COLD FRONT PASSES, WHY NO RAIN?

Written by: Bob Metcalfe

Most Rochesterians are fairly weather-astute. We all know about lake effect snow, warm fronts, and what setups typically bring rain.

Well today would "normally" be a rainy setup, but it isn't. So why is it that we aren't receiving rain with the passage of a cold front Friday afternoon? Two words: DRY AIR!

I remember as a beginning meteorology student at Oswego one particular day where I made a fool of myself in front of the whole class. We all had to take turns doing the "forecast" in front of the class. We cared about the deep science, the "whys" of the day. So I saw a big cold front that was racing in towards the area and without any hesitation said "We're gonna see one heck of a burst of rain." There were even nods of agreement from some of my fellow newbie met-majors. But I didn't look at the whole picture. The air ahead of the front was BONE DRY. We're talking Sahara Desert dry. It can't rain without moisture. In fact, it was so dry, that clouds didn't even form when the front did arrive later that day.

So needless to say, I always check the moisture profile just ahead of a front. Although not "bone dry", we'll avoid rain threats while the front pushes in, as some clouds do form.