HECS Checklist.....What to Look for to Avoid

[H2Otown_WX]

Yeah...people think that cold temps always equals good ratios and they don't. Specific cloud temperatures produce certain crystals and the temp at the surface really plays no role unless you're dealing with 32F or greater air causing some melting of the flake. In the arctic this time of the year they typically don't receive high ratio snow. It's a dense, "dry" snow and their primary crystal types are columns and bullets because of their -20C to -40C cloud temps. You need to have cold enough temps in the clouds for nucleation to occur though. If your coldest cloud temp is only -4C you'll have no ice in the cloud and therefore no snow even if the entire column is below freezing.

Are you saying in the Arctic the cloud temperatures are too cold to have high ratio snows?

[weatherwiz]

Messenger speacializes in that area and he was warning us of that, but it fell on deaf ears for the most part.

MattMOFO also mentioned it at one point.

I'd advise you pay closer attention to Messenger's posts in the future.

I must have totally been oblivious to that or didn't think anything of it

This was an event though in which you really had no idea what was going to actually transpire until the darn thing was happening...I mean there really weren't much negatives being presented to us in the models.

[weatherwiz]

Is that why my temp went from 22 at the start and was up to 28 by 2am? I found that strange and worrisome at the same time.

I'm not actually sure about the temperature rises...I don't think the wrapping of dry air had anything to do with it...although it possibly could have. Maybe some sort of weak WAA thing or maybe just latent heat related.

Good question though. Maybe someone can answer this better.

[40/70 Benchmark]

I must have totally been oblivious to that or didn't think anything of it

This was an event though in which you really had no idea what was going to actually transpire until the darn thing was happening...I mean there really weren't much negatives being presented to us in the models.

There were and they were alluded to in the initial post; the hope that more of us can deam them readily identifiable moving foreward served as the impetus for the creation of this thread.

[weatherwiz]

There were and the hope that more of us can deam them readily identifiable moving foreward was the impetus for the creation of this thread.

I was actually thinking along those lines but didn't see much talk during the event of things that were being shown on the models that were negatives that we missed...unless I just totally missed or can't remember this for some reason.

I do remember some of the models kind of shifting things further west...like the 18z NAM the day prior and how some of the models clearly indicated dry slot potential, despite the juicy QPF....the NAM to a degree and definitely the GFS hinted at the hole over a good part of the CT Valley as the GFS was forecasting significantly less QPF over this area.

[weatherwiz]

There were and they were alluded to in the initial post; the hope that more of us can deam them readily identifiable moving foreward served as the impetus for the creation of this thread.

Yeah I'm on the same page now, I read the initial post but I was misunderstanding that those factors were actually modeled and were just missed.

[dendrite]

Too cold.... or no....

It's just that certain crystals form at certain temperatures, pressures, and RH/supersaturations. The huge, honkin, perfect dendrites form at around -15C via deposition, but as you get colder and colder you get smaller, more compact crystal types. I see a lot of people say they're getting perfect dendrites, but they don't even go out to see what the crystal type is. You can have decent snow growth with plates and needle aggregates as well. You can have poor snow growth with all crystals types including dendrites too. /rant

[40/70 Benchmark]

Yeah I'm on the same page now, I read the initial post but I was misunderstanding that those factors were actually modeled and were just missed.

Yea, I could have communicated that better.

The negatives should have been stressed more, but the fact of that matter is that we are all 3-bunners and even when people attempted to touch upon them, we looked the other way.

I made the timing analogy to matters of the heart, well here is another; love is blind.

It's just that certain crystals form at certain temperatures, pressures, and RH/supersaturations. The huge, honkin, perfect dendrites form at around -15C via deposition, but as you get colder and colder you get smaller, more compact crystal types. I see a lot of people say they're getting perfect dendrites, but they don't even go out to see what the crystal type is. You can have decent snow growth with plates and needle aggregates as well. You can have poor snow growth with all crystals types including dendrites too. /rant

Thanks; we are looking for that temp at the H7 level, I presume....

[dendrite]

Are you saying in the Arctic the cloud temperatures are too cold to have high ratio snows?

They can sometimes get high ratios, but what I'm saying is it's a myth that they're always getting ridiculously high ratios because of how cold they are. At some point the cold is a detriment to high ratios. What determines ratios is the crystal type...the cloud temps help determine crystal type. The columns and bullets/rosettes they receive are not high ratio producing crystals. It's more like accumulating cane sugar.

[H2Otown_WX]

They can sometimes get high ratios, but what I'm saying is it's a myth that they're always getting ridiculously high ratios because of how cold they are. At some point the cold is a detriment to high ratios. What determines ratios is the crystal type...the cloud temps help determine crystal type. The columns and bullets/rosettes they receive are not high ratio producing crystals. It's more like accumulating cane sugar.

Yeah that's what this snow seemed like..sugar.

[weatherwiz]

Yea, I could have communicated that better.

The negatives should have been stressed more, but the fact of that matter is that we are all 3-bunners and even when people attempted to touch upon them, we looked the other way.

I made the timing analogy to matters of the heart, well here is another; love is blind.

Thanks; we are looking for that temp at the H7 level, I presume....

This is exactly why it's ALWAYS important to look at the negatives first...this can be hard though I guess for many as usually when you're looking at the models for a storm, whether it be severe wx or snow you always tend to look at the positives first and start to neglect some of the negatives. It's probably better to look at the negatives and see what you need to offset those negatives. When dealing with something that's an HECS you're not going to have many negatives...everything is going to look just about perfect so maybe next time we see something that appears it could be rather big we should step back and look for the negatives...if there are alot presented and some uncertainty at hand it may be best not to go balls out but rather play it more safe. I think sometimes when we see a few things look very good we either want to ignore the negatives or look for something that will offset it and start being "wishful".

[40/70 Benchmark]

This is exactly why it's ALWAYS important to look at the negatives first...this can be hard though I guess for many as usually when you're looking at the models for a storm, whether it be severe wx or snow you always tend to look at the positives first and start to neglect some of the negatives. It's probably better to look at the negatives and see what you need to offset those negatives. When dealing with something that's an HECS you're not going to have many negatives...everything is going to look just about perfect so maybe next time we see something that appears it could be rather big we should step back and look for the negatives...if there are alot presented and some uncertainty at hand it may be best not to go balls out but rather play it more safe. I think sometimes when we see a few things look very good we either want to ignore the negatives or look for something that will offset it and start being "wishful".

Ryan is always does this and did this time, as well, but sometimes for whatever reason it just doesn't work out as expected.

We have guidlinesin place that make weather more predictable than it otherwise would be, but it would be terribly misguided of us to assume that it will always adhere to them.

[Tropopause_Fold]

It's just that certain crystals form at certain temperatures, pressures, and RH/supersaturations. The huge, honkin, perfect dendrites form at around -15C via deposition, but as you get colder and colder you get smaller, more compact crystal types. I see a lot of people say they're getting perfect dendrites, but they don't even go out to see what the crystal type is. You can have decent snow growth with plates and needle aggregates as well. You can have poor snow growth with all crystals types including dendrites too. /rant

that is a statement...but you are 100% correct.

i had monster aggregates for a lot of the event (when it wasn't rain. lol) the precip was so hvy they did a nice job of accumulating.

[Damage In Tolland]

Messenger speacializes in that area and he was warning us of that, but it fell on deaf ears for the most part.

MattMOFO also mentioned it at one point.

I'd advise you pay closer attention to Messenger's posts in the future.

LOL.

[Damage In Tolland]

But at least we have no bare spots.

You'll have plenty by tomorrow afternoon

[40/70 Benchmark]

LOL.

I'm not saying the guy is Harvey Leonard, but he tends to focus on the one aspect that Paul would like to learn more about....mid level centers.

[Ginx snewx]

You'll have plenty by tomorrow afternoon

No frickin way, LOL,

OK how's does this happen

QPF BOS 1.61 ratio 11-1

PVD .62. 15-1

ORH 1.45. 8.75-1

BDL 1.25 13-1

[Baroclinic Zone]

I'm not saying the guy is Harvey Leonard, but he tends to focus on the one aspect that Paul would like to learn more about....mid level centers.

Some people seemed quick to discredit what he had to say but I do think he did really well with this one. Both him and I were harping on how the warmth would be overplayed in the SE MA area from me up into the Brockton area and it panned out petty well imo and there ended up being a mini jackpot of snow around the brockton/raynham area.

[OSUmetstud]

I'm not saying the guy is Harvey Leonard, but he tends to focus on the one aspect that Paul would like to learn more about....mid level centers.

He did point out the low cut-off too far SW for SNE to get a HECS which ended up being correct.

[HoarfrostHubb]

No frickin way, LOL,

OK how's does this happen

QPF BOS 1.61 ratio 11-1

PVD .62. 15-1

ORH 1.45. 8.75-1

BDL 1.25 13-1

And somehow I only wound up with 9"... not something I see very often when ratios around us are so much higher.

And Messenger was a force with this storm.

[40/70 Benchmark]

Some people seemed quick to discredit what he had to say but I do think he did really well with this one. Both him and I were harping on how the warmth would be overplayed in the SE MA area from me up into the Brockton area and it panned out petty well imo and there ended up being a mini jackpot of snow around the brockton/raynham area.

He did point out the low cut-off too far SW for SNE to get a HECS which ended up being correct.

To be fair, he did blink at one point call for 15-30" imby....

[40/70 Benchmark]

No frickin way, LOL,

OK how's does this happen

QPF BOS 1.61 ratio 11-1

PVD .62. 15-1

ORH 1.45. 8.75-1

BDL 1.25 13-1

The only one that I would even raise an eyebrow to would be PVD...the others don't seem out of sort to me.

It harkens back to what Dedrite was getting at in that low level temps are not that large a determinant of ratios, but rather the mid levels are.

We have established that the mid levels were somehow tainted across the interiof, which compromised snow growth; however the I 95 corridor did not suffer the same fate thanks to the extra lift attributed to the cf.

It makes sense that I95 had better ration than the interior.

[bobbutts]

Thanks for this topic, certainly learned something. I'll admit to looking at the surface pressure, low position, and select model qpf and banking on more widespread heavy snows for NE and over 1' for myself.

It's very easy to just say NAM sucks or whatever and move along but that does nothing to help future forecasts.

[CoastalWx]

On vacation and just taking a peek, but the snow in BOS was not totally CF related. If you recall, we had echoes redeveloping near the canal and moving nw. We had very strong convergence in the 950-850 layer here, aiding in big upglide over se mass and BOS area. CF def enhanced precip, but it wasn't all CF related.

[ORH_wxman]

The only one that I would even raise an eyebrow to would be PVD...the others don't seem out of sort to me.

It harkens back to what Dedrite was getting at in that low level temps are not that large a determinant of ratios, but rather the mid levels are.

We have established that the mid levels were somehow tainted across the interiof, which compromised snow growth; however the I 95 corridor did not suffer the same fate thanks to the extra lift attributed to the cf.

It makes sense that I95 had better ration than the interior.

The ORH water equiv def looks wrong. No way we had 1.45" of liquid in this snow. I'm guessing we had close to 1" of liquid, maybe just a bit shy. I don't have the tools to do a core sample, but just going of past knowledge, no way its over 1".

[H2Otown_WX]

No frickin way, LOL,

OK how's does this happen

QPF BOS 1.61 ratio 11-1

PVD .62. 15-1

ORH 1.45. 8.75-1

BDL 1.25 13-1

I highly doubt BDL got 1.25" of QPF. I also don't think they had 12.9" of snow seeing as surrounding towns had 3-4" less than that. http://www.erh.noaa.gov/box/pnsevents/Dec_26-27_2010/Dec_26-27_2010_BOXPNS.txt

[Baroclinic Zone]

To be fair, he did blink at one point call for 15-30" imby....

Well that did verify.

[40/70 Benchmark]

Well that did verify.

No it did not....I received 1'.

[40/70 Benchmark]

The ORH water equiv def looks wrong. No way we had 1.45" of liquid in this snow. I'm guessing we had close to 1" of liquid, maybe just a bit shy. I don't have the tools to do a core sample, but just going of past knowledge, no way its over 1".

Oh, I missed that.

[Collinsville]

I highly doubt BDL got 1.25" of QPF. I also don't think they had 12.9" of snow seeing as surrounding towns had 3-4" less than that. http://www.erh.noaa....2010_BOXPNS.txt

Its even worse they went with 13.9". There was no good banding that persisted over them which is the only way they would almost double most others.

As for their qpf, it must have been adjusted to better match that total cause the ASOS certainly didn't come up with that number. It was 8.4 to 1 here with .87" to 7.3" snow. I did actual snow core samples not made up.