Possible east coast snowstorm?

[usedtobe]

Earlier today I posted this on the mid altantic forum prior to seeing the Euro. I thought I post it here has I also try to show for why a negative AO is more highly correlated to mid atlantic snow storms than the NAO.

Today's 132 hr GEFS ensemble mean 500h pattern is not a bad one for the December 30th event. That doesn't mean it's a lock to occur and that we will be snow rather than rain as there is still time for things to change and for a stronger low to track towards KY. However, this particular mean would support a low squeezing to our south. I like the map because it shows how you can have a very positive NAO but still have a weakly negative AO and have blocking in a decent place to get a storm to track to our south. On the map note there is a nice vortex near the maritimes south of an area above normal heights and that there is still quite a big of red above normal heights over the higher latitudes giving the AO a slightly negative look. However, also look at where I've drawn the magenta line from iceland down towards the Azores. The heights over Iceland are lower than normal while higher than normal heights are located towards the Azores. That's a pretty strongly positive NAO index look.

However, in this case the high heights over eastern Canada and the below normal heights over the Maritimes with the remains of the old Boxing day storm provide the block. I've also annotated where the likely locations of jet streaks would be located (the arrow). Having the upper low near the Maritimes places confluence to our north and also places the right entrance region a a jet streak in close enough proximity to interact with a jet steak from the shortwave approaching the east coast. Such a double jet streak structure is a good one if you want a storm to develop along the east coast. If you look at KU storm, most have a similar jet streak structure as the interaction between the two acts to increase the upper divergence, is favorable for rapid intensification of the low and is frontogenetic.

If you look at the right hand panel you can see quite a bit a variation in how the Maritimes low is handled. That feature will play a big role in how suppressed out dec 29/30 low ends up. if the low moves too quickly east the surface low could still take a track similar to the boxing day storm. If it stays as the mean is forecasting, we have a chance for snow. Anyway, it's an interesting set up.

[Amped]

Good stuff as usual WES. 6z GFS was insane with the deepening rates of this storm, about 44mb between 150hrs to 168hrs! That is if I'm reading the numbers correctly of course.

[usedtobe]

The 120 hr European ens mean 500h today had many of the same similarities as the GEFS that I posted in the medium range thread and it has some similarities to the anomaly pattern found with DCs 8 inch or greater composite. That's not to say it will produce an 8 inch storm or even a snow storm as there are too many days out there to know for sure and the block on the euro is not as storm as on the typical composite. Below I've attached the euro 120 hr and the dca 8 inch or greater 500h anomaly composite for about a day before the storm. Compare the location of the negative height anomaly near western TN on the euro forecast and note and how closely it mimics location on the 8 inch or greater composite. Both also have a negative height anomaly south of the positive anomaly that stretches across the Baffin Bay region. The maritimes low is quite a bit weaker than the composite but is in a good place though its size worries me some that it could become displaced farther east than we'd like but on this forecast, it's right where we want it.

On the forecast you can also infer a possible double jet structure by looking at where the closest spacing of the height lines occurs in relation to the approaching trough and another to the southwest of the trough over the maritimes. That jet streak configuration is really a good one if you want an east coast storm to develop. This kind of set up is present with most KU storms. I'm not saying this will be a KU storm as we're 120 hrs in advance of the storm and the ens means could still be wrong especially if the weaker than normal block gives way too soon.

The importance of the Boxing day storm in the evolution and track of this one can be shown some on the 120hr euro ens mean surface forecast. I've annotated a rough frontal location on it with a dark black curving line. Note that the 850 temp lines are packed down across the southeast as cold air was forced southward by the boxer day storm. a Frontal trough is already located along the southeast coast. That feature will start lifting north in response to the approaching 500h trof. As it lifts northward the low will track along that front.

It's been a long time since I've liked a set up this much for my part of the mid atlantic. That doesn't mean we get a storm but that there is more potential than we've seen for a couple of year. I also think the storm has the potential to impact the northeast as well as the mid atlantic. Too bad it's still 5 to 6 days away. Lots can change and for the mid atlantic more often than not the changes are not in our favor.

[usedtobe]

The 00Z dec 25 euro and its ens mean still looks pretty good with the set and track of the approaching trough but the 06Z GEFS ense mean has shifted the maritimes block farther east and consequently has the low taking more of a Chill storm look on a number of its members. Plus the 06Z operational has DC pretty much right on the 850 zero line. We need the euro handling of the maritimes low over that of the 06 GEFS. That feature and how far south the approaching trough tracks are both big deals for this storm and still could make it a rainstorm rather than snow storm. That block actually looks a little stronger on the euro than yesterday but crummier on the GEFS ens mean. The 06Z gefs ens mean scared me as it is how we get in the mid atlantic typically get screwed. Note how many bad looking members some the 06Z has for the mid atlantic around DC. There still is a lot of uncertainty with the storm. What is a little scarey for us dc guys is that the GFS and its clones tend to suppress storms more often than wrap them up too much.

This will probably be the last post in the thread as the mid atlantic forum has a thread on it and there doesn't seem to be enough interest here to keep it going as the local forums seem to be discussing the storm potential.

[am19psu]

Wes, this is a great thread. It's the holidays and I'm off, so I don't have a lot to add to what you've already written. Thanks for starting it.

[NaoPos]

0z Euro is gonna make a lot of people

Happy along the I-95 corridor

[usedtobe]

Looks like some people in the northeast cashed in on the storm pretty well but not DC.