cae

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10 hours ago, yoda said:

00z UKMET meteogram is 5-6mm of snow at DCA

So this response is a bit late, but the 00z UKMET on weather.us has DC getting shut out, with the 5mm (0.2 in) line clearly south of the city, more in line with other 00z guidance.  That makes me wonder how geographically accurate the meteocentre maps and meteograms are.

I hope everyone who's getting snow enjoys it.  Looks like I'm on the wrong side of the DC snow shield for this one.

8 minutes ago, JakkelWx said:

3k nam at hr 27...

That's composite reflectivity.  The NAMs have been giving us a virga storm for a while.  North of DC much of that doesn't reach the ground.

One more RGEM ensemble map.  Mean qpf as snow. 

RGEM ensemble basically tightened up the gradient from yesterday's 12z run, with a bump up in the number of members giving Richmond at least 0.1" qpf as snow.  After today's 12z runs, it doesn't look like such an outlier any more.

15 minutes ago, NorthArlington101 said:

Are all the Canadian models running with the same data? That’s probably the wrong term but hopefully you know what I mean. 12z CMC holds.

I know what you mean - and yes, there's a reason they're all showing similar solutions.  The HRDPS doesn't have the RGEM's wet bias, so it's probably more realistic here. 

Often when the RGEM and 3k NAM differ on where the cutoff is going to be, it's because of how they handle virga.  I think that may be the case here.  The below images are from the 00z 3k NAM run.  They alternate between simulated composite reflectivity (with p-type) and simulated base reflectivity.  The virga reaches north of DC.  I suspect the RGEM has more of the precip reaching the ground.

The RGEM could be wrong (it's made similar mistakes in the past), but it shows that we don't necessarily need a change in track to see some precipitation around DC.  Just less dry air near the surface.

1 hour ago, psuhoffman said:

Meteocentre has 18z ggem?

I think it's like the 18z Euro - a short run used to set the boundary conditions for the RGEM. 

Since the GGEM has been consistently on the northern edge of guidance, I'd be cautious about putting too much weight in the RGEM.  With that said, for those of us north of DC the 12z RGEM ensemble is saying there's a chance...

1 hour ago, osfan24 said:

Man, what's going on to our northeast is a disaster that just keeps getting worse and worse.

I'm not sure that's where we should be looking.  The snow actually shifted substantially north in the 12z run compared to 00z, even though the trough over Canada dropped down.  I looked through some maps to figure out why, and I think it's related to he trough over the North Atlantic slowly trending north. 

I'm not sure the trend will continue, and the model consensus at this point doesn't look favorable.  But I think that might be a feature to watch in future runs.  (fwiw, I'm not too worried about the EPS though, as they'll start closely tracking the op around now.)

17 minutes ago, nj2va said:

Oh they (OP and ENS) have favored SW VA/W NC for days but they’ve been bouncing around up here (similar to the OPs)...maybe that’s due to DC/NVA being on the northern fringe so any jog will have a significant impact here?  I don’t remember an event where the snowfall means jumped from run to run like it has with this event.

The GEFS means can bounce around quite a bit due to their underdispersion.  We saw it several times last year too.  I think there's supposed to be a fix for this in the FV3 ensemble, but that isn't expected to be out until early 2020.  Hopefully by this time next season we'll all be complaining about the new para-GEFS.