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December 22-23, 2022: Warm Rain to Arctic Chill


WxUSAF
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2 hours ago, MN Transplant said:

The 6z NAM Nest was a good scenario for us.  
 

One interesting thing that has been happening is that the models have done away with the Friday morning warmth.  Instead of the 50s, we are in the lower 40s before the front blasts through.  

12z NAM is mostly upper 30s ahead of the front. Almost cold enough that the frontal rain line is frozen… freezing level around 925mb.

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2 minutes ago, Interstate said:

GFS is stubborn that is for sure.

It is. Not sure I’m going to believe it until the snow is falling though. 
 

p.s. if you look though, gfs may be slowly backing down on the amount of precipitation behind the front over the last 4-5 runs.

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Doesnt the GFS have the tendency to leave too much precipitation behind arctic fronts and also be a little too strong with cold pushes? Its being consistent but I find it hard to believe we'll be 19 degrees at 1PM. I buy a quick burst of snow for the N&W elevation areas but Im pretty skeptical a bout the metros and low lands cashing in on much of a changeover

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16 minutes ago, Ravens94 said:

Definitely a coastal low signature trying to form in NC

17 minutes ago, alexderiemer said:

I would laugh so hard if we somehow still get a coastal out of this...talk about a Christmas miracle...

It's been there for a while, but the problem is that we get relatively flooded with warmth from southerly flow ahead of the vort in the Midwest.

What the GFS did all those days ago was to have confluence keep that vort from cutting, then eventually getting below us and giving us a double dip from the southern energy and that northern stream vort. With the confluence no longer coming into play, that vort cuts and floods us with warmth, then the precip from the southern energy falls into a warmer column. It's not until the front comes through that temps support the possibility of frozen.

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13 minutes ago, NorthArlington101 said:

I'm not sure its ever been a useful tool but it's nice to see the FV3 hi-res kind of agree with the GFS. It doesn't always do that, e.g., it looks nothing like it's parent(?) for the Thursday morning part of the system.

IIRC the GFS is based on an FV3 core. So it sort of makes some sense that they'd agree. Believe the FV3 is slated to replace the various hi-res/regional models. 

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48 minutes ago, Baltimorewx said:

Doesnt the GFS have the tendency to leave too much precipitation behind arctic fronts and also be a little too strong with cold pushes? Its being consistent but I find it hard to believe we'll be 19 degrees at 1PM. I buy a quick burst of snow for the N&W elevation areas but Im pretty skeptical a bout the metros and low lands cashing in on much of a changeover

good point. and we don't often score when cold rushes as precip moves out sooner than modeled. 

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Here's further proof that some of the snow maps we are seeing from the GFS are simply processing artifacts.  Check out the following examples from Dupage and Pivotal.  The snow accumulation products are clearly not able to handle the fast-moving front and are incorrectly partitioning the precipitation between rain and snow.  However, the snow depth products do not have the same problem.  The GFS may still be wrong about 0.5-1.0" on the backside of the front, but that is the actual projection.

594627440_gfs6hrsnow.png.76e4903f2b5d6940b229d33a99f21bae.png1803885650_gfssnowdepth.png.b641fd9f19ea04ae89d7c4bfb3050c86.pngpivotal.thumb.png.888b51c2a944b551eb20b0616432b2c9.png1388596323_pivotaldepth.thumb.png.b03059b455d6107678aa6a70ef31f8a5.png

 

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The last time it was this cold on Christmas for this area was 1983.  And too, back then the wind chill numbers were different due to the scale changing.
And the last time we had real cold with wind was end of Jan 2019?
So many people are not used to this, Jack Frost is definitely going to be nipping for sure!

For the "storm of a lifetime" [sic] we may get a wind and wind chill advisories?

At least the bitter cold is relatively short lived!  Still, it doesn't take long to get logs stuck to the ground like they've been gorilla glued! :P

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1 hour ago, MN Transplant said:

Here's further proof that some of the snow maps we are seeing from the GFS are simply processing artifacts.  Check out the following examples from Dupage and Pivotal.  The snow accumulation products are clearly not able to handle the fast-moving front and are incorrectly partitioning the precipitation between rain and snow.  However, the snow depth products do not have the same problem.  The GFS may still be wrong about 0.5-1.0" on the backside of the front, but that is the actual projection.

 

         Here is how it works.     Inside the GFS, there is a bucket for snow accumulation.   Anything from the direct model integration of the microphysics scheme that reaches the ground as snow or sleet goes into the snow accumulation bucket as a liquid equivalent.   This liquid equivalent is output as a snowfall product.

          The snow (+ sleet) is also passed into the land-surface part of the model where an SLR is applied.   This determines how much snow is on the ground in the model.

           The disconnect has 2 sources:      1)  users apply their own ratios.  Most use 10:1, but some use the generous Kuchera.   Kuchera for this case will love the crashing temps and put some weenie ratios and end up with big accumulations     2)  the snow depth is instantaneous, and some melting (not in the Friday example) or compacting may occur by the time shown

            The model is absolutely "handling the fast-moving front".   Right or wrong, it has snow falling on the cold side of the front.   The products showing "snowfall" do have an element of post-processing artifacts, especially the Kuchera.

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6 minutes ago, NorthArlington101 said:

Unfortunately for our I-81 comrades the 12z EURO is putting out a icier solution than earlier runs. Cut back snow totals a decent bit.

1671728400-1HHbxGlFHtk.png

1671728400-vOFHFzCehW8.png

Quite the difference compared to the gfs for the I - 81 crew. (Mby included)

I wonder which one will be correct lol

:lol:

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