Does it REALLY rain all the time in Seattle?

You have heard the complaint--in fact, you may have made it yourself:
It seems like it is ALWAYS raining around here during the winter. Endless precipitation.

The funny thing, it really isn't true. Let me prove it to you.

Let's start with a plot of the probability of getting at least a trace of precipitation (.01 inch) anytime during the day for Seattle Tacoma Airport:

There is roughly a 50-70% chance from early November through April 1. Sothe odds are, if you stand out there all day, you will get wet. Duh!

But you don't do you? You are only outside for a short errand or walk or run or whatever.
So let's ask a more interesting and important question. What is the chance you will get wet during a particular hour?

Ready to be shocked and amazed? According to a study by Professor Phil Church and Mark Albright (published in Weatherwise Magazine, December 1974) only 18% of hours had measurable precipitation in November, 19% in January, and 15% in February.

You heard it right. Even during our rainiest months, more than 80% of the hours are dry.

You don't believe me, do you? Well, lets look at a plot of cumulative rain at my department over the last 72 hr...a very wet period indeed. (the rain is the blue line in the upper panel, the lower one is solar radiation). During rainy periods the blue line moves upwards, during dry periods it is level. You can see there are plenty of level (dry) periods (at least 60% of the time), and heavy precipitation intervals (when the line moves up quickly) are relatively rare (perhaps10-15% of the time).

Now most Northwest natives understand this--you can find a few dry hours on almost any day to have fun or do your chores (like remove the leaves from the street drains!). Few days are complete wash outs. If you use the weather radar effectively, you can see the dry periods and time them for maximum advantage. Or befriend a meteorologist!

Talking about wash outs, there was a relatively rare, very intense, rainfall that hit north Seattle around 2 AM last night. Several of you have sent me emails about it. Streets turned to rivers and the rain was deafening. Some of you got .3-.5 inches in less than an hour. Take a look at the radar image..you can see the intense band (red line).