Weather Blog

What's the best date to plan a snowball fight?

What's the best date to plan a snowball fight?
Madie Baker's snowball disintegrates as she throws it at a friend in a downtown park Tuesday, Nov. 23, 2010, in Seattle. (AP Photo/Elaine Thompson)

One of our most popular charts on our weather site is the "Odds It'll Rain on our Wedding Day?" chart that shows how much it's rained on each date in Seattle history.

We've had a few people ask if we could do a similar chart with snowfall. Obviously snow isn't as frequent as rainfall around here, but some days so stick out more than others.

This chart shows how many days it has snowed at least 0.1" at Sea-Tac Airport from January 1945 through September 1996, and then again from December 2003 through January 2011.**

(Why the gap? See after the chart below)

Day Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
1 1 5 5 0 0 0 0 0 0 0 0 3
2 7 2 2 1 0 0 0 0 0 0 0 2
3 6 3 7 0 0 0 0 0 0 0 1 1
4 6 2 5 0 0 0 0 0 0 0 0 1
5 6 1 3 0 0 0 0 0 0 0 0 3
6 3 0 1 0 0 0 0 0 0 0 1 2
7 4 0 2 0 0 0 0 0 0 0 0 3
8 7 1 2 0 0 0 0 0 0 0 0 1
9 4 4 5 0 0 0 0 0 0 0 0 0
10 7 2 2 0 0 0 0 0 0 0 0 2
11 6 2 1 0 0 0 0 0 0 0 1 3
12 5 1 1 1 0 0 0 0 0 0 0 5
13 6 1 2 0 0 0 0 0 0 0 1 3
14 6 3 2 0 0 0 0 0 0 0 0 2
15 5 1 1 0 0 0 0 0 0 0 1 1
16 4 2 1 2 0 0 0 0 0 0 0 2
17 4 4 0 1 0 0 0 0 0 0 2 1
18 6 0 1 0 0 0 0 0 0 0 2 6
19 5 2 1 0 0 0 0 0 0 0 3 4
20 7 2 1 0 0 0 0 0 0 0 3 6
21 6 0 1 0 0 0 0 0 0 0 1 4
22 6 1 0 0 0 0 0 0 0 0 2 3
23 7 3 0 0 0 0 0 0 0 0 1 2
24 2 2 0 0 0 0 0 0 0 0 1 3
25 6 0 1 0 0 0 0 0 0 0 1 4
26 6 2 1 0 0 0 0 0 0 0 2 3
27 6 1 1 0 0 0 0 0 0 1 3 6
28 7 5 1 0 0 0 0 0 0 0 0 4
29 4 1 1 0 0 0 0 0 0 0 2 7
30 5 - 0 0 0 0 0 0 0 0 2 7
31 5 - 0 - 0 - 0 0 - 0 - 3
                         
Total 165 53 51 5 0 0 0 0 0 1 30 97

** So why the 7 year gap of snowfall data? When the National Weather Service moved to automated observation equipment in 1996, the decision was made to stop measuring daily snowfall, according to agency officials, figuring it wasn't a significant statistic.

The decision blew a hole into a lot of long record keeping of snow. There was a change of heart in the mid 2000s that maybe they should be keeping track of the data, and the records started anew.

In the period while Sea-Tac Airport was no longer recording snow, the National Weather Service office did track snowfall at their location along the shores of Lake Washington at Sand Point, but being near water at sea level meant they likely received a lot less snow during the period than Sea-Tac might have recorded.