Where can I find data for annual high and low temperatures?
You can find this data from NCDC.  You can find the data for Portland, OR here.  These are annual summaries (ancsum) and for Portland they have extreme minimum daily temperature (EMNT) and extreme maximum daily temperature (EMXT) dating back to 1910.  From the linked page you can request data in various formats and select the date range and the specific variables you want.  They will put together the requested data and email you with a link to download it.  Here is some example data from the dataset:

COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201301  55  23
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201302  61  30
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201303  77  29
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201304  78  36
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201305  85  40
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201306  97  49
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201307  92  53
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201308  91  57
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201309  95  47
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201310  74  32
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201311  60  24
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201312  57  12
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201401  58  25
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201402  58  19
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201403  69  32
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201404  83  39
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201405  91  42
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201406  85  48
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201407  99  54
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201408  99  54
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201409  94  51
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201410  85  47
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201411  63  26
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201412  64  21
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201501  60  24
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201502  64  32
COOP:356751 PORTLAND INTERNATIONAL AIRPORT OR US    201503  73  30


These are extreme max/min temperatures for each month, so for this station you have annual maximums of 97 F and 99 F for 2013 and 2014.  You have annual minimums of 12 F and 19 F for the same two years.  There are multiple stations and they have varying temporal coverage.  You can request this data for each of the cities that interest you.