Warmest Day of the Year in the US
The June values in New Mexico, Arizona, and Texas reflect the impact of the North American Monsoon,
a period of increased rainfall affecting the U.S. Southwest. Because
these areas tend to be cloudier and wetter from July through September,
the temperature is highest on average in June. For example, the warmest
day of the year in Terlingua, TX is June 11th. Conversely, the
persistence of the marine layer
along the Pacific Coast leads to cool temperatures in early summer,
with the warmest days on average occurring as late as October. In fact,
daily high temperature normals peak on October 2 in San Francisco.