March 13/14th PSU Storm

[stormtracker]

2 minutes ago, snjókoma said:

The 3K NAM is not 6" for DC... its a couple inches of snow followed by hours and hours of pouring sleet followed by another inch. Meh. OPM would still be closed.

Agreed.  So far, NAM seems to be our worst case scenario, with GFS being the best.

[nj2va]

1 minute ago, snjókoma said:

The 3K NAM is not 6" for DC... its a couple inches of snow followed by hours and hours of pouring sleet followed by another inch. Meh. OPM would still be closed.

It'd be about 2" or so of snow for DC.  Like you said mostly sleet.  

[PivotPoint]

4 minutes ago, EB89 said:

3K Para

The nam's idea on that map looks pretty clear to me. It simply takes its time intensifying as opposed to some of the other guidance suggesting the intensification (and subsequent ccb forming) happening off the Delmarva as opposed to the nam which does it past cape may. Hence we lose 3-6 inches the other guidance is adding in.

[BTRWx]

Just now, stormtracker said:

Agreed.  So far, NAM seems to be our worst case scenario, with GFS being the best.

and that's okay 30 hours from the good stuff

[motsco]

sleet does accumulate.

[Deck Pic]

4k doesn't support the 12k at all. 

[MD Snow]

1 minute ago, WhiteoutMD said:

thats not what I see 

Actually, if you compare snowfall maps there is shift east in frozen accumulations (sleet etc) on both the 4k and 3k.

[yoda]

So... next up... 00z RGEM at 36 hrs (12z TUES)

[pasnownut]

Just now, Deck Pic said:

4k doesn't support the 12k at all. 

3k and 4k do not support 12k

 

Nut

 

[PivotPoint]

1 minute ago, nj2va said:

It'd be about 2" or so of snow for DC.  Like you said mostly sleet.  

That graphic you posted shows more then 2" for DC btw 

[high risk]

2 minutes ago, BTRWx said:

Is much of it rain like ttb shows with its somewhat questionable algorithm?

 

     those snow maps are great for cold snow events with no mixing issues and good ratios.    but they fail badly in events with mixing or marginal temps because:

1)   "pure" sleet gets added in to the totals

2)   even when it is actually snowing in the model, the 10:1 ratio is way too generous for these wet snow bombs

3)   if the model has 2" of liquid that's 50% raindrops and 50% mangled snowflakes, you'd never see that accumulate in the real world, but the model would spit out  2" x 50% = 1" liquid of snow.     TT then applies a 10:1 ratio giving a fictitious 10" of snow.

[stormtracker]

1 minute ago, yoda said:

So... next up... 00z RGEM at 36 hrs (12z TUES)

No doubt, probably warm with that low position

[Bob Chill]

Snow maps are inherently flawed and bad guidance when walking the line. It would go a long ways of people would post 850s and 925s, soundings etc that go along with qpf panels. Snowmaps are a great shortcut when it's an all snow event which this will not be for a good number of us. 

This is a discussion thead that goes into fine details at different levels of the atmosphere. A snow map or 2 if fine but the prolific posting of them without any other more detailed analysis isn't analyzing the complicated part of this storm. 

[BTRWx]

3 minutes ago, high risk said:

 

     those snow maps are great for cold snow events with no mixing issues and good ratios.    but they fail badly in events with mixing or marginal temps because:

1)   "pure" sleet gets added in to the totals

2)   even when it is actually snowing in the model, the 10:1 ratio is way too generous for these wet snow bombs

3)   if the model has 2" of liquid that's 50% raindrops and 50% mangled snowflakes, you'd never see that accumulate in the real world, but the model would spit out  2" x 50% = 1" liquid of snow.     TT then applies a 10:1 ratio giving a fictitious 10" of snow.

appreciate the good points, but I asked about the rain output...particularly around hr 30 http://www.tropicaltidbits.com/analysis/models/?model=nam3km&region=eus&pkg=mslp_pcpn_frzn&runtime=2017031300&fh=32&xpos=0&ypos=0

[snjókoma]

4K Nam is similar to the 3K... 3" of snow followed by sleet/rain followed by another 3". Again, not horrible. 

[high risk]

2 minutes ago, BTRWx said:

appreciate the good points, but I asked about the rain output...particularly around hr 30 http://www.tropicaltidbits.com/analysis/models/?model=nam3km&region=eus&pkg=mslp_pcpn_frzn&runtime=2017031300&fh=32&xpos=0&ypos=0

        I tried to answer that in point #3 but wasn't very clear.    If the model has all rain, it won't tally as snow.   But the model microphysics can keep track of multiple species and can mix things.    So while the precip type algorithm, based on the wet bulb temp profile may show rain, like in that map, the microphysics might actually have a mix.    And whatever part of that mix is sleet or snow will add to the snowfall tally.

[Amped]

Trend never stops.  Rgem digging even further southwest.

[DCAlexandria]

Trend never stops.  Rgem digging even further southwest.

Is that bad?


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[stormtracker]

Just now, DCAlexandria said:

Is that bad?


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Yes, for us

[snowfan]

Here's the 4k at 9z tue for dc and bwi. Pingers for dc, should be snow barely for bwi.

 

[Amped]

[BTRWx]

2 minutes ago, high risk said:

        I tried to answer that in point #3 but wasn't very clear.    If the model has all rain, it won't tally as snow.   But the model microphysics can keep track of multiple species and can mix things.    So while the precip type algorithm, based on the wet bulb temp profile may show rain, like in that map, the microphysics might actually have a mix.    And whatever part of that mix is sleet or snow will add to the snowfall tally.

Makes sense, thanks!

[mitchnick]

9 minutes ago, stormtracker said:

No doubt, probably warm with that low position

You feeling the same gut punch we've come to know and expect like I am?

[cae]

9 minutes ago, Bob Chill said:

Snow maps are inherently flawed and bad guidance when walking the line. It would go a long ways of people would post 850s and 925s, soundings etc that go along with qpf panels. Snowmaps are a great shortcut when it's an all snow event which this will not be for a good number of us. 

This is a discussion thead that goes into fine details at different levels of the atmosphere. A snow map or 2 if fine but the prolific posting of them without any other more detailed analysis isn't analyzing the complicated part of this storm. 

I think it depends on which snow map we're looking at.  The ones from TT are not very useful if you're in an area where there will be p-type issues.  But the pivotalweather ones factor out sleet and zr, and if you use the Kuchera ratio they also provide more realistic ratios for areas with borderline temps.  I find they paint a more realistic picture, probably better than I could by staring at a bunch of 850 and 925 maps.  (This is also because I have limited skill in this area.)  Unfortunately pivotal weather is relativley slow -- I'm still waiting for the 3k NAM to finish loading.

[Bob Chill]

Rgem track slp west of the sound in NC to overhead in OC. Thats a bad track and the midlevels take a beating. 

[WinterWxLuvr]

6 minutes ago, Bob Chill said:

Snow maps are inherently flawed and bad guidance when walking the line. It would go a long ways of people would post 850s and 925s, soundings etc that go along with qpf panels. Snowmaps are a great shortcut when it's an all snow event which this will not be for a good number of us. 

This is a discussion thead that goes into fine details at different levels of the atmosphere. A snow map or 2 if fine but the prolific posting of them without any other more detailed analysis isn't analyzing the complicated part of this storm. 

That's a good point.  Even the "better" looking NAMs have snow maps showing snow in North/South Carolina.  Those NWS offices are forecasting nothing of the sort. 

GFS will be out soon.  Put this NAM talk to bed.

[Buddy1987]

1 minute ago, stormtracker said:

Yes, for us

Shoot, usually that is a good look for us out this way, but 850s dont seem to be cooperating whatsoever so far tonight.

[EastCoast NPZ]

42 minutes ago, Bob Chill said:

Para nam zoomed QPF. Looking pretty nice with that kinda of distribution. 

Yes, please.

[Buddy1987]

Just now, Bob Chill said:

Rgem track slp west of the sound in NC to overhead in OC. Thats a bad track and the midlevels take a beating. 

Bob is there any positives for mid levels out this way with a track like that? Usually that is a good look for us out on the Blue Ridge.

[stormtracker]

Just now, mitchnick said:

You feeling the same gut punch we've come to know and expect like I am?

Yes sir.  It's gonna do what it do man.  I've already entered the acceptance stage.  I'm in for the ride at this point.  This is always high risk/high reward where we are.  Sometimes we pull all 7's and sometimes...well..we get that feeling we're getting now.   Maybe we can get a good amount of sleet at least?  Lemons, lemonade.