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February Medium/Long Range Disco Thread 2

WxUSAF

By WxUSAF,
in Mid Atlantic

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BTRWx

BTRWx

Posted
Posted
1 hour ago, eurojosh said:

Pity it doesn't go out to ten days... has anyone seen any p-type maps for hr 240?

It does have that option for snowfall at least!  Near D.C. it's a carbon copy for 6 days, but not sure which hour it would cut off on.

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Amped

Amped

Posted
Posted

I haven't changed my opinion since yesterday even after seeing the Euro.  These coldfronts coming down from PA always take way longer than any model says when there's not a strong pressure gradient.   The only way we do well from an anafront is if models are showing temps dropping into the mid 20s before the precip ends.  Here they don't even get down to 32 in most places.    Even the NE MD crush zone might get screwed on this one.

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gymengineer

gymengineer

Posted
Posted
2 minutes ago, HighStakes said:

This system could work out for us. Some similarities to the late February in 2011. We did well here with about 6 inches. It was a race to get the cold air in but we did win out. Areas not to far to the south struggled. That storm did have a stronger cold push behind opposed to this upcoming one which is more marginal. We are at peak climb so that could help the borderline areas do better.

Yeah you're right about areas south of you. 2/11 was a horrific short term bust for us-- WSWarning for 3-6" of snow after the changeover based on increasingly optimistic short term trends on the models. The 12Z runs at the start of the event blew the southern edge. We had less than an inch. 

People have mentioned the Euro's performance in the 2015 Super Bowl storm but I think a worse miss was the 72-hr lead time miss on the March storm last season. 3 or 4 runs in a row leading up to 72-hours out showed a bombing low to our southeast with a major snowfall at our latitude. That didn't happen obviously but it took the Euro another couple of cycles to completely lose the band of moderate precip on Sunday. 

And of course the Euro's most notorious recent bust was holding onto the slow and deep solution for NYC's possible all time greatest in 1/15. 

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CAPE

CAPE

Posted
Posted
15 minutes ago, Bob Chill said:

18z GFS is basically a 50 mile NW jog with precip totals from the euro. It was a SE shift in general from 12z. Especially in the areas NE of here like NYC. 0z should look just like the euro and then we'll have consensus. lol. 

Euro actually shifted some from 0z to 12z. Biggest difference to the NE. It was a tad colder, low track further south, and just a touch weaker but that was just noise probably. So its all looking good. Until the Euro shifts 50 miles at 0z.

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MAG5035

MAG5035

Posted
Posted
1 hour ago, packfan98 said:

BIG discrepancy in snowfall amounts between various euro models that you can look at. WXBELL v EUROWX - huge implications for DCA BAL

C4AOaw4WEAE6aYm.jpg:large

Is there any chance that DT has the wrong map from EUROWX?  That's a huge difference!  Sleet??

I'll start with the disclaimer that of course these model snow output maps should only be used as a general reference. Should also mention that the bigger issue right now is the track and the agreement amongst models is certainly still a work in progress. My worry about the Mid-Atlantic region is whether the cold is able to press down enough before this followup wave behind the cutter runs along the boundary. But at any rate.. a couple thoughts on these snow outputs. 

While the Wxbell map may be a bit liberal with snow amounts on the southern end, I'd be careful with the Kuchera method (Eurowx map) in this kind of marginal setup. Kuchera applies the warmest temp in the lowest 500mb into an equation, which is: 

T = maximum temp in lowest 500 mb (K) 
if T > 271.16 
    ratio = 12 + 2*(271.16 - T) 
else 
    ratio = 12 + (271.16 - T)

That equation uses Kelvin as well, so to refresh.. 0ºC = 273.15K

With this setup, that warmest temp is going to be at or near the surface. So with model output of 1-2ºC (274-275K) in that near surface layer, it's gonna come up with a ratio of 4 or 6:1. Dynamically, with decent lift at the 700mb level the ratios probably would be pretty decent (>10:1). Of course surface temps and ground temps will affect that to a point. It may start with that kind of calculated crappy ratio but as temps fall and snow starts piling up, you may start to realize a much better ratio...especially if the precip is heavy.  

I also believe this method doesn't get triggered unless the model ptype output is straight snow. Since this is a quick event which practically happens in between 6hr frames, I can see how that can get pretty ambiguous for DC and just south since temps fall from the mid 30s to 32-35ºF. I don't have Euro p-type maps, so I'm not sure what they look like. I guess my point is that the Kuchera method is only as good as the accuracy of the model output, and in these highly marginal setups where a degree or so can make all the difference between rain, slush, or an all out snow bomb... I would take it with about as much of a grain of salt as the general WxBell 10:1 map. Also if anyone else has anything to add or correct me on Kuchera method, feel free. 

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HighStakes

HighStakes

Posted
Posted
13 minutes ago, gymengineer said:

Yeah you're right about areas south of you. 2/11 was a horrific short term bust for us-- WSWarning for 3-6" of snow after the changeover based on increasingly optimistic short term trends on the models. The 12Z runs at the start of the event blew the southern edge. We had less than an inch. 

People have mentioned the Euro's performance in the 2015 Super Bowl storm but I think a worse miss was the 72-hr lead time miss on the March storm last season. 3 or 4 runs in a row leading up to 72-hours out showed a bombing low to our southeast with a major snowfall at our latitude. That didn't happen obviously but it took the Euro another couple of cycles to completely lose the band of moderate precip on Sunday. 

And of course the Euro's most notorious recent bust was holding onto the slow and deep solution for NYC's possible all time greatest in 1/15. 

Good observations. Another storm that comes to mind was the early february storm in 2014. This was the one right before the ice storm. Once again a case of trying to get the cold in. I think we were well into the 50's the day before with rain. We got lucky here and enough cold made it in. Ended up with 6-7 inches of extremely wet snow. Areas just to the south only 2-3 around Reisterstown. Virtually nothing once you got to the beltway. 

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psuhoffman

psuhoffman

Posted
Posted
3 minutes ago, C.A.P.E. said:

So who has the cahoonas to start a thread? Yes, you will be held accountable. But it is time. Step forward.

It's time because this isn't long range anymore and we actually do have some stuff including a day 10 window and a possible better pattern later to talk about in here. 

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Bob Chill

Bob Chill

Posted
Posted

Weeklies are the best overall pattern we've seen since 09-10 and it begins early week 3. I'll let psu do the detailed analysis but it's cold, blocky (ao and nao), and southern jet undercutting it all. 

If things broke right inside of the mean height pattern we could pull off a Brady before it's all said and done. 

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BTRWx

BTRWx

Posted
Posted
1 hour ago, MAG5035 said:

I'll start with the disclaimer that of course these model snow output maps should only be used as a general reference. Should also mention that the bigger issue right now is the track and the agreement amongst models is certainly still a work in progress. My worry about the Mid-Atlantic region is whether the cold is able to press down enough before this followup wave behind the cutter runs along the boundary. But at any rate.. a couple thoughts on these snow outputs. 

While the Wxbell map may be a bit liberal with snow amounts on the southern end, I'd be careful with the Kuchera method (Eurowx map) in this kind of marginal setup. Kuchera applies the warmest temp in the lowest 500mb into an equation, which is: 

T = maximum temp in lowest 500 mb (K) 
if T > 271.16 
    ratio = 12 + 2*(271.16 - T) 
else 
    ratio = 12 + (271.16 - T)

That equation uses Kelvin as well, so to refresh.. 0ºC = 273.15K

With this setup, that warmest temp is going to be at or near the surface. So with model output of 1-2ºC (274-275K) in that near surface layer, it's gonna come up with a ratio of 4 or 6:1. Dynamically, with decent lift at the 700mb level the ratios probably would be pretty decent (>10:1). Of course surface temps and ground temps will affect that to a point. It may start with that kind of calculated crappy ratio but as temps fall and snow starts piling up, you may start to realize a much better ratio...especially if the precip is heavy.  

I also believe this method doesn't get triggered unless the model ptype output is straight snow. Since this is a quick event which practically happens in between 6hr frames, I can see how that can get pretty ambiguous for DC and just south since temps fall from the mid 30s to 32-35ºF. I don't have Euro p-type maps, so I'm not sure what they look like. I guess my point is that the Kuchera method is only as good as the accuracy of the model output, and in these highly marginal setups where a degree or so can make all the difference between rain, slush, or an all out snow bomb... I would take it with about as much of a grain of salt as the general WxBell 10:1 map. Also if anyone else has anything to add or correct me on Kuchera method, feel free. 

Awesome explanation and much appreciated! 

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