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December 16-17, 2020 Winter Storm Obs/Nowcasting

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@mappy @losetoa6 @Eskimo Joe @HighStakes @showmethesnow @DDweatherman 

I have been super busy all day...today was a big due day for tons of paperwork and reports before the holiday break.  So forgive me if this was discussed, I haven't been able to keep up.  But wanted to highlight the chances for our area tonight to get a little surprise.  I am going to use the 18z euro because it has been the most consistent on the train...shown it for 5 runs straight now and it gets more pronounced every run.  For the record the NAM's don't really like this idea...the HRRR is hit or miss run to run, but the RGEM 10K and 3K both are in the euro camp.  

We can see that area of precip breaking out to our SW in response to the mid and upper level energy approaching from the ohio valley...

image1.thumb.png.fc3fe5be878d3daa38cd23d5105b8e18.png

 

image2.thumb.png.5d66a9a1d1e1ad9455034d1a4e9b5f9c.png

 

image2.1.thumb.png.566ee0f3d42506e7a66259a228ab2ddf.png

But as of now that energy is not phased up with the coastal and the developing precip is mostly mid and upper level instability related without any connection to the deep moisture transport associated with the coastal system.

However...by 6z we can see the mid and upper levels have caught up and are phasing in with the coastal system and the results to the banding of precip (if that does indeed happen in sync like that) over our area.

image3.thumb.png.6942331cb8a6390a4ace695291023191.png

image4.thumb.png.907869018cffb70288a144ac61051483.png

image5.thumb.png.942447a76c729dcde66b8ba9c1d9b80d.png

As the mid and upper level energy catches up to the surface system and phases that mid and upper level energy and instability will now have access to deeper moisture transport from the coastal.  So we see the banding associated with it really explode.  Keep in mind this is a 1 hour precip plot so that is heavy precip across all of central and northeastern MD.  The red line denotes where I believe the rain snow line would be at this time.  Looking at soundings across guidance the wam layers left at that time are thin enough that heavy precip would overcome north of that line...but that precip moves out slowly over the next 4 hours and that line sags south a bit.  

This next plot is the precip associated with that band that falls between 3z and 9z.  The purple line is my estimate of where north of there all of this would be snow.  The red line is the southern extent of where the changeover gets before about 80% of the precip is moving out.  Not saying there cannot be any snow TV south of that line...but that is my estimate of where I think it is reasonable to think accumulating snowfall could get with this band.  But keep in mind...if that band were to really get going more then even this prog shows....it could cool the column as the heights crash further south.  Stranger things have happened.  Probably the best example of a banding feature like this maxing out was that xmas day miracle snow we got in 2002.  

image6.thumb.png.712377009cdd3ee43d4ea31f83f3d6f0.png

From the QPF if the euro is correct this could actually be a pretty sizeable amount along the northern tier of MD.  Some places could get 4-6" which is an event in its own right.  Maybe even more if everything maxes out perfectly.  Of course...if the mid and upper level energy fails to sync up perfectly it could all just be a band of light precip that cannot overcome the leftover warm layers near 800mb and nothing comes of it.  

Now...how likely is this.  The Euro has been doubling down every run for over 24 hours.  The short range Canadian twins agree.  The HRRR is kinda in between and the NAM says no thank you...it has the banding but too light to trigger the cooling needed to result in anything significant south of the PA line.  The upper level pass is slightly north of ideal...but not bad.  The mid level pass is really good.  It's a matter of do they sync up right.  Models suck at that.  These things surprise both good and bad all the time.  I am going to be an optimist here and say this does come together and we have a decent shot at some accumulating snow across the northern tier of MD tonight.  

 

 

 

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Officially had 0.6" in Crofton before the slopfest, and 0.8" at the NCWCP in College Park. Pretty tight gradient into northern AA with over an inch in Odenton, 2" in Severn. 

Looking at the CTP obs thread in the PA/NY group makes me want to cry. Getting raked up there, now over a foot in many areas. 

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3 minutes ago, BristowWx said:

IP/SN mix now 31.  Let’s see where this goes.  

31 here as well in Gainesville. Loud ice pellets atm

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2 minutes ago, BristowWx said:

IP/SN mix now 31.  Let’s see where this goes.  

I had to go check the street light after your observation.  I am not sure if there is any snow mixed in yet here, or if there are just some really big chunks of ice falling from the sky.  Either way, it is some interesting weather tonight. 

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1 minute ago, PWC Split said:

I had to go check the street light after your observation.  I am not sure if there is any snow mixed in yet here, or if there are just some really big chunks of ice falling from the sky.  Either way, it is some interesting weather tonight. 

Yes big chunks.  Saw them in the light.  Went outside it’s  IP and drizzle.  May not go to snow..or it might. 

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10 minutes ago, psuhoffman said:

@mappy @losetoa6 @Eskimo Joe @HighStakes @showmethesnow @DDweatherman 

I have been super busy all day...today was a big due day for tons of paperwork and reports before the holiday break.  So forgive me if this was discussed, I haven't been able to keep up.  But wanted to highlight the chances for our area tonight to get a little surprise.  I am going to use the 18z euro because it has been the most consistent on the train...shown it for 5 runs straight now and it gets more pronounced every run.  For the record the NAM's don't really like this idea...the HRRR is hit or miss run to run, but the RGEM 10K and 3K both are in the euro camp.  

We can see that area of precip breaking out to our SW in response to the mid and upper level energy approaching from the ohio valley...

image1.thumb.png.fc3fe5be878d3daa38cd23d5105b8e18.png

 

image2.thumb.png.5d66a9a1d1e1ad9455034d1a4e9b5f9c.png

 

image2.1.thumb.png.566ee0f3d42506e7a66259a228ab2ddf.png

But as of now that energy is not phased up with the coastal and the developing precip is mostly mid and upper level instability related without any connection to the deep moisture transport associated with the coastal system.

However...by 6z we can see the mid and upper levels have caught up and are phasing in with the coastal system and the results to the banding of precip (if that does indeed happen in sync like that) over our area.

image3.thumb.png.6942331cb8a6390a4ace695291023191.png

image4.thumb.png.907869018cffb70288a144ac61051483.png

image5.thumb.png.942447a76c729dcde66b8ba9c1d9b80d.png

As the mid and upper level energy catches up to the surface system and phases that mid and upper level energy and instability will now have access to deeper moisture transport from the coastal.  So we see the banding associated with it really explode.  Keep in mind this is a 1 hour precip plot so that is heavy precip across all of central and northeastern MD.  The red line denotes where I believe the rain snow line would be at this time.  Looking at soundings across guidance the wam layers left at that time are thin enough that heavy precip would overcome north of that line...but that precip moves out slowly over the next 4 hours and that line sags south a bit.  

This next plot is the precip associated with that band that falls between 3z and 9z.  The purple line is my estimate of where north of there all of this would be snow.  The red line is the southern extent of where the changeover gets before about 80% of the precip is moving out.  Not saying there cannot be any snow TV south of that line...but that is my estimate of where I think it is reasonable to think accumulating snowfall could get with this band.  But keep in mind...if that band were to really get going more then even this prog shows....it could cool the column as the heights crash further south.  Stranger things have happened.  Probably the best example of a banding feature like this maxing out was that xmas day miracle snow we got in 2002.  

image6.thumb.png.712377009cdd3ee43d4ea31f83f3d6f0.png

From the QPF if the euro is correct this could actually be a pretty sizeable amount along the northern tier of MD.  Some places could get 4-6" which is an event in its own right.  Maybe even more if everything maxes out perfectly.  Of course...if the mid and upper level energy fails to sync up perfectly it could all just be a band of light precip that cannot overcome the leftover warm layers near 800mb and nothing comes of it.  

Now...how likely is this.  The Euro has been doubling down every run for over 24 hours.  The short range Canadian twins agree.  The HRRR is kinda in between and the NAM says no thank you...it has the banding but too light to trigger the cooling needed to result in anything significant south of the PA line.  The upper level pass is slightly north of ideal...but not bad.  The mid level pass is really good.  It's a matter of do they sync up right.  Models suck at that.  These things surprise both good and bad all the time.  I am going to be an optimist here and say this does come together and we have a decent shot at some accumulating snow across the northern tier of MD tonight.  

 

 

 

we love when you talk dirty. 
 

Thank you for the breakdown. I hope so! I’m dead smack in that area

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8 minutes ago, MN Transplant said:

That central PA radar is gorgeous.

I have family in Scranton, they have travel emergency notices going to their phones.  I hope to be getting pics tomorrow morning.

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1 minute ago, Chris78 said:

Had about .5 of sleet this evening for a total of 6" so far of snow/sleet.

 

Snow is trying to mix back in now. Moderate sleet/ snow mix now.

I think the changeover is finally occurring now here too....after several head fakes.

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Just now, DDweatherman said:

And as @psuhoffman said the NAM was out, it throws us some snow tonight on the 0z.

That ULL catches the coastal quick enough and I think our area sees an additional 3” or so

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Just finished shoveling 180 feet of aleety slush mushy icy mess.. And it started sleeting like crazy. Everything is covered and white again with ice pellets. Snow is trying to get involved but it is slow to transition. That was not fun. But it kind of was fun! 

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Seems  like the dry slot and warm nose always goes further  north and west than expected. Alot  of TWC reporters not  in snow.

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1 minute ago, snowmagnet said:

I was stuck at 32.5 for several hours. Finally around 31 now.  It still is raining, but sounds a bit more icy, maybe changing over a bit. 

Yeah didn’t think this would be much ZR but there are trees hanging down everywhere here.  Can’t buy a flake however since about 1.  

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1 minute ago, jayyy said:

That ULL catches the coastal quick enough and I think our area sees an additional 3” or so

You’d think with almost all models hitting on that now at <6 hrs lead time, we should get a couple inches... and it would dump pretty good with the ULL. 

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Just now, ldub23 said:

Seems  like the dry slot and warm nose always goes further  north and west than expected. Alot  of TWC reporters not  in snow.

yeah sadly funny thing is some one called me out saying i was lying about the dry slot.

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