“Cory’s in LA! Let’s MECS!” Jan. 24-26 Disco

[dendrite]

Just now, EastonSN+ said:

GFS AI gets the 540 line pretty far inland.

 

That won’t matter in this with a SW flow setup. The big warming influence on those thicknesses are 700mb and higher and those levels are plenty cold for snow. 

[Layman]

2 minutes ago, EastonSN+ said:

GFS AI gets the 540 line pretty far inland.

 

Is there an easy, noob-friendly answer as to the significance of the 540 line?

[dryslot]

Its a pretty deep DGZ on this one.

[WxWatcher007]

Just now, dryslot said:

Its a pretty deep DGZ on this one.

Just throw as much precip as possible back our way and north country climo will handle the rest. 

[Sey-Mour Snow]

The NBM is wild.. looking deeper at the online tools gsl website..

Has snow liquid ratios 16-18:1 to start for many, dropping closer to 12:1 at the end of overrunning.. with 1-1.5" qpf for all of SNE..  

 

 

[dendrite]

5 minutes ago, Layman said:

Is there an easy, noob-friendly answer as to the significance of the 540 line?

It’s the thickness of the 1000-500mb layer and it’s dependent upon the average temperature of the layer. The warmer it is…the more it “expands”…the taller is it. The colder….the more dense…the lower it is. But this isn’t a standard avg 1000-500 layer…this airmass will be biased cold in the lower half and warmer than average in the upper half. So the 540 thickness rule of thumb for RA vs SN doesn’t really apply. Forecast soundings are better and easy to find for all models today. If you’re going to bother with thickness it would be better to use partial ones like 700-850 for midlevel warming.

[Typhoon Tip]

I'm with Brian on that ... I wasn't or hadn't had a chance rather to look at those specific mid level mechanisms but if we're SE of a 700 mb closed circulation envelopes, then even if we do get a coastal going like that 990mb ( which is just getting respectable actually - ) there will be vestiges and interference preventing impacts from that latter..

Course, we could lose some of that in future guidance ... just speaking to what we see at this time.  

Also, not to be contrary to the first point, still ...we don't need to ton of support above 700 mb to generate CCB snow...that's kind of wild card there.  I think Will might have just hinted at this but if there's a growth region subtended below the 700 where there is a generating 850 to 925 E anomaly/moisture insert... there can be some accumulating snow production falling in that shallower layer. 

[Layman]

2 minutes ago, Southshorewx said:

On normal days/storms that is the line for surface temp 32°. This setup is running into a ton of cold air and blocking so doesn't mean as much.

 

1 minute ago, dendrite said:

It’s the thickness of the 1000-500mb layer and it’s dependent upon the average temperature of the layer. The warmer it is…the more it “expands”…the taller is it. The colder….the more dense…the lower it is. But this isn’t a standard avg 1000-500 layer…this airmass will be biased cold in the lower half and warmer than average in the upper half. So the 540 thickness rule of thimb for RA vs SN doesn’t really apply. Forecast soundings are better and easy to find for all models today. If you’re going to bother with thickness it would be better to use partial ones like 700-850 for midlevel warming.

Very helpful and understandable - thank you both!

[ORH_wxman]

3 minutes ago, Typhoon Tip said:

I'm with Brian on that ... I wasn't or hadn't had a chance rather to look at those specific mid level mechanisms but if we're SE of a 700 mb closed circulation envelopes, than even if we do get a coastal going like that 990mb ( which is just getting respectable actually - ) there will be vestiges and interference preventing impacts from that latter..

Course, we could loos some of that in future guidance ... just speaking to what we see at this time.  

Also, we don't need to ton of support above 700 mb to generate CCB snow...that's kind of wild card there.  I think Will might have just hinted at this but if there's a growth region subtended below the 700 where there is a generating 850 to 925 E anomaly ... there can be some accumulating snow production in that layer. 

The DGZ is essentially from the sfc to 700mb on Monday so anything low level is gonna be quite efficient. The question is just how much lift can we generate in the low levels. Stronger onshore flow will certainly help as you push that marine boundary layer into the arctic dome…that alone will generate decent low level lift. But that’s why getting a decent secondary staying to our south as long as possible is key. Once it reaches our latitude, winds in the BL will be less and less onshore.  

[radarman]

If this turns into widespread 10-12" you hope there won't be a lot of disappointment here

In the next few days I'll be watching out for drying midlevels showing up, especially if the trough keeps trending west.   As mentioned if it goes the other way and you start seeing mesobands and mid-level magic or ivt snows then we'd start to push the expectations up.

2/5/14 was widespread 10-14" even down to DC and it was an awesome storm.  Just hope a redux of that wouldn't be considered a fail.

[weatherwiz]

1 minute ago, ORH_wxman said:

The DGZ is essentially from the sfc to 700mb on Monday so anything low level is gonna be quite efficient. The question is just how much lift can we generate in the low levels. Stronger onshore flow will certainly help as you push that marine boundary layer into the arctic dome…that alone will generate decent low level lift. But that’s why getting a decent secondary staying to our south as long as possible is key. Once it reaches our latitude, winds in the BL will be less and less onshore.  

This is why I can't wait until we get into meso model range. The mesos I think should handle this very well and this is when we can really talk about the potential for >15" totals and where those would be most likely to occur.  

[dendrite]

4 minutes ago, Layman said:

 

Very helpful and understandable - thank you both!

The 540 critical thickness was more important in forecasting in the 1990s when we were more limited on the model data we received. It’s definitely outdated now.

Usually it can snow even with a 552dm thickness in these overrunning SWFE setups.

[LSC97wxnut]

Guess NWS-Boston has seen enough, Watches are up.

[ORH_wxman]

Just now, radarman said:

If this turns into widespread 10-12" you hope there won't be a lot of disappointment here

In the next few days I'll be watching out for drying midlevels showing up, especially if the trough keeps trending west.   As mentioned if it goes the other way and you start seeing mesobands and mid-level magic or ivt snows then we'd start to push the expectations up.

2/5/14 was widespread 10-14" even down to DC and it was an awesome storm.  Just hope a redux of that wouldn't be considered a fail.

I think you are thinking of 2/13/14….the 2/5/14 storm was much more of a SWFE with a latitude gradient south of SNE. 

[Fozz]

Watches are up!

[wxsniss]

3 minutes ago, ORH_wxman said:

The DGZ is essentially from the sfc to 700mb on Monday so anything low level is gonna be quite efficient. The question is just how much lift can we generate in the low levels. Stronger onshore flow will certainly help as you push that marine boundary layer into the arctic dome…that alone will generate decent low level lift. But that’s why getting a decent secondary staying to our south as long as possible is key. Once it reaches our latitude, winds in the BL will be less and less onshore.  

Without digging deeper for a better example, 0z ICON last night had the closest depiction of this

we have a closed low 925-850 just southeast-east with easterly flow well into 0z-6z Tuesday

Not totally outlandish either for these lower levels...

Higher up 850-700 probably not happening fast enough

[radarman]

1 minute ago, ORH_wxman said:

I think you are thinking of 2/13/14….the 2/5/14 storm was much more of a SWFE with a latitude gradient south of SNE. 

Yeah you may be right.  13" on 2/13/14 11.25" 2/5/14 those blend together.

[mahk_webstah]

20 minutes ago, EastonSN+ said:

991 at the Cape?  That seems pretty significant.

[Sey-Mour Snow]

BOX going 6-12" locally 12"+

[Damage In Tolland]

7 minutes ago, Fozz said:

Watches are up!

They are?

[nbweather]

29 minutes ago, HoarfrostHubb said:

Any similarities to 1/29/2022?

That was a stronger coastal with more QPF in a shorter window. One of the reasons the NBM is high with 48hr accumulations for this event is because it maintains a SLR of 15:1 or higher for the event. Higher SLR's are certainly possible, especially with good lift in the DGZ, and a deep DGZ. But longer drawn out events where you apply a high SLR are more prone to a somewhat drastic difference in the snow depth at the end of the storm versus modeled snow amounts with the SLR applied.

[Prismshine Productions]

Going 8-12" down here

Sent from my SM-S166V using Tapatalk

[Baroclinic Zone]

1 minute ago, Sey-Mour Snow said:

BOX going 6-12" locally 12"+

Nice conservative initial call based on probabilities at this lead time

[weathafella]

1 minute ago, Damage In Tolland said:

They are?

Yes Cory, they are…

[CoastalWx]

Ukie looks great. LFG!

[dryslot]

Gun to head, 8-12" up here right now.

[mattm4242]

A widespread 10+ feels likely, and that’s cool to me.

[Damage In Tolland]

4 minutes ago, weathafella said:

Yes Cory, they are…

I clicked on BOX and they werent showing 

[TheSnowman]

11 minutes ago, ORH_wxman said:

I think you are thinking of 2/13/14….the 2/5/14 storm was much more of a SWFE with a latitude gradient south of SNE. 

Will has an Einstein a level Memory.    

 

I bet you even remember model runs from every storm!  Only model runs I remember are before the 2010 DC storms because the DGX had an almost Perfect showing of what would happen in the 2nd storm a week out, and the models of storms I Missed since I nothing else to jmdo but watch incessantly.  

[Lava Rock]

From the sky is falling to busting out the nooses, to bitching about the season last week to high fiving and jubilation now. good luck one and all