On Mon, 10 Dec 2012 16:20:27 +0000, StaffHerb wrote:

I have a spreadsheet of weather data that I've collected over the past
30 years. Among other data, the columns on one sheet have a date, High
Temperature & Low Temperature. On another sheet I have the days of the
year listed along with the highest High Temperature, lowest High
Temperature, etc. This gives me the value for each date, but I'm
wondering if there is a way that I can also get the last date on which
that value occurred.

It's hard to tell your layout due to how the newsgroup has reformatted things. So let's assume that

Dates are in column A
Max temps are in column B
Min temps are in column C

The MaxMax Temp would be =max(b:b)
The MinMax Temp would be =min(b:b)

The date for the first MaxMax Temp would be
=INDEX(A:A,MATCH(MAX(B:B),B:B,0))

The date for the last MaxMax Temp would be
=LOOKUP(2,1/(B:B=MAX(B:B)),A:A)

For MinMax replace max(b:b) with min(b:b)

And for the MaxMin and MinMin parameters, refer to C:C instead of B:B

And you can replace the whole column references with partial column references, if you like.