Based on the weather in Napa, California, United States Of America as of May 30, 2016 3:35am local time

Why? Because it's not very warm out.
Current Conditions
Mostly Cloudy
Temp: 52.7°F11.5°C
Wind: 2.4 MPH3.9 KPH
Precipitation: None

Next 2 hours: Yes

Next 4 hours: Yes

Next 8 hours: Yes