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Feb 12-13 Sleet/Snow/ZR Event


JoshM

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The Euro maintains.  We can stress over details, but it's pretty similar to its last two runs and that's the important thing.  It's a little warmer in the upper levels than the 00z run, but it's a monster storm and seems to have upped QPF some.  Looks like a heavy snowstorm changing over to raging sleet for MBY and then flipping back over to snow at the end.  It's really close, though, and if it's 1C too warm at 850, it might be all-snow (and with really heavy rates, that is quite possible, IMO).  The storm is a real monster for the western half of NC and upstate SC.  It would shut down things for days!

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The Euro maintains.  We can stress over details, but it's pretty similar to its last two runs and that's the important thing.  It's a little warmer in the upper levels than the 00z run, but it's a monster storm and seems to have upped QPF some.  Looks like a heavy snowstorm changing over to raging sleet for MBY and then flipping back over to snow at the end.  It's really close, though, and if it's 1C too warm at 850, it might be all-snow (and with really heavy rates, that is quite possible, IMO).  The storm is a real monster for the western half of NC and upstate SC.  It would shut down things for days!

also.... per Larry the euro has a know bias for overdoing HP levels but at the same time it is notorious for not dropping temps enough in CAD regimes......so this could get very interesting if the Euro holds serve and is correct in what it has grabbed hold of.

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is the 850 line south of the charlotte metro or are we betting on the CAD being strong enough to keep temps aloft at or below freezing?  This seems to always be the biggest concern with CLT and winter weather

 

if I had to guess, I'd say the city is safe for the most part. Probably 8 or 9 tenths of all snow, followed by .4 of either IP or ZR. In other words, perfect sledding conditions.

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also.... per Larry the euro has a know bias for overdoing HP levels but at the same time it is notorious for not dropping temps enough in CAD regimes......so this could get very interesting if the Euro holds serve and is correct in what it has grabbed hold of.

The Euro over does the strength of HP's? But then also is to warm with 2m temps in CAD setups?

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The Euro over does the strength of HP's? But then also is to warm with 2m temps in CAD setups?

 

Yeah I was thinking about this earlier.  I believe that Larry has said that the strength of the high pressure is often too high on the mid/long range runs than what verify sometimes.  A separate issue is IF there is a CAD high in place, that the surface temperatures and longevity of the cold are underdone.  I'm sure Larry will come in and verify if my thinking is correct.

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I don't think I'm seeing 850s nearly as supportive of snow for a lot of NC & SC.  The upstate has a nice chunk that drops 850s for a heavy band of precip though.. before warming.. but 850 is atrocious for many

 

Even by 144 when the precip is gone; CLT's 850s finally drop even.

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I don't think I'm seeing 850s nearly as supportive of snow for a lot of NC & SC.  The upstate has a nice chunk that drops 850s for a heavy band of precip though.. before warming.. but 850 is atrocious for many

 

It's not for the whole event, but 850s are below 0C at the start, then warm to maybe 1C for some areas during the middle (after a lot of precip has already fallen) and fall back below 0C at the tail end.  I guess you could argue that with heavy precip rates, you could even get snow with some layers between 0C and maybe 0.5C, but that's always touch-and-go.  It looks like the mountains and extreme northern foothills (Mt. Airy, for example) never get above 0C at 850 mb.  I'd think that areas north and west of I-85 are snow for a good portion of the storm, at least, and probably raging pellets otherwise.

 

Does the Euro have any bias to overdo/underdo 850 mb temperatures?  I know it has a tendency to be a little warm at the surface, but I don't know if that translates upwards at all.

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 For GA verbatim, the 12Z Euro is just as wet or wetter (mainly 1-1.75"), but it is ~3-6 warmer.

 

 For C GA, MCN and AGS are no longer cold enough for ZR verbatim (upper 30's instead of ~32). Also, based on 850's of +6 to +7C it would be pretty hard to get a ZR storm. So, this run looks like a  cold rain for them with ovr 1" of qpf. Considering the warm Euro bias in these siituations, I'd expect middle 30's with this setup...say 33-37.

 

 For ATL-AHN, qpf is a quite wet 1.25-1.50". Verbatim, they are about 3-5 warmer than the last two runs with middle 30's (say ~34-36) vs. mainly 30-32. However, based on what I feel is a Euro sfc temp. warm bias when there is steady precip. with a good wedge in the SE and considering 850's largely in the +3 to +5 C range, the wheelhouse for N GA major ZR storms when there is good wedging, I'd say we're back to a  major ZR storm for N GA (similar to the 12Z Euro run from yesterday vs. the mainly IP imo from the 0Z run this morning). I'd guess coldest temp.'s would verify about 5-6 colder in this setup with, say, ~28-31...i.e., cold enough for a severe Zr storm if 1.25-1.50' of qpf were to verify.

 

In summary, if the 12Z Euro were to verify, I'd call it a cold rain/near miss for central GA but a severe ZR for the ATL-AHN corridor even though verbatim it isn't giving  them ZR.

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It's not for the whole event, but 850s are below 0C at the start, then warm to maybe 1C for some areas during the middle (after a lot of precip has already fallen) and fall back below 0C at the tail end.  I guess you could argue that with heavy precip rates, you could even get snow with some layers between 0C and maybe 0.5C, but that's always touch-and-go.  It looks like the mountains and extreme northern foothills (Mt. Airy, for example) never get above 0C at 850 mb.

 

Yeah maybe.  I do see a good many 0's around central before hte warm up and then going up to 3, but to your area its better.

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I don't think I'm seeing 850s nearly as supportive of snow for a lot of NC & SC.  The upstate has a nice chunk that drops 850s for a heavy band of precip though.. before warming.. but 850 is atrocious for many

 

Even by 144 when the precip is left; CLT's 850s finally drop even.

 

Charlotte is at zero until hour 132. It's cutting it a bit close but typically the best snow rates are closest to where the transition zone is. 

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Charlotte is at zero until hour 132. It's cutting it a bit close but typically the best snow rates are closest to where the transition zone is. 

 

Thanks.  It is very close though... like really close looking closer at the city/area proper.  Not sure if that's a good thing for you guys.. it'd be paralyzing if that ended up all ice.

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The Euro over does the strength of HP's? But then also is to warm with 2m temps in CAD setups?

that is what I understood Larry to say.....

 

A known observation is that the Euro (until very close to the event) underestimates the level and duration of the cold air at the surface.  And I think recently his has noticed that in the medium range that the Euro tends to over estimate the magnitude of the high pressure systems .....

 

Larry....don't want to put words in your mouth, so by all means correct me if I am mixed up.

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The Euro still looks wonky to me with it's track. If the wedging is as strong as it looks initially, then why would the storm track into the wedge, like it does. It might be me only seeing the 24 hour panels, so maybe it reforms in there somewhere.

It's hard to buy a lot of snow with this setup. I would bet there is a warm layer in there somewhere this isn't represented by looking solely at the 850s.

I've often heard about the Euro bias of underdoing the surface cooling with CADs, so as mentioned, that might be at work here.

I'm still not happy about how rapidly the high moves out. I do not like that. If we lose that any sooner, well, you know....

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I just took a look at the horrible snow maps.. and it's a bit worrisome to still see "snow" here in KCAE.. when we all know that won't verify as the white stuff.

 

Wondering if as the precip/cold enters or is pulling out the temps drop for some reason to show it?  Hm.. maybe I'm a bit overly optimistic saying KCAE looks good for no ice...  weird...

 

ATL has it / very close too..

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that is what I understood Larry to say.....

 

A known observation is that the Euro (until very close to the event) underestimates the level and duration of the cold air at the surface.  And I think recently his has noticed that in the medium range that the Euro tends to over estimate the magnitude of the high pressure systems .....

 

Larry....don't want to put words in your mouth, so by all means correct me if I am mixed up.

 

Yes, that's what I've said more or less.

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