If you’re in Nashville you’re no doubt sitting around waiting for this massive ice-mageddon that is supposed to happen today. Make no mistake, ice storms can be extremely dangerous when they actually happen, but more often than not they end up being far less severe than initially forecast. This is because these types of storms are incredibly complex and the most difficult of all weather phenomena to forecast. Here’s how they work, and why I’m usually skeptical of forecasts involving them:

When an ice storm happens there is always a strong mass of cold air in place (just look at how cold it was yesterday and monday!). Then a low pressure system moves in from the south or southwest, creating a mid-level wind flow from the south or southwest. Mid-level in meteorology is loosely defined as 5,000-10,000 or so feet above sea level. This southerly wind flow brings both warm air and moisture with it, creating a layer of warmer air above the cold air at ground level. This means the precipitation starts out high up as snow or rain, then becomes all rain as it falls through the warmer layer, then refreezes when it gets to the stubborn layer of cold air at the surface. Depending on the thickness of this cold layer, the rain drops will freeze while falling (sleet), or will freeze upon contact with the ground (freezing rain). Usually in these situations, the surface temperature is right at or just below freezing. This freezing precipitation only lasts as long as the cold layer stays below freezing, and that surface layer always eventually warms up. Here’s a graphic I’ve posted on this blog before, to illustrate:

Based on the forecast models, and published forecasts I’ve seen, there’s no doubt Nashville will see some frozen precip today, but I have a feeling that it will change to all rain, and the surface temp will creep up to the mid 30’s by late afternoon or so. The current forecast calls for the ice to remain the longest in the northeastern counties of middle TN, so those folks may see enough accumulation to start downing trees and power lines. I doubt there will be enough accumulation for that to be a major problem in Nashville, and all areas south and west. I’m fairly certain that Nashville’s heat island effect will aid in getting the surface temps up sooner rather than later. Furthermore, most roads have been salted heavily, and even the secondary roads have some salt on them transplanted by car tires, and with the surface temp hovering right around freezing the salt will have no problem preventing ice on the roads. Since the temperature is forecast to continue rising as the night goes on, due to the warmer air in the mid-levels working its way down, there shouldn’t be any problems at all by midnight or so.

PLEASE DON’T THINK THAT I’M TELLING YOU TO DRIVE NORMALLY IN WINTER WEATHER. YOU SHOULD ALWAYS ERR ON THE SIDE OF CAUTION WHEN THERE’S A CHANCE OF WINTRY ROAD CONDITIONS. PLEASE BE CAREFUL, ESPECIALLY IF CROSSING A BRIDGE OR OVERPASS AS THOSE FREEZE MUCH EASIER.

What I’m saying here is that this will NOT be ice-mageddon. For Nashville at least.

Here we go again. I recommend investing in Kroger stock this year, because they’re gonna get a big boost in sales in TN from all these “snowstorms” wherein a meteorologist utters the word “snow” and 75% of the population immediately clears the milk, bread, and egg isles. (Apparently people only eat french toast during snowstorms?) As usual, I’ve been monitoring the progress of the forecast and find it interesting that the NWS hasn’t issued the winter storm warning yet, only a watch. I’m sure the warning will come, but it’s kinda funny that they’re hesitating, no doubt because of the giant snow fail from a few weeks ago. (To be fair, some areas around the midstate did get something close to the forecasted amounts, though no one really got the full 2-3 inches that was initially forecast…) This system is a little different than the last one, however. This one will most definitely have enough moisture to generate the 3-5 inches, unlike the last system which had moisture “issues.” The big limiting factor with this system will instead be temperatures. Nashville will literally be right on the dividing line between having an ice/rain mix and having an all snow event. If this system decides to track just 50 to 100 miles further north than the models think it will, that will cause more warm air to advect farther north, and we’ll end up having mostly rain friday changing to a little snow on the backside fri. night into sat. morning. If it decides to track slightly further south, we’ll have all snow, but much less of it, and areas to the south of us could actually see more snow than Nashville does. This system has a little better chance of “success” in giving us a good ol’ fashioned snowfall than the last one, but I wouldn’t place any bets yet.

Big rumors abound in the blogosphere about Obama’s budget proposal due to land in Congress on Monday. The biggest rumor is that it will completely cutout NASA’s Constellation program, which is the rocket system currently under development to not only replace the Space Shuttle, but also put men back on the Moon. I reported many times on the progress of the Augustine Commission and its recommendations for how NASA should proceed given that its current “trajectory” was financially unsustainable. One of the options they proposed was to eliminate the Constellation program and let commercial spaceflight companies like SpaceX takeover the duties of getting astronauts to the International Space Station and other low-earth orbit missions. I have a feeling that if the budget really does cut the Constellation funds, that’s where we’ll be headed next. Honestly I think it may not be a bad idea, because it would allow NASA to focus more on getting man further out into the solar system, and eventually to Mars. I tend to agree with Dr. Phil Plait’s (the Bad Astronomer) sentiments on the issue (as usual) but I’m not in total agreement with him that we should still go back to the moon. But then again, he’s the astronomer with a Ph.D and I’m not. For even more info, check out Universe Today. Check those blogs again on Monday afternoon, as I’d say they’ll be able to update waaaay sooner than I will once the actual budget info is released.