Weather Blog

17 hours of drizzle, then 27 minutes of deluge

17 hours of drizzle, then 27 minutes of deluge

The Puget Sound area got quite the "tour" of rainy weather on Sunday, first getting hours of the traditional Seattle-esque drizzle, then several minutes of a tropical downpour.

For example, Seattle had 17 hours of off-and-on drizzle (mostly "on") that registered a paltry 0.03". It was the type of day that highlights how Seattle can be one of the most frequently-rained on cities in the United States, yet is barely in the top half for annual rainfall -- it just doesn't rain that hard around here.

At least, not often.

But sometimes it does.

Like...Sunday evening.

That's when a heavy downpour moved up the I-5 corridor in the evening and dropped that much and more in just a few minutes, hitting Olympia and Tacoma particularly hard but weakening a touch as it moved north into Seattle and, eventually, Everett.

This video from from Olympia's deluge: 



Here are some of the rainfall tallies by time to get idea of the wholesale shift in weather pattern from day to night:

OLYMPIA:

  • 4 a.m to 6:54 p.m.: 0.07" (15 hours)
  • 6:54 p.m.-7:42 p.m.: 0.08" (48 minutes)
  • 7:42 p.m. to 7:54 p.m: 0.48" (12 minutes)
  • 7:54 p.m. to 9:54 p.m: 0.06" (2 hours)

TACOMA:

  • 3:58 a.m to 8:58 p.m. (17 hours): 0.06"
  • 8:58 p.m. to 9:58 p.m (1 hour): 0.55"

SEATTLE:

  • 3:53 a.m. to 8:53 p.m.: 0.03" (17 hours)
  • 9:26 p.m. to 9:53 p.m.: 0.03" (27 minutes)
  • 9:53 p.m. to 10:38 p.m.: 0.16" (45 minutes)
  • 10:38 p.m. to 11:24 p.m.: 0.09" (46 minutes)

Going back on the subject of drizzle, I decided to look up just when do we get the most drizzly months? It turns out, it's in the spring, when we are away from the winter storms but also not quite into the summer when what little rain we do get many times tends to be big clumps, as we saw Sunday night.

I would declare the drizzliest month as May 1974, when the month had 18 days of measurable rain that amounted to 1.37" of rain, or 0.08" per day. It just barely passed February of this year when we got 1.58" of rain for 18 rainy days. Honorable mention would go to June of 1950 when we had 13 measurable rainy days with just 0.59" to show for it in the rain gauge.

It was interesting to note that there has never been a year where October or November has had 13 or more rainy days and amassed less than 2 inches of rain. (December 1978 had 15 rainy days to only capture 1.37" in the rain gauge)

As you might expect, the rainiest months on a per-day average coincided with the rainiest months overall with November 2006's off-the-charts-record 15.63" of rain working out to nearly 0.68" of rain per day.

But overall, the rain is heavier in the winter than in the summer, or at least more frequently heavy and often. Here is the average rain per day by month:

Jan. 0.29"
Feb. 0.25"
Mar. 0.22"
Apr. 0.18"
May 0.16"
June 0.16"
July: 0.13"
Aug. 0.16"
Sept. 0.19"
Oct. 0.26"
Nov. 0.33"
Dec. 0.31"