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Misc 2020/21 Fall and Winter Whamby Thread

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KyloG said:
If the 85 to 77 corridor can’t produce a moderate ice storm from this setup...

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I'm going to put this in here. I was thinking that earlier myself. But let's just say it doesn't happen for anyone outside the nw foothills like the Euro says. What does that say going forward? A 1038 high and blocked by a NAO and we can't push the cad into clt or the upstate? That usually produces in GA and the midlands of SC. Wouldn't be a great sign for the future imo.
 
RainlessSnowless & Grumpy said:
I'm going to put this in here. I was thinking that earlier myself. But let's just say it doesn't happen for anyone outside the nw foothills like the Euro says. What does that say going forward? A 1038 high and blocked by a NAO and we can't push the cad into clt or the upstate? That usually produces in GA and the midlands of SC. Wouldn't be a great sign for the future imo.
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The Euro is not a reliable model during CAD events.
 

I've seen setups like this fail when the CAD was being set into place as precip already began and most areas started out as rain before wet bulbing to freezing, and quite frankly that's probably not going to happen here and it's looking less & less likely as time progresses given the synoptic scale tweaks on most NWP the past few days. More often than not, when CAD does "fail", we actually bust colder not warmer.
 
Webberweather53 said:
I've seen setups like this fail when the CAD was being set into place as precip already began and most areas started out as rain before wet bulbing to freezing, and quite frankly that's probably not going to happen here and it's looking less & less likely as time progresses given the synoptic scale tweaks on most NWP the past few days. More often than not, when CAD does "fail", we actually bust colder not warmer.
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That and the in-situ CAD junk we’ve had lately the last 2 years, this is our first legit looking classical CAD in a while
 
Webberweather53 said:
I've seen setups like this fail when the CAD was being set into place as precip already began and most areas started out as rain before wet bulbing to freezing, and quite frankly that's probably not going to happen here and it's looking less & less likely as time progresses given the synoptic scale tweaks on most NWP the past few days. More often than not, when CAD does "fail", we actually bust colder not warmer.
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Yeah, I'm remaining conservative on this, on the eastern side of things only because of January 2019, which I busted being just inside just barely the lines at 33 degrees the entire storm, with this one not looking any different. However, I agree with you on ice potentially making it further south, potentially into the upstate.
 
Myfrotho704_ said:
That and the in-situ CAD junk we’ve had lately the last 2 years, this is our first legit looking classical CAD in a while
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I know a lot of people have mentioned the January 2019 event as an analog here, I don't think it's that good & dynamically this one is much different because the CAD in Jan 19 was in-situ building in as the precip was ongoing and most places outside of the escarpment started out as rain before wet bulbing to freezing after light-moderate precip was already being observed.
 
Ollie Williams said:
Yeah, I'm remaining conservative on this, on the eastern side of things only because of January 2019, which I busted being just inside just barely the lines at 33 degrees the entire storm, with this one not looking any different. However, I agree with you on ice potentially making it further south, potentially into the upstate.
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I don't think Jan 2019 is a great comparison because that was more of an in-situ CAD at least locally (even tho it looked the part synoptically) w/ the below freezing air building in after the precip (in the form of cold rain) already began for most east of the mountains. Timing is everything and we have trended towards a more classic CAD this time around as our southern stream s/w backs away and many locations will start out close to if not below freezing as legitimate precip gets underway.
 
Webberweather53 said:
I know a lot of people have mentioned the January 2019 event as an analog here, I don't think it's that good & dynamically this one is much different because the CAD in Jan 19 was in-situ building in as the precip was ongoing and most places outside of the escarpment started out as rain before wet bulbing to freezing after light-moderate precip was already being observed.
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I honestly wonder if we see FR drizzle/IP
Pellets breakout as early as midnight Wednesday, everytime you can almost bet on more precip breaking out over the shallow CAD dome with WAA earlier
 
Myfrotho704_ said:
I honestly wonder if we see FR drizzle/IP
Pellets breakout as early as midnight Wednesday, everytime you can almost bet on more precip breaking out over the shallow CAD dome with WAA earlier
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Possibly and that's something that could give some areas even well outside the main strike zone a T of IP. Seen this occur many times as well even w/ surface temps in the upper 30s-lower 40s and an encroaching warm nose, evaporative cooling can do wonders.
 
Webberweather53 said:
I don't think Jan 2019 is a great comparison because that was more of an in-situ CAD at least locally (even tho it looked the part synoptically) w/ the below freezing air building in after the precip (in the form of cold rain) already began for most east of the mountains. Timing is everything and we have trended towards a more classic CAD this time around as our southern stream s/w backs away and many locations will start out close to if not below freezing as legitimate precip gets underway.
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Do you think Raleigh has any shot at a light glaze on Wednesday morning? Pretty much every model keeps temperatures here above freezing for now.
 
Webberweather53 said:
I don't think Jan 2019 is a great comparison because that was more of an in-situ CAD at least locally (even tho it looked the part synoptically) w/ the below freezing air building in after the precip (in the form of cold rain) already began for most east of the mountains. Timing is everything and we have trended towards a more classic CAD this time around as our southern stream s/w backs away and many locations will start out close to if not below freezing as legitimate precip gets underway.
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When you compare Jan 2019 to this event, one thing that immediately sticks out to me is the placement of the synoptic features such as the low-level sfc high over southern Canada.

In Jan 2019, when the sfc low in the southern US is over Arkansas, our CAD high is still centered over central Ontario & the longitude of Lake Superior.



1607880665945.png


Oth, for this CAD event, when our sfc low is in roughly the same location, the sfc high in southern Canada is already over far western Quebec and near the longitude of Lake Ontario instead. This implies that our low-level air mass has had more time to build in ahead of the main precipitation & is a much more favorable look for ice & classic CAD.

1607880655648.png
 
CyclonicFury said:
Do you think Raleigh has any shot at a light glaze on Wednesday morning? Pretty much every model keeps temperatures here above freezing for now.
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My call for Raleigh specifically would be for really cold rain, a trace-few hundredths of an inch of ZR and a trace of sleet would probably be an optimistic high-end scenario as it currently stands.
 
So brad is saying ice only north of I-40? Man I'm confused

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Webberweather53 said:
I've seen setups like this fail when the CAD was being set into place as precip already began and most areas started out as rain before wet bulbing to freezing, and quite frankly that's probably not going to happen here and it's looking less & less likely as time progresses given the synoptic scale tweaks on most NWP the past few days. More often than not, when CAD does "fail", we actually bust colder not warmer.
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In terms of overperforming CAD events, I will never forget March 6-7, 2014. I think the NWS was forecasting about 0.1-0.15" ice then a changeover to rain for my area, and instead this happened, on top of a compacted inch of snow/sleet:
march_672014.jpg

Needless to say, power was out for a few days. It's also noteworthy that CAD events like this can have very sharp gradients; while northern Orange county had a large amount of ice that lasted throughout the day on the 7th, Chapel Hill and Durham changed over to rain and had no problems.

To complement your Jan. 2019 discussion, here's the WPC analysis for that system:
1607881940685.png
This is clearly a better setup for snow and ice than what we're dealing with, with a stronger high pressure even further south than what we have, and no primary low in Arkansas. And that makes sense since this event was able to produce a decent onset snow/sleet before changing to ZR.

It seems to me like these two events provide good lower and upper bounds and that we'll end up somewhere between the two of them.
 
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