Based on the weather in Napa, California, United States Of America as of February 14, 2016 6:36am local time

Why? Because it's cold. simple as that.
Current Conditions
Temp: 48.2°F9°C
Wind: 3.8 MPH6.1 KPH
Precipitation: None

Next 2 hours: Yes

Next 4 hours: Yes

Next 8 hours: Yes