see a slug of moisture riding up from the south just in time to enhance moisture into the frontal passage. Up in my neck of the woods I think we are looking at instability snow and/or rain showers at best as the 500's swing through with very little to nothing with the frontal passage. And I am not really impressed with the 500's at this time but will reserve judgment until we get within 48-72 hours as the models should pick up by then on any possible energy rotating through. 

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3 hours ago, C.A.P.E. said:

I like where the advertised pattern is heading in general towards the end of the month. It will become a bit milder for a time. Guidance indicates continued disruptions of the SPV, with some warming and height rises. Just need to keep the SPV on the weak side- a SSWE is not required for a good response in the HL troposphere to allow cold air delivery into the midlatitudes. Looking at the teleconnections on the EPS, AO stays slightly negative, NAO trends negative, and this is clearly seen at h5 on both the EPS and GEFS in the LR with heights building across Greenland into Baffin. We shall see if it materializes. The PNA trends neutral, and WPO/EPO positive. So it looks like while we lose the big coupled blocking ridge out west, we will see improvement in the NA, hopefully in the form of a legit -NAO (blocking ridge) towards the end of the month. I don't think the PAC is going to turn hostile- this looks to be more of a relaxation. Ofc time will tell, lol.

 

 

Great minds think alike. Of course it doesn't hurt that if I am wrong at least I have a fellow shipmate to go down on the Titanic with me. :D

Pretty much agree with everything you are saying except differ somewhat on what the models suggest in regards to the AO (or at least I believe we see a much more robust signal). Looking at the mid and upper levels is suggestive to me that we see some fairly impressive height builds over the pole and polar regions (2-3 weeks). These same things are also suggestive of major fracturing and displacement southward of the pv at 500's, aka strong -ao.

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0z Euro SPV currently, and at the end of the run. It is forecast to undergo continued perturbation from the periphery, ending up with 2 main areas of lower heights.The area of lowest negative height anomalies ends up a bit further north than the current location, but much less consolidated/significantly weaker. 

1573344000-EFbmtabutis.png

 

1574208000-flAyvGzkjXA.png

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The more I visit this site the more I love it , plus Simon updated the site with this new data, which I have not seen anywhere else  ( lower stratospheric anomalies ) :

 

New product online at https://simonleewx.com/polar-vortex-forecasts/ GEFS forecasts of tercile anomaly categories of 100 hPa 60°N zonal-mean zonal wind. These lower stratospheric anomalies are important for influencing the what happens in troposphere, and are often more relevant than 10 hPa.

 

 

Polar Vortex Forecasts

All charts are updated once daily between 8:30-10:30 AM London time. Please feel free to share any images from this site on social media or elsewhere.

00Z GFS 0.5° & GEFS 1.0° 10 hPa 60°N ensemble plume 

GEFS & GFS ensemble

00Z GFS 0.5° 10 hPa 60°N forecast evolution

White crosses indicate a strong vortex event (>41.2 m/s) following Tripathi et al. 2015.

GFS forecast evolution

CFSv2 1.0° 10 hPa 60°N bias-corrected ensemble plume

This is produced by taking the 4-member ensembles from 00, 06, 12 and 18Z yesterday and combining into a 16-member ensemble, out to 45 days. The bias is calculated as the difference between the 1999-2009 hindcasts (available from the S2S database) and ERA-Interim reanalysis. The CFSv2 has a significant bias toward a weak vortex, especially for forecasts launched in early winter, so accounting for this drift is necessary.

It should be noted that a simple linear bias correction does not necessarily solve the problems produced by the bias, as the bias can interfere with the model dynamics.

CFSv2 ensemble

00Z GFS 0.5° & GEFS 1.0° 1000 hPa Northern Annular Mode (NAM) ensemble plume

This is calculated using the method of Gerber and Martineau (2018) using standardized anomalies of 65-90°N geopotential height (with respect to 1979-2018 ERA-Interim climatology) with the global mean anomaly removed. I thank Zac Lawrence for calculating the filtered ERA-Interim climatology used here.

NAM ensemble

00Z GEFS 1.0° 100 hPa 60°N tercile categories

The tercile-category anomaly of the lower-stratospheric polar vortex, defined by the 100 hPa 60°N zonal-mean zonal wind, has been used as a diagnostic for the behaviour in the ‘coupling layer’ between the stratosphere and troposphere, i.e. the level in the stratosphere where circulation anomalies are important for influencing tropospheric weather regimes (e.g. Charlton-Perez et al. 2018, Lee et al. in review). The chart below shows the percent of GEFS members in each tercile anomaly category, based on daily 1979-2018 ERA-5 climatology.

U100-60 GEFS terciles

00Z GFS 0.5° & GEFS 1.0° Scandinavia-Greenland dipole ensemble plume

This dipole pattern, defined in Lee et al. (2019) as the MSLP difference between a grid box over Scandinavia and a grid box over north-east Greenland, can be used as a diagnostic of anticyclonic wave breaking in the north-east Atlantic which can enhance vertically-propagating wave activity and weaken the stratospheric polar vortex. In the paper, we use 40 hPa as a threshold (strong Scandinavia high + deep Greenland low) as this is similar to what occurred before the February 2018 major SSW, but values above 30 hPa are noteworthy.

S-G ensemble

 

 

 

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33 minutes ago, showmethesnow said:

To say I am less then enthused about the prospects at this time, especially west of the bay would be an understatement. As the snow maps suggest I believe the best chances for anything of substance will be confined to the eastern/southern portions of MD and NE Va as we do see a slug of moisture riding up from the south just in time to enhance moisture into the frontal passage. Up in my neck of the woods I think we are looking at instability snow and/or rain showers at best as the 500's swing through with very little to nothing with the frontal passage. And I am not really impressed with the 500's at this time but will reserve judgment until we get within 48-72 hours as the models should pick up by then on any possible energy rotating through. 

This is where I am with it. If there is to be an area of light accumulations at the tail end, it will probably, oddly enough, be to my east/SE. I think most of us have a shot as seeing snow in the air, whether from the weak wave or instability flurries as the cold moves in.

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Awesome image below,  and on top the current disconnect between the stratosphere  and the troposphere ,  Hugo is a reliable source of great information on this topic. 

 

 

Image

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1 hour ago, showmethesnow said:

Great minds think alike. Of course it doesn't hurt that if I am wrong at least I have a fellow shipmate to go down on the Titanic with me. :D

Pretty much agree with everything you are saying except differ somewhat on what the models suggest in regards to the AO (or at least I believe we see a much more robust signal). Looking at the mid and upper levels is suggestive to me that we see some fairly impressive height builds over the pole and polar regions (2-3 weeks). These same things are also suggestive of major fracturing and displacement southward of the pv at 500's, aka strong -ao.

I think the AO has chance to go more significantly negative moving forward, so we agree there too. Part of that post I was just giving the current projections on the teleconnections verbatim from the EPS through the end of its run. Things are evolving upstairs in the HL regions, and for now it looks like steady as she goes with continued PV disruptions.

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16 minutes ago, midatlanticweather said:

What does it mean? 

 

This was another thing I liked seeing amidst our current projected warmup in the extended. What we were seeing regards to the PAC Jet and the tropical jet. Currently we see a strong PAC jet exiting off Asia into the Pacific but it is getting quickly hammered in the central Pacific so as that it is weakened and under goes major gyrations within the flow as it approaches N America. During the projected warmup we see the disruption to the jet in the central Pacific let up a touch so that we see a slightly stronger/straighter/more consolidated jet approaching our shores. But this looks to be brief in nature as the disruptions ramp up once again. This in my mind is a good omen that we will not be plagued with a strong overwhelming jet this winter. Also it looks as if the tropical jet (via the Pineapple express) is ramping up somewhat as well. Not to mention that we continue to see split flow off the SW coast popping up time and again. I also noted a week or two ago about another possible source of a tropical jet (disassociated from the normal PAC one as this one would pull moisture up from the equator through generally Mexico) that might be a player at times. And we are still seeing that feature showing up, the anticyclonic rotation generally situated around the Gulf/Mexico/Central America. 

All in all I like what we have seen and are projected to see in the coming two weeks. Makes me tend to believe that if this winter ends up being a dud it won't be because the PAC failed us.

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Webb's been plugging a warm December for awhile, but that’s because he’s showing that the atmosphere is behaving very Nino-ish, even if the SSTs are neutral/warm neutral. 

 

 

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54 minutes ago, WxUSAF said:

Webb's been plugging a warm December for awhile, but that’s because he’s showing that the atmosphere is behaving very Nino-ish, even if the SSTs are neutral/warm neutral. 

 

Our winters always feature warm stretches and I'm not concerned about mild periods unless they are warm AND hostile against snowfall for weeks on end. I know you feel identical on this. 

If this ends up being a notable cold winter I (and everyone else) will be surprised. But we care most about snowfall so my focus is always exclusively on that. Seasonal guidance for Dec looks really crappy for the east coast in general and has yet to waver. This plot really sucks... lol. Euro seasonal and cansips are similar enough to worry a little. 

cfs-mon_01_z500a_nhem_1.png

 

The good thing is seasonal and even weekly guidance busts horribly as much as it gets it right. I really like what's been happening this month and long lead stuff the last few months didn't show the strong height anomalies in good places that we're seeing now. That's encouraging because persistance in the med term is often a sign that it will continue instead of flip to crap. That cuts both ways of course like last year being the ultimate tease of the promised land just around the corner but persistance held on for months. 

The million $ question is will the current height pattern or some decent variation persist or reccur in Dec? No way to know yet but I'm not buying what Dec guidance is showing until it actually starts happening. If we roll into Dec with a nice -ao and pna and/or epo ridge then all bets are off on a warm shutout Dec. The case for this is slowly building at least. 

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Given that last December I literally didn't even see a flake of snow, it can only go up from there for this year, even if there are torchy days/weeks/full month.  I had no expectation that November cross polar flow would lock in for 9 weeks, so not surprised in the least that's going to break down.  But I like the trend to Aleutian low (also Ninoish) as well as the signs that the PV (trop and Strat) keeps getting beat up.  

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4 minutes ago, WxUSAF said:

Given that last December I literally didn't even see a flake of snow, it can only go up from there for this year, even if there are torchy days/weeks/full month.  I had no expectation that November cross polar flow would lock in for 9 weeks, so not surprised in the least that's going to break down.  But I like the trend to Aleutian low (also Ninoish) as well as the signs that the PV (trop and Strat) keeps getting beat up.  

Yep, and frankly I just can't get excited or depressed about seasonal or weekly models after last year.

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1 minute ago, osfan24 said:

Yep, and frankly I just can't get excited or depressed about seasonal or weekly models after last year.

Yup.  They've been terrible of late (see the predictions for this month) and were terribad last year when we had 3 months of KU pattern advertisements.  Keep focused on the next 2 weeks and that's about all we can have any faith in.  

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1 hour ago, WxUSAF said:

Webb's been plugging a warm December for awhile, but that’s because he’s showing that the atmosphere is behaving very Nino-ish, even if the SSTs are neutral/warm neutral. 

 

 

It makes sense since most of the other pattern drivers are in a state most common with a nino. On top of that the enso is warm neutral so not like it’s that far off. That might be a bad sign for December but good for winter since some of the nino analogs that fit in other ways were the better years. But I tended to toss them because enso differences are hard to ignore but perhaps of this behaves like a nino...

Btw have you seen any good studies on why every so often a nino year bucks the trend of warm December?  2/3 go mild, but then there are years like 2002 and 2009.  Those years had opposite North Pacific sst patterns so there isn’t an easily identifiable cause. Both featured NAO help in December where most other ninos the NAO didn’t cooperate until later. But that isn’t very helpful in a predictive way without establishing causality.  

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24 minutes ago, WxUSAF said:

Yup.  They've been terrible of late (see the predictions for this month) and were terribad last year when we had 3 months of KU pattern advertisements.  Keep focused on the next 2 weeks and that's about all we can have any faith in.  

Exactly. 2 weeks is the only thing worth focusing on with weak or neutral enso. I got rabbitholed last year because the consensus was as stunning as the pattern being shown. Fool me once...

There are some features where skill is notably higher in the weekly/seasonal guidance. The no brainer stuff is mod or strong enso. You won't find many of those years that behaved far differently than expected. Outside of that it's no longer worth it to to me to spend time overanalyzing anything way out there in time. It's futile. Idgaf about qbo, sswe, or mjo or any other secondary feature. As a matter of fact seeing lots of chatter about the strat or qbo or mjo or AAM or mountain torque is typically a great indicator that we're in trouble or things arent going as planned 

The AO is the next best predictive feature other than mod/strong enso. Especially in Dec. A nasty -AO or +AO has like 80% predictive skill in our region for better or for worse. Imho- the AO is the single most important thing to focus on for the next 6 weeks. So far so good there...

MJO is a great signal when it correlates and a complete headfake when it doesnt. We've had cold and snow in all warm phases of the mjo or vice versa. From what I've seen the mjo has good predictive skill but only when something(s) else are working with it. What those "somethings" are is complicated and muddy. I'll just stick to the simple stuff like the AO and the persistant long wave pattern in the nPac this year. 

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1 minute ago, psuhoffman said:

Btw have you seen any good studies on why every so often a nino year bucks the trend of warm December?  2/3 go mild, but then there are years like 2002 and 2009.  Those years had opposite North Pacific sst patterns so there isn’t an easily identifiable cause. Both featured NAO help in December where most other ninos the NAO didn’t cooperate until later. But that isn’t very helpful in a predictive way without establishing causality.  

I feel like I did see some chatter on Twitter about that in the last few weeks, but can't recall who/what/where. You could wag low solar for the 2009, but that doesn't jive for 2002, so...  Every December has been warm lately and if the atmosphere is acting like a Nino, then going warm December is even easier.  Question is whether it's wall-to-wall torch, or just averages out AN with some cold mixed in.  Would be nice if we end November/start December on the AN side and then turn cold by mid-month when climo helps us more and more.  

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9 hours ago, C.A.P.E. said:

I don't think the PAC is going to turn hostile- this looks to be more of a relaxation. Ofc time will tell, lol.

Man, if we can avoid that Pac jet from hell, like we had last winter that would be awesome! 

 

 

 

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Even "if" you buy into this,  which based on most variables, persistence, and the cycle since 2000 which support Webb in his assumptions, then what about the timing.

December could start out warm, and I put out there that we may be ahead of the typical response for December ( warm ) and hence return to a colder period in mid December versus in early Jan.  

 

 

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5 hours ago, frd said:

 

Even "if" you buy into this,  which based on most variables, persistence, and the cycle since 2000 which support Webb in his assumptions, then what about the timing.

December could start out warm, and I put out there that we may be ahead of the typical response for December ( warm ) and hence return to a colder period in mid December versus in early Jan.  

 

 

I agree...If we are solely basing the dec pattern on projecting the MJO, then by Dec 1st we should see the colder pattern coming on LR ens.  Although, this tour of the cold phases looks very similar to the last....even down to the slower movement in 1/2.  Who knows though...forecasting the MJO past a week is iffy.

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