Sunday, March 1, 2015

CU: Buried under snow

As far as weather forecasting goes, snow is quite the challenge. Even then, the extent to which forecasts missed yesterday's snowfall, which ended only today, is surprising. Here's some 101 on weather forecasting: weather models, using things called CAPE and CIN, can determine whether it is going to precipitate or not at a time step. Based on the forecast soundings (the vertical temperature profile), they can also predict whether that precipitation will be snow, freezing rain or simple rain.

The problem comes in determining the quantity of precipitation (and also the time, really). Models express precipitation in liquid equivalent - for snow, that means the amount of water (in in. or cm) that you would get if you melted a certain amount of snow (10 in or 10 cm). But to convert that liquid equivalent to actual amount of snow on the ground is more an art than science, because it can depend on a variety of factors. People who have lived in snowy regions will know that snow can come in a variety of forms, only some of which are conducive for snowball fights! So, it's pretty hard to determine the exact thickness of snow that you get.

Still, this week was quite a spectacular fail, with forecasts by and large predicting 4-6", while outside, there is at least a foot of fresh snow on the ground, if not a foot and a half. That's off by 100-200%! And that means, instead of trudging on the sidewalks, pedestrians are forced to literally trek through mountains of snow. Yes, we're buried in here! 

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