I was looking into this last night, just out of plain old geography/weather nut curiosity (I probably have more time for that than John does.) Of course John's right, but here's what I found:
I too presumed you meant
Hartland, WI (Waukesha County).
You probably aren't going to find any records for Hartland, WI specifically, so it comes down to how close (to Hartland) is close enough?
You can find the Preliminary Climatology Data (CF6)
here for only two stations in southeastern WI, either Milwaukee (at roughly 25 miles, but with quite a different climate so close to Lake Michigan) or Madison (> 50 miles) from April 2003 to date.
Worst case, as John suggested, you can try the
National Climatic Data Center, but you may have to do some extensive and tedious digging at that site. If you're up to it, I suggest you start with
Data & Products | Find a Station in the left column, then perhaps by
State/Division/County/City.
A quick search by
State/Division/County/City (But as they say, some stations not identified by county!) found 14 stations in Waukesha County, with
several (Waukesha city, Waukesha County Airport, Oconomowoc, Dousman) within a 7-9 mile radius of Hartland. That should give you a start, with potentially much more research to do from there.
Note too, that
you may have to pay for the data you retrieve from the NCDC (perhaps as little as a few dollars), but if so, you'd better be sure that the data you have identified is going to serve your purpose, and has a narrow enough focus that you won't have to pay a huge tab for a bunch of irrelevant data.
Another possible resource is the
Wisconsin State Climatology Office, although in general I have found the state climatology offices to be next to useless.
That's the best I was able to do, so does John have any other professional weapons available?
