December 2019 Med/Long Range Disco

[CAPE]

1 minute ago, WinterWxLuvr said:

Yeah but the reality is that most of March is a winter month. More so most years than early December. So I would actually think our winter lined up more with the solstice to equinox than to the calendar.

Yeah for our general region that has been the case lately. Overall though, it seems pretty logical.

This makes the most sense for us:

Jan-Feb-March = Winter

April = Spring

May-June-July-August-September = Summer

October-November-Dec = Fall

[CAPE]

4 minutes ago, pasnownut said:

if one looks a the 500's wrt Op and Ens....they are notably different.  Ens looks just fine for now, and for whatever one believes in LR guidance, I'll roll with the ENS (also because I like that look much more.)

 

Its pretty clear now that whatever NA blocking does develop, it will break down around the Dec 5th time-frame. So it makes some sense we will get our 12/5 snowstorm. After that the EPO will bring the big cold and hopefully a clipper type pattern, as anything amped will likely cut if the NAO goes positive as advertised.

[CAPE]

Yeah we lose the NA ridging, but this is an intriguing look. As Bob said, its a pattern that can be frustrating with cold shots tending to be more fleeting, and I would like this pattern a lot  more in mid Jan than mid Dec, but I am not going to be picky given what we usually see in Dec. I like the idea of having a piece of the TPV in that location with the big EPO ridge.

[frd]

Seems the difference between the GFS and the GEFS strat forecasts have narrowed recently.  Looking at the various models  nothing seems to indicate a SSW is imminent. 

As some experts have mentioned having a SSW so early is very rare. Having one might also disrupt any current HL blocking in place. 

A lot of chatter recently on various other weather boards regarding the evolution of the troposphere and the stratosphere as we move through December.

The recent and medium term attacks on the vortex, according to some strat experts, is expected to decline.  Some are referencing momentum ( AAM, GLAMM , etc. ) and that is a  very complex subject. 

What appears to be evident is the early state of the vortex which was interim strong for the date a while ago, has weakened.  It is expected to continue to be perturbed. Some of the precursors that lead to the weakening and the drop in zonal winds are forecasted not to be as robust as they were a month ago. 

There again are two schools of thought on this mater.

One that states the vortex will keep getting attacked in December and the other which states they expect the vortex to get stronger  as we loose all HL blocking. Hence, the implications for this on the January forecast, as there is a significant lag effect in a warming, not so much in a simple displacement or favorable elongation.

Isotherm goes for the breaking down of blocking with his winter best window later in the season. while HM seems more optimistic. There is seems to be a battle going on behind the scenes as to what techniques and science will yield a correct forecast this year.  

I follow about 12 strat experts  whom specialize in this area.  Currently this is the most disagreement  I have come across in several years. There is no consensus out there and maybe that is a good thing.  Also, keep in mind, when there was almost 100 % consensus the outcomes were still incorrect last year. 

According to these strat pros the science behind the evolution in  the troposphere and the stratosphere will guide the weather models.  These guys I believe using modeling in predicting the long term weather to a degree,  but rely mostly on  a host of other data, such as drivers and the evolution of the HL to derive what they think will drive the long range models. Some do not even look at weather models, a fascinating topic that continues to evolve.   

 

 

  

 

 

[showmethesnow]

Interesting the changes we see just after 3 days of runs within the medium range and the repercussions they have further down the line. Below we have a GEFS run from just 3 days ago (day 8). Note that we are seeing the PAC heights occurring off the Aleutians with a +EPO over Alaska. -NAO is present as well as the troughing/weakness in the SW which looks to be mainstay as we have seen over the last few years. We also have ridging running up the East coast in response to this SW troughing. 

***Note: with the one feature I am keying on (the PAC heights), prior runs were also showing these heights in the north central Pacific so this one run is not an aberration.***

And this is the temp profile running through the CONUS in response to the above. Nothing earth shattering. Cold anomalies embedded within the SW trough, warm with the ridging in the East. Also see warm anomalies with the increased heights south of the Aleutians as well as cold associated with the +EPO.

 

Now look at the differences we see at 500's on the models just 3 days later (day 5). The PAC heights are now located running up into Alaska as we see the initial development of a -EPO. In response we are seeing the beginnings of a major dump into the SW. We are also not seeing any response with ridging in the east as of yet as we are still early in the process. A stronger version of the -NAO is present and will come into play later.

And below we have the response in temps. Notice instead of pedestrian cold in the west from prior we are now seeing a fairly significant cold shot moving down. With the developing EPO we are seeing warmth flow into Alaska as well as a typical signature of a neg NAO with warmth situated over Greenland.

 

Now lets move 2 days (day 7) later from the current run above. A negative EPO has been established and with that flow around the EPO dumping directly into the southwest we are seeing a strong, deep south pushing trough/closed low being established. In response we are seeing very strong ridging popping up in the east. This look alone would have me shutting off my computer for at least the next week as I lie whimpering in my bed. But we have a savior and that is coming from the N Atlantic with a NAO/50/50 combo as it is pushing back against the ridging in the east and will be a key player in forcing the NS southward later on. Now what we will see occur further in the evolution of the pattern depends on both these features existing and being established for a period of time. No 50/50 and that ridging probably pops all the way into the NAO domain which is the last thing we want to see. No -NAO and we don't see the 50/50 get trapped underneath for a period of time. In other words, without a long duration NAO/50/50 combo what we see occurring in the west would quickly degenerate into a horrible look for our chances for the foreseeable future as the western cold would get shunted northward into Canada long before we could even sniff it.

 

 

Below we have the temps for the above time frame. We have some fairly significant cold into the SW and we see warmth surging northward in the east. Now if you note the cold anomalies in the central/western portion of Canada these are indicative of the push back to the east coast ridging we are seeing from the nao/50/50.

 

 

Now at day 11 we are seeing this. The NAO and 50/50 have done their magic. They have shifted the NS and accompanying upper latitude trough eastward and southward into the Midwest. This setup is now allowing the western cold to migrate eastward instead of withdrawing northward in the central US which would be the typical response we would see on the initial cold dump being so far westward and south. Of course we are once again seeing the SW weakness (get used to it, I think that feature will be a common one once again). But note at this time we are now losing both the -NAO as well as the 50/50. Now this may or may not be a problem. Now the NS/upper latitude troughing may get established and stay in place in the east. Then again maybe not. Over the last few years there has been an inclination for that feature to migrate back westward when there was no forcing in place to keep it in the east. Thus we would see a reload of a dump into the west (wash/rinse/repeat). But there may be indications that something else may come into play keeping that feature in the east regardless. If you note the pv lobing out into north/central Canada. Think that is a precursor of the 500mb pv migrating unto our side of the globe. This could possibly be the forcing mechanism we are looking for.

 

Below we have the temps for day 11 above. Note that we are seeing a migration of the some fairly significant cold eastward into our region instead of northward into Canada. And we can thank the NAO/50/50. Now though the cold is fairly significant at this time I would not be surprised if we see even deeper departures as this period of time nears.

 

Now finally we have day 16. Note that we still have the -EPO with a +PNA thrown in. Of course the SW weakness is there. But notice that we do in fact see the pv rotating onto our side of the globe with a fairly deep southward push. In response we are also seeing the upper-latitude trough/NS stay planted in the east.

 

And we can see temps at this point are CONUS wide. Again, I think we would probably see stronger departures if the GEFS is somewhat accurate with the 500's.

 

Just a quick comment on what we see occur with the pv. The pv at this time is currently sitting on the other side of the globe. What initiates it's migration across the pole is probably mostly due to the strong and long duration EPO that we see develop at day 5. At day 16 we still see it and it extends it beyond the pole. This is providing the forcing on the pv to move.

I know I went over many of these things on my previous post but I think it is kind of important we keep an eye on the next week or two as I think what we see in regards to the models and what actually verifies will be a good indication of what to expect this winter excepting a major pattern change. We will more then likely see the same tendencies and bias within the models over the course of the winter and should also get a good idea how these different features will interact when it comes to real life weather and not model land.

One last thing. Much of what I have posted above is in regards to what the GEFS is showing us and not so much predictions on my part especially later in the run. At this time I am very confident we do see a major cold snap drive deep into the SW. I am almost as confident we see that push eastward eventually reaching our region with at least a fairly significant initial cold shot  instead of retreating northward into Canada. Questions arise quite quickly afterwards though as we lose both the NAO and 50/50 and their forcings on the NS (If in fact we lose them). Assuming the -EPO is a feature we will see for the duration (we lose the epo in the longer ranges and all bets are off) the major question then becomes where does the NS dip southward? It stays in the east whether from forcings or on its own then we are most likely looking at a long cold spell well beyond the end of the extended (well below temps first half of winter). If that migrates back westward then there is a good chance we are looking at a major warm up after a brief cold interlude as the EPO once again dumps deep into the SW before something forces the NS easterly again. So basically, anything beyond day 11 I am looking at with quite a bit of skepticism. Could be a matter of one run to another where we go from heavy winter gear to pulling out the shorts.

 

****Ignore this pic below. It won't let me get rid of it.********

[Bob Chill]

9 hours ago, Mr. Kevin said:

Bob, do you think we have a ways to go since the -pna looks to last for a while? Troughing on west coast isnt what you want to see imo for sustained cold. I guess the main reason for the -pna is perhaps the unfavorable mjo?

Taking current d10+ ens guidance verbatim, looks like we play with some fire. Epo ridge is a bit too west and there's no coupled +pna so that implies some very cold air dumps right down into the rockies before bleeding east. There will be a battleground between airmasses. 

It's entirely possible the mjo is influencing the pna. Could be any # of things really. -PNA periods in late fall are as normal as the redskins having losing seasons.

[WxUSAF]

EPO driven patterns can work for us as we know, but storms are hard to predict and appear at short notice. I’m not sold on the NAO going poof 7-10 days after it arrives. Overnight Eps keeps a bit of it going all the way until 360hrs. GEFS seems good at sniffing out changes in the long range, but typically rushes things. 

Either way, seems like we’ll have an active pattern with the STJ looking very Nino like and plenty of cold around with the EPO and NAO. That’s a good recipe any time and especially in early December when we need some help. Climo snowfall the first two weeks of December is pretty low, but for now, odds seem better than  climo. I still like the 3rd-8th period or so,  but remember that we often do better towards the end of a good pattern, not the beginning. FWIW, I’m not sure I’ve ever seen HM honk like this. Well at least not for awhile.

[Ralph Wiggum]

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

Its pretty clear now that whatever NA blocking does develop, it will break down around the Dec 5th time-frame. So it makes some sense we will get our 12/5 snowstorm. After that the EPO will bring the big cold and hopefully a clipper type pattern, as anything amped will likely cut if the NAO goes positive as advertised.

How r u that confident the NA fizzles Dec 5 when we dont know where we are headed 180 hours out? Could go either way. I guess if u look at the 384 ens and weeklies there is support for what you are saying and heck it may be accurate. But that is conjecture at this point....we've seen this LR thing do a 180 as recently as the NAO development which wasn't even supposed to occur just 240 hours ago.

[Ralph Wiggum]

Speaking out loud here but watch....we finally get a pattern that may feature NAO blocking and a neg AO periodically and a SSWE comes along and could muck it up. You know how the saying goes, careful what we wish for. I dont see any red flags tbh nor do I see any victory parades being scheduled. Steady as she goes for now. But how we emerge from T-Giving week as our transition and press into Dec is going to be telling imho.

[frd]

19 minutes ago, Ralph Wiggum said:

Speaking out loud here but watch....we finally get a pattern that may feature NAO blocking and a neg AO periodically and a SSWE comes along and could muck it up. You know how the saying goes, careful what we wish for. I dont see any red flags tbh nor do I see any victory parades being scheduled. Steady as she goes for now. But how we emerge from T-Giving week as our transition and press into Dec is going to be telling imho.

 

What is your opinion of the AO trends?  A divergence here. 

Latest is even more so. Can not get that one to post.   

 

[mappy]

friendly reminder, this is a thread that will be strictly moderated. see the guidelines thread if you need a reminder.  

[pasnownut]

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

Its pretty clear now that whatever NA blocking does develop, it will break down around the Dec 5th time-frame. So it makes some sense we will get our 12/5 snowstorm. After that the EPO will bring the big cold and hopefully a clipper type pattern, as anything amped will likely cut if the NAO goes positive as advertised.

NAO/EPO/AO....whatever it takes to get us snow.  Gotta say that the 6z GEFS surely depicts the EPO on roids.  Cross polar flow is a term that might need dusted off if that comes to light.  

[poolz1]

As others have noted...the first 15 days of Dec '13 look pretty much identical to what is being advertised on the gefs in the LR.  There is one exception IMO...of course this idea is all dependent on the GEFS being correct in LR. 

As Dec 13 rolled forward the WAR became a big player in our weather. Currently the GEFS does not have much of a WAR and what pos height it does have is more of a muted SE ridge that extends southward from Bermuda to the eastern Gulf.  I would think this should provide more energy/juice with it's return flow and thus aiding the STJ and what would normally be relatively moisture starved systems and enhancing overrunning situations.  Nothing to block the flow and create slow moving KUs but maybe something more than just quick hitting moisture starved systems we are used to with EPO driven patterns.

So many ways for this pattern to morph as we move forward into the first half of Dec but, imo there are more options for a positive outcome than options for a shutout pattern to develop.

 

[CAPE]

1 hour ago, Ralph Wiggum said:

How r u that confident the NA fizzles Dec 5 when we dont know where we are headed 180 hours out? Could go either way. I guess if u look at the 384 ens and weeklies there is support for what you are saying and heck it may be accurate. But that is conjecture at this point....we've seen this LR thing do a 180 as recently as the NAO development which wasn't even supposed to occur just 240 hours ago.

Can never be totally confident in anything, but I will give you a few reasons.

The ensembles have been strongly hinting at the breakdown, and now we see it across ens guidance for several runs now. NA blocks have rarely come to fruition as advertised during winter in recent years. Even though they are lower skill and tend to be discounted(unless they show a "good" pattern), cannot completely dismiss that the seasonal/climate models have pretty unanimously been depicting HL -heights for December.

[cbmclean]

Just now, pasnownut said:

NAO/EPO/AO....whatever it takes to get us snow.  Gotta say that the 6z GEFS surely depicts the EPO on roids.  Cross polar flow is a term that might need dusted off if that comes to light.  

Shouldn't have too much dust on it.  Didn't we just have a nice cross-polar episode a few weeks a when we had our big cold shot?

[WxUSAF]

1 minute ago, cbmclean said:

Shouldn't have too much dust on it.  Didn't we just have a nice cross-polar episode a few weeks a when we had our big cold shot?

Yes, also EPO driven.

[pasnownut]

4 minutes ago, poolz1 said:

As others have noted...the first 15 days of Dec '13 look pretty much identical to what is being advertised on the gefs in the LR.  There is one exception IMO...of course this idea is all dependent on the GEFS being correct in LR. 

As Dec 13 rolled forward the WAR became a big player in our weather. Currently the GEFS does not have much of a WAR and what pos height it does have is more of a muted SE ridge that extends southward from Bermuda to the eastern Gulf.  I would think this should provide more energy/juice with it's return flow and thus aiding the STJ and what would normally be relatively moisture starved systems and enhancing overrunning situations.  Nothing to block the flow and create slow moving KUs but maybe something more than just quick hitting moisture starved systems we are used to with EPO driven patterns.

So many ways for this pattern to morph as we move forward into the first half of Dec but, imo there are more options for a positive outcome than options for a shutout pattern to develop.

 

I'd take the muted WAR option and hope for bowling balls/clippers....UNLESS Bob's NAO theory is right and we can keep that in the neg phase.  Then i'd take some ridging in the Atlantic to help turn anything that rides the boundary up our way.  

[frd]

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

Can never be totally confident in anything, but I will give you a few reasons.

The ensembles have been strongly hinting at the breakdown, and now we see it across ens guidance for several runs now. NA blocks have rarely come to fruition as advertised during winter in recent years. Even though they are lower skill and tend to be discounted(unless they show a "good" pattern), cannot completely dismiss that the seasonal/climate models have pretty unanimously been depicting a +NAO for December.

 

Love this post by Anthony .  Had to bring it here because it explains his thought process on the - NAO in regards to someone stating it was North Atlantic ridging but

not a - NAO. 

The image is from the GFS for November 30, 2019. Of course things are evolving past this to the dates HM mentions below. 

 

From HM : 

Be careful here. This retrograding RW will induce upstream cyclonic wave breaking with time. The ridge between each and above each will change forms frequently, day-to-day, but the process is still a form of -NAO or blocking. The RW will arrive here 12/3-12/6. Each run will change how each low breaks and how each wave interacts with each other. Don't go too crazy here with defining what style the NAO is at a particular time. Just watch the full process and avoid the noise. 

 

In regards to  this :

 

 

 

 

 

 

[Ralph Wiggum]

42 minutes ago, frd said:

 

What is your opinion of the AO trends?  A divergence here. 

Latest is even more so. Can not get that one to post.   

 

Trends have been good, no doubt. Going neutral and neg as we move farther along in fall is never bad. It does have to level off at some point, can only go so low and remain there so long. I think that the EPO is sort of a reflection of that balance. I can see a pattern where the EPO ridge develops and propogates East with bridging to the NAO while the AO fluxes states between + and - thru the winter. I had HL blocking as a key player in my outlook and think that holds. Just need to see what form it takes and how it morphs in between phases.

[showmethesnow]

2 hours ago, Ralph Wiggum said:

How r u that confident the NA fizzles Dec 5 when we dont know where we are headed 180 hours out? Could go either way. I guess if u look at the 384 ens and weeklies there is support for what you are saying and heck it may be accurate. But that is conjecture at this point....we've seen this LR thing do a 180 as recently as the NAO development which wasn't even supposed to occur just 240 hours ago.

 

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

Can never be totally confident in anything, but I will give you a few reasons.

The ensembles have been strongly hinting at the breakdown, and now we see it across ens guidance for several runs now. NA blocks have rarely come to fruition as advertised during winter in recent years. Even though they are lower skill and tend to be discounted(unless they show a "good" pattern), cannot completely dismiss that the seasonal/climate models have pretty unanimously been depicting HL -heights for December.

If the models (in particular the GEFS which I have looked at closely the last 2 days) is correct with its depiction of the EPO on steroids (strength and extending beyond the pole) through the period and beyond it makes a strong argument that we do see the NAO disappear sometime in the extended. Quite often we will see the pv or a portion forced onto our side of the globe typically getting slotted near or even into the NAO domain and in fact this is what we see with the GEFS. That said, I am not totally sold on seeing that occur (losing the NAO). The models have been under playing or even showing it as non-existent quite often this this short season so far and it would not surprise me whatsoever if this is the case here. Assuming for the moment that the GEFS is somewhat right in regards to the EPO and subsequent pv migration our way,  putting a -NAO into the equation adds some interesting possibilities. With a -NAO in place we would probably see the pv forced much farther south into mid or even southern Canada. This EPO and deep dropping pv combo would mean we would see a severe cold outbreak into the central and/or eastern US depending on exactly where it drops. Also I wouldn't even rule out the possibility that the pv itself or an extension of it gets planted into the 50/50 region. Needless to say good things can happen if that were the case. But all of this is pure speculation at this point as I see no indications as of yet that we will in fact have a -NAO at that time.

[Chris78]

Quite a cold dump into the east the first week of December.

[CAPE]

9 minutes ago, showmethesnow said:

 

If the models (in particular the GEFS which I have looked at closely the last 2 days) is correct with its depiction of the EPO on steroids (strength and extending beyond the pole) through the period and beyond it makes a strong argument that we do see the NAO disappear sometime in the extended. Quite often we will see the pv or a portion forced onto our side of the globe typically getting slotted near or even into the NAO domain and in fact this is what we see with the GEFS. That said, I am not totally sold on seeing that occur (losing the NAO). The models have been under playing or even showing it as non-existent quite often this this short season so far and it would not surprise me whatsoever if this is the case here. Assuming for the moment that the GEFS is somewhat right in regards to the EPO and subsequent pv migration our way,  putting a -NAO into the equation adds some interesting possibilities. With a -NAO in place we would probably see the pv forced much farther south into mid or even southern Canada. This EPO and deep dropping pv combo would mean we would see a severe cold outbreak into the central and/or eastern US depending on exactly where it drops. Also I wouldn't even rule out the possibility that the pv itself or an extension of it gets planted into the 50/50 region. Needless to say good things can happen if that were the case. But all of this is pure speculation at this point as I see no indications as of yet that we will in fact have a -NAO at that time.

Yeah its certainly possible we see some ridging hold on in the NAO space as the PNA/EPO ridge builds. That would potentially provide the anomalous cold we need in early Dec but also keep enough of a suppression mechanism in place to maybe allow a stronger shortwave to track underneath.

[midatlanticweather]

I can see clearly that there is nothing clear in the long range. I think we need to continue to focus on the upper patterns because that will dictate what we see at the surface. CALL ME CAPTAIN OBVIOUS! I just am stating, it will not be a clean transition so our daily rundown is likely to stir different outcomes.. but the -EPO seems pretty likely! That -NAO is key and I just want to see it hold.. If we get lucky like 2013, we will get small overrunners.. just hope we get the right side of the front and that it stays close enough to matter. As mentioned the WAR was SO important. But, I do think we had a few true storms that year, including a few larger systems. Not sure if it was due to a -NAO, phasing, or just transient 50/50.. The cold has to be available to tap though, no matter what, and I think we see that is possible... then the individual players will start to show. Somewhere in the thread Bob mentioned short leads to little events.. so I am just looking for the "ducks" to be on the pond and hope we end favorable.   

[midatlanticweather]

11 minutes ago, Chris78 said:

Quite a cold dump into the east the first week of December.

 

Roll that a day or two further and you see a transient cold! We have to see how it shakes out. Stuff in the long-range are always difficult

[WxUSAF]

26 minutes ago, Chris78 said:

Quite a cold dump into the east the first week of December.

Barney Claus comes to visit! I’m banking on the GFS long range cold bias here. That’s just cold and dry and then it lifts out for a cutter. A more modest EPO flex coupled with a 50-50 low could keep the storm track under us with sufficient cold air. Looks like GGEM is going that route.

[Chris78]

46 minutes ago, WxUSAF said:

Barney Claus comes to visit! I’m banking on the GFS long range cold bias here. That’s just cold and dry and then it lifts out for a cutter. A more modest EPO flex coupled with a 50-50 low could keep the storm track under us with sufficient cold air. Looks like GGEM is going that route.

Yep. We've seen this before. Cold/dry ,warm/wet.

[Bob Chill]

GEFS continues to look very cold during the first week of Dec. -EPO driven patterns are volatile with temps so the smoothed mean can be deceiving in that it shows cold to very cold temps for the first 7 days of Dec. If the GEFS is right in transitioning to a -EPO driven progressive pattern the ground truth will be a series of fronts and big temp swings and not 7-10 straight days of cold weather. 

While the pattern isn't perfect or one that makes me think easy snow, the fact that Dec looks to start off with some sig cold shots is very encouraging. Haven't had a Dec kick off with legit cold around since 2013.  

[CAPE]

5 minutes ago, Bob Chill said:

GEFS continues to look very cold during the first week of Dec. -EPO driven patterns are volatile with temps so the smoothed mean can be deceiving in that it shows cold to very cold temps for the first 7 days of Dec. If the GEFS is right in transitioning to a -EPO driven progressive pattern the ground truth will be a series of fronts and big temp swings and not 7-10 straight days of cold weather. 

While the pattern isn't perfect or one that makes me think easy snow, the fact that Dec looks to start off with some sig cold shots is very encouraging. Haven't had a Dec kick off with legit cold around since 2013.  

It's a pattern with fleeting cold shots and challenges of timing a disturbance with a fresh batch of cold. A pattern i will gladly roll with given most of the alternatives, but also one I think has a much higher success rate in mid to late winter than early December. Hopefully it becomes a clipper-fest, rather than a cutter-fest. 

[psuhoffman]

Since we are getting to the time when we can start legit tracking, and specific patterns matter for our snow chances thought I would post this.  This first image is the composite of our 5 biggest snowfalls region wide in the last 50 years.  All of these featured a nearly identical setup and this is the money h5 look if we want an HECS

What sticks out here is the NAO blocking as well as a perfectly aligned PNA ridge in the mountain west and the presence of the lower heights to our northeast indicating the 50/50 feature.  That trifecta is the best look for a snowstorm here.

But most of our snowstorms aren't an HECS and we often have to work with a "flawed" pattern.  I see lots of posts worrying about one feature or another and what phase it needs to be and often its not that simple.  Take, for example, the EPO in that image above.  Without the NAO that pacific look would be atrocious and would flood the CONUS with pac puke air.  But with the combo of the NAO/PNA it works.   There are a lot of moving parts that play off each other.  Changing one impacts what we need from another.  It's like a big balancing act to get the general longwave pattern to line up in a way favorable for us.  

So if the guidance is correct and we head towards a -EPO, -PNA, +NAO pattern what would that look like?  First of all we need the EPO to be centered far enough east that the ridge builds over the top of the PNA trough into northwest Canada.  This look from last February did not work because the EPO was centered too far west to suppress the height patterns over the east and prevent the SE ridge from going ape.

Look where the pacific ridge is centered, south of Alaska and north of Hawaii.  Way too far west to do us any good.  There was some ridging over the top but not enough to offset that problem.  We needed either a further east EPO ridge or more blocking.  It was frustratingly close to good, and we did get some snow during that period, but in the end it was mostly a let down.

But we have had snow in a -EPO, -PNA, +NAO period before.  This is a composite of several decent winter events across our area from such a pattern.  I also only used years that had some similarities to this one and were in my analog set for one reason or another.  The composites are centered around the snowfall events of Dec 5 2002, Feb 6 2003, Feb 26 2003, Dec 8 2013, Dec 10 2013, and Mar 5 2015.

You can see the difference in where that EPO ridge is centered compared to last year.  All of these systems had some commonality.  They were all progressive waves.  That doesn't mean a decent snowfall isn't possible.  Some of those dropped as much as 8" in parts of the area, but it is not an HECS or even MECS pattern.  Anything that is too amplified is very likely to cut.  It is a big storm pattern for the Lakes and New England as a wave that amplifies would be perfect for them in this setup.  For us we want a progressive pattern and ideally get something slightly amplified with some 50/50 help to get a moderate event out of it.  But it is far from ideal and there are many examples of a -EPO pattern that is just cold and dry and it warms up before any organized system comes along.  But it is not a shutout pattern and we have had snow from this look, and these were examples of somewhat similar years where that happened to some part of our region.  

We can all look at the guidance and decide which pattern this coming one seems more similar too but of course proceed with caution as the guidance is likely to adjust some with the look at day 10-15...but for the record this is the current advertised look on the GEFS for early December.  

I do like where the EPO ridge is centered there and where the trough axis is across the CONUS.  But...that doesn't guaruntee anything.  It just means that IF the guidance is correct that would be a pattern that could produce something if we get lucky.  But there are a lot of if's in that statement.  But if these looks are close, perhaps our first legit threat window for frozen is close at hand.  Happy tracking!!!

 

 

[psuhoffman]

1 hour ago, Bob Chill said:

GEFS continues to look very cold during the first week of Dec. -EPO driven patterns are volatile with temps so the smoothed mean can be deceiving in that it shows cold to very cold temps for the first 7 days of Dec. If the GEFS is right in transitioning to a -EPO driven progressive pattern the ground truth will be a series of fronts and big temp swings and not 7-10 straight days of cold weather. 

While the pattern isn't perfect or one that makes me think easy snow, the fact that Dec looks to start off with some sig cold shots is very encouraging. Haven't had a Dec kick off with legit cold around since 2013.  

The CFS has been shifting to a colder look lately.  The weeklies already shifted the god awfull look to only a couple weeks before its building a decent look up top again towards January.  The whole run after week 3 is ambiguous and useless garbage actually but the idea of a wall to wall suckfest seems to be evaporating on the long range guidance.