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Jan 16/17 Event Obs/Disc


mappy

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8 minutes ago, WVclimo said:

Snow is tapering off.  1.2" on 0.08" liquid.  For all those numerous runs of the NAM and RGEM that showed 0.20-0.40" of QPF, the GFS and the last 48 hours of Euro runs were much closer to what fell.

Thats a gradient!  To say I have a dusting is being generous and you are barely 10 miles to my NW.  

Light snow. 30*

Oh well.... You lose some, you lose some..

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Should have known with the lowering DP's earlier.......snow evaporating off radar to my west. I am done with 10 minutes of pixie dust. Fully expect to see snow blossom on a Richmond to Greensboro line within the hour. Classic, classic transfer for here.

MAYBE it can back in to here, but that would be asking a lot, kudos to the King, nailed it.

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9 minutes ago, poolz1 said:

Thats a gradient!  To say I have a dusting is being generous and you are barely 10 miles to my NW.  

Light snow. 30*

Oh well.... You lose some, you lose some..

Sorry you weren't able to get in on it, Poolz.  It's a very fluffy snow.  Doesn't even stick to your shoes.  I think another 10 miles to my NW, in the Big Pool/ Ft. Frederick area, they probably picked up twice what I have here.  Crazy how little the precip shield moved all day.

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42 minutes ago, WVclimo said:

Snow is tapering off.  1.2" on 0.08" liquid.  For all those numerous runs of the NAM and RGEM that showed 0.20-0.40" of QPF, the GFS and the last 48 hours of Euro runs were much closer to what fell.

Yep. I was hoping for once they would be right. Some of there runs over the last 2 days gave me 4 to 6 inches. GFS and Euro nailed the liquid aspect of it out our way.

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Just now, Tenman Johnson said:

It's funny but right this instant there are radar returns  from just nw of Richmond to Lancaster PA except for s blank area right around D.C.

Looks like it's trying to fill in, but mostly virga. Looks like decent returns to the South, but not sure if virga or not either. 

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Unless some sort of miracle happens, this will be my last post on what I think is going on in the atmosphere.  This is for people like me who are just trying to figure this stuff out.  Those of you who know what you're talking about, please correct me if any of this looks wrong.  I apologize in advance for the length of this post and the number of images.

I'm going to compare two Euro runs:  00z on Sunday night and 12z today.  00z on Sunday was a better run for our region.  I'll first show some gifs for 12z tomorrow, or 7:00 in the morning.  The firsts shows four images in order:

1)  Precipitation over the last 3 hours from the 00z run.
2)  The winds at 850 mb from the 00z run.  Notice that around DC they're coming from the south, bringing moisture with them.
3)  The winds at 850 mb from the 12z run.  Notice that around DC they're coming from the west, bringing dry air. 
4)  Precipitation over the last 3 ours from the 12z run.  The dry air has shut of precip around DC.

NFzEKTv.gif

Notice what happens between 2) and 3) above.  There is a small dip in the 850 mb winds just to the east of Toronto.  In the 12z run, it pushes down a little more, getting the DC area into the western flow and cutting off our snow.  I've mentioned this all before, and PSU had a very nice explanation this morning that the shift in winds is related to the development of the first wave, which manifests itself on the surface as the coastal that hits areas to our north.

I've been trying to figure out how this shift relates to all of the H5 maps we're always looking at.  So the next couple of gifs will start at the 850 mb wind maps shown above and go up to the 500 mb level to see what happens.  Let's start with the 12z (no snow) run first.  Pay attention to what is happening near Toronto.  The images in this gif are, in order:

1)  The winds at 850 mb from the 12z run.  This is the same as 3) above.
2)  The winds at 700 mb from the 12z run.  Notice how you can still see a "dip" in the winds near Toronto.  I believe this is the first wave PSU was talking about, or something close to it.
3)  The winds at 500 mb from the 12z run.  Notice how the speeds appear to be pinched just below Toronto.  I believe the dip just above the pinch is related to the similar features at 700 and 850 mb.  The H5 is just about to close off, but to see that we need to look at the geopotential height plots.  That's what we'll see in 4)-7).
4)  The H5 map corresponding to 3) above. 
5)  The H5 map 3 hours later.
6)  The H5 map 3 hours later.  Now we can see a closed contour forming near the KY/VA border.
7)  The H5 map 3 hours later.  We can clearly see the closed contour, with the split occurring near southern PA.

aTHAwvA.gif

Next let's look at the same thing for the 00z (more snow) run.  The images in order are:

1)  The winds at 850 mb from the 00zz run.  This is the same as 2) in the very first image.
2)  The winds at 700 mb from the 00z run.  The dip near Toronto is less distinct.
3)  The winds at 500 mb from the 12z run.  The pinch in the wind speeds is gone, or at least hard to spot. 
4)  The H5 map corresponding to 3) above. 
5)  The H5 map 3 hours later.
6)  The H5 map 3 hours later.  Unlike the 12z run, there is no clearly closed contour.
7)  The H5 map 3 hours later.  H5 has closed off, but now the split has occurred near southern NY.

z343xw3.gif

So now we (finally) get to the insight I think I've gotten out of all of this.  In the 00z run, even though H5 appears to close off later, we get more snow.  Why?  I think the answer has to do with the two different sides of the H5 split.  Up until now, I'd always paid attention to the bottom half.  Closure in H5 favors greater circulation near the bottom half of the split, which can generate winds coming from the east.  That's good around here.  But I'd never paid much attention to the top half of the split.  I suspect that the top half of the split is more likely to produce winds that come from the west at lower levels, as opposed to winds that come from the south (if there were no split).  In the 00z run, where the top half of the split stays farther north, so did the winds from the west at 850 mb.  In the 12z run, the top half digs farther south, and I think this is associated with the southern shift in the winds from the west.

So I think I may have been hoping for the wrong thing.  I wanted to see H5 close off to get the easterly winds.  But now I think the wave associated with the top half of the split actually ended up producing our winds from the west.  In a sense, this all comes back to what PSU said.  We just happened to be caught between the two waves at the worst place.  My takeaway from this is that H5 closing off is not always a good thing - it could indicate trouble at the lower levels, depending on where you are relative to the split.  If you've read this far, thanks.  And to the more knowledgeable readers, I apologize for the non-technical language.  I hope you were able to follow along.

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