February 8-9 Cold Rain Event

[Fozz]

7 minutes ago, nw baltimore wx said:

I can't recall which red-tagger said it (maybe das), but I'm fairly sure they said that the 4k nam has been getting the best verification scores of the nam nest.  This was about 3 weeks ago.  Of course, having said that, I don't think it did very well in the most recent "storm."

I'm really glad to hear that. Let's hope it nails the changeover time for us.

[RUMG11]

1 minute ago, high risk said:

Here is super important point to realize about NAM snowfall maps:    if the model has 1" of liquid for an event, and the model thinks that during all of the precip, half of the elements falling from the sky are snowflakes and half are raindrops, it generates 0.5" liquid as snow.    The 10:1 ratio is then applied to get 5" of snow, even though we all know that a 50/50 rain/snow mix won't accumulate 5".    The best parameter to check is the accumulated snow depth from f00 on the EMC page.   You can see it for the NAM nest (4km), with a northeast zoom, near the bottom of  http://www.emc.ncep.noaa.gov/mmb/mmbpll/nam_conusnest/

 

   I've attached the 6z plot of snow depth from f00 (the start).    Even though the TT map shows a lot of central MD getting good accumulations, the model thinks that very little is on the ground by 15z Thursday, until you get up to the MD/PA line.

Great post. This is due to the extreme mixing to start, and just how far north the R/S line pushes. The straight QPF maps undersell how much snow accum is lost due to rain and initial melt off once snow takes over.

[mappy]

3 minutes ago, high risk said:

Here is super important point to realize about NAM snowfall maps:    if the model has 1" of liquid for an event, and the model thinks that during all of the precip, half of the elements falling from the sky are snowflakes and half are raindrops, it generates 0.5" liquid as snow.    The 10:1 ratio is then applied to get 5" of snow, even though we all know that a 50/50 rain/snow mix won't accumulate 5".    The best parameter to check is the accumulated snow depth from f00 on the EMC page.   You can see it for the NAM nest (4km), with a northeast zoom, near the bottom of  http://www.emc.ncep.noaa.gov/mmb/mmbpll/nam_conusnest/

 

   I've attached the 6z plot of snow depth from f00 (the start).    Even though the TT map shows a lot of central MD getting good accumulations, the model thinks that very little is on the ground by 15z Thursday, until you get up to the MD/PA line.

Thanks for the post. It's also why I posted a QPF map to follow. No way am I seeing 9-10" of snow from this. Half of that is realistic given this will not be a 10:1 ratio kind of snow. However, the maps are pretty to look at  

[gymengineer]

3 minutes ago, high risk said:

Here is super important point to realize about NAM snowfall maps:    if the model has 1" of liquid for an event, and the model thinks that during all of the precip, half of the elements falling from the sky are snowflakes and half are raindrops, it generates 0.5" liquid as snow.    The 10:1 ratio is then applied to get 5" of snow, even though we all know that a 50/50 rain/snow mix won't accumulate 5".    The best parameter to check is the accumulated snow depth from f00 on the EMC page.   You can see it for the NAM nest (4km), with a northeast zoom, near the bottom of  http://www.emc.ncep.noaa.gov/mmb/mmbpll/nam_conusnest/

 

 I've attached the 6z plot of snow depth from f00 (the start).    Even though the TT map shows a lot of central MD getting good accumulations, the model thinks that very little is on the ground by 15z Thursday, until you get up to the MD/PA line.

 

That would be quite a bust for the coastal cities that are currently under a WSWarning. 

[WxUSAF]

Thanks high risk. That makes sense because TT looks weird saying 2" otg IMBY by 9z when it's clearly still raining or maybe rain snow mix. 

NAMs all show it clearly that snow will be heavy once it flips around 9-11z, depending on location, but it's not going to last long. Going to be like 3-4 hours of meteors tops, so better hope it can stick. 

Euro continues to look different in the low placement and associated heaviest precip. Well, I guess the Canadian agrees. 

[osfan24]

Just now, gymengineer said:

That would be quite a bust for the coastal cities that are currently under a WSWarning. 

Yeah that map looks overdone. It gives NYC no snow basically, instead of a foot. Seems highly unlikely.

[BTRWx]

Thoughts on the latest surface analysis?  I like the look...

 

 

[RUMG11]

Give me the Euro + CMC over the NAM any day of the week. 3-4 years ago we'd all be saying that 

[high risk]

1 minute ago, gymengineer said:

That would be quite a bust for the coastal cities that are currently under a WSWarning. 

 

  Well, I only posted a map that's through 15z Thursday.    The problem with looking at a map later in the day is that you really want to look at these maps right after the snow ends in your area, as the snow depth parameter accounts for compacting and melting.     The plots later on show that Boston does fine, but it could indeed be a much closer call in NYC and PHL.

    

[packbacker]

14 minutes ago, Fozz said:

How good was the 4K NAM?

Because looking at that, I'd lock that one up right away.

4km NAM was probably best with temps/mid levels.  For QPF, a blend of the GEFS/EPS mean was close to what verified.  Good luck, I hope it snows for as big of area as possible...screw this nina. 

[mitchnick]

1 minute ago, BTRWx said:

Thoughts on the latest surface analysis?  I like the look...

 

that map is an hour or two old when we get it

better to go here where it updates at the half hour

[high risk]

2 minutes ago, osfan24 said:

Yeah that map looks overdone. It gives NYC no snow basically, instead of a foot. Seems highly unlikely.

 

    well, here's the map later in the day.   certainly suggests that NYC, Newark, and points east have a close call on big amounts.   Again, this is the 6z run.   The 12z graphics aren't available for a while yet.

[gymengineer]

1 minute ago, high risk said:

 

  Well, I only posted a map that's through 15z Thursday.    The problem with looking at a map later in the day is that you really want to look at these maps right after the snow ends in your area, as the snow depth parameter accounts for compacting and melting.     The plots later on show that Boston does fine, but it could indeed be a much closer call in NYC and PHL.

    

NYC and PHL have both had our 3/6/13 style busts over the years too. 

[RUMG11]

5 minutes ago, osfan24 said:

Yeah that map looks overdone. It gives NYC no snow basically, instead of a foot. Seems highly unlikely.

Now you understand why mets don't simply take whatever QPF the models spit out and make it their forecast. There's a ton going on with this system. Go feel outside right now lol

[BTRWx]

3 minutes ago, mitchnick said:

that map is an hour or two old when we get it

better to go here where it updates at the half hour

Thanks, also weatherscope is near real-time.  The WPC map implies to me that the front is advancing quicker than forecast.  What do you all think?

[Fozz]

7 minutes ago, high risk said:

 

    well, here's the map later in the day.   certainly suggests that NYC, Newark, and points east have a close call on big amounts.   Again, this is the 6z run.   The 12z graphics aren't available for a while yet.

 

14 minutes ago, mappy said:

Thanks for the post. It's also why I posted a QPF map to follow. No way am I seeing 9-10" of snow from this. Half of that is realistic given this will not be a 10:1 ratio kind of snow. However, the maps are pretty to look at  

This is why I want the models to give my area at least 6" of snow. Not because I won't be happy to see 3-4", but because if any less of it falls as snow in such a marginal storm, that will probably lead to a very dicey situation with a lot of the snow possibly not even accumulating or with a delay in the changeover really screwing things up.

[mappy]

1 minute ago, Fozz said:

 

This is why I want the models to give my area at least 6" of snow. Not because I won't be happy to see 3-4", but because if any less of it falls as snow, that will probably lead to a very dicey situation with a lot of the snow possibly not even accumulating or with a late changeover really screwing things up.

Yup -- I know what you mean. Every little bit helps. 

[yoda]

12z RGEM at 12 hrs 1003mb SLP extreme SE KY (or right over where the borders of KY/WV/VA meet)

24 hrs 993mb SLP ~100 miles east of Ocean City

[BTRWx]

13 minutes ago, mitchnick said:

that map is an hour or two old when we get it

better to go here where it updates at the half hour

 

4km 12z NAM below

 

[Fozz]

13 minutes ago, mappy said:

Yup -- I know what you mean. Every little bit helps. 

That's also why I think there will be a very sharp gradient (probably sharper than what the maps show), which I hope is south of me but it may very well be between us. Those who get the changeover while the heavy precip is falling will see a lot more snow than those who don't change over until the storm is almost over (which might be only a 10 mile difference in some cases), and that especially matters when the previous day was 65 degrees.

[BTRWx]

Here is a better comparison for dp.

 

4km NAM

Weatherscope dp Screenshot for 10am

[yoda]

Anything on how good the WRF-NMM is?  Cause we'd all run with this

[mappy]

6 minutes ago, Fozz said:

That's also why I think there will be a very sharp gradient (probably sharper than what the maps show), which I hope is south of me but it may very well be between us. Those who get the changeover while the heavy precip is falling will see a lot more snow than those who don't change over until the storm is almost over (which might be only a 10 mile difference in some cases), and that especially matters when the previous day was 65 degrees.

I'm not too worried about temps today, yes, not so high today means less dropping tonight, however, temps still need to drop regardless of it being 65 or 55 for a high. The cold air could stall and everyone is screwed. 

For my backyard specifically (per 4km NAM) -- I don't hit freezing until 4am, but my column is plenty cold prior to that. So I could be at 34° or 33° and snow. That will add to accumulations, albeit on grassy/deck surfaces, vs waiting until it's actually 32 at the surface. Rates will definitely matter. Best hour of precip is between 3-4am with close to .3 qpf for me in that hour. Impressive for sure, if it's snowing of course. 

[RUMG11]

RGEM is holding steady... keeps the R/S much further SE then the NAM

[Interstate]

Looks like the RGEM is slower this run

[SomeguyfromTakomaPark]

RGEM takes the low across the bay around where the rappahannock river enters the bay.

 

9z - Temp high 30s in DC with heavy rain

12z - Temp below freezing and snow

[NorthArlington101]

1 minute ago, yoda said:

Anything on how good the WRF-NMM is?  Cause we'd all run with this

 

I always thought that it was one of the two SREF model cores... But I'm realizing that I'm wrong. No idea what that it, I usually only check it when I'm desperate. 

[Paleocene]

FWIW the position of the low at 00z tonight on the 12z RGEM matches last night's euro almost exactly - centered over southern WVA. However, the RGEM run looks too warm for snow around the beltway as the low passes to our south.

[NorthArlington101]

Take it and run!

[yoda]

We buy and run with the 12z RGEM

Damn it, ninja'd by NorthArlington