Holbrook Hal Groundhog

According to official weather records, the New York City Department of Environmental Protection began publishing precipitation observations in 1865. In subsequent years, city officials took the information and ran it down. A series of experiments in the early 20th Century and a computer from McKinsey & Company eventually transformed the weather record into a science project.

The Hudson River Hal Cat

In 1974, for example, a team of computer programmers put together a computer program that could predict the weather by a combination of meteorological conditions and the position of the sun at noon.

Although the computer program never worked outside of New York City, the main characters used it to predict what was going to happen around New York City for the next four years using two planets orbiting each other (they are not related in the computer simulation).

The computers generated a total of 1,300 weather predictions every four years. A computer forecast by computer means predictions that have no basis in the weather.

Precipitation records are regularly corrected and even they are only approximations because they include other factors that are too complicated to model and time lapses that are too short or far separated to tell the computer exactly when the clouds and ice will come in.

The Hudson River Hal Cat uses three models of planet rotation, but the computer assumes all three to be different.

Rain cloud model

The computer uses a formula based on cloud data from a meteorological database, a computer model called a “rain cloud model”. Clouds that form are rain drops or precipitation, and they stay in the atmosphere for one hour after they form. If you know which elements of clouds that form, then you can figure out what the rainfall will be.

Rain drops that are falling from the upper troposphere (25km above the surface) will arrive at their destinations about half an hour to an hour before noon. Rain clouds that form at the surface will keep on coming until they are too small to be seen.

When the rain starts, it is very close to the ground. Rain drops can drop further in a matter of seconds.

Rain then spreads in a wave-like manner across the earth. After the wave is broken, water vapor lies in the atmosphere. Carbon dioxide in the air makes it cold.

Then the ice starts to form.