A couple ways you can tell it will likely rain soon in Seattle; no weather app needed
Getting a forecast is pretty easy these days. You can watch or read a meteorologist's forecast (good!) or cheat and look at your phone app (bad! -- OK, maybe a little bias there.) But did you know there are some ways around Western Washington you can tell it will rain tomorrow without having to rely on either?
The first is perhaps among the most reliable: A lenticular cloud (or "hat" cloud) that forms over Mt. Rainier.
The cloud is formed when you have three ingredients: Warm, moist air that is just on the cusp of saturation, laminar flow (when you have winds constant with height -- as in little to no turbulence or shear) and something big to get in the way, like, Mt. Rainier.
When the air flows over the mountain, it will create waves downstream where the air is now going up and down, and up, and down -- like ripples on a pond or waves on the ocean.
When the air goes up, it cools a little bit and when conditions are on the cusp of saturation, that slight cooling is enough to create a cloud. When the air sinks back down again, an opposite drying effect occurs and the cloud disappears.
While to us it might look like the clouds are floating in place, in fact, the air is streaming through the cloud as it hovers there -- the cloud is just showcasing the right spot in the atmosphere where the air is undergoing its lift and sink. Sometimes this occurs right over the summit, giving the mountain a hat.
So why does this predict rain? Because that needed moist air with laminar flow usually occurs in the hours preceding a weather system. Think of it as Rainier donning a rain hat!
The second signal is when there is a rainbow halo around the sun or a milky halo around the moon.
The halos are usually seen when there are high cirrus clouds overhead. Those clouds are made of tiny ice crystals, which will refract the sunlight much like a prism will and voila! You have a rainbow halo around the sun.
It works the same way with moonlight.
So why does this predict rain? Usually those cirrus clouds are on the leading edge of an approaching cold front.
Neither of these are slam dunk indicators -- I've seen halos around the sun during dry stretches when just some cirrus clouds float in from a distant storm, or hat clouds on Rainier when the storms miss the area. But I'd say it's a good indicator more often than not.
Or then, there's this more sure-fire way :)
What about a red sky at morning? Do sailors take warning?
This one is more of a gray area.
The famous "Red sky at night; sailor's delight. Red sky at morning; sailors take warning" saying is based on the fact that weather generally moves west to east in the mid-latitudes. If you can see the sunset, that means it's clear to the west and there are no storms in your immediate future and sailors, along with anyone else with outdoor plans, would be delighted.
The red sky at morning is a bit more dubious. That is assuming that if the weather is clear to your east (as in, you can see the sunrise) then based on natural progression of weather, it must mean a storm is due to come in from the west, and sailors should take warning. There is something to be said that if you see those high cirrus clouds that help make a better easel for a pretty sunrise (as in the photo above) -- those clouds are a sign of an approaching front.
But in the dry late spring and summer season, red skies at dawn are a near daily occurrence. Going to have to go with checking what the meteorologists say on that one...