December 18-20 Potential Talking Points

[earthlight]

Awesome image, I was hoping you would post it. I have access to similar maps at SV and would post a zoomed in version, but the quality is just awful. And at the file name.

[RowanBrandon]

CoastalWX, what does that image mean?

[Zir0b]

I actually disagree with this. Yes it is physically possible for this to be a coastal runner but the pattern doesn't support it...pattern supports pretty much what the 18z GFS showed with a track that is good for I-95 and EAST or further suppressed, not further NW. Just like the pattern didn't support the last storm as anything but an apps runner/lakes storm this has the same kinda deal assocaited with it just shifted south and east

Which is why I said it's a POSSIBILITY, although probably small... don't forget what happened to New England on 2/25-26. A huge block like we're going to have could cause the low to get captured and hook inland...someone is going to get screwed.

[CoastalWx]

CoastalWX, what does that image mean?

It's the avg vertical velocity and RH through the 850-500 mb layer. Basically, you want the yellows, oranges and reds within the shaded areas. The colors represent lift in that layer. The shaded areas are RH. If you have good vv's within an area of high RH, then that may indicate good snow banding/snow growth. It's a good tool to indicate dryslots. Even an area of 75% RH can indicate a dryslot, which is why this product is a good cross check to model qpf.

[RowanBrandon]

Thank you, sir. I appreciate it.

[Kaner587]

Which is why I said it's a POSSIBILITY, although probably small... don't forget what happened to New England on 2/25-26. A huge block like we're going to have could cause the low to get captured and hook inland...someone is going to get screwed.

true...pattern is different then 2/25-2/26 though, but I would welcome a storm like that any day. Either way you make a good point but with all the guidance south and east minus the Ukie I think its safe to say this time around we have to worry less (not no worry just less) about a track too close.

[IsentropicLift]

It's funny how after the 12z gfs alot of people were ready to dismiss this storm as a miss and then optimism grew with the rest of the 12z package and then once again the 18z gfs is back on board. We should all remember this the next time one model run trends bad and everyone wants to commit weenie suicide.

[CooL]

wow the gfs really amps this thing up and digs that PV south almost to the lakes, i can only imagine if the storm phases alittle earlier and closes off south of New England ...Everyone go eat dinner, watch the game, and get ready for the 00z's

[SnoSki14]

We're in slightly closer range, the storm begins showing up by end of Day 4 and into Day 5. I would like to see some run to run consistency though for the next few runs, not like last night's 0z gfs run and today's 12z run. If the next 4 runs show a similar outcome than that's probably what we'll see. The gfs might be a tad east with the low, it looks like a SECS rather than a MECS, at least from about the city and points N and W. However at the same time, there would very little worry for mixing (except from the immediate coast) would this run as the 850s and surface are completely below freezing several miles east.

Overall I think it's a great one, hopefully it either stays the same or gets even better from here.

[Dsnowx53]

The differences between 12 and 18z are very apparent at 90 hours. The blocking is a bit better defined and stronger on the 18z GFS, which forces more energy to go westward from our vortex before diving SE and merging with our southern stream wave...this allows for much better timing between the two features, while also helping to amplify the downstream flow more.

This pattern isn't as delicate as a lot of people make this out to be...strong blocking can FORCE this kind of thing to happen; it's not like we're threading the needle in an otherwise bad pattern.

[Kaner587]

The differences between 12 and 18z are very apparent at 90 hours. The blocking is a bit better defined and stronger on the 18z GFS, which forces more energy to go westward from our vortex before diving SE and merging with our southern stream wave...this allows for much better timing between the two features.

This pattern isn't as delicate as a lot of people make this out to be...strong blocking can FORCE this kind of thing to happen; it's not like we're threading the needle in an otherwise bad pattern.

I know! Thats why I am so confused when people like Wes and others who know what they're talking about say we have to thread the needle.

[SnoSki14]

Would this storm be a classic Miller A? I think so because it originates in the gulf.

[earthlight]

I think it's time for some objective analysis. What changed when compared to the 12z GFS which was so flat and less amplified? What is different aloft that causes these changes? There are obviously some changes in relation to the Polar Vortex, but these are actually relatively minute in comparison to some of the changes we have seen with similar features historically at this range. The modeling is in surprisingly decent agreement regarding that feature. This is not to say things won't change, just that for now, there is certainly some agreement there.

The real change this run is over the Rockies in a shortwave that drops southeast out of Montana. I was discussing this feature earlier on the 12z GFS as the model was coming out this afternoon. This feature was not on the 12z GFS as a result of a stronger ridge building over the Rockies initially. You can see the feature on the 12z GFS is way slower--all the way back near the Pacific coast. As a result, you can see also the differences in heights on the 12z run. The pieces are extremely separated. It's also worth nothing how much further east the shortwave over the Great Lakes is on the 12z run.

The 18z run was much more bullish with the shortwave diving southeast from Montana through the Plains into the broad trough over the Central and Southern US. This run actually misses the phase with the Polar Vortex, but the shortwave over the Plains that dives southeast works to amplify the trough rapidly. If you loop the images at H5 throughout the run you can see the work that the shortwave in discussion does for this synoptic setup. We should definitely watch carefully for this feature the next several runs. We still have a very long way to go, and pieces like this will come and go, but for the time being this one is definitely important.

[Kaner587]

Would this storm be a classic Miller A? I think so because it originates in the gulf.

It is because the southern stream energy is originally the culprit for this storm exiting the gulf with plenty of moisture and just gets ramped up with the PJ energy upon phasing.

[Riptide]

I know! Thats why I am so confused when people like Wes and others who know what they're talking about say we have to thread the needle.

Perhaps the idea of threading the needle is used simply because we are in a strong la nina. Miller A's can become as rare as gold.

[Kaner587]

Perhaps the idea of threading the needle is used simply because we are in a strong la nina. Miller A's can become as rare as gold.

thats for sure...I still can't believe this MIGHT happen

[earthlight]

The 18z GFS ensemble mean doesn't change much at the surface but the H5 mean heights are way more amplified than the 12z run. Just something to chew on.

[Dsnowx53]

I know! Thats why I am so confused when people like Wes and others who know what they're talking about say we have to thread the needle.

Yeah, I really don't get it, either. When you have a very strong, anomalous block retrograding westward, that in itself can be a feature that amplifies the entire pattern, and thus can make up for the lack of a true PNA ridge...also the GOA low is JUST far west enough where it's not a HUGE problem.

I mean, we have a huge W-E flow vortex sitting to our north, which is being somewhat forced to be stretched out and almost split into two because of the retrograding block...the vortex has nothing else to do BUT split because the block to the north is splitting it in half...that way we maintain one piece to the east for cold, confluent purposes, and another one to the west, which helps to amplify the entire pattern, and can phase with our southern stream shortwave.

Obviously, timing issues can be difficult to work out, but we don't need everything to work out at an exact, precise moment. The blocking gives you some room for error, as it helps to keep certain players on the field essentially a constant. As we've seen in some of the runs lately, the timing of the phase has differed, but the overall look has been very similar.

[am19psu]

I know! Thats why I am so confused when people like Wes and others who know what they're talking about say we have to thread the needle.

Perhaps the idea of threading the needle is used simply because we are in a strong la nina. Miller A's can become as rare as gold.

Nah, it's because of the wavelengths involved. Without a strong +PNA, even with pronounced North Atlantic blocking, these systems can swing out to sea then head back to the Maritimes. The phasing helps keeps the wavelengths shorter. That's why the skeptics (myself included) are calling it a thread the needle event.

[earthlight]

GFS Ensembles are pretty much holding serve at 18z (individuals)...they jump around and change as usual, but the general idea remains the same.

[Kaner587]

I think it all goes back to the strength of the block. The block was more defined on the 18z GFS, which thus allowed for a better splitting of the vortex, and thus you see a huge chunk of energy in North Dakota instead of Wisconsin. This allows more troughing initially in the Rockies, instead of riding which inhibits the shortwave on the 12z GFS. Also, with everything being displaced to the west on the 18z GFS because of the splitting, that allowed for a more amplified pattern in general...from there a phase is almost inevitable. It actually occurred slightly late, but we still got a good solution out of this. This goes to show that this is NOT an all-or-nothing event...it's not a "it has to phase with the southern stream shortwave at this exact time or else" kind of thing.

ya at first it seemed like that but its becoming increasingly clear there is a zone in which it needs to phase that would produce a variety of solutions from HECS to advisory event.

[Dsnowx53]

I think it's time for some objective analysis. What changed when compared to the 12z GFS which was so flat and less amplified? What is different aloft that causes these changes? There are obviously some changes in relation to the Polar Vortex, but these are actually relatively minute in comparison to some of the changes we have seen with similar features historically at this range. The modeling is in surprisingly decent agreement regarding that feature. This is not to say things won't change, just that for now, there is certainly some agreement there.

The real change this run is over the Rockies in a shortwave that drops southeast out of Montana. I was discussing this feature earlier on the 12z GFS as the model was coming out this afternoon. This feature was not on the 12z GFS as a result of a stronger ridge building over the Rockies initially. You can see the feature on the 12z GFS is way slower--all the way back near the Pacific coast. As a result, you can see also the differences in heights on the 12z run. The pieces are extremely separated. It's also worth nothing how much further east the shortwave over the Great Lakes is on the 12z run.

The 18z run was much more bullish with the shortwave diving southeast from Montana through the Plains into the broad trough over the Central and Southern US. This run actually misses the phase with the Polar Vortex, but the shortwave over the Plains that dives southeast works to amplify the trough rapidly. If you loop the images at H5 throughout the run you can see the work that the shortwave in discussion does for this synoptic setup. We should definitely watch carefully for this feature the next several runs. We still have a very long way to go, and pieces like this will come and go, but for the time being this one is definitely important.

I think it all goes back to the strength of the block. The block was more defined on the 18z GFS, which thus allowed for a better splitting of the vortex, and thus you see a huge chunk of energy in North Dakota instead of Wisconsin. This allows more troughing initially in the Rockies, instead of riding which inhibits the shortwave on the 12z GFS. Also, with everything being displaced to the west on the 18z GFS because of the splitting, that allowed for a more amplified pattern in general...from there a phase is almost inevitable. It actually occurred slightly late, but we still got a good solution out of this. This goes to show that this is NOT an all-or-nothing event...it's not a "it has to phase with the southern stream shortwave at this exact time or else" kind of thing.

[Dsnowx53]

ya at first it seemed like that but its becoming increasingly clear there is a zone in which it needs to phase that would produce a variety of solutions from HECS to advisory event.

Yeah, that's a good way to put it...there is a ZONE in which it needs to phase, but that zone isn't exactly a 10-mile radius (it's a lot wider), and it doesn't necessarily have a time constraint, either.

I mean, on the 18z GFS, the surface low started off in Northern Florida, and we STILL got the job done!

[earthlight]

I think it all goes back to the strength of the block. The block was more defined on the 18z GFS, which thus allowed for a better splitting of the vortex, and thus you see a huge chunk of energy in North Dakota instead of Wisconsin. This allows more troughing initially in the Rockies, instead of riding which inhibits the shortwave on the 12z GFS. Also, with everything being displaced to the west on the 18z GFS because of the splitting, that allowed for a more amplified pattern in general...from there a phase is almost inevitable. It actually occurred slightly late, but we still got a good solution out of this. This goes to show that this is NOT an all-or-nothing event...it's not a "it has to phase with the southern stream shortwave at this exact time or else" kind of thing.

I think we can look at the 06z GFS as a testament to how important the block, and even more so the energy over Montana into the Plains is. This run was actually really poor with the separation of the Polar Vortex and the flow was pretty flat initially, but watch the shortwave over Montana and Idaho dive into the Plains and eventually the broad trough over the Southeast which amplifies rapidly thereafter.

http://www.meteo.psu.edu/~gadomski/AVN_6z/f108.gif

http://www.meteo.psu.edu/~gadomski/AVN_6z/f126.gif

http://www.meteo.psu.edu/~gadomski/AVN_6z/f138.gif

http://www.meteo.psu.edu/~gadomski/AVN_6z/f150.gif

[Kaner587]

Yeah, that's a good way to put it...there is a ZONE in which it needs to phase, but that zone isn't exactly a 10-mile radius (it's a lot wider), and it doesn't necessarily have a time constraint, either.

I mean, on the 18z GFS, the surface low started off in Northern Florida, and we STILL got the job done!

exactly I was probably going to say a 100 miles maybe a couple hundred(completely pulling this out of my behind but it seems to make sense lol) but we're in agreement here that as long as all the players are on the field timing will determine who is in the jackpot.

[Dsnowx53]

I think we can look at the 06z GFS as a testament to how important the block, and even more so the energy over Montana into the Plains is. This run was actually really poor with the separation of the Polar Vortex and the flow was pretty flat initially, but watch the shortwave over Montana and Idaho dive into the Plains and eventually the broad trough over the Southeast which amplifies rapidly thereafter.

http://www.meteo.psu...AVN_6z/f108.gif

http://www.meteo.psu...AVN_6z/f126.gif

http://www.meteo.psu...AVN_6z/f138.gif

http://www.meteo.psu...AVN_6z/f150.gif

That's a very good observation. It goes to show that we have multiple sources which can help to amplify this pattern, despite there being no true PNA ridge. Also, it seems that in the 3 of the past 4 GFS runs that showed hits, the amplification resulted from slightly different degrees of factors each time...it's not like there is only one thing that can happen at one time in order for the pattern to amplify correctly. Once again, when you have a huge block, it allows for more room for error.

Obviously, this thing can still fly out to sea, since perhaps we might not get that strong Montana s/w OR a well-defined splitting, but I think it goes to show that we have some options here, which is why I don't think we're necessarily threading the needle.

[earthlight]

That's a very good observation. It goes to show that we have multiple sources which can help to amplify this pattern, despite there being no true PNA ridge. Also, it seems that in the 3 of the past 4 GFS runs that showed hits, the amplification resulted from slightly different degrees of factors each time...it's not like there is only one thing that can happen at one time in order for the pattern to amplify correctly. Once again, when you have a huge block, it allows for more room for error.

Obviously, this thing can still fly out to sea, since perhaps we might not get that strong Montana s/w OR a well-defined splitting, but I think it goes to show that we have some options here, which is why I don't think we're necessarily threading the needle.

There's honestly way too much talk about the PNA going on right now, if you ask me. This pattern is acting kind of like a split flow with a huge -NAO/greenland block and a PV in Southeast Canada which is more than we can ask for. Agree with the rest of your post.

On another note, we are getting within a day or two of the ECMWF "red zone", where it has been historically amazing. It may even lose it's accuracy for a run or two after this time frame, but it's normally spot on here (96-108hrs)..we are still a day or two away. For instance, check out the 96 hr forecast below from a thread in the main weather forum and then compare it to the verification. I would call that deadly.

+96hr ECMWF OP and Ensemble forecast

0hr verification

[Dsnowx53]

There's honestly way too much talk about the PNA going on right now, if you ask me. This pattern is acting kind of like a split flow with a huge -NAO/greenland block and a PV in Southeast Canada which is more than we can ask for. Agree with the rest of your post.

On another note, we are getting within a day or two of the ECMWF "red zone", where it has been historically amazing. It may even lose it's accuracy for a run or two after this time frame, but it's normally spot on here (96-108hrs)..we are still a day or two away. For instance, check out the 96 hr forecast below from a thread in the main weather forum and then compare it to the verification. I would call that deadly.

+96hr ECMWF OP and Ensemble forecast

0hr verification

Exactly. The huge block, and the vortex splitting and/or the strong shortwave entering Montana are killing two birds with one stone...they are influencing the pattern the way a PNA ridge would inherently influence a pattern, anyway...we don't need a true PNA ridge.

[NJwinter23]

Though I see what you and John are saying and generally side with your take on the PNA situation, perhaps thread the needle isn't the best term, but I think you have to admit that this is at least more of a "thread the needle" than if we had the +PNA. I think timing is more crucial with this setup than if we had the +PNA, but I agree it may be getting a little too much attention given the amazing retrograding block.

[Edge Weather]

I remember watching closely the qpf modeled by the ECMWF last year for some of the big storms and I was watching one closely that hit us where the EC put the bullseye in Hunterdon County, NJ along the Delaware River about 72 hours before the storm. The verification was exact, spot on the mile. It really is an amazing model. I hope it comes on board soon.

There's honestly way too much talk about the PNA going on right now, if you ask me. This pattern is acting kind of like a split flow with a huge -NAO/greenland block and a PV in Southeast Canada which is more than we can ask for. Agree with the rest of your post.

On another note, we are getting within a day or two of the ECMWF "red zone", where it has been historically amazing. It may even lose it's accuracy for a run or two after this time frame, but it's normally spot on here (96-108hrs)..we are still a day or two away. For instance, check out the 96 hr forecast below from a thread in the main weather forum and then compare it to the verification. I would call that deadly.

+96hr ECMWF OP and Ensemble forecast

0hr verification