Yes

you do need a jacket based on the weather in Seattle, WA 98105, USA 1 second ago

Why? Because it's cold. simple as that.
44°F6°C & Mostly Cloudy

Wind is 4 mph7 km/h from the S, gusting to 14 mph22 km/h
March 29
8am43°F6°C4 mph7 km/h SCloudy
9am43°F6°C4 mph6 km/h SMostly Cloudy
10am43°F6°C3 mph5 km/h SECloudy
11am44°F6°C3 mph4 km/h SEMostly Cloudy
12pm46°F8°C2 mph4 km/h SEMostly Cloudy
1pm48°F9°C2 mph3 km/h SEMostly Cloudy
2pm50°F10°C1 mph2 km/h EPartly Cloudy
3pm53°F11°C1 mph2 km/h NPartly Cloudy
4pm54°F12°C3 mph4 km/h NPartly Cloudy
5pm56°F13°C4 mph7 km/h NWMostly Clear
6pm57°F14°C6 mph10 km/h NWMostly Clear
7pm57°F14°C8 mph12 km/h NClear
DateLowHighWindDayNight
March 2943°F6°C57°F14°C5 mph7 km/h from NPartly CloudyClear
March 3042°F6°C58°F14°C6 mph9 km/h from NPartly CloudyMostly Clear
March 3141°F5°C59°F15°C6 mph10 km/h from NMostly ClearMostly Clear
April 143°F6°C63°F17°C4 mph6 km/h from SMostly ClearMostly Clear
April 246°F8°C63°F17°C8 mph13 km/h from SMostly CloudyDrizzle
April 340°F4°C49°F10°C7 mph12 km/h from SWRainMostly Cloudy
April 438°F3°C50°F10°C4 mph6 km/h from NWMostly CloudyMostly Clear

Yes

Low of 43°F6°C, High of 58°F15°C
Wind: 6 mph9 km/h
Precipitation: None

Support This Page