psuhoffman

There is a lot wrong with that euro op run. It shunts the majority of the next heat flux from the WAR off to the east and does not develop a true Greenland block. The NAO is weakly negative but it’s muted compared to other guidance (and the previous EPS runs frankly). The pna ridge is also shallow. The result of those two factors is the trough in the east has less amplitude (less depth) and so nothing digs enough to tap gulf moisture or amplify. This the all NS result you observe. Let’s see if the EPS agrees. The EPS hasn’t looked as good as the GEFS but it wasn’t that steaming pile of garbage either.

DUDE...did you just imply the NAM state doesn’t correlate to snowfall here? (For the record it is the #1 correlation to DC snow).

The euro doesn’t that’s for sure

And yet the ground truth is about the same in many spots lol

Last observation for now...the Uber long range look with a western trough but a west based -NAO and 50/50 is one where we can get front end thumps to dry slot type storms. The mean track will try to be to our west but that’s a pretty good CAD setup and not just weak insitu type that would lead to the type where it’s really hard to dislodge and we can do some frozen with a track pretty far NW track. Before that I see 2 discreet threat windows. The one around the 19 and another a few days later. The TPV gets further displaced and slides into SE Canada or even into the 50/50. That’s a more canonical (recently) big snowstorm look. The look is much better on the GFS guidance then the euro so hopefully it scores the coup here. The euro isn’t awful and a slight adjustment away but it sets up the trough too far west for the 19th and then goes too heavy with the trough out west after that. It’s a balancing act like a see saw. With a -NAO we can overcome a -pna to a point but if the western trough goes totally ape it becomes harder. Luckily the euro still has a bias I believe of doing that, I’ve noticed it still seems that way recently anecdotally. So for now Im cautiously optimistic in a more gfs like progression.

Para gfs fringes us with back to back storms because the TPV dives in slightly further east which is possible too at that range. A good longwave pattern gets us in the game but details that cannot be seen at range will determine the specific outcome of synoptic events.

Rain is a legit threat in this type setup BUT so long as the trough doesn’t go negative before our longitude and the surface low gets to the coast before turning north we would be ok. We have had plenty of nice snowstorms with this look. ETA: what I mean is yea if the storm cuts inland because the trough went negative too far west it would rain. And that “could” happen. But the scenario the GFS showed where everything went exactly how we want and the storm came up off the coast and it still rained...that’s nonsense.

This is a different longwave setup then the one you’re describing. We haven’t had this look much recently, it’s not that uncommon historically but it’s been virtually extinct lately. But the TPV displaced in south central Canada will promote lower heights in the lakes and ridging to our northeast. And if we didn’t have a huge western ridge and a -NAO with a decently cold antecedent airmass that would be a death sentence which is what we’re used to lately. But with a trough of that depth/longitude/axis we actually need that. Anything that forms down south would end up way OTS otherwise. That’s the kind of look where a storm runs the coast. Us being the furthest west of the megalopolis actually is favorable here. These type setups were more common in the past and can leave eastern NE more susceptible to a flip sometimes if it takes an inside track. The key for us is the trough not going negative too early or trending further west. There was a high to our northeast. Weak but it’s there. The lakes low is behind the dominant southern wave and the coastal develops a closed mid level circulation before that should interfere. But that’s another detail we need. The northern stream needs to feed into the southern wave not the other way. If the NS is the dominant SW this won’t work. Ideally if future runs trend towards a 50/50 low this goes from a very good look with MECS potential to a perfect HECS one but with the TPV in southern Canada that’s a tough ask as that’s going to promote ridging in front. But it also is going to dig the trough just to our west so it compensates for that issue some also.

The signal for the 19/20th has only become more pronounced in the last 24 hours. All the parts are there. Severely displaced TPV in southern Canada. Colder antecedent airmass. -NAO. Very nice wave depth and alignment signature. But the details models will not get accurate at this range will determine exactly how it plays out. No sense getting upset over those details that will change every run for another couple days. 150 hours seems to be about the magic spot where the globals start to hone in on some synoptic level details. We’re still 2 days from that. I will say this about the 12z gfs. If we get a big rainstorm on January 19th from a 984 low 75 miles east of Ocean City with a closed h5 low track across southern VA and a TPV just north of Michigan I am done for the year and I mean it. That’s absolutely ridiculous. And don’t someone tell me how this or that was 2.5 miles off from being perfect. If that setup doesn’t get us a snowstorm we’re wasting our time.

SHOCKING

I don’t know if you were pointing this out or not, sometimes I suck at context clues, but this is exactly what I’m talking about. We are downwind of the pac! Almost always our airmass will be pacific in origins. And before it was in the pacific it was probably over Asia! But air masses do change characteristics some. There is a huge difference between a pacific Maritime airmass that originated in the tropical or subtropical pacific blasting straight across the US at mid latitudes and a pacific airmass that originated in the colder north Pacific then traversed Alaska and the Yukon before diving into the US. The former will never work. The latter better darn well work because that’s responsible for 90% of our snow. How common do you think a direct cross polar flow from Siberia is? And guess what more often then not when we get those arctic blasts once in a blue moon it’s a cold dry pattern then warms before any storm comes because typically to get that you need a full latitude wave 1 EPO ridge configuration and that is NOT good for getting a favorable storm track here. If we need a direct flow from Siberia to get snow we (as DT would say) are fooked.

@Ralph Wiggum the WAR is displaced pretty far NE there. You have to take the totality of factors and how they play off each other. With a severely displaced TPV in southern Canada a ridge in the central Atlantic extending up through the NAO isn’t a bad thing. It can actually help prevent suppression in that scenario. I’m going to say this again...this isn’t directed at you but a general observation. I think because we have been stuck in a rut where NOTHING has been working out and DC is in a record snow drought the last 5 years people are starting to think unless we have this 100% absolutely textbook dead perfect pattern where every little feature is within 20 feet of where it was for some blizzard in the past it won’t work. And I don’t blame you because that’s how it’s felt lately. Even pretty decent looks produce nothing. But 90% of our snow, maybe not our HECS 20” storms but our regular old plain snowstorms, happened in a somewhat flawed pattern. The flaw might be a valid excuse why it was only 6” instead of 20” but I’m seeing all these posts picking apart really decent looks as if it can’t snow in that pattern when we have had plenty of snowstorms in exactly that pattern. That perfect textbook everything exactly where we want look only comes along a couple times a decade. We cannot rely on getting that to get any snow or frankly snow will be a VERY rare thing around here (which granted it has been lately). To sum it all up my point is if we want this snow drought to end what we really need is to hope we start getting more luck with pretty good but not perfect patterns that are more common not waiting around for that pattern that comes once a decade.

Long shot but there could be a wave on the front around the 16th

I was a meteorology major at PSU for 3 years. But in the end I dropped the meteorology in favor of sociology and later decided to go into teaching and coaching in the inner city. I did get a good foundation from my classes at PSU. I had a class with Jon Neese who was later on TWC. I think I used to annoy the crap out of him in the weather station. But honestly I learned 90% from experience and doing my own research and reading. I’m the weirdo who reads a textbook just because I want to understand something.

You can’t see it directly there but you can see the evidence because there is a 1004 surface low with h5 low ejecting so obviously it has an associated SW and vort. It’s just assumed from secondary evidence.

A low transfers when it meets resistance and can no longer progress and reforms somewhere else along the thermal boundary. This can happen because of the upper level support jumping or a surface feature blocking progress. Often the jump we want is a system moving northeast up the west of the Apps to jump to the coast. What typically causes this is when a cold high is blocked in to the north impeding the low, and CAD banked in against the mountains so the path of least resistance is to jump east to the baroclinic zone along the coast. The example from the 18z gfs is below. the primary in the Midwest has hit a brick wall of confluence. Note that system to its north hit the same wall and has actually done a loop and is retrograding west because it’s an arctic wave removed from any thermal gradient so it had nowhere to jump too. It simply put er in reverse lol. That primary in IN can’t go anywhere. So it’s going to transfer to the triple point along the front in the Carolinas. That’s common because there is often a lot of lift there that can promote pressure falls and an enhanced baroclinic boundary. It’s also along the warm front providing a path east under the block for the storm to progress so it transfers the energy there.

A storm in 1972 transferred from the UP of MI to SC. That was probably the most extreme example.

Recently no. Are there examples of that in the past yes. It takes a blocking regime and a cold airmass.

Just a little blocking when storms transfer from Indianapolis to Hatteras

I think, as wxusaf, that it’s a bit of both bad luck and the background stage becoming incrementally more hostile. In December we had a nice AO ridge but it was a bit north of perfect. That can work though if you get other things to line up and we almost did but that SW that dive in out west really screwed us by amplifying the trough more. But it’s hard to get a big snow in mid December. The first iteration of the -NAO this month ended up too extreme imo. That was part of the problem. I posted this from a couple days ago. That ridge is centered way too far south and extends too far SW. Not only did that suppress 3 waves but it prevents colder air from draining into the pattern to the west of the block. Center that further north without that extension into Quebec and we get a slightly colder profile and less suppressed systems and I bet one of them “works out”. This next flex of the blocking looks more ideal but now there are questions about what kind of PAC we get. Ideally I would have liked one more bite of the apple with the current pac and a better NAO. But I don’t have the magic crayon. And the look we see now is pretty darn good. And I’m biased by my location. If I were you I would definitely go with the colder but possibly dryer option. We have way different climo.

It just depends. Not all blocking patterns are the same. But a -NAO split flow isn’t uncommon and usually a good thing. It’s not a cold pattern. Feb 2010 was one. The Polar jet was directed across Canada by the trough in the pac but the southern stream was splitting into the SW and coming across the gulf coast. But the pac jet wasn’t as intense and the profile in Canada wasn’t as awful to start. But it wasn’t cold. Actually north of us was very mild. And even here it would have been 45 that week had there not been snow. It’s a pick your poison thing. A split flow cuts off the polar air but normally in winter we can develop a just cold enough airmass under the flow to get snow with a good track. This year that didn’t work out. A -EPO -NAO non split flow is much colder but it can be a dryer pattern if storms dive in too far north to amplify under us and the STJ is cut off in that case. So there are pros and cons to both. FWIW the split flow option accounts for a lot of our HECS storms.

Blocking patterns aren’t always cold. Often they are quite mild north of the storm track. This year has been to the extreme though.

Shockingly this would make the 3rd time this cold season the EPS caved to the GEFS wrt long range longwave pattern. The op GFS has been awful with synoptic details in the medium range lately but the GEFS since it’s major upgrade has been extremely good with pattern recognition.