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December 16/17 Winter Event


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Just now, WxUSAF said:

That looks like rain or maybe rain/snow mix at best for most of MoCo/HoCo and 495 part of VA at 0z Thursday with those 925 and 850 temps.  Hopefully those temps crash back eastward at that point.

Adding the surface which looks above freezing in and around dc for the duration.

72873656-9080-408D-BADD-0883FAD6EC33.png

8D115BD7-FBCF-4F46-84B6-6F310E3B4410.png

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@high risk

The NAM does sometimes sniff stuff out.  It nailed the sleet fest coming from range in March 2017 when all the globals had snow.  But the problem is, its wildly inconsistent at range...which is to be expected for a model designed to handle convection and meso scale banding.  It is useful in showing thermals better and a better detailed representation of what the storm might look like...but wrt synoptic level general things like track, at range it's hard to take any one run seriously because you don't know what it is onto something or when it is just on something.  

@BTRWx's Thanks Giving

You NEED to stop with those crap snow depth maps.  I have no idea how they are calculated but over the years they have been just as garbage as the weenie weatherbell ones.  They end up seeming right for the same reason some of the trolls here do...because we fails so often.  The models are often wrong and thigns shift worse.  And when that happens...it makes a map like those look good.  But whenever a storm actually does what the guidance says...those bust low.  WAY LOW.  I will give you one example just because I looked at the soundings.  The NAM one you posted shows Westminster with 3" of positive snow depth.  But they get about an inch of QPF with all levels at or below freezing.  They get another .8 of QPF that is obviously sleet from the sounding.  The surface is below freezing the whole time.  Heck even if the whole storm was sleet that would be more than 3"!!!  That is just crazy stupid.  Now maybe the storm shifts even further NW and then 3" in Westminster isn't a bad idea.  If the track actually penetrates inside the mouth of the Potomac...that would be trouble for up here...but a track like that NAM had over the southern Bay in up the eastern Delmarva supports a big snow (with some mixing yes) up here...and the model shows that if you look at the actual soundings and hour by hour plots...then that depth map shows something completely different.  THis is not the only time but its a current example of how that map is just WRONG.  

 

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1 minute ago, LP08 said:

Adding the surface which looks above freezing in and around dc for the duration.

 

 

Without seeing a sounding, I can't be sure, but that seems a lot like the 18z GFS for the R/S line area.  Nearly isothermal profile right around freezing from ~850mb to the surface.  Very tiny margin between hours of heavy wet snow and driving rain.  

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Just now, WxUSAF said:

Without seeing a sounding, I can't be sure, but that seems a lot like the 18z GFS for the R/S line area.  Nearly isothermal profile right around freezing from ~850mb to the surface.  Very tiny margin between hours of heavy wet snow and driving rain.  

My goal in mby is to hopefully avoid a driving rainstorm after a few hours of snow.  Hopefully during lulls we can hold on to 33-35 and stay “frozen” for most of the storm.  

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If the low does go due north up the Bay that is too close for comfort.  20- 30 miles east would make a big difference.  May be an hour by hour outcast Late Wed. Afternoon/evening.  We are only 48 hours out, but we are still 48 hours out....another 30 miles west track no one will be happy east of the Blue Ridge or in Northern MD.  

2020 has proven anything is possible.

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3 minutes ago, LP08 said:

My goal in mby is to hopefully avoid a driving rainstorm after a few hours of snow.  Hopefully during lulls we can hold on to 33-35 and stay “frozen” for most of the storm.  

Yeah, I was thinking sleet, but 18z GFS and Euro seem more like snow vs. rain.  

These are really tiny thermal details.  I'm pretty much just in "chips fall" time.  Seems like we know the basic deal here. 

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