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Originally Posted by SIKSUKR
Being a skiing snow lover I get frustrated with discrepencies in real snowfall totals also.Really,how could you possibly forecast 18 inches that fell 40 miles away in Boston and 30 inches in Franconia while in between many towns recieved only 6- 10 inches.Pretty much impossible to forecast these differences.
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Thank you. To this statement I would add that the same kind of effect is even more common in summer with rain, but no one thinks about it much because rain has less impact on our daily activities than snow does. Any major weather system -- winter or summer -- is always going to have embedded pockets of high energy. In summertime this leads to reports that some towns got 4-5 inches of rain while the rest of the area got an average of 2 inches. But to most people, those numbers are just a point of interest, as in, "Oooh wow, that town got 5 inches of rain. Oh well, on with my day!"
If we forecast a chance of showers and thunderstorms for any given day, you know from experience that not everywhere is going to get one. Some places stay dry while the next town over gets a raging thunderstorm. If you travel right after it passes, you can tell where it hit because you suddenly go from dry road to wet road.
But rain doesn't leave us with lasting memories like snow does. That's why, when winter comes, it's so easy to forget that weather is highly localized. You get the same effects in winter as in summer, except those extra-energetic pockets of the storm end up dropping a huge amount of snow, instead of just being an area of heavier rain.
The maps generated by the computer models might show an intense storm right off the coast. We know that an intense storm is going to end up looking like a comma on the radar, and that whoever lives in the space between the comma head and comma tail will get very little action from it. That area is what we call "the dry slot." There's no predicting where it will end up.
In summertime, it's easier for us to look like we got it right, because if we say it's going to be a rainy day, and the ground becomes wet in all places, no one really notices whether they got a half-inch of rain or a tenth of an inch. Wet is wet. It all looks the same until there's enough to cause a flood.
In winter, the difference between 0.5" liquid and 0.1" liquid becomes noticeable to laypersons because, on average, a half-inch of rain becomes 5 inches of snow, and a tenth of an inch of rain is only an inch of snow. One requires plowing and shoveling, and the other doesn't. Now let's say there's cold air aloft, and the area of more intense snow is able to pull a downdraft of that colder air. That changes the liquid-to-snowfall ratio so that the half-inch of liquid becomes 7 inches of snow instead of 5, in
just that location. That extra 2 inches of snow is noticeable to most people.
But the underlying meteorology remains: The difference between the two locations is just 0.4" of liquid, which in summer would go unnoticed. The ground would be equally wet in both places, and everyone would say we were correct in predicting rain.
The snowfall forecast maps in winter are misleading. You get the map with a design that looks like a bullseye or an egg over-easy. 3-6 inches for one zone, 6-10 inches for the bullseye or "yolk." After the storm, the National Weather Service makes accurate maps of how much snow actually fell. Those designs have no simplicity to them at all. It's like looking at splattered modern art. The snowfall forecast maps are a generalization that usually ends up being correct -- in general -- but they can't foretell any details.
The resolution on the computer models just isn't that good yet. Great resolution is available in the addictive online games you've probably heard about. A digital 3D model of the atmosphere is just a little bit harder to create.