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Wintry The Webber/1300m/Kylo/Jon/Whatalife Storm January 12th-14th

12z WRF-ARW, major ice!
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Webberweather53 said:
Looks very similar to the CMC a few days ago that was immediately discounted because its surface depiction simply looked different from the other models. That’s exactly why I said urged many to be catious and wait for the high res models inside 36-48 hours before tossing and look where we currently stand lol. Could we flip back to those earlier more amped and warmer solutions? Absolutely but I would have hated to jump the gun on this and throw the cmc out right off the bat.
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Even if the CMC ptype depiction was somewhat closer to right, it was entirely for the wrong reason and as I showed, the very next run at 00z it immediately jumped to the FV3 solution with the Miller B slp track. I'm not going to trust a model that can't get the synoptic pattern down just because it's innate cold bias causes it to incorrectly stumble towards a right solution once every ten storms. I'm not saying this critically towards you, this is my position on the CMC, which I see as less useful than even the NAVGEM, with it's known biases (at least they are known and you can somewhat know how to account for them). The CMC known bias is mainly that it just plain sucks lol. It has not always been that way either, but I feel like the past 2 or 3 winters it has been terrible.
 
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Snowflowxxl said:
As Forsyth said, this model was wayyyyy off in December. Same with the NAM. Both cold bias.
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The NAM wasn't actually as bad as you may remember. It was just a degree or so off and was quite close. I'd use it this time around and adjust a degree up. Regardless it still concerns me there is some chance we could get icing in this area and that all FFC has is 2 hours of sleet in the forecast. However they said they are watching it through their confidence in icing is low.
 
I don’t think you can discount the WRF models or any mesoscale model just because those are the ones that can really see through the atmosphere and depict how a CAD event may play out. Much better than any other model could. Not saying it is correct but you cannot discount these models in these final hours leading up to the event just because they may have been off some last time. Also different scenarios and pieces in play here LIKE much drier air ahead of this system than of the last one. These usually tend to bust cold because cold dry air is heavy and doesn’t usually want to move quickly at all.
 
Nick_boynton_ said:
I don’t think you can discount the WRF models or any mesoscale model just because those are the ones that can really see through the atmosphere and depict how a CAD event may play out. Much better than any other model could. Not saying it is correct but you cannot discount these models in these final hours leading up to the event just because they may have been off some last time. Also different scenarios and pieces in play here LIKE much drier air ahead of this system than of the last one. These usually tend to bust cold because cold dry air is heavy and doesn’t usually want to move quickly at all.
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Right, just because one model(s) were off on the last winter event, it does not necessarily mean that it will do bad this time around. Truth is, we won't know they're wrong until after the event. It's one of those, "if you do, you don't, if you don't you do."
 
ForsythSnow said:
The NAM wasn't actually as bad as you may remember. It was just a degree or so off and was quite close. I'd use it this time around and adjust a degree up. Regardless it still concerns me there is some chance we could get icing in this area and that all FFC has is 2 hours of sleet in the forecast. However they said they are watching it through their confidence in icing is low.
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FFC is putting 2 hrs of sleet in the forecast? It won't be cold enough for sleet. Maybe sleet at the onset. Maybe that's what they're getting at?
 
Euro juiced up again in the CAD areas, also little warmer but again not sure it's handling the wedge all that accurately...

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1300m said:
Even if the CMC ptype depiction was somewhat closer to right, it was entirely for the wrong reason and as I showed, the very next run at 00z it immediately jumped to the FV3 solution with the Miller B slp track. I'm not going to trust a model that can't get the synoptic pattern down just because it's innate cold bias causes it to incorrectly stumble towards a right solution once every ten storms. I'm not saying this critically towards you, this is my position on the CMC, which I see as less useful than even the NAVGEM, with it's known biases (at least they are known and you can somewhat know how to account for them). The CMC known bias is mainly that it just plain sucks lol. It has not always been that way either, but I feel like the past 2 or 3 winters it has been terrible.
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Right, the reason I was cautious to toss the solution from the CMC a few days back is largely because the few times this model gets a forecast correct is in a case like this, it’s the most aggressive of global NWP with CAD and that’s usually what ends up verifying even if the pattern changes some up until verification. I’ve seen CMC pick up the CAD correctly several times since in the past several years or so even if the synoptic pattern was off a little, any other instance other than a special case like this I completely ignore the CMC.
 
1300m said:
It's hard to discount the Euro though, keep in mind it is a higher resolution model than the RGEM.
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I'm president of the Euro club and yes it is the highest course model, but its had its sins in the past outlining Cads, not being cold enough 2m and eroding them to fast.
 
NCSNOW said:
I'm president of the Euro club and yes it is the highest course model, but its had its sins in the past outlining Cads, not being cold enough 2m and eroding them to fast.
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Hasn't always been 9km and this is not a classic CAD either. What it is showing is entirely reasonable. It's effectively an insitu-CAD and those will erode on the edges faster because there's nothing to offset the latent heat release. Thus the reason I include an area from CLT to RDU in T to .10" in my forecast map (some brief ice accrual before latent heat wins out), which the Euro doesn't really advertise, but otherwise, I think the Euro looks very realistic.
 
Webberweather53 said:
Right, the reason I was cautious to toss the solution from the CMC a few days back is largely because the few times this model gets a forecast correct is in a case like this, it’s the most aggressive of global NWP with CAD and that’s usually what ends up verifying even if the pattern changes some up until verification. I’ve seen CMC pick up the CAD correctly several times since in the past several years or so even if the synoptic pattern was off a little, any other instance other than a special case like this I completely ignore the CMC.
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I think the cold bias of the CMC is why it actually does better in CAD situations like this. Even though it normally would be a little too cold it's this same bias that actually works in its favor here. I see computer models the same as I would a tool. A screw is useful in certain situations but I wouldn't take a hammer and try to drive a screw into wood with it, it just wouldn't work. It's the same way with models; learning their strengths/weaknesses and then applying this knowledge in selecting the right "tools" to accurately forecast and blend the data. If I were in Western NC I would be hoping for a lot of sleet to cut down on zr accumulation.
 
Yes the EURO has higher resolution than the 12KM Nam and the RGEM but not as good as the 3Km NAM which handles the thermal profiles the best of all the models IMO, in MOST cases. That is why you can never really discount a model (except the GFS) this close in. Anybody have the UKMET? if it is in lock step with the EURO it is usually a done deal with those 2 teaming up
 
1300m said:
Hasn't always been 9km and this is not a classic CAD either. What it is showing is entirely reasonable. It's effectively an insitu-CAD and those will erode on the edges faster because there's nothing to offset the latent heat release. Thus the reason I include an area from CLT to RDU in T to .10" in my forecast map (some brief ice accrual before latent heat wins out), which the Euro doesn't really advertise, but otherwise, I think the Euro looks very realistic.
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There’s definitely a strong in-situ component to this CAD event that’s driven by precip but synoptically this does look a lot more like a classic CAD to me. Weaker, in-situ events usually see a much weaker surface high sliding offshore of New England or the Mid Atlantic by the time the surface low approaches the foot of the Apps like we had in November, the position and strength of the cold high in southern Ontario and Quebec fits more with the classic cases here imo.
 
With this setup, there’s a meso 1032-1035 hp near Dc that slides offshore but the big 1040 hp is north of the Great Lakes still supplying some dry/cold air after the meso high has pushed offshore, hard to say whether it’s a in-situ or classical, I’d say classical
 
This event is going to be a close call for significant ZR in my neck of the woods in NE Charlotte, trace amounts to a quarter inch all on the table and there’s a chance I may have to drive thru this crap this weekend on my way back from the airport (pls no). I’ve already had my share of ice after dealing with the ice storm in Oklahoma City about a week or so ago, I’m low key rooting for 33F cold rain.
 
Webberweather53 said:
There’s definitely a strong in-situ component to this CAD event that’s driven by precip but synoptically this does look a lot more like a classic CAD to me. Weaker, in-situ events usually see a much weaker surface high sliding offshore of New England or the Mid Atlantic by the time the surface low approaches the foot of the Apps like we had in November, the position and strength of the cold high in southern Ontario and Quebec fits more with the classic cases here imo.
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Looking at the synoptic map I agree with you it looks like a classic CAD no doubt. But effectively, when you have winds in the Mid-Atlantic out of the south, effectively to me that is more of an insitu CAD with reduced/shut off CAA. If this wasn't the case and we were getting some reinforcement of dry air, this would be a much bigger deal for areas outside of the deepest part of the CAD dome like CLT to RDU IMO.

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1300m said:
Looking at the synoptic map I agree with you it looks like a classic CAD no doubt. But effectively, when you have winds in the Mid-Atlantic out of the south, effectively to me that is more of an insitu CAD with reduced/shut off CAA. If this wasn't the case and we were getting some reinforcement of dry air, this would be a much bigger deal for areas outside of the deepest part of the CAD dome like CLT to RDU IMO.

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Definitely, there’s a pretty huge disconnect between what you’d expect to see with this CAD from the synoptic pattern and how the surface is responding, it would help if we had a deep, fresh snow pack over New England and the mid Atlantic in advance of this we would probably see a more classic response.
 
Webberweather53 said:
Definitely, there’s a pretty huge disconnect between what you’d expect to see with this CAD from the synoptic pattern and how the surface is responding, it would help if we had a deep, fresh snow pack over New England and the mid Atlantic in advance of this we would probably see a more classic response.
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I agree, the snowpack situation is another hindrance. It is definitely not the classic response one would expect from this setup. I'm very interested to see if it unfolds in the way I think it will, or if areas further east somehow muster more.
 
MichaelJ said:
Yes the EURO has higher resolution than the 12KM Nam and the RGEM but not as good as the 3Km NAM which handles the thermal profiles the best of all the models IMO, in MOST cases. That is why you can never really discount a model (except the GFS) this close in. Anybody have the UKMET? if it is in lock step with the EURO it is usually a done deal with those 2 teaming up
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It's the HRRR and not a good model for CAD events but here it is at 32 hours out showing the snow and ice starting. It's worth noting it does favor more of a showery nature to the precip like the 3km NAM vs steady precip like the RGEM shows.
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Webberweather53 said:
There’s definitely a strong in-situ component to this CAD event that’s driven by precip but synoptically this does look a lot more like a classic CAD to me. Weaker, in-situ events usually see a much weaker surface high sliding offshore of New England or the Mid Atlantic by the time the surface low approaches the foot of the Apps like we had in November, the position and strength of the cold high in southern Ontario and Quebec fits more with the classic cases here imo.
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Yep. Just look how much colder the lows verified this AM for RDU. Most models has 25-28 and it hit 22, and the HP analysis looks like a joke. We will have to watch how this cold air is handled to north as we near Saturday night. Even lame HP’s in non-ideal locations can verify several degrees colder, it doesn’t have to be a monster CAD to do so.

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The HRRR at hour 35 has quite a bit of snow in Western NC with only a thin band of ice. Again it's the HRRR so I would take it with a grain of salt but interesting at least.
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Peachtree city sounding the horn already

Winter Weather Advisory

URGENT - WINTER WEATHER MESSAGE National Weather Service Peachtree City GA 252 PM EST Fri Jan 11 2019 GAZ008-009-015-016-120400- /O.NEW.KFFC.WW.Y.0001.190112T1800Z-190113T0600Z/ Union-Towns-Lumpkin-White- Including the cities of Dahlonega and Cleveland 252 PM EST Fri Jan 11 2019 ...WINTER WEATHER ADVISORY IN EFFECT FROM 1 PM SATURDAY TO 1 AM EST SUNDAY... * WHAT...Light freezing rain expected. Total ice accumulations from a trace up to one tenth of an inch possible, mainly above 2000 feet. * WHERE...Higher elevations (above 2000 feet) across Union, Towns, Lumpkin and White Counties. * WHEN...From 1 PM Saturday to 1 AM EST Sunday. * ADDITIONAL DETAILS...Minor ice accumulations are most likely on elevated objects like trees, overpasses, and bridges. Plan on some slippery road conditions, mainly on bridges and overpasses. PRECAUTIONARY/PREPAREDNESS ACTIONS... A Winter Weather Advisory means that periods of freezing rain will cause travel difficulties. Expect slippery roads. Slow down and use caution while driving.


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One other model I haven't seen mentioned is the HRDPS, basically the higher resolution version of the RGEM (like the 3km NAM is to the 12km). It's showing substantial qpf for Western NC, over 1.5" it looks like with a lot of that as ice in addition to a big wedge of sub 32F temps.
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Our locals have now firmly ruled out wake chatham and orange for any ice accrual. So we get to watch tv while the triad waits for power restoration.
 
NAM and 3k still has lots of ice for parts of GA, Upstate, and WNC. I'd be willing to say all these places sees atleast .25" of ice.

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I think the showery solutions from the hrrr/nam 3km May be right, there will be steep lapse rates ( 7-7.5 c in between 850-500mb and a little bit of elevated cape, that favors convective, showery type weather, would actually help ice accretion during one of those pauses/breaks in between where ice can successfully build up
 
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