I was looking at today's almanac (your's)data...it seems we had a trace of snow on this day in 1957...could you explain how that happened? :) ...especially when the record low for that date was 58 degrees. It must have been quite a day.
Posted July 22, 2008
MIKE MOSS SAYS: Steve, Ah yes, 1957 - the infamous "Summer with a Winter..." - just kidding of course. What actually happened is the database that we use to populate our Almanac pages had originally been fomatted to exclude the "snow" column during the summer months, but was recently re-formatted to include that data, as observed and recorded by the National Weather Service for RDU.
As it turns out, the NWS and the National Climatic Data center started recording all frozen precipitation in the "snow" category back in the late 1980s. In the middle of July, that means that a hailstorm crossing over the airport can result in a "snow" category value, which would usually be a trace due to the ephemeral nature of most hail around here.
So, if you see a trace in the snow category when it just doesn't make sense, that's usually what's going on - we will probably do something like change the wording on our almanac so it says "Frozen Precipitation (snow, sleet, hail)" instead of just "snow," which should make it a bit less mysterious when it pops up on a summer day.
Incidentally, regarding tricky categories for recording precipitation, freezing rain counts toward rain and not towards snow, but does count in measurements of surface snow depth! That makes some sense, because it falls as a liquid but almost instantly becomes a solid on the ground or other surfaces...
Thanks for the heads up!