jeff sisson's blog (email me)

Same temp map

15 Aug 2023

An experience I’m guaranteed to have on any given summer: it’s 90°F indoors and probably some nasty level of humidity, and I’m stewing in the living room wondering how many other people are in the exact same situation right now. I added a little feature called “same-temp” to the Big Boy Weather station that answers this. It’ll show you everywhere else (in the Contental United States) it’s currently 90°F:

Contental United States of 90°F

…or everywhere else it’s currently 60°F:

Contental United States of 60°F

…or wherever it’s it’s currently 72°F:

Contental United States of 72°F

The maps update a couple of times an hour, and use data produced by the National Weather Service to create the National Forecast with a file format called “GRIB2”. GRIB2 files are cool: they’re about 50MB a piece and they describe meteorological data like temperature or rainfall, with instructions for how to project the data onto specific points on the earth. It’s a funky file format…every other horizontal line of “latitude” changes direction from east/west to west/east…and temperature data is in degrees kelvin, which always makes me think of hell…

I like working with file formats like GRIB2 because there’s something pure about something that’s “just a file”! Even though GRIB2 files are “used by the big guys that make the operational weather forecasts”, I can be a small guy using GRIB2 to write my own software to make these little maps of every place in the Contintental United States that shares a given temperature. I keep a sqlite database with a list of all of the cities on OpenStreetMap for exactly this occasion, and so the map will show a handful of place names that share whichever same temp you’re looking at, too. If you click on one of the same-temp links, you can dial the HTML slider and cruise the full temperature range. It can be fun (or disturbing?) to realize other specific places you’ve never been to where someone else may be sweating (or shivering) as you are right now…

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