December 2019 Med/Long Range Disco

[CAPE]

Might be time for me to change my profile pic to the Dec 2009 one.

On second thought, I did that last year around this time..

[RDM]

6 minutes ago, Bob Chill said:

18z gefs is loaded with members showing height patterns that make me think snowstorms are possible in early Dec. Looks like an active pattern with plenty of cold near or overhead. STJ would be juiced on most of these solutions too

No kidding on the STJ.  Several of those members show it ripping from way off Baja.  No lack of moisture in many of those setups.  

[WxUSAF]

14 minutes ago, C.A.P.E. said:

Might be time for me to change my profile pic to the Dec 2009 one.

On second thought, I did that last year around this time..

That’s been on my mind a lot. We got majorly teased last year and then it all turned to total crap for 30 days. Although we did miss a KU by like 100 miles...

[BristowWx]

Once we actually see the -NAO materialize  it will go a long way to bolster confidence.  Bob said 4-5 days.  So Monday.  I can wait. 

[Bob Chill]

1 hour ago, BristowWx said:

Once we actually see the -NAO materialize  it will go a long way to bolster confidence.  Bob said 4-5 days.  So Monday.  I can wait. 

Check out the h5 loops on the 18z gfs & gefs and stare at Greenland. Starts in 4 days and never lets up through the end of the run

[nj2va]

4 minutes ago, Bob Chill said:

Check out the h5 loops on the 18z gfs & gefs and stare at Greenland. Starts in 4 days and never lets up through the end of the run

Double closed contour too lol

[cbmclean]

32 minutes ago, Bob Chill said:

Check out the h5 loops on the 18z gfs & gefs and stare at Greenland. Starts in 4 days and never lets up through the end of the run

I will accept the existence of a -NAO when it happened a week ago.

Actually, scratch that, -NAOs can exist in March - November, just not in Dec - Feb.

[Mr. Kevin]

1 hour ago, Bob Chill said:

Check out the h5 loops on the 18z gfs & gefs and stare at Greenland. Starts in 4 days and never lets up through the end of the run

Bob, from what i understand, the mjo is going into unfavorable phases for colder weather. The -pna is going to be impressive for a while, which i thought is unusual in a elniño pattern or atmosphere. What are your thoughts on this SSW event? Is this the real deal or just a mirage? 

[CAPE]

9 hours ago, BristowWx said:

Once we actually see the -NAO materialize  it will go a long way to bolster confidence.  Bob said 4-5 days.  So Monday.  I can wait. 

The question is how long it lasts. It appears to break down pretty quickly on the EPS, while the GEFS at least keeps a neutral look towards the end of the run. Signs of some improvement on the Pac side and in the EPO domain, more so on the GEFS. Could be a warmish period ahead if/when the positive heights break down in the NA, and at the same time the Pac remains less favorable. Before that(should it occur), maybe there will be a chance or 2 at something the very end of Nov into the first few days of Dec with the favorable looks.

[BristowWx]

45 minutes ago, C.A.P.E. said:

The question is how long it lasts. It appears to break down pretty quickly on the EPS, while the GEFS at least keeps a neutral look towards the end of the run. Signs of some improvement on the Pac side and in the EPO domain, more so on the GEFS. Could be a warmish period ahead if/when the positive heights break down in the NA, and at the same time the Pac remains less favorable. Before that(should it occur), maybe there will be a chance or 2 at something the very end of Nov into the first few days of Dec with the favorable looks.

I still see the closed contour high near Greenland...a touch less strong and a touch further east than the 18z money run yesterday....I assume I can use the op for this as we are close to 00z Monday 23 Nov which is the time I am looking at for my own reference...but point well taken how long does it last because with that -PNA it just serves to prevent a lava flow in the east...that's what those extreme red colors look like to me on the temp anomaly maps...molten lava

[CAPE]

42 minutes ago, BristowWx said:

I still see the closed contour high near Greenland...a touch less strong and a touch further east than the 18z money run yesterday....I assume I can use the op for this as we are close to 00z Monday 23 Nov which is the time I am looking at for my own reference...but point well taken how long does it last because with that -PNA it just serves to prevent a lava flow in the east...that's what those extreme red colors look like to me on the temp anomaly maps...molten lava

I was looking at the ensemble runs and discussing what they are depicting for the first week in Dec. I try to keep the LR discussion in this thread, because that's what it is by definition lol. December is still 10 days away, and this has been an active thread for at least 10 days now. But yeah the op runs are useful for the early next week time frame.

[frd]

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

The question is how long it lasts. It appears to break down pretty quickly on the EPS, while the GEFS at least keeps a neutral look towards the end of the run. Signs of some improvement on the Pac side and in the EPO domain, more so on the GEFS. Could be a warmish period ahead if/when the positive heights break down in the NA, and at the same time the Pac remains less favorable. Before that(should it occur), maybe there will be a chance or 2 at something the very end of Nov into the first few days of Dec with the favorable looks.

Not sure about early December. Depending on the location of the block and the set up in the Pac we may revert back to what we had last winter with cutters as one of the primary storm tracks.

After the block breaks down, if the Pac does not improve the SE ridge will grow more prominent ( High North of Hawaii )  and we will warm. I mean the NAO is transient and then we enter the warm MJO phases  Here it can last a while before moving on. So, in the end we waste the  NAO block and enter the typical December Nino warm up, only to transition to colder by the end of December or early January. 

Could be totally wrong, time will tell.  

[frd]

 

Fascinating data by HM. Need to read the replies and further answers by Anthony to appreciate it it fully. 

There is more than meets the eye just looking at the chart.  

 

 

 

 

[CAPE]

15 minutes ago, frd said:

Not sure about early December. Depending on the location of the block and the set up in the Pac we may revert back to what we had last winter with cutters as one of the primary storm tracks.

After the block breaks down, if the Pac does not improve the SE ridge will grow more prominent ( High North of Hawaii )  and we will warm. I mean the NAO is transient and then we enter the warm MJO phases  Here it can last a while before moving on. So, in the end we waste the  NAO block and enter the typical December Nino warm up, only to transition to colder by the end of December or early January. 

Could be totally wrong, time will tell.  

I am always 'cautious' when guidance advertises a NA block, for obvious reasons. Looks likely that there will be a period of blockiness at this point. Remains to be seen how long it persists. I haven't looked at the MJO forecasts for a couple days- last I looked it was forecast to move into the COD then perhaps emerge at a low amplitude, maybe in phase 1 or 2. The GEFS seems to be moving in the right direction overall in the LR on the Pac side and with heights building in the EPO region. Most recent runs of the EPS are showing some signs too.

Time will tell. We just can't know. 

[LP08]

One thing new at Weathermodels this year is the EPS 24-SNOW city by city.  I think this will be a good and easy way to show potential windows.

Pretty cool!

[showmethesnow]

I don't know about others but whenever I see this look in the PAC and West CONUS I cringe. We have been snake bitten for several years now with full latitude troughing into the SW with the PAC ridging too far off the West coast (Hawaiian ridging) to help dislodge it and force the mean trough eastward. It is a very difficult setup to overcome for our snow chances here in the east. And we have been seeing this pop up quite often in the extended forecasts for the last month or more. But this year could very well be different, in a possible very good way. What we have been seeing from the models quite often as these looks near in time is that the models either back off on the energy dropping into the trough, shift the mean trough easterly, or quickly disengage from the full latitude trough not planting it there. Or some combination of the three. In other words, what initially looks horrible in the long range actual morphs into a passable look if not in fact a good look. Not only that but what energy does drop down into the weakness in the SW has tended to cutoff allowing not only any NS energy but followup PAC energy as well to bypass this weakness and flow eastward allowing the mid-latitude trough to shift eastward as well. And it is mostly due to one feature that isn't currently seen but has tended to pop up as these periods near in time. That feature is a northern based +PNA over cutting a southern -PNA induced by the SW weakness. I have a strong suspicion that we will see this occur once again.

One other thing to note is that we are seeing a strong -NAO. Even though we are seeing this -NAO notice that it really isn't conducive for transporting cold air into the east as the NS is locked up into Canada. We might be able to get away with this in the heart of winter but not so much now. I will further elaborate about this a little later.

 

 

Now I mentioned a northern based +PNA showing up as the above looks neared in time and here is an example. I don't have the maps to go back far enough but if I recall correctly when this period of time first hit the extendeds we were seeing an even stronger looking full latitude SW trough then above with no signs of ridging into the NW. But look what is actually verifying. A strong N +PNA. What this is doing is allowing any NS energy to flow eastward as well as splitting the PAC flow creating a cutoff low in the SW. Now this look would excite me if we were just another month into the season (climo just isn't there yet)). Now some would see that ridging in the central US and dismiss the potential out of hand. But let me show you how this evolves.

 

Roughly two days later and this is what we see. We have seen energy ejected from the cutoff SW low and it is moving eastward. This is creating a split flow. Now if you look in the east notice that the ridging that was moving eastward from the central US is being beat down by the NS energy that was allowed to bypass the SW weakness and move eastward. Now move this setup a month ahead and we are looking at more agreeable climo temps as well as a farther sagging south of the NS jet which would possibly put our local into play for frozen.

 

Now for those that still can't see the potential on the above let me throw out what we are seeing at 250 mbs with the jets. We are seeing the interplay between 4 different jets where they all are converging in the east. First we have the PAC jet which is getting split by the cutoff low and northern +PNA. The northern portion is rotating around the +PNA creating a NS jet that is dropping down into the central/eastern US. The southern portion of the split PAC jet is flowing around the cutoff low where it is joining with a southern jet streaming from Hawaii (pineapple express). Now the fourth jet I have brought up the possibility of being in play this winter several times before and here we see it. What we have been seeing is an anticyclone in the upper levels of the atmosphere that has generally been rotating around the Gulf of Mexico and Mexico. This feature has been creating this secondary tropical jet to pop up quite often.  As I said, this look would excite me if it was just a little deeper into the season. As is if we see similar looks this season it could very well be a fun ride for us.

 

 

Now if the PAC and the Western CONUS doesn't cooperate we do have a possible fall back to go to. ***For the record I actually believe we are going to be seeing much better looks there as we near in time***

Now I mentioned the -NAO on the first map. Quite often a -NAO alone isn't enough to over ride a strong western trough and the first map above shows this. Typically you need to see 1 of two things in conjunction with it for our snow chances. First off strong heights in central and eastern Canada pressing down towards the US border is one such feature which will buckle the NS down into the US. One run several days ago showed this but unfortunately I could not find it to give you an example. So basically, bright reds over top of us in southern Canada is a good thing.

That brings us to the second thing, a 50/50 low and low and behold both the GEFS and the EPS are showing this in the extended. The GEFS begins rotating a lobe of the PV into the 50/50 position at day 9/10 and holds it there for an extended period of time as energy keeps rotating up and reinforcing it. Now the key here is, where does it actually place this 50/50? Below at roughly day 12 we see it locked underneath the Greenland ridging/higher heights. Now this isn't quite a prime location. It is too far north where there is very little influence on the mid-latitude flow so we are seeing a fairly flat flow as there is very little backing of that flow. This in turn is not giving any incentive for the NS to drop southward. 

 

 

But look what occurs when we see that PV stray farther southward where it can impact the mid-latitude flow (A run from a couple of days ago as an example, very similar looks are scattered throughout recent runs so this is a very viable solution). Notice that the pv has strongly pressed into the mid-latitude flow where we are seeing extreme buckling from the backing of that flow. A natural response is to see ridging develop upstream from that low as well as well as a trough behind that where the NS drops. The stronger the backing of the flow the stronger the response with the subsequent ridging and troughing. In this case we are seeing major amplification of these features. With the -EPO being advertised here as well this would probably be a significant cold shot incoming.

 

So some of you may be asking, 'So what does all this mean?'. 

IMO we are looking at the possibility of some major changes here in the east at 10+ days as well as a possibly quite stormy period as well. Now this is all contingent on the models being somewhat correct on the features I am outlining. Features that are popping up inside of 10 days on the models I might add. Doesn't mean the models are right but it does add a little more confidence. 

So in a nutshell. At this time I think odds strongly favor that we see a fairly significant cold shot into the eastern US in the extended ( beginning of Dec), a cold shot that could very well have staying power as we see shots of reinforcing cold air. Now how severe and duration will depend on several things. I am favoring we see a northern based +PNA but the question is, do we see a -EPO along with it for cross polar flow? And I would not rule that out whatsoever. We get that +PNA and -EPO and that can drive some very cold air down especially if we see the 50/50 low cooperate in buckling the flow in the east. Now as far as stormy. Right now everything I am seeing indicates we will probably have a succession of storms in the eastern US. Now as far as timing and how they may impact us it is too soon to say. Right now if I had to take a guess I would probably favor an initial storm roughly day 10/11 (I reserve the right to adjust that somewhat from what i see in future runs). Though I won't rule it out, the first storm will probably be a no-show (except the mountains) as it will be more of a stage setter then anything else as it drives in the initial cold and sets up a boundary through the general region. Once that boundary sets up I expect we will see impulses riding along that for a period of time. Depending on where we sit as far as the boundary will determine what we see. Think we then see energy eject out of the SW (think the split flow I showed above with the ejected SW cutoff) and produce a significant storm in the east dragging some very cold to potentially extreme cold in behind it. And again as far as what to expect with that possibly storm it is far to early to even hazard a guess. 

[WinterWxLuvr]

1 hour ago, LP08 said:

One thing new at Weathermodels this year is the EPS 24-SNOW city by city.  I think this will be a good and easy way to show potential windows.

Pretty cool!

I think ensemble snowfall prediction is the most useless tool out of them all.

Snowfall is dependent up systems that are not very easily predicted far in advance. 
 

Ens patterns are one thing but I’m not a believer in snowfall totals.

[LP08]

Just now, WinterWxLuvr said:

I think ensemble snowfall prediction is the most useless tool out of them all.

Snowfall is dependent up systems that are not very easily predicted far in advance. 
 

Ens patterns are one thing but I’m not a believer in snowfall totals.

I agree that the totals in and of themselves are useless, but I think in a reasonable time range (sub 180) it will be nice to see "clusters" of hits so to speak.  I think the clustering will make an easier view of potential during patterns that look promising.  Just my 0.02.

[WxUSAF]

14 minutes ago, WinterWxLuvr said:

I think ensemble snowfall prediction is the most useless tool out of them all.

Snowfall is dependent up systems that are not very easily predicted far in advance. 
 

Ens patterns are one thing but I’m not a believer in snowfall totals.

You shouldnt be. As I think @LP08 is alluding to, it’s maybe useful as a quick look on whether a period of time has potential, but that’s it. Especially as we go into winter, our “background” ensemble snow mean through D15 is like 2”. 

[dallen7908]

Wish it were this simple

My_back_yard_snow = max (ensemble mean - 2", 0")

Perhaps it's closer to this ... 

My_back_yard_snow = 0.667*ensemble_mean(d0-3) + 0.667*max(ensemble_median(d3-7)-2") + climatological_mean(d7-15) 

 

 

[WxUSAF]

8 minutes ago, dallen7908 said:

Wish it were this simple

My_back_yard_snow = max (ensemble mean - 2", 0")

Perhaps it's closer to this ... 

My_back_yard_snow = 0.667*ensemble_mean(d0-3) + 0.667*max(ensemble_median(d3-7)-2") + climatological_mean(d7-15) 

 

 

That’s probably not a terrible equation? I’d be really interested if you actually did a running comparison of that and see how it verified. 

[poolz1]

12z GFS op puts into question the storm to open up Dec being a big cutter.  Much dif h5 look...not surprisingly being a D9 op run but I think it shows how tough that time period will be for models to predict.

[Bob Chill]

Not that I think the GFS has discrete features modeled accurately d10-11 but the run is a great example on how we can still score with a -PNA. It's all about the NAO and 50/50. If the NAO is real then it could provide an extended window. 

[Bob Chill]

51 minutes ago, WxUSAF said:

You shouldnt be. As I think @LP08 is alluding to, it’s maybe useful as a quick look on whether a period of time has potential, but that’s it. Especially as we go into winter, our “background” ensemble snow mean through D15 is like 2”. 

One thing that can be very misleading about ind ens member output is the resolution is lower than the op and if you loop the members that produce, some always do it in a way that's pretty much not possible irl. 

I agree about clusters though. Get a nice group of similar solutions and outcomes and it increases confidence in the opportunity. Conversely, if there are a few giant hits embedded in an otherwise crappy run the snow mean can be very misleading. 

One thing we can all agree on is ens member snow output is massively biased to the upside and is a very unreliable way to assess our chances. 

[nj2va]

5 minutes ago, poolz1 said:

12z GFS op puts into question the storm to open up Dec being a big cutter.  Much dif h5 look...not surprisingly being a D9 op run but I think it shows how tough that time period will be for models to predict.

Certainly will change on a D9 OP but it looks like it transfers to the coast and we actually get frozen out of it.  A time window to watch for sure with the blocking and 50/50 low which saves us.

[poolz1]

2 minutes ago, nj2va said:

Certainly will change on a D9 OP but it looks like it transfers to the coast and we actually get frozen out of it.  A time window to watch for sure with the blocking and 50/50 low which saves us.

I tend to forget how a stout west based block can create havoc....Its only on paper right now but its a sight for sore eyes after the past few years.. 

[CAPE]

27 minutes ago, Bob Chill said:

Not that I think the GFS has discrete features modeled accurately d10-11 but the run is a great example on how we can still score with a -PNA. It's all about the NAO and 50/50. If the NAO is real then it could provide an extended window. 

Yeah this is pretty close to the best possible setup/evolution to score a solid frozen event with a less than favorable Pac.

[psuhoffman]

CMC has a similar idea. Forces the system under the block just slightly too far north for us. Frozen Mason Dixon north. But same idea for that range. 

[WEATHER53]

Main thing is every depiction shows strong high pressure to our north. I don’t know if those waters north of Alaska have anything to do with it. Don’t know if the status of the variety  of indexes are aligned to keep those water open and assist in high pressure being favorably set up to our north  but that looks like the general battle plan well into December.

 

[psuhoffman]

GEFS goes ape with the epo ridge in early December and floods the whole conus with cold. Enough SE ridge though to suggest the boundary would be close enough for some threats.  That kind of a pattern is when some SE ridge isn’t a bad thing. Otherwise it would just be cold and dry.