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December and a Hint of January Pattern Discussion


Bob Chill

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It is ridiculously wet...but changes over sooner...

 

I'll let you guys see the panels 1st instead of doing more play by play..

I'm not sure that's good but I'd worry about freezing rain even in the city after the changeover given where that high was located.  We'll have to warm from the east at the low levels. 

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I'm not sure that's good but I'd worry about freezing rain even in the city after the changeover given where that high was located.  We'll have to warm from the east at the low levels. 

 

It is a big snowstorm for Skyline Drive,.,..might have to take a drive out there if it holds as we get closer in

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I'll say it now.. but I likely will have to say it in the future. DON'T focus on the 850 temps, look to 750-800mb temps to find that warm layer. If you can find maps of 700-850mb thickness, generally below 154dm is all snow.

 

Very true, and thats why I like the soundings as the GFS runs

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I'll say it now.. but I likely will have to say it in the future. DON'T focus on the 850 temps, look to 750-800mb temps to find that warm layer. If you can find maps of 700-850mb thickness, generally below 154dm is all snow.

 

everyone has been hammering that  point home...

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so much for clown maps..looks like weatherbell is as bad as the others

 

IAD

 

attachicon.gifiadsounding.PNG

 

i think they are all the same other than resolution. but they will continue to suck overall at least in changeover type snows. which is pretty much everything here... 

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good post....We are probably screwed for a while if/when the EPO relaxes....a lot of cold air locked up in Canada and the west, and a sharp gradient pattern from N to S...probably a good SWFE pattern...I'm still very very cautiously optimistic about a cold/snowy regime from just after Christmas through about 1/10

 

I wonder about the timing of that though coming much closer to your end date if we are to believe the tropical forcing state is being realized properly by the models now?

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i think they are all the same other than resolution. but they will continue to suck overall at least in changeover type snows. which is pretty much everything here... 

 

It is still over an inch QPF of snow/sleet

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I haven't looked at the new runs for next Sun-Mon, but yesterday while at work I saw the broad, strong, deep SW flow aloft that as you all noted would no doubt lead to an elevated warm layer. It's definitely got that mix to freezing rain look, considering the strength of the low level high and CAD wedge, something we haven't seen in a long time, but certainly would make since given (1) the availability of arctic air to our north which continues to be re-enforced, and (2) the lack of blocking over the northern Atlantic which would allow for a more confluent, frontogenetic look at mid levels and thus deeper cold (sub 0C) air.

As Wes and others have noted, model soundings are the way to go when attempting to diagnose where exactly that elevated warm layer will be. However, this far out, I like to look at critical 850-700 mb thicknesses, since I can view it over an area rather than at a point (as with a sounding). For the most part any 850-700 mb thicknesses below 1540m is good enough for snow, i.e. approximate to the layer average temperature below 0C. 850-700 mb thicknesses bove 1550 m would favor rain or freezing rain depending on the surface temp. In between 1540 and 1550 m is where it gets messy, though typically in such events with mid level SW flow aloft extending well to our north (i.e. no confluence or frontogenesis over the northeast), we don't stay there very long. We may start out at snow/sleet, but then switch to fzra or rain at some point -- because we just don't have the frontogenesis above 850mb to our north to keep that layer cold.

Either way, I'd be excited just to have an event. An event that looks like this one used to happen with more regularity in the '80s and '90s around here...just not lately. Again, it has everything to do with the fact that, for a change, we actually have bona-fide arctic air to work with not too far north of us.

it sure would be nice if NCEP maps had a 1540 thickness line on their maps instead of lines at 1520 and 1560; you can't tell where the 1540 thickness line is with that spread

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I wonder about the timing of that though coming much closer to your end date if we are to believe the tropical forcing state is being realized properly by the models now?

 

I like the 1/5-1/10 period the most of that window, so makes sense..it is all mostly guesswork for me

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