Saturday, October 31, 2009

It's Things Like This That Threaten My Mental Health

So, I have this question that is absolutely killing me. And I need to ask it because I really do want an answer, even though I know I won't get one that satisfies me. Of course, I don't mean any offense to anyone here, even though it will probably sound like I do…

Over this past summer, I kept putting off major yard work because I would look at the weather forecast and rain would be predicted. Sometimes, this would happen for days in a row. Something else would get put on the schedule in anticipation of said rain, but that rain never seemed to materialize when it was forecast. The daytime hours would be filled with heavy clouds with absolutely no rain. It might move in at 10 in the evening that same day, but I swear it never, ever happened when the forecast said it would. So my yard work would go undone.

Today, I have a metric crap ton of leaves in my yard that I need to move, mulch, or otherwise get rid of, so despite the forecast of "rain starting around noon," I went out and got started. You see this coming, right? At noon, as I stood there with my leaf blower, clearing the six-inch thick carpet of yellow away from my two giant maple trees (I've already done one round of this), the sky opened up and the rain began to pour down.

Why is it that today, of all days, the forecast was spot on?

Really. I want to know...

1 comment:

JamieO said...

Good question, and I got some answers. No offense taken here, as forecast busts, forecast communication, and how weather makes forecasts hard to communicate are three interesting subjects to me.

First off, forecast busts. They happen. There are some doozies, classics - The March 2001 blizzard that didn't happen is an example. Forecast accuracy is about 65% or so at 48 hours, pretty reliable. There are situations that are just so complex or random they are hard to forecast.

Making these things worse, computer forecast models are simply awful. The best is the European one, btw. The US models can be awful.

Difficult-to-forecast weather situations leads us to the busts you experienced.

Summer forecasts for rain often will be a crapshoot more often than not due to the scattershot nature of it. This unusual summer notwithstanding, most of our June/July/Aug rain is from popup t-storms/showers.

These are difficult to forecast. That's why you will see/hear things like "shower or storm in some areas" or "not everyone will see rain." Where this rain happens is near impossible to forecast even four hours out. The rain happens due to the atmosphere being just like boiling water, the biggest bubbles become storms. Where they will happen is like forecasting exact location down to cm of a wide-awake Monkey - you can easily predict down to the room but not that exact, lol.

So while you were wondering where the rain was, someone in Boalsburg could have been thinking, wow, great forecast. That bad storm you got last summer? Five miles south of State College missed it. Fall, winter, and spring precip tends to be more of a general area of precip.

This leads us to communication. How do you communicate this stuff? The NWS chooses to say things like "40% chance of showers" which I think is confusing to people - does that mean one my yard-that-needs-tending has a 40% chance of seeing rain, or does that mean 40% of the area sees it? AccuWeather will say "a shower or two in some spots" or "a steady, soaking rain today".

Another problem with communications is it is often out of the hands of the forecaster. I have heard old forecasts being read on the radio, like hearing this on a Saturday: "Today, sunny, 35. Tonight, increasing cloudiness late, 22. Tomorrow, snow developing in afternoon 34. Sunday, snow ending in the morning, 30" See the problem here if you are out, hear that, and it starts snowing on you at 1 pm. Right forecast, wrong delivery. Guess who is blamed?

You also have stuff like misleading icons, the tendency for people to hear "a brief shower late today" as "lots of rain all day," and poor delivery by the meteorologist her/himself. An example of the last is going on too much about the reasons for the weather - people tend to just want to know if they need an umbrella. These are all very real reasons.

Finally, you offered a big clue as to why it didn't rain. All the clouds. What? It seems counter-intuitive, but the sun is the heat to make the atmosphere act like boiling water, heating the ground and making air rise. If you have plans on a summer afternoon with bad t-storms in the forecast, the last thing you need is a sunny morn.

Yeah, weather's weird. Just like the people who forecast it.