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12z Model Suite Discussion Thread Jan. 2nd / 3rd


REDMK6GLI

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With the exception of the city due to UHI, are 20:1 ratios possible or is 15:1 more likely?

Ratios aren't determined by surface temps. You want to see good lift at the layer of the atmosphere between -12 and -18C, that's where dendrites form and have the best ratios. If there isn't a lot of lift there, the ratios won't be as high. I've seen snow at temps below 15 and have it consist of needles, essentially sugar flakes with a straight 10-1 ratio because the temps were too cold where the flakes were forming.

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Ratios aren't determined by surface temps. You want to see good lift at the layer of the atmosphere between -12 and -18C, that's where dendrites form and have the best ratios. If there isn't a lot of lift there, the ratios won't be as high. I've seen snow at temps below 15 and have it consist of needles, essentially sugar flakes with a straight 10-1 ratio because the temps were too cold where the flakes were forming.

At hr 66 its minus 10 at 850  surface is 18   At hour 72 its minus 15 the surface is 8 

that's 15 to 1 min

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With the exception of the city due to UHI, are 20:1 ratios possible or is 15:1 more likely?

 

Edit: This was answered in PB GIF's post

you need to know the temps at about 700MB to get an idea of ratios....if they are between -12C and -21C you will get 15:1+

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Ratios aren't determined by surface temps. You want to see good lift at the layer of the atmosphere between -12 and -18C, that's where dendrites form and have the best ratios. If there isn't a lot of lift there, the ratios won't be as high. I've seen snow at temps below 15 and have it consist of needles, essentially sugar flakes with a straight 10-1 ratio because the temps were too cold where the flakes were forming.

Ah ok so it's possible that being too cold can work against us.  Do we have any snow growth forecasts for the storm or is it too premature? Sorry for all these questions btw (not IMBY type at least).

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thanks.

 

is there a specific height? I was once told many years ago it was in the 700MB range....true?

It is where the lift is occurring, which very often maximizes around 700 hPa but that isn't always the case. I've been only vaguely paying attention to this storm (mostly to see if my flight can leave on Thursday night :lol:) but I'll check BUFKIT to see where the maximal lift is forecast to be.

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It is where the lift is occurring, which very often maximizes around 700 hPa but that isn't always the case. I've been only vaguely paying attention to this storm (mostly to see if my flight can leave on Thursday night :lol:) but I'll check BUFKIT to see where the maximal lift is forecast to be.

much appreciated Loco

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Based on the graph, and assuming a 700mb growth region, based on the skew-t's it looks like a 12:1 ratio. Correct me if I'm wrong.

based on this for JFK at 66hr (GFS)....it would be closer to 15:1, assuming 700mb is the layer with max growth

131231183437.gif

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