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What is Is My Weather Weird?

A service that tells you how weird your weather is today. Simple, right?

How it works, in 3 steps

1. Look at today's forecast for 5,000 locations in the U.S. and worldwide.

IMWW uses daily temperature and precipitation (rain & snow) forecasts from The Weather Company/IBM, rated as the most accurate forecast by ForecastWatch. The forecast locations correspond to the historical weather records used in step 2. stations Some of the 5,000 weather stations used to calculate weird weather.

2. Measure how weird the weather is for each location compared with historical data.

The 5,000 locations were chosen because they have have plenty of daily temperature and precipitation data going back to at least 1950. The data comes from the Global Historical Climatology Network, the largest, most widely used, and most highly analyzed source of historical weather data. Only the most reliable records were used for IMWW, and in addition to the quality controls that come with this data we did a comprehensive review to ensure a fair comparison with today's weather.

An important question is, Weird Compared to What? We look at historical data before 1990, which gives us enough data from the 1900s to make statistically useful conclusions for many locations, and it's recent enough that many of us might think of it as 'normal' weather (more on that idea later). image Example of historical daily high temperatures for Tulsa, OK.

There are some tricky aspects to this step, such as choosing the right statistical distributions to fit to the data; for instance, note that we care much more about what's happening at the extremes of the data than in the middle 'normal' section.

Weirdness Levels

The weather weirdness levels are define as:

Weirdness Description How often expected (roughly)
Unusual Used to happen less than 10% of the time Every 10 years
Odd Used to happen less than 5% of the time Every 10 years
Strange Used to happen less than 3% of the time Every 30 years
Crazy Used to happen less than 2% of the time Every 50 years
Bizarre Used to happen less than 1% of the time Every 100 years
Bonkers Pretty much never happened before Never

Data Groupings

One important idea for the weirdness calcuations is that the weather on, say, March 14 is not going to be that much different than on March 13 or March 16, on average. So to determine what's normal or weird for March 14, we include historical data from a number of days before and after that date. Specifically, 7 days before and after are used, giving 15 days of data for each year of weather history. Since we require 40 years of historical data for every weather station, this comes to at least 600 days of weather data to help us learn what was weird before 1990.

Weirdness by Day of the Year

Weather Weirdness is then calculated for every day of the year, which looks something like this for each weather station and each weather type (daily high temperature, daily low temperature, and precipitation).

image Weird weather levels for daily low temperature for every day of the year in Tulsa, OK.

3. Make a (nearly) continuous map of weird weather in the U.S.

We don't want to be limited to just the 5,000 locations, and if the weather is weird at one spot, it's probably weird nearby as well. In fact, the data shows us this is true. So we can estimate weather weirdness in between the individual locations, accounting for things like distance between stations.
image Points are weather stations, colored hexagons show weird weather near and between stations