Yes

you do need a jacket based on the weather in Guerneville, CA 95446, USA 1 second ago

Why? Because the rain is just enough to ruin your hairstyle but not your mood and sorry, it's too cool for just a hoodie!
58°F15°C & Rain

Wind is 6 mph10 km/h from the North, gusting to 17 mph28 km/h
October 13
9pm59°F15°C7 mph11 km/h WestRain
10pm58°F14°C5 mph9 km/h NorthwestRain
11pm58°F14°C4 mph6 km/h SoutheastDrizzle
October 14
12am57°F14°C3 mph5 km/h SouthDrizzle
1am55°F13°C1 mph2 km/h EastRain
2am54°F12°C3 mph5 km/h WestDrizzle
3am52°F11°C3 mph4 km/h NorthDrizzle
4am52°F11°C3 mph4 km/h NorthDrizzle
5am51°F10°C2 mph4 km/h NorthwestDrizzle
6am50°F10°C2 mph3 km/h NorthDrizzle
7am50°F10°C3 mph4 km/h NorthDrizzle
8am49°F10°C2 mph3 km/h NorthDrizzle
DateLowHighWindDayNight
October 1350°F10°C59°F15°C4 mph6 km/h from SouthwestRainDrizzle
October 1448°F9°C61°F16°C2 mph4 km/h from NorthwestDrizzleMostly Cloudy
October 1549°F10°C65°F18°C3 mph4 km/h from SouthwestPartly CloudyMostly Clear
October 1646°F8°C70°F21°C3 mph4 km/h from WestMostly ClearMostly Clear
October 1746°F8°C74°F23°C3 mph4 km/h from SouthwestMostly ClearMostly Clear
October 1850°F10°C77°F25°C3 mph5 km/h from SouthClearMostly Clear
October 1951°F10°C66°F19°C5 mph8 km/h from SouthwestMostly CloudyMostly Clear

Yes

Low of 48°F9°C, High of 61°F16°C
Wind: 2 mph4 km/h
Precipitation: 71% rain

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