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

[high risk]

4 minutes ago, usedtobe said:

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.  

   Good to see you here @usedtobe!      I'm also a huge proponent of the snow depth product in these marginal temperature events, but I like to throw in the caveat that it will be underdone in these type of events if the rates are really good.    

[nj2va]

8 minutes ago, umdterps29 said:

Is this the type of storm that will have upslope for the Garrett County area? If so, is the upslope intensity usually modeled pretty accurately, or is it typically more/less intense than what is shown on these models?

Garrett County may get some orographic enhancement from the LP as it’s in our area.  Upslope would come on the back-end as the low is heading NE away from the area.  You want to root for the follow up wave that GFS has been keying in to deepen the storm and ‘bomb’ it out for SNE.  That energy as it crosses the mountains and deepens the SLP off the east coast would provide some extra lift for upslope snow showers.  

18z GFS shows this scenario.  Garrett County and the mountains get more snow from the upslope than the initial storm.

[psuhoffman]

12 minutes ago, high risk said:

      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.

TT seems to count qpf other sites deem non snow.  It’s always crazy generous on the south side compared to all other outlets. 

[psuhoffman]

@high risk example 

[Deck Pic]

My backyard is looking increasingly like this...maybe i'll be able to swing 0.75" or something

10 am  Light snow 35

11 am Light to moderate snow 33-34

11:30 am Mod snow 33

12:30 pm Mix 34

1:30 pm Rain 35

 

[Terpeast]

Just now, psuhoffman said:

@high risk example 

Is it like that for 3k too?

[high risk]

1 minute ago, psuhoffman said:

TT seems to count qpf other sites deem non snow.  It’s always crazy generous on the south side compared to all other outlets. 

             Assuming you're talking about 10:1 maps?   That's really odd, as the models generate a water equivalent of snow field in mm that should simply be converted to inches and multiplied by 10.      The only thing that they could be doing is trying to make their own determinations about how much of a period of QPF is snow, but that would involve a lot of assumptions on their end that would not work well.     I'd be very interested in seeing an example.

[Fozz]

10 minutes ago, umdterps29 said:

Is this the type of storm that will have upslope for the Garrett County area? If so, is the upslope intensity usually modeled pretty accurately, or is it typically more/less intense than what is shown on these models?

Good upslope requires a stronger surface low than what this storm is offering.

[clskinsfan]

Rgem just refuses to budge at all. It's going to go down in flames most likely. But it is a stubborn bastard man. 

[high risk]

2 minutes ago, psuhoffman said:

@high risk example 

       Thanks for this example!    WB must be making their own determinations about how much QPF is going into each precip type.     As I mentioned, the only "accounting" in the actual models (RAP/HRRR excluded) is a snow water equivalent bucket that counts whatever fraction of the falling precip is snow or sleet.     It's "good" in that the WB approach wipes out the sleet and also the accumulations when the profile doesn't support pure snow, but they're trying to match precip the accumulates over a longer period of time with the instantaneous precip type, so that won't always work very well.

       Ultimately, the RAP/HRRR do things the right way:  they have separate buckets for each precip type and output each of them.   It removes the guesswork.    This approach will be used in the new RRFS, and the GFS is going to adopt it too.

[nj2va]

5 minutes ago, Fozz said:

Good upslope requires a stronger surface low than what this storm is offering.

MLK 2022 was a top 5 favorite storm for me - the upslope was epic for ‘part 2’ of that.  Blizzard conditions at times.  IIRC, you were staying in Accident or close by and chased that event right?  The 500 energy that enhanced the upslope was textbook.  This is definitely not that, ha.

[psuhoffman]

14 minutes ago, BTRWx's Thanks Giving said:

This particular frame from the euro gives me hope. It tries to stay frozen not far from D.C. almost up to the end of the precip. With these dynamics from this map, would that imply sleet?

Look at my post last page. I used the 3k NAM but I noticed it on the euro. Same thing you’re referencing. 

[Ellinwood]

20 minutes ago, usedtobe said:

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.  s

Snow depth maps are precisely my main influences with my forecast for this system, though with some touch-ups because some web sites will under-do snow depth if the rates can overcome the marginal surface temps.

[WesternFringe]

11 minutes ago, Terpeast said:

Is it like that for 3k too?

Yes, always is.  I notice it when comparing Pivotal maps vs TT

[psuhoffman]

10 minutes ago, Terpeast said:

Is it like that for 3k too?

Years ago it was like that for everything. I don’t even look at them usually so can’t say anymore. 

[psuhoffman]

6 minutes ago, high risk said:

       Thanks for this example!    WB must be making their own determinations about how much QPF is going into each precip type.     As I mentioned, the only "accounting" in the actual models (RAP/HRRR excluded) is a snow water equivalent bucket that counts whatever fraction of the falling precip is snow or sleet.     It's "good" in that the WB approach wipes out the sleet and also the accumulations when the profile doesn't support pure snow, but they're trying to match precip the accumulates over a longer period of time with the instantaneous precip type, so that won't always work very well.

       Ultimately, the RAP/HRRR do things the right way:  they have separate buckets for each precip type and output each of them.   It removes the guesswork.    This approach will be used in the new RRFS, and the GFS is going to adopt it too.

Thanks for the info!  

[psuhoffman]

6 minutes ago, nj2va said:

MLK 2022 was a top 5 favorite storm for me - the upslope was epic for ‘part 2’ of that.  Blizzard conditions at times.  IIRC, you were staying in Accident or close by and chased that event right?  The 500 energy that enhanced the upslope was textbook.  This is definitely not that, ha.

I was at snowshoe for that. Was epic! 

[psuhoffman]

6 minutes ago, SnowDreamer said:

@high risk

@Terpeast

The Tropical tidbits map are particularly bad, but they DO say *includes sleet*, so I give them a pass for being way way off. Here's another example from the 3K between WxBell and Pivotal. Granted it's not the most relevant example, but these maps do not look close to me in the circle area. 

One is 12z the other 18z

[SnowDreamer]

2 minutes ago, psuhoffman said:

One is 12z the other 18z

Well **** me. Thanks lol

[clskinsfan]

8 minutes ago, SnowDreamer said:

@high risk

@Terpeast

The Tropical tidbits map are particularly bad, but they DO say *includes sleet*, so I give them a pass for being way way off. Here's another example from the 3K between WxBell and Pivotal. Granted it's not the most relevant example, but these maps do not look close to me in the circle area. 

 

Yes. They are not quite at the point to be correct about micro climates. But they have gotten much better about incorporating elevation into them. Especially the Blue Ridge. Getting better all of the time. 

[clskinsfan]

3 minutes ago, psuhoffman said:

One is 12z the other 18z

True. But I get his point. 

[AtlanticWx]

this is just a thought but shouldn't the snow stick almost immediately because of how cold the ground is from the two days of pretty cold temperatures along with those 20 degree DPs up until onset? why use snow depth 

[WinterWxLuvr]

50 minutes ago, psuhoffman said:

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. 

A lot wetter

[Ellinwood]

2 minutes ago, AtlanticWx said:

this is just a thought but shouldn't the snow stick almost immediately because of how cold the ground is from the two days of pretty cold temperatures along with those 20 degree DPs up until onset? why use snow depth 

Surface temperatures are marginal for a good chunk of the area (just above freezing) and much of the event occurs during daylight hours and questionable snow rates. Getting good rates will be key in the more marginal areas. There's also a relatively stout isothermal layer in the lower levels that will likely hurt accumulation in lighter rates. A lot of the accumulation for the 1-3" crew will depend on how heavy the rates are and how long the heavier rates last.

[WxUSAF]

Snow depth is good to check against in marginal situations like this but I’m not sure I’ve ever seen actually accumulations that match snow depth forecasts. Even the December post-deluge changeover beat the snow depths by like a factor of 2.

[EastCoast NPZ]

T - 2" in the Shen Valley

2 - 4" elevations > 1000 ft.

Areas to the East - good luck.

Mt. PSU could jack in the middle of the Sahara, so 6" for him.

My first and final calls.  Let's see how I do.

[snownut]

52 minutes ago, EastCoast NPZ said:

T - 2" in the Shen Valley

2 - 4" elevations > 1000 ft.

Areas to the East - good luck.

Mt. PSU could jack in the middle of the Sahara, so 6" for him.

My first and final calls.  Let's see how I do.

4” or bust in your backyard!

I have siblings in Front Royal, Stephens City, Clearbrook and kids in Leesburg and Aldie so I will get their updates.  

I will send you photos next week of the 50 “ plus expected here over the next 8 days

[high risk]

6 minutes ago, WxUSAF said:

Snow depth is good to check against in marginal situations like this but I’m not sure I’ve ever seen actually accumulations that match snow depth forecasts. Even the December post-deluge changeover beat the snow depths by like a factor of 2.

     That's fair.    The depth field is underdone in events with warm ground going in, marginal temps, and good rates.     But it's a strong alternative to 10:1 maps when you have a lot of sleet (or other mix) or poor rates with marginal temps.     In events that argue for rates overcoming temps, a blend of the 10:1 and snow depth, with a solid lean towards the depth, often works well.  

[clskinsfan]

28 minutes ago, EastCoast NPZ said:

2 - 4" elevations > 1000 ft.

I know you have been screwed a lot the past few years. But you are gonna get more than 4 at your new house. I will be completely shocked if I am wrong. These are the storms I promised you that your move would cash in on. 

[EastCoast NPZ]

3 minutes ago, clskinsfan said:

I know you have been screwed a lot the past few years. But you are gonna get more than 4 at your new house. I will be completely shocked if I am wrong. These are the storms I promised you that your move would cash in on. 

I'm back in stephens city now.  My old place out in the Junction will probably do ok; I had 1,000' there and it was usually 3F colder than Winchester.  In the low-lands of Stephens City and it's odd UHI, I'm ****ed.  I was here for 10 years prior and I know exactly how these marginal events go.