Scott, you might appreciate this. I found the monthly records for Vestmannaeyjar, Iceland. All-time record low in April at this station (-16.9 C/ 2 F on 4/1/1968). Same dynamics as the Aleutians here, with the coldest minimums dependent on sea ice.
As a related question, as far as I know the latest in the spring season that the coldest day of the year was recorded in the lower 48 almost surely belongs to Fort Bragg California on 5/24/1965. It has an official reading of 29 for that date, though I do wonder how accurate it is.
That same year, Crescent City also recorded a 34 in 5/6/1965, which was only 4 degrees away from the coldest reading of the year. Crescent City had its coldest day of the year on 4/1/1945 and 4/1/1976 and April readings have gotten close to the coldest day of the year in several other years.
Both San Francisco Downtown and Napa have gotten very close to the coldest day of the year in the middle of May. On 5/16/1906, San Francisco City was 42, only 2 degrees away from the coldest reading of the year. More recently, on 5/10/2003, San Francisco City was 43, only three degrees above the lowest reading of the year. On 5/18/1974 Napa was 30, only one degree above the coldest reading of the year.
Point Piedras Blancas has actually gotten close to the coldest reading of the year on 8/18/1954! Only a few days in February and September were colder. In other years, June and July have come pretty close to the coldest readings of the year as well. Several Mays have days very close to the coldest of the year. Nearby Big Sur has recorded the coldest day of the year in April several times.
On the flip side, LAX has recorded it's highest reading of the year with a 91 on 1/31/2003. Other early hottest days of the year at LAX were on 2/7/1954, 2/4/2001, and 2/21/2002. On occasion Sand Diego has also seen the hottest day of the year in February
San Diego, Long Beach, and LAX have both seen the hottest day of the year in November. In San Diego 13 out of the last 116 years had the highest reading in November, a rather remarkable 11% of the years. The latest hottest day of the year in San Diego was on 11/24/1932.
Point Piedras Blancas had its highest temperature of the year with an 85 on 12/6/1959, which is one of the highest temperatures ever recorded there, exceeded only by a few days in October.