The 540 Line

Now we’ve known about the chance of snow for a little bit over a week now and there were a couple of factors pointing towards that, but a big one was the 540 line. The 540 line is a distance indicator between how far certain pressure values are apart in the atmosphere. 540 refers to the distance of 5,400m between the 500mb and 1000mb heights, with a lower value meaning cooler temperatures. Now this isn’t a perfect determiner of if we will see snow or not, but the lower the pressure height above you, the colder it will be, and the 540 line historically is the point where we have a 50/50 shot of seeing snow or rain. Thankfully the pressure height for us in Michiana will be lower than 540, which means we have a greater chance to see snow, but we will have to see.

The 540 line can be used to determine if a band of precipitation will be bringing rain or snow to an area, though it isn’t perfect at determining that. What it is good at determining are the other conditions in an area, mostly the noticeable cold that an area could feel. The 540 line is found on a 500 millibar map, and on this one it is clearly marked with the separation between the orange and the gray. Again, we’re expecting the 540 bar to move to the south us, part of a little blob of cold air making its way over the Great Lakes region. But after that blob moves back north, we’re not expecting too much more of truly cold temperatures, with straight lines in the jet stream, hopefully bringing more average temperatures to Michiana. We can see the change it’ll bring in the high temperatures for the next 7 days: today, very mild conditions, the rest of the week, below average.