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2018/2019 Mountains and Foothills Fall/Winter Thread


Tyler Penland
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Starting to get worried about sleet around here in Asheville. 3km NAM is even colder a 850mb. Surface temps look to stay in the low 30’s per NAM, but RGEM is colder. Will all depend on how deep the frozen layer is above your house. If you are getting sleet, it’s cold enough and deep enough to re-freeze the precipitation. If you by chance have snow, then your 700mb temps are not warm enough to initially melt the precipitation. If your surface temps are below freezing but it’s raining, the frozen layer is not deep enough to re-freeze the precip. I am very interested to see how this unfolds.

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2 minutes ago, Hvward said:

Starting to get worried about sleet around here in Asheville. 3km NAM is even colder a 850mb. Surface temps look to stay in the low 30’s per NAM, but RGEM is colder. Will all depend on how deep the frozen layer is above your house. If you are getting sleet, it’s cold enough and deep enough to re-freeze the precipitation. If you by chance have snow, then your 700mb temps are not warm enough to initially melt the precipitation. If your surface temps are below freezing but it’s raining, the frozen layer is not deep enough to re-freeze the precip. I am very interested to see how this unfolds.

I feel like the surface maps the last couple runs of the NAM nest have warmed and the HP system is sliding a little too fast to the east than what would be ideal. Should we take into account the fact that models usually tend to erode the CAD too quickly in this instance? 

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6 minutes ago, Hvward said:

Starting to get worried about sleet around here in Asheville. 3km NAM is even colder a 850mb. Surface temps look to stay in the low 30’s per NAM, but RGEM is colder. Will all depend on how deep the frozen layer is above your house. If you are getting sleet, it’s cold enough and deep enough to re-freeze the precipitation. If you by chance have snow, then your 700mb temps are not warm enough to initially melt the precipitation. If your surface temps are below freezing but it’s raining, the frozen layer is not deep enough to re-freeze the precip. I am very interested to see how this unfolds.

To add to this, there are some "negative" factors working against ice accumulations.  First is that the scenario is rain changing to sleet/freezing rain.  It is very hard to accrete ice when the transition is warm to cold (whereas ice is easier to accrete starting out cold and then warming to a rain).  There is just residual latent heat in the rain, even on tree branches, that must be overcome before freezing rain can even begin.  Then there are the very heavy precip rates which are expected tonight during the peak window of maximum CAD.  Heavy rates offset cooling and can actually lead to less ice accretion.  Yes NAM and RGEM are cold.  GFS is not.  It has zero (!) freezing rain.  NAM always seems to portray doomsday scenarios for ZR when reality is closer to GFS.  Will there be pockets of freezing rain and ice accumulations?  Sure.  Widespread?  Probably not.

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8 minutes ago, Hvward said:

Starting to get worried about sleet around here in Asheville. 3km NAM is even colder a 850mb. Surface temps look to stay in the low 30’s per NAM, but RGEM is colder. Will all depend on how deep the frozen layer is above your house. If you are getting sleet, it’s cold enough and deep enough to re-freeze the precipitation. If you by chance have snow, then your 700mb temps are not warm enough to initially melt the precipitation. If your surface temps are below freezing but it’s raining, the frozen layer is not deep enough to re-freeze the precip. I am very interested to see how this unfolds.

Hey man hope all is well. How good is the wrf model 0z showed pockets of sub 850s and 700mb?

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Oh and the 12Z NAM just came in a ton warmer at the surface.  It has a very narrow window of sub-freezing surface temperatures between 1am and 4am before rapidly warming as the precip comes to an end.  Overall, the system looks sped up to me.  Less QPF and much less ice (even by NAM standards).  850 temps are above freezing from AVL southwest (and just barely below 0 northeast).  NAM has consequently greatly scaled back the ZR ice accumulation forecast.  Just about a non-event at this point.  Interesting trend.

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19 minutes ago, Tyler Penland said:

HRRR is mostly snow/sleet on the mountain. Looks like fun.

Sent from my SM-G960U using Tapatalk
 

How does the HRRR usually handle these situations? Do the soundings support the snow output shown on the maps?

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11 minutes ago, NC_WX10 said:

How does the HRRR usually handle these situations? Do the soundings support the snow output shown on the maps?

No. Soundings support sleet and freezing rain. Elevation dependent which affects the depth of the cold layer. 

 

My  experience is the HRRR does poorly in these setups. Just look at its runs today - all over the place from one run to another. 

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37 minutes ago, Boonelight said:

Hey guys, thanks for the welcome! I do appreciate it. I come from the midlands of SC to this winter wonderland.

Welcome man!  I moved to Asheville from the midlands the day of the flood and bought a house in Wolf Laurel last June.  Just wait, winter is great up here! My name is Timm.

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46 minutes ago, McDowell_Weather said:

This is our own thread say whatever you want bud.

 

39 minutes ago, Buckethead said:

Welcome man!  I moved to Asheville from the midlands the day of the flood and bought a house in Wolf Laurel last June.  Just wait, winter is great up here! My name is Timm.

Heath, Timm, good to meet you. I’m David. 

Timm, I lived in Forest Acres when the floods came. I’ve never witnessed such destruction. Forest Drive was a river.

I’m so looking forward to winter here. 

32° here with light sleet and rain.

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