As promised, here is a weather post about the rain. To any potential meteorologists who read this, please take note that I am a n00b and don't understand all the terminology or know the names of every single type of cloud. However, I am fascinated by how the weather works, love free data and need to know on a daily basis how wet my bike ride will be.
This post is broken into 4 sections:
1. Basic Forecast Reading
2. Satellite Imagery
3. Timing your ride with the radar
4. Model Output - It will change your life!
Basic Rain Forecasts
Here is a typical picture where I am disappointed in overall design. This happens all the time, an entire week of rain forecasted with the exact same picture icon of rain. The reason I'm disappointed is partly because it will rain a lot. However, the rain will be significantly different between each of these days and even within each day. Yet if you were to just look at the picture in the forecast you would think it'll be the exact same each day. Hardly! However, there are very subtle elements that actually show what kind of rain is forecasted.
%Chance of rain
This is actually quite useful and usually tells a lot of the story. 100% chance means you are going to get drenched - a massive storm is coming where it will probably rain rain most of the day. 70-90% means it will almost certainly rain but at times it may not rain that intensely. 40-60% usually means a sprinkle. 20-30% could mean a mist. 0-10% means mostly sunny!
Rainfall amounts
Here is the game-changer. As noted before we Pacific Northwesterners could probably have as many names for rain as Eskimos have for snow. There is pouring rain, windy rain, hailing rain, freezing rain, steady rain, bipolar rain, drizzle, sprinkle, mist and I'm probably missing some. Anyways, the distinguishing factor between most of these guys is the volume of rain that gets dumped out of the heavens. And the forecast actually reports these things.
Check out the Wednesday and Wednesday Night forecast. Exact same picture - exact same rain? Absolutely not! Wednesday says "Rainfall amounts around a half of an inch." Wednesday Night: "Rainfall amounts less than a tenth of an inch." Huh? How much is that? Admittedly it's a bit hard to convert a picture of falling rain into inches or fractions of inches of rain standing on the ground. So here is my nifty rainfall amount conversion scale:
< 0.1 inch: some rain, but not much. Safe for bicycling without fenders or rain gear.
0.5 inch: Pouring rain at times. Rain gear is a must even for short rides.
1 inch: TORRENTIAL RAIN
1-2 inches: FLOODING RAIN. Places without good drainage will flood. Landslides will happen on unstable slopes.
2 inches+: MONSOON RAIN. Ok, this entry is mainly to poke fun at Randy who claims that any rain storm he biked in had "MONSOON RAIN" quantities of rain. I did a little research and well again it's a little variable on what a monsoon is. It can range from the weakest Arizona Monsoon of 0.35 inches to the worst Bangladesh Monsoon in recorded history which had 13.4 inches of rain in 24 hours!
Timing Your Ride With the Radar
So, the next most advanced tool at your disposal is the weather radar. It shows a real-time picture of rain. Generally speaking, yellow stuff is pouring rain and anything more intense than that is rain you can go tell a story about. If you prefer not to ride in the rain, watch the weather radar and wait until the rain cloud moves away from your location. For example say you were at the red marker on the following maps:
Wait for it...
Almost...
Game on!
Unfortunately, it isn't always that easy and sometimes the raincloud will just stretch forever that you'll get rained on unless you wait for hours. However, the radar can even be helpful because sometimes there will be very short burst of rainclouds lasting only maybe 10 minutes with a gap of 30 minutes to the next raincloud which is often enough for a commute.
Satellite Images
I used to look at Satellite images, but have really started losing faith in them as an overall predictor of how much it will rain. There are kind of 3 types of rain cloud systems that come in and I've made screenshots of two of them.
Here is the "bipolar" type system:
All those little clouds probably mean something really fancy to meteorologists, but in general it usually means weather can be bipolar, ie raining hard for 20 minutes and then sunny for 20 minutes and then raining hard again. The radar is key for these kinds of clouds if you have a short ride.
Next is the "steady" system
This type of cloud usually will have a well defined start and end to the rain system. If you're lucky it will be a north-south type of cloud which passes quickly, if you're unlucky it will be an east-west type of cloud and if you're really unlucky it will be an east-west type of cloud that stretches all the way to Japan! Usually the rain is "steady" meaning it will rain consistently for the duration of the system. However, sometimes weird stuff can happen with these clouds where there is no rain at all. Here is a picture of the radar for the above satellite image:
Massive rain shadow over Portland! Why? I have no idea, but it was a dry bike ride.
The final system is the Cyclone the one that sorta looks like a hurricane. These are actually quite similar to the steady systems in how they dump rain.
Model Output - it will change your life!
Now the real game-changer I recently discovered is model output. I have found it to be very accurate. However, to me, to be very accurate is to predict whether it will be dry or have rain >0.1 inches, so ballparks work well for me. Once the rain is above 0.2 inches I could care less how much more because it will be a rainy ride regardless and the rainy clothing I have works in all levels of rain.
So, to take a look at this, go into the Wundermap and then check only the model output box, unless you like to clutter things. The default option is the precipitation view, "MSL". In the settings, it shows the start time of the latest model data in GMT or England time. So you have to do a little math, ugh. Then you have the option to increment the forecast in 3 hour increments. Or hit the play button, that is pretty cool too.
Update 2012-12-19!!
Recent articles including this detailed post from Cliff Mass have been confirming that the European model is way better than the North American model, so use the ECMWF as the model.
Example: Tomorrow I need to do a 2 hour ride. Should I commute to work in 2 hours or ride 2 hours after work? Let's check what the model says.
Here is the precipitation at 9am:
And here it is for 6pm:
Looks like 6pm will be the less rainy one!
The model data does go out to a maximum of 384 hours (16 days), but I start losing faith in it quickly until I don't even bother at the 6 day mark. The model data also has some cool stuff like temperature (map type "2mAG"), wind and precipitation type for each time period as well.
In Conclusion
So there you have my internalization of weather forecasts regurgitated to this blog as it relates to how I use data to determine whether I may or may not get rained on in my bike ride.
Let me set the stage for perhaps another post that I may come up with that is non-weather related. With that obvious radar image shot above I was waiting for the cloud to pass and then I would bike to Dave's Killer Breadquarters. However, I waited too long after the raincloud passed (partly in order to get the final screenshot) so although I bike to the Breadquarters in 27 minutes (even though Google said it would take 54 minutes), I was 7 minutes late after it closed.
Ah crap, it's after 11! Must sleep now.
