NYC/PHL: December 24-27th Potential

[earthlight]

Over the past day or two (maybe three, hard to remember) many of us have watched the model guidance develop strong cyclones off the east coast near or around Christmas. It's drawn the attention of many snow lovers throughout the forums and obviously been the main topic of discussion, with good reason. A week or two ago I made a post detailing how this pattern could be best defined as a "ticking time bomb". We have several main upper air players on the field already which have been here for several days. The storm that missed out to sea yesterday and today was our first opportunity, and we couldn't cash in. That's fine, though, because that system will actually have a positive impact on the upper air pattern by the time the next system develops.

There are several main differences for people to consider being projected on the upper level pattern and height field on most models. I have seen many posters comparing the two setups; and to be honest they aren't alike in any way. I made a post where I called the H5 "Eerily similar", which was meant more in jest..because the shortwaves themselves give the same oriented look. That being said, the differences can be found in almost every aspect of the upper air pattern. I spoke earlier of how the previous storm would help us, and you can see that immediately on the height anomalies on the GFS this afternoon. The blocking heights have retrograded well to the west--but extend far enough back towards Greenland to keep the blocking pattern in place.

This is important as it allows for the mean trough to set up shop a bit further west. But it couldn't do so without the modeled ridging spike on the west coast. The actual CPC or CDC data may not reflect a +PNA, but this is easily the most supportive spike we have seen in the Western CONUS this winter. This has huge impacts on our pattern. It allows for rapid amplification to the east, and with the very strong shortwave forecast to be in place and the phase forecast to occur with the northern stream energy, things could get serious very quickly. Notice the ridge axis as well as the 70+kt mid level jet streak at the trough base still west of the Mississippi River! Several posters have posted ridge axis maps saying they are too far east--but they are being posted at the later frames. I haven't seen more than one or two model runs the past few days have a poorly positioned or too far east ridge axis when it matters..which is right when the image posted as the trough is amplifying.

Obviously, there are still many modeling differences at this time. The envelope of solutions has been "somewhat small", especially considering the past systems inconsistencies. That being said, I can't stress enough how dramatically the upper air pattern can change as we approach the event. We cannot ignore how good the models have been indicating the mean pattern..straight down to the synoptic pattern..will be. Superensemble mean height anomalies have been triggering good analogs for days now. But we can't take this for granted, because we can see modeling differences pull the rug right out of us. Let's just keep that in mind as we move forward.

After saying that, we can get into a bit more synoptic detail on what some of the models are actually showing the past few days. This is all speculation given the modeling right now, but I think as fans of meteorology and, for some, fans of snow, we can't ignore it. Some of this is really just awesome stuff--straight through the atmosphere. The scary part is that the pattern supports it..if the phase can line up correctly. We've all seen the H5 charts depicting the big phase and upper level low closing off south of Southern New England. But we can look at the 200-300mb jet streams as a testament to the dynamics in place. That's a 120kt 300mb jet streak pointed straight off the coast just outside the benchmark with an H5 capture already underway.

When you have an atmospheric dynamic situation like this, once the PVA gets up the coast along the baroclinic zone..the bomb goes off. And that's what we're seeing the models depicting. Is it right? Who knows, and probably not. But is it an awesome display of the potential of the pattern? Yes. The 700mb vertical velocities from today's 18z GFS are below. You can see the heavy deformation banding and frontogenesis in the CCB to the northwest of the deepening surface low at that time.

I don't like making predictions at this range--but I can say this. If the models were to be correct with their upper air depictions, this storm would definitely be remembered for a while. But we need several things to happen; and there are several things which need to be watched on the models the next few days. First, the shortwave needs to come east as modeled. It's currently modeled to be very strong, which is good, we haven't seen any models dampening it. In fact, see the latest WV satellite out west showing the moisture feed into our system coming ashore straight from the Central and Southwest Pacific Ocean. Second, we need the ridge in the west coast to amplify. This has been well modeled and I don't have much concern in this regard. Third, we need the northern stream to cooperate. Again, well modeled that there will be a ton of energy coming across the top of the ridge. Finally, we need the confluence and blocking to be there. This is another situation that should be "easier" to attain than usual given the current upper air setup across Canada and the North Atlantic. So let's kick this thread off the right way and enjoy the days preceding the Holidays. Wishing everybody who posts in the thread a blessed holiday and most important, lots and lots and lots of snow.

[TwcMan]

Good post man....Model madness starting soon

[Saturn510]

Excellent write-up !!! Hope the models trend towards favorable snow outcome for all of us.

[Collegestudent11]

The one thing to notice is that the QPF maybe underdone in this case. There is a sub 1000 mb low that is projected to be not that far off the benchmark, and some models runs show very light QPF. With a setup like that there is another factor to watch, lest the area be under prepared.

[ag3]

Incredible post.

[daxx]

This is a great post. Thanks

[tombo82685]

heres the comparison at h5 between 15 sref and 21z sref. The new 21z srefs seem like they are more amplified.

[tombo82685]

heres the 15z sref compared to 21z sref for mslp. The mslp also looks a bit further north. Looks liek the faster the s/w and stronger it is the further north this will be.

[jrodd321]

What a post. John is by far one of the best posters on this board. Great writeup man.

Model madness starts tonight.

[ptb127]

Merry Christmas earthlight!!

[njrealtor84]

Usually don't post, but enjoy sitting back and reading about everything. Great post to start the thread. Really puts some things in perspective and helps people realize how different this scenario really is.

[Manny]

Since last year, since I joined the other board, John has been one of the most productive, optimistic, objective, analytical, and informative posters. The write-up is excellent, and def gives much more hope that this storm has far more potential than the previous one.

[Colin]

Wonderful post. Should be fun to track, if nothing else.

[Zir0b]

good post, it should be on the main forum

[LVblizzard]

heres the 15z sref compared to 21z sref for mslp. The mslp also looks a bit further north. Looks liek the faster the s/w and stronger it is the further north this will be.

I don't see much of a difference other than a weaker low. Overall, the last 2 runs of the SREF valid 6z Friday look almost identical to me, both at H5 and the surface.

[CooL]

Great point about the ridge axis and how it amplifies the shortwave once its over the midwest and then the ridge axis shifts east, but it doesnt really matter..Lets hope we dont get alot of models going ots tonight

[greg ralls]

good post, it should be on the main forum

I agree, but I'm glad it's here to serve as a springboard to the discussions about the next few model runs. Couldn't ask for a better 1st post in a thread!

[SteveB]

Probably the best post since this board came around. Excellent stuff earthlight!

[tombo82685]

I don't see much of a difference other than a weaker low. Overall, the last 2 runs of the SREF valid 6z Friday look almost identical to me, both at H5 and the surface.

i thought the blue is the sref mean with the low pressure? The darker the blue the more consensus.

[LVblizzard]

i thought the blue is the sref mean with the low pressure? The darker the blue the more consensus.

The blue is the spread in the SREF members. There's a thread explaining that somewhere in the main forum.

[ace0927]

unfortunately Tom, I have to disagree....

heres the comparison at h5 between 15 sref and 21z sref. The new 21z srefs seem like they are more amplified.

[tombo82685]

The blue is the spread in the SREF members. There's a thread explaining that somewhere in the main forum.

yea thats what i thought it was, the darker the color the more consensus of the low pressure being in that region. Even if its not further north, it didn't move south nor does it look less amplified with the h5 maps.

edit: yea, i see it, the more i look at it does look a little less amplified.

[earthlight]

Thanks for all the comments dudes. I appreciate every one of them. I'm still learning too so we're in this together.

Anyway, the NAM looks a good bit more amplified through 51 hours. The shortwave on the CA coast is closed off--the Euro has been doing that for two runs.

[tornadojay]

Excellent write-up John. 2 thumbs up!!

[hazwoper]

s/w in the S CA appears to be "bowling" a bit more (stronger) and in turn is helping to pump the ridge out ahead of it a tad more than 18Z

[tombo82685]

s/w in the S CA appears to be "bowling" a bit more (stronger) and in turn is helping to pump the ridge out ahead of it a tad more than 18Z

yea deff agree, the s/w is a little further north, but yes the ridge is bigger out ahead of this.

[Jefflaw77]

Thanks for all the comments dudes. I appreciate every one of them. I'm still learning too so we're in this together.

Anyway, the NAM looks a good bit more amplified through 51 hours. The shortwave on the CA coast is closed off--the Euro has been doing that for two runs.

I know that everyone has commented already on your post, but seriously, your writing skills are seriously second to none.. Your analysis is thorough as hell and extremely helpful to all of us novices..

In any event, seriously- what are your credentials?? Are you a pro meterologist? How old are you? etc etc.. Seriously, you don't have to tell me or reveal any of this, but again, I can't think of anyone who writes and/or explains weather patterns like you on this forum or anywhere else for that matter.

Jeff

[tombo82685]

closed low on the nam at hr 63, which 18z didn't have. good trends so far.

[hazwoper]

this thing is going south. look at that confluence off the eastern seaboard. that is a big change since 18Z

[tornadojay]

well, the NAM just wrapped up at hour 84. The shortwave is located in central kansas to oklahoma. The heights were definitely building out west in the last couple of frames.