A couple in their sixties or seventies walked up to the desk, and the wife takes charge:
We just got back from my son's house, and while we were gone it snowed. I know it, because there's snow in my yard. What I want you to tell me is how much snow there is. My neighbor told me it snowed on December 13th and again on the 16th, and you have to tell me how much snow it snowed in them storms.
Well, I told her that it would take me some time to find this information, and that I'd call her when I did. I took down her number, and over the course of the next couple hours, searched for some kind of snowfall record in between helping other patrons.
The first place I always try for weather data is NOAA. I tried various searches in Google and restricted to the noaa.gov site, but didn't have much luck. I did find snowfall monitoring data files, which seemed promising because each file was for a specific month and year, broken down by day, and covered lots of cities in every state. However, the nearest city to this patron's yard didn't have data, so that didn't help.
So, I kept searching. I must tried twenty different ways to find this data, from scanning news reports from days after these storms to trying to contact local weather monitoring stations for their data to checking snowfalls at nearby airports. But in every case, either the data was missing, or the station was too far away to extrapolate to this woman's yard, or the data wasn't free, or the website seemed too unreliable to even bother with.
Then, happily, a colleague of mine walked by, and I asked her to help me out. I was getting frustrated, and I hoped a new approach to the problem would produce something useful.
We both looked, and found the Weather Underground's historical data about the same time. This was a wonderful little tool, letting us search by zip code and date. But the "precipitation" listed for that day was much lower than we expected. I remember getting about 8 inches of snow in each storm, but wunderground was reporting 0.81 inches.
Eventually we decided they were reporting "precipitation" as the equivalent of rainfall, not the snow that accumulated. This realization led us on a tangent to see if we could find a formula to convert inches of rain to inches of snow.
And it was then that my colleague found it.
She tried a simple search for "snowfall chelmsford," and noticed the url of one of the returns was accuweather.com linking in to their current weather report for North Chelmsford. At the bottom of that page was a link to a Past Weather Check.
Although this data only seems to go back one month, it was far enough to cover the two dates the patron provided. And, best of all, it gave both precipitation and snowfall, for our exact zip code.
This came about three hours after the patron originally asked me the question, and with much relief I called her to give her the amounts. Even her response, "yeah, that's about what my neighbor said" [click] couldn't dampen my spirits after answering this one (with a tremendous amount of help from a coworker, of course).
But recent-past questions like this are always tough, especially weather questions. It's easier to find what the weather was like years ago than what it was like a week ago, which just seems wrong to me. But as long as I keep bookmarking these resources, maybe next time the answer will come a bit quicker.