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Old 03-06-2008, 12:56 PM   #11
CanisLupusArctos
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Default model vs reality trend

Rose, I have noticed the same behavior from the NWS in Gray this winter.

There's an interesting trend I've noticed in the past few weeks. The models have been consistently favoring warmer/wetter solutions, while reality has consistently been providing colder and whiter conditions than the models had forecast even 24 hours before.

Even this most recent storm had been forecast to be mostly rain with maybe some sleet, and little or no accumulation for the NW end of the lake. We ended up with 1.3 inches of snow, followed by freezing rain, NOT plain rain. Total ice accumulation was about 0.25" on top of the snow. A few nights ago we had a low of ZERO here, while my friends in the Boston area were surprised to hear me say it got that cold up here. They didn't have a huge snowpack to help chill the night off, once it got clear and calm. The models had called for a chilly night here, but not zero. On the morning of February 29 we had a low of -17... even at midnight, there were no models or human forecasters (including myself) who thought it would go that low. I've watched situations like that happen more than once in the past few weeks... in storms and in clear weather alike.

I think this "cold air favoring" is the result of our incredibly deep snowpack that extends from central Canada all the way to the eastern tip of Maine. The models seem to have been predicting what would normally happen without this record snowpack. When you put ice packs in a cooler, it keeps the food cold. When you put a giant ice pack on the landscape, it does the same thing on a larger scale. It becomes a lot harder for a warm front to scour out the last remaining cold air at the surface, because the snowpack is actively cooling the air at the surface. On sunny days like today, it's also acting as a giant mirror, deflecting lots of solar energy right back into space.

With that said, I'm nervously favoring a colder solution than the models are indicating. I wouldn't be surprised if this storm's predicted track started taking steps closer to the coast instead of inland, as the models are now predicting. Normally in March, cold air moving southeast from Canada doesn't have as much 'oomph" behind it, like it does in January, and this is what I think the models are latching onto -- 'typical March.' But I think our unusually deep snowpack is probably going to help preserve the cold air's eastward-moving force. That is not something the models would predict.

If the storm does go west of us, I think we'll hold on to the initial snow for longer than the models indicate, and when we go over to freezing rain, we're likely to stay with freezing rain for most of the storm. Southern areas where there is not as much snow on the ground would likely see plain rain, and probably flooding as well.

If the storm goes east, we'll have a lot less to worry about in the short-term--just a matter of where to put the snow, and keeping roofs shoveled, but otherwise a gift of time for more people to prepare for the eventual melt.

There is one other thing to consider, should rain fall here: The most recent storm left our snowpack without a fluffy surface, so its former ability to absorb water is now gone (except for where the sun is softening it up). What's more, the surface of the snowpack (which still stands at 35 inches at Black Cat) is now "bullet-proof" ice. The weight of the ice compressed the pack by 7 inches, and if I spray water on it, it just flows across the top of the snowpack now. This tells me that there's a much greater "runoff" factor for any rain we get from this upcoming storm.
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