Friday, 11:55 a.m.
The stage is set for a big winter storm to sweep across the country this weekend and dump a lot of snow over a wide swath from the central Plains to parts of the mid-Atlantic and New England. The storm is already bringing a lot of rain into California, along with much-needed snow in the Sierra. Over the course of the weekend, it will slide through the central and southern Rockies with some rain and mountain snow before redeveloping over southeastern Texas and Louisiana by Sunday evening. At that point, the moisture from the storm will be spreading through the Ohio Valley into the northern mid-Atlantic, some of it as snow, some of it as ice and some of it as rain.
Pretty much as expected, watching the run-to-run changes on the models is, well, any number of things. Amusing? Bewildering? Frustrating? Suffice it to say they all have changes, and while the main theme of a storm remains unchanged, the details over any one location remain in flux. Since I know everyone wants to see it, here's the very latest thinking of snow accumulations for the storm:
Rest assured there will be some subtle changes in this map going forward, as it is a fluid situation.
What are the factors that must be examined and watched over the next 48 to 72 hours that will impact snow totals in any given location? There are many of them. Among them:
1) Positioning of the front Sunday. This is the front that will slide across the Great Lakes tomorrow and through the Northeast tomorrow night. Look at the 12z Feb. 28 GFS surface forecast for Sunday morning:
Compare that to the 12z NAM forecast:
The differences are subtle, but noteworthy. The NAM has the front slower and farther back, with a clear wave along the front heading northeastward toward central or south-central Pennsylvania later Sunday. This holds us the arrival of the cold air and ultimately leads to a warmer solution (less snow), and one with a weaker end game (also likely to mean less snow). So, where this boundary sets up Sunday will have a huge impact on how deep the arctic air is or isn't as the bigger feature approaches from the southwest Sunday night and Monday.
2) Speed of the trailing storm. The faster it moves, the less moisture can get squeezed out of the clouds, plain and simple. The general consensus, though, is that it's a long enough event to cause some places to pick up more than a foot of snow.
3) Length of time of precipitation in a non-snowy form. This is especially a critical factor from the Red River Valley on north and east into the southern half of Missouri and points east up into southern Ohio and Kentucky, as well as in parts of the mid-Atlantic. Should the low-level arctic air push be delayed somewhat, then the ice zone would have to be shifted farther north as well. Regardless, all it means is the period of time it can purely snow and accumulate is somehow limited. Here's where our current thinking is on who will have to deal with at least some period of sleet and/or freezing rain:
4) Dryness of the cold air. This helps determine the snow-to-water ratio. Typically we assume snow has a 10:1 value, but with a bitter, arctic air mass in place all across the north, there's likely to be some sort of 'fluff' factor involved that allows the falling snow to have bigger spaces in between them, and, thus stack better. This could push ratios into the 15:1 or even 20:1 category deep into the cold air.
5) Local enhancement bands. These may hardest to predict when you get right down to it. These may not show up at all in the models until the storm is underway. Then the very short-term models can take over and more accurately portray these heavier bands of snow that often develop in storms. To use the last big as an example, one such band developed right over my backyard in Centre County and soon became evident this enhanced band would last a few hours and help wipe out the initial snowfall estimates. Again, these will be harder to pinpoint until the storm is underway.
I know one thing. This weather is just killing my outdoor riding schedule! I don't even have 200 outdoor miles in yet for the year! Call me a wimp, but I'm just not ready to risk life and limb for that kind of activity! Now, if this is next year, and a bigger, more challenging ride is on my horizon in the summer, like RAAM, then I might have a different take! For now, I'll suffer along like everyone else and be thankful that I have varied disciplines to train for in the lead up to a marathon, a half marathon, a half ironman, and a full ironman if all goes well over the course of spring and summer. Again, assuming we actually HAVE spring this year!
By the way, I know one of my loyal readers lives in Michigan and must be loving all of the cross-country skiing this winter! But I know he's also been part of a crew for that aforementioned ride. If you're reading this, please send me an e-mail! I want to pick your brain!
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