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January 6-7 Storm Discussion: we’re due?


WxUSAF
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21 minutes ago, WxUSAF said:

I love how on TT, the 3k NAM keeps accumulating snow even after the flip to rain. 

       That's because the code that accumulates snow is inside the model and is driven by microphysics, and the code that generates precip type is outside of the model and is driven (mostly) by the temperature profiles.

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5 minutes ago, high risk said:

       That's because the code that accumulates snow is inside the model and is driven by microphysics, and the code that generates precip type is outside of the model and is driven (mostly) by the temperature profiles.

If the code that accumulates snow is inside the model and driven by physics, then why are snow accumulations so wildly different on different websites? Presumably they all use the exact same data from the model.

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I AM GOING TO BE POSITIVE HERE

So don't miss it, and snow god's don't make me regret it

Something to keep an eye on... I wouldn't expect this per say, but if we are trying to be optimistic I see one thing today that leaves the door open somewhat for a better result NW of 95 here.  I am using the 3k NAM but I've noticed the same general trend in the euro its just a couple degrees warmer so not quite as close but going the same way

There has been a trend on the euro and NAM to weaken that inverted trough or trowal feature and allowing the developing coastal to develop a more closed circulation sooner.  This cools the column some compared to earlier runs.  

If you look close you can see that in the height fields here

GIF.thumb.gif.c9ec33bbeb659b5f5630dc25ce90c720.gif

The result is the column was VERY close to support snow during the most critical 3 hour period from 95 NW.

This was the 12z run...12z.thumb.png.5316e3ac523f06c5a3fd6d6764c2b6a5.png

That isn't really close in the yellow area.  Looking at soundings it was a pretty thick area of close to 2C above freezing in the mid levels.  
But look at 18z same time 

18z.thumb.png.d984d2a23794cf24b06639065627be7e.png

It's REALLY close to supporting snow.  I looked at soundings, 850 is about the warmest layer and its barely above freezing in this region.  One more move the same as this and it would be snow in this area.  

I didn't cherry pick this hour...it might even be colder the hour before and after if you look.

Before

before.thumb.png.dc03b0fd733ade9128be81fb6b19b49e.png

After

after.thumb.png.2ce8e43046627b9642ad47539441dbdd.png

  But this is in the middle of a 3 hour period where this area gets .3-.5 qpf.

nam-nest-md-precip_3hr_inch-4582000.thumb.png.4c2f554c725c0fa80742741fbfe65c50.png

If it were to be 1 degree colder that would mean a 3-4" thump in this area.  

It's possible, not likely but possible, that if this were to be just 1 degree colder than guidance thinks...suddenly if flips the other way in this area.  

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13 minutes ago, notvirga! said:

Yeah would just look at rgem as a trend. Its snowfall numbers are frequently bonkers 

It’s not just snowfall. Look at its precip totals. I’m telling you guys that’s the key. Heavy precip will do the trick for a lot of people.

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15 minutes ago, Weather Will said:

WB 18Z RDPS 25% of this would be more than I have had in over 2 years....

IMG_2674.png

If this holds then I’m skinning all the way to the top of Whitetail even if they’re too bone-headed to reopen.

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25 minutes ago, NorthArlington101 said:

18z RGEM ticked better for the cities... better for everyone, really. Still goes nutso for our favored spots.

sn10_acc-imp.us_ma.png

Rgem snow algorithm must be more generous. Its thermals are almost identical to the 3k I posted but it leans snow v rain on those clown maps. It is wetter too. 

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6 minutes ago, WinterWxLuvr said:

It’s not just snowfall. Look at its precip totals. I’m telling you guys that’s the key. Heavy precip will do the trick for a lot of people.

I agree with you about that. Definitely will need the heavy precip for good accumulations but no one is getting a foot of snow in Winchester, 3-6 or 4-8 is probably top end. This is the model that gave me 45 inches in one storm a couple years ago and I got 3. 

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28 minutes ago, SnowDreamer said:

If the code that accumulates snow is inside the model and driven by physics, then why are snow accumulations so wildly different on different websites? Presumably they all use the exact same data from the model.

      Do you have an example?    The 10:1 maps should be the same everywhere.     The snow depth maps should be too, except that while Tropical Tidbits only counts positive changes in depth (i.e. they ignore when the amount goes down due to melting or compacting), while others may count any change.      Even the Kuchera method should, in theory, yield the same result across sites.

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18z GFS splashes my neck of the woods with a half-inch tomorrow evening, up from snow TV in most prior runs.

I'll let you folks know how she's coming in as she steers across the middle of the country. Rooting for y'all to get a hit after a very disappointing winter last year.

Good luck!

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2 minutes ago, NorthArlington101 said:

at the 850 level. This kind of stuff basically kills the thump in the cities. does it ever go the opposite way? :underthewx:

1704556800-fuu35tAo8gc.png

As others have said, the GFS (and/or all the models) have to get QPF and/or intensity right to get surface temps correct. DP's leading in are cold, give folks heavy precip and I'm thinking they'll roll the dice - a la what PSU said. 

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5 minutes ago, NorthArlington101 said:

at the 850 level. This kind of stuff basically kills the thump in the cities. does it ever go the opposite way? :underthewx:

1704556800-fuu35tAo8gc.png

A degree or so in F is noise. Nothing has changed today. Still time to bleed colder and the mesos can catch that better than the globals.

Also, higher thumpy qpf will help, not hurt. 18z is a bit lighter than 12z

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Personally, in these really marginal temp event,  I use the snow depth product.  It's more conservative with amounts which is a good think. If it's really cold other snow maps are probably preferable.  The GFS snowdepth product from the 18Z run.  6597273e42172.png

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