Right now on the “Current Surface” map at weather.com, there is a low sitting on the Oklahoma panhandle, and extending south from it is a sort of dashed purple line. It was there yesterday too, I think. What does that line indicate? I couldn’t seem to find anything on the site that says what it is.
I beleive that is what local meteorolgists call a “dry line”.
Ah, I see. Thank you.
Dashed line seems to indicate a trough, generally.
http://www.weathergraphics.com/edu/ybtf/
http://www.meteor.wisc.edu/~hopkins/aos100/sfc-anl.htm
(maybe the color is just bad on weather.com? supposed to be brown?)
Purple (but not dashed–see symbol chart on link below) is usually used with an occluded front, from what I can find.
http://64.55.87.13/dstreme/extras/wxsym2.html
But perhaps a purple dashed line also refers to an occluded front?
http://www.angelfire.com/mt/montalk/cloudbust2.html
Or an outflow boundary?
http://www.spc.noaa.gov/faq/tornado/sfcanls.htm
I beleive that is what local meteorolgists call a “dry line”.
I’m sorry–could you repeat that? 
Oh, and find a cite, please. The dry-line illustration I found looks quite different:
on page http://www.southlandwx.com/symbols.html
scroll down to see http://www.southlandwx.com/sym22.jpg
search for dry line on google and click on the first link. There is a picture about halfway down the page. The dashed line on the map is how they show dry lines on the weather reports on the local news.
I too have seen the Weather Channel use the purple (violet) dashed line to indicate where the dry line is located…other forecasters and/or channels have used different symbols to indicate the dry line, but for the Weather Channel and Weather.com, it’s the line that the OP described…
Actually, I recall that yesterday at some point the map had something like the symbol toadspittle linked to in place of the line I described, which was there before and then of course returned again. Assuming I didn’t just imagine this, what might be the reason for this change?
I keep looking at this map, by the way, because I need information for a weather log I have to keep for a class I’m in.
I’ve never heard those dashed lines referred to as a “dry line” before. I’m a Weather geek…I consider myself fairly educated on the subject and I’ve only ever head them used to represent troughs or occuled fronts.
It may have something to do with where you live. One of the websites I searched says that dry lines only regularly occur in a few states: Texas, Oklahoma, New Mexico and maybe a couple of others. It said they almost never occur east of the Mississippi. I see them on the local weather reports all the time, especially during the spring. Anyway, I think I set a new personal record today for posts in a day. I better quit for the day.
It is a dry line. Where “fronts” indicate the boundary between air masses of different temperatures, a dry line indicates the boundary between air with different humidity (dewpoints, to be specific). Humid air is actually lighter than dry air (contrary to what you hear from baseball announcers), so you get moist air lifted by dry air at the “dry line”, which is why you often get nasty thunderstorms and tornadoes at that boundary.
LM, BS Meteorology