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Ryan Snoddon - CBC Newfoundland & Labrador

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SNOW RATIO & FLUFF FACTOR


It may have been the lightest 30 cm you've ever shoveled!
Everyone is talking about how light the snowfall was over Metro & Eastern Newfoundland last night, it was classic 'Superman snow', you really do feel like Superman shoveling it! 

You've likely heard me use the term 'Snow Ratio' or 'Fluff Factor' when talking about an incoming system. Snow ratio is the snow to liquid ratio with a snowfall & it's different with every system. It makes the difference between light & fluffy snow & the heavy wet cement we can often see, especially here in Newfoundland & even more so in St. John's. 
So why was this snow event so fluffy?
For the most part, it comes down to the temperature at the surface and also aloft.
Winds can also be factor. Stronger winds can help to compact the snow, but lighter winds have less impact. 

TEMPERATURES ARE KEY
The general rule of thumb is... the closer to 0 the temperature is, the more liquid water in the clouds & the more liquid content in the snow that falls to the surface. The high liquid content makes the snow stick closer together in your driveway and makes it heavier to shovel. On the other hand, the colder the temperatures are, the lighter & fluffier the snow is. At colder temperatures the snow has little to know liquid water content, which makes it lighter. Lighter snow has far more air pockets between all of those snow crystals, allowing it to accumulate & build up much faster.

Fluff Factor.png
Again the temperatures ranges are general and values are only approximate. Every situation is different.  

"AVERAGE" SNOW
Again every Snow event is different, but with a typical snow event with temperatures near or few degrees below 0, the "Average" snow ratio is near 10:1. That means when you take 10 cm of Snow it would melt down to 1 cm of liquid water equivalent. 
All of the forecast model snowfall projections I show you on Here & Now & on the blog are projecting at a 10:1 ratio. 

WET SNOW
These types of snow events are little more prominent here along the Coast. With some storms, we can see wet snow falling through temperatures right at 0 or even slightly above freezing, perhaps even mixing with rain. In those cases we see a water logged snowfall which could be in the 5:1 ratio range. 5 cm of Snow melted down would equal 1 cm of liquid. We've all been soaked to the bone in those heavy wet snow events.

FLUFFY SNOW
In cases where temperatures are approaching (generally) -7 to -10, we can see snowfall ratios in the 20:1 range.  20 cm of snow melts down to just 1 cm of liquid. These light fluffy snow events are more rare here on the Island than they are in Labrador and on the mainland. In some cases with very cold temperatures snowfall ratios can be as high as 30:1 or more.

LAST NIGHT
Overnight & into Wednesday morning YYT had 1.38 cm of liquid equivalent. More a more typical snow event, that would have meant about 13-14 cm of snow to deal with. However with last night's chilly temps (-8 overnight & wind gusts just 30-40 km/h ) we had 30 cm from that 1.38 cm. 
That's a Snowfall ratio of 22:1. Rare for St. John's for sure. 
Superman Snow at it's finest! 

FOR MORE
Of course this is just the 'Coles Notes' for looking at snow ratio.
Besides the temperatures at the surface, aloft and the winds mentioned above, solar radiation, humidity in atmosphere and more, all factor in when determining the snow ratio.
For you fellow weather weenie's out there who are interested, here are a few cool links with more info on the snow to liquid ratio and winter precipitation forecasting in general.

-National Weather Service Precipitation Type Information. 
-MetEd Study of Snow to Liquid Ratios- Thanks to EC's Devon Telford for this link.
Note: You will need a login for MetEd, but it's a fantastic site if you're a weather enthusiast. 

Ryan

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