December Medium/Long Range Discussion

[poolz1]

I understand it's a LR prog but it is an ens.  If comparable neg 850 temps were forecasted over the east at that range we would consider it to be highly impressive for an ens run.  Just more evidence the PV will probably not fully recover at all this winter....the hits keep coming and this one could be the real deal.

[CAPE]

Anyone think this looks interesting? Remember what happened in SNJ a few days ago. This might be worth watching.

 

[CAPE]

5 hours ago, psuhoffman said:

Wet snow is my favorite, get it to freeze up at night and I can hold snowcover up here for a while sometimes. Dry snow sublimates and blows away. 

Yeah airy, fluffy, high ratio snow is awesome when its falling(and for immediate measurement), but it literally disappears. Thick, heavy paste can stick around for awhile, as can sleet or a snow/sleet mix.

[psuhoffman]

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

Yeah airy, fluffy, high ratio snow is awesome when its falling, but it literally disappears. Thick, heavy paste can stick around for awhile, as can sleet or a snow/sleet mix.

Yea two winters that weren't great in DC but great if you like snowcover up here we're 93 and 94. Both had a string of snow ice mix events...none were all that heavy like 3-4" each but they put down such a thick paste there was snowcover here for 8+ weeks straight in 94 and 5 weeks in 93. Pure numbers it was only about average snowfall both years but I would take a year with over a month of 6"+ snowcover anyday.  

On topic today's runs continue to show the same...there could be a fluke the week before Xmas is something tracks right but the real pattern looks to get right right around or just after Xmas. 

[CAPE]

9 minutes ago, psuhoffman said:

Yea two winters that weren't great in DC but great if you like snowcover up here we're 93 and 94. Both had a string of snow ice mix events...none were all that heavy like 3-4" each but they put down such a thick paste there was snowcover here for 8+ weeks straight in 94 and 5 weeks in 93. Pure numbers it was only about average snowfall both years but I would take a year with over a month of 6"+ snowcover anyday.  

On topic today's runs continue to show the same...there could be a fluke the week before Xmas is something tracks right but the real pattern looks to get right right around or just after Xmas. 

Yup this reflects my thoughts as well. Most likely our first legit chance will be towards New Years. I am totally fine with the prospects for the pattern becoming much more favorable as we move into Jan. December snow is awesome and all, but way more times than not, it just doesn't happen.

[Bob Chill]

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

Yup this reflects my thoughts as well. Most likely our first legit chance will be towards New Years. I am totally fine with the prospects for the pattern becoming much more favorable as we move into Jan. December snow is awesome and all, but way more times than not, it just doesn't happen.

Much will hinge on how quick the -epo can pop and how much time it takes for the first legit cold push to get here. One of the good parts of a -epo pattern is once the cold moves in the snow chances can improve immediately.

During the multiple recent -epo stretches we sometimes had snow during or shortly after the first strong frontal passage. Other times it was a carving process that took a while. Late Jan/early feb 2015 was pretty hard on the nerves but once it flipped it was game on for weeks. We wont talk about Dec last year. Lol 

The wildcard is the atl. We didn't have any help there previously and still did quite well. Both the gfs and eps look ok with the atl side. Main difference is how quickly the first real cold gets here. Gefs is fast and eps is slow. Seems like that's always the case with this kind of pattern change. Somewhere in the middle usually verifies. 

[AfewUniversesBelowNormal]

Scandinavian block November rolled forward into December is going to verify despite El Nino, impressive. 

[poolz1]

Only when it's warm....

[Bob Chill]

25 minutes ago, poolz1 said:

Only when it's warm....

At least the run has our white Christmas overrunning event setting up d16. 

[poolz1]

19 minutes ago, Bob Chill said:

At least the run has our white Christmas overrunning event setting up d16. 

It close.....You're obviously missing the little innocuous s/w up in Tuktoynukville that will tail whip it down to the Carolinas....

[Maestrobjwa]

31 minutes ago, Bob Chill said:

At least the run has our white Christmas overrunning event setting up d16. 

Ohhhh no...what's butt-ugly stain in the northeast? Not playin' that game again! (If there's even a hint of that if this comes up again at at a non-fantasy range...I'm jumpin'! Lol)

[Bob Chill]

Just now, Maestrobjwa said:

Ohhhh no...what's butt-ugly stain in the northeast? Not playin' that game again! (If there's even a hint of that if this comes up at range...I'm jumpin'! Lol)

That feature is actually what we need to keep storms from cutting and tracking west... 

If you root for a ridge or above normal heights there then all well get is rain over and over again. 

[Maestrobjwa]

10 minutes ago, Bob Chill said:

That feature is actually what we need to keep storms from cutting and tracking west... 

If you root for a ridge or above normal heights there then all well get is rain over and over again. 

Now...what exactly would it look like when if it WAS too much/more suppressive?

[CAPE]

1 hour ago, Maestrobjwa said:

Now...what exactly would it look like when if it WAS too much/more suppressive?

It would look like the current set up at 500 mb. There are degrees of everything. Differences are subtle. Too much of a "good" thing for the upcoming storm. The ideal is an upper blocking ridge over the Davis Straits with a low stuck underneath off of the Canadian maritimes- the so called 50-50 low. Keeps a trough in the east with cold draining down and a favorable storm track. Still a risk of suppression with that set up too, but it generally favors the MA.

[psuhoffman]

57 minutes ago, Maestrobjwa said:

Now...what exactly would it look like when if it WAS too much/more suppressive?

When you are missing storms by 1000 miles it's a bad pattern. When you miss by 100 miles it's usually more bad luck.  The difference between a richmond and a D.C. snow is a 100 mile change in the heights to our north. There is no way you can see that from range. Slightly too much confluence and we smoke currus. Not enough and we rain. It's a tightrope everytime!!!  There is NO pattern that guarantees snow. Just need a good pattern then need good luck on top. But stop worrying about it from range. Can't see discreet problems from long range. 

[Bob Chill]

21 minutes ago, psuhoffman said:

When you are missing storms by 1000 miles it's a bad pattern. When you miss by 100 miles it's usually more bad luck.  The difference between a richmond and a D.C. snow is a 100 mile change in the heights to our north. There is no way you can see that from range. Slightly too much confluence and we smile currus. Not enough and we rain. It's a tightrope everytime!!!  There is NO pattern that guarantees snow. Just need a good pattern then need good luck on top. But stop worrying about it from range. Can't SW discreet problems from long range. 

Well said. I'd take a repeat of this setup 100 times in a row. We'd prob get snow at least 50 times. 

It can be hard to visualize and ens mean and what it means for sensible wx in real time until you do this for awhile. This week looked really good from over 10 days out (and still does) but like you said, we missed by 100 miles. On a global scale you can spit farther than that. 

[Bob Chill]

54 minutes ago, Maestrobjwa said:

Now...what exactly would it look like when if it WAS too much/more suppressive?

The exact same with tiny differences. What would it look like if we got rain? Exact same with tiny differences. 

I highly recommend reading the KU book on east coast winter storms. It would help you immensely with wrapping your head around this stuff. 

[Bob Chill]

Bit of a model war between the eps and gefs. Both have the -epo going by the ends of their runs but euro is slower. Gefs imply cold getting here by the 24th-25th. Eps would be a few days after because it holds the trough out west longer. 

Iirc- we've seen this same model war multiple times with a developing -epo. Gefs has been better. Euro has caved to the faster progression on the gefs. Hopefully that happens again. 

[MDstorm]

3 minutes ago, Bob Chill said:

Bit of a model war between the eps and gefs. Both have the -epo going by the ends of their runs but euro is slower. Gefs imply cold getting here by the 24th-25th. Eps would be a few days after because it holds the trough out west longer. 

Iirc- we've seen this same model war multiple times with a developing -epo. Gefs has been better. Euro has caved to the faster progression on the gefs. Hopefully that happens again. 

Same thing happened last year.  Euro suite had us torching for Christmas at longer lead times, while GFS had the colder air getting here more quickly.  We all know how that turned out... Christmas was not a torch.

[nj2va]

I’m with WxUSAF that we’ll be tracking between Christmas and NY.  It’s going to get real active around here in two weeks.

[Ji]

Bit of a model war between the eps and gefs. Both have the -epo going by the ends of their runs but euro is slower. Gefs imply cold getting here by the 24th-25th. Eps would be a few days after because it holds the trough out west longer. 
Iirc- we've seen this same model war multiple times with a developing -epo. Gefs has been better. Euro has caved to the faster progression on the gefs. Hopefully that happens again. 

I remember something similar happened last Christmas eve. A war. Euro had us in the 80s at one point. Ended up being a low 40s

[CAPE]

7 hours ago, nj2va said:

I’m with WxUSAF that we’ll be tracking between Christmas and NY.  It’s going to get real active around here in two weeks.

I am in this camp too. The advertised pattern is evolving similarly on both the EPS and GEFS, with the usual noise and run to run variability in the LR. 0z EPS backed off some on the broad trough out west, while GEFS is depicting a trough in the SW at day 15. The biggest takeaway is both models are advertising an Aleutian low and a ridge developing over AK. The 0z runs are actually in good agreement heading towards Xmas- Verbatim, temps in the east would be right about average, with a trend for colder beyond that.

[WxUSAF]

GEFS supportive of the @Bob Chill overrunning setup around Xmas although 6z GEFS popped a +AO out of nowhere. 

[CAPE]

5 minutes ago, WxUSAF said:

GEFS supportive of the @Bob Chill overrunning setup around Xmas although 6z GEFS popped a +AO out of nowhere. 

Yeah the GEFS has been pretty consistent with a signal for an event leading up to Xmas. @showmethesnow has been pretty bullish on this period for a while.

[showmethesnow]

23 hours ago, showmethesnow said:

Keep an eye on the period just before Christmas into Christmas. The setup on the last few days of runs are moving in a positive direction for that period of time (talking at the end of the model runs so take it for what it is worth). Like seeing the strong height anomalies over central/eastern Canada which would tend to force systems southward and keep them from cutting. Also gives much more leeway for the trough setting up farther to the west then we prefer to see. And as far as the trough being favored in the west at this time? Guessing that may be somewhat misleading. With those higher heights in Canada that probably argues for shifting that trough eastward more to the central CONUS. What we may be seeing with that western trough may actually be the models are seeing a cut off low/southern based trough. And with the setup at that time I think it would argue that feature would be over cut and bypassed by the NS flow giving us a split flow. Short of a full blown dump of the NS into the SW we would probably be fine. 

Just by going with what the models show at this time, we are at the end of the model runs after all, I would not be surprised if what we were to see through that period of time is a SW trough/low over-cut by a +PNA with a trough setting up in the central portion of the CONUS. With the higher heights in Canada this would be a good setup for any possible system during that period of time. As far as temps for any possible system? Think they would be much more favorable then most would think because we would more then likely see cold undercutting the higher heights in that setup.

Again, just speculation from models at the end of their runs so take it for what it is worth. 

Thought I would revisit a comment from yesterday because I do believe the models are continuing in this direction. Now though I am increasingly getting interested in the Christmas time period this is not a forecast just speculation on what the models show at this time.

This is the overnight run of the EPS. What we have is energy planted in the southwest with a trough set up in the southern stream. Now to the north we see a northern based +PNA over cutting this southern -PNA/trough. This northern +PNA is forcing the northern stream to bypass the southern trough and create troughing in the central CONUS as the NS sees the higher heights in Canada. What we are seeing is a split flow. Now as far as temps. With that northern based +PNA we are also seeing a -EPO (ridging through Canada) creating an EPO/PNA ridge. This combo of a epo/pna ridge and the higher heights through the whole of Canada is a great setup at delivering cold into the CONUS and moving it eastward as it sees the higher heights in Canada. The models have been picking up on this in recent runs as they have been getting more aggressive with the cold as well as showing a quicker progression eastward of that cold.

 

 

Now below I am using yesterdays 12Z because I thought it was clearer with the players that I am discussing. Notice we are seeing the same features. -EPO/+pna ridge. SS trough in the southwest, NS trough in the central US, higher heights over Canada. This is very good agreement between the models on the general pattern heading into Christmas.

 

 

Now the above pattern is a very good pattern and ups the odds a good deal for seeing snow around Christmas time. Not saying we see snow, just that if we in fact see a semblance of this pattern then odds would be greater then a typical year. What makes this pattern special as well is it places several options on the table at once to score snow.

 

Such as a quick hitting clipper. And this is nothing more then energy embedded within the NS that drops down in the central CONUS and runs east. Snows are typically of the 1-3 inch type deal though higher amounts are possible if enough cold is in place for the higher ratio snows that we quite often see with these type systems.

 

Then we have the southern stream system. This is energy dropping under the base of the trough/energy in the southwest and running east. These systems are typically moisture laden and can provide copious amounts of snow if given a chance. The evolution of a strictly southern stream system would probably be that of a gradient snow as we have overrunning of the moisture over the colder dome of air to the north. Typically we would see a more west to east track with only marginal strengthening of the low in this pattern.

 

Below is where are bigger storms can come from. And that is when we see a phase between the NS and the SS. Now in the pattern projected the odds of a successful phase are much greater then what we would typically see because the sweet zone is expanded. Typically when we see as phase west of the Mississippi we see the low then amplify and cut to our west. But this isn't the case here. With the higher heights we are seeing extending through all of Canada this would tend to force any systems southward instead of gaining latitude. So if we were to see a phase farther to the west chances would be good that what we would end up with is a big bowling ball at 500s rolling across and we know how much fun then can be. Later phase over or to the east of the Mississippi and then we tend to see those coastal NEasters that we love with the deepening low and the winds to go with it.

 

 

Now one final one. The ejection of the SW energy/trough itself. Many of our biggest storms occur when this occurs especially when we see a phasing. I will just leave it at that.

 

 

One final comment. Both the NS and the SS have been very active so far this winter. I will leave you to do the math on that when it comes to my comments above.

[Kmlwx]

Fantastic write-up! Always enjoy reading your posts!

[showmethesnow]

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

Yeah the GEFS has been pretty consistent with a signal for an event leading up to Xmas. @showmethesnow has been pretty bullish on this period for a while.

About as bullish as one can be for the end of the extended on the models.

Like the general over all setup in the extended though and favor a semblance of that coming into play. The one thing that does me worry me a touch is if it isn't as progressive with the ridging in the west (the northern based +PNA). If it isn't, the pattern probably goes in the crapper just like that. Probably would lose a week or more just trying to reset. Don't see that +PNA and what we more then likely end up is with a full throttle dump of the NS into the SW trough popping a SE ridge from hell. But I don't favor that scenario at this time.

[gopper]

12 minutes ago, showmethesnow said:

 

Now one final one. The ejection of the SW energy/trough itself. Many of our biggest storms occur when this occurs especially when we see a phasing. I will just leave it at that.

 

 

One final comment. Both the NS and the SS have been very active so far this winter. I will leave you to do the math on that when it comes to my comments above.

showmethesnow, Thank you for your always insightful posts!  You have a natural way of explaining things in terms that the novice can understand and you show picures with your explanation that makes it even more helpful!  You also intertwine positivity with reality very well!  Keep up the great work!!

Can you explain why the operational GFS is not currently picking up on any snowy scenarios out towards Christmas?  Is this just the case of one operational run won't show the big picture and we need to focus on the ensembles at this point?

 

[CAPE]

5 minutes ago, showmethesnow said:

About as bullish as one can be for the end of the extended on the models.

Like the general over all setup in the extended though and favor a semblance of that coming into play. The one thing that does me worry me a touch is if it isn't as progressive with the ridging in the west (the northern based +PNA). If it isn't, the pattern probably goes in the crapper just like that. Probably would lose a week or more just trying to reset. Don't see that +PNA and what we more then likely end up is with a full throttle dump of the NS into the SW trough popping a SE ridge from hell. But I don't favor that scenario at this time.

Nice write-up as usual. And you got me hooked in now! lol. This certainly looks like the earliest period for something to track. Some recent GEFS runs have had members showing some frozen, enough to notably tick the snowfall mean up during that period. The EPS also has a storm in that window, but it tracks it well NW. But yeah. 15 days out.

[showmethesnow]

Just now, gopper said:

showmethesnow, Thank you for your always insightful posts!  You have a natural way of explaining things in terms that the novice can understand and you show picures with your explanation that makes it even more helpful!  You also intertwine positivity with reality very well!  Keep up the great work!!

Can you explain why the operational GFS is not currently picking up on any snowy scenarios out towards Christmas?  Is this just the case of one operational run won't show the big picture and we need to focus on the ensembles at this point?

 

I really don't focus on the ops until we get inside the day 5 at the earliest. To me after day 5 they are nothing more then a glorified ensemble member which is just showing one of many options on the table. I guess the easiest way to show this is jump onto tropical tidbits and then scroll through day 10. Quite often they are all over the place even at 500 mb. Even day 6 or 7 can see drastic run to run changes. Now on the other hand the ensembles when you scroll through them show much less variability even when you get into the extended.