---
title: "Wind Chill"
id: 57626
type: "computer_media"
slug: "wind-chill"
url: "http://localhost/computer_media/wind-chill/"
markdown_url: "http://localhost/computer_media/wind-chill.md"
published_at: "2024-10-06T00:54:40+00:00"
modified_at: "2026-04-03T07:58:12+00:00"
author: "David Anderson"
featured_image:
  url: "http://localhost/wp-content/uploads/2024/10/wind-chill.png"
excerpt: "Enter a temperature and wind speed to get the classic Siple-Passel wind chill index, with automatic restart after displaying the result."
category:
  - name: "Archived Media"
    slug: "archived-media"
    taxonomy: "category"
    url: "http://localhost/category/archived-media/"
post_tag:
  - name: "Downloadable"
    slug: "downloadable"
    taxonomy: "post_tag"
    url: "http://localhost/tag/downloadable/"
  - name: "TS 1000"
    slug: "ts1000"
    taxonomy: "post_tag"
    url: "http://localhost/tag/ts1000/"
model:
  - name: "Timex/Sinclair 1000"
    slug: "ts-1000"
    taxonomy: "model"
    url: "http://localhost/model/ts-1000/"
genre:
  - name: "Education"
    slug: "education"
    taxonomy: "genre"
    url: "http://localhost/type/education/"
media_contents:
  - id: 56726
    title: "Synchro-Sette November 1983"
    type: "computer_media"
    url: "http://localhost/computer_media/synchro-sette-november-1983/"
media_type: "Program"
mediadate: "November 1983"
images:
  - url: "http://localhost/wp-content/uploads/2024/10/wind-chill.png"
media_type_tags: "Education"
---

# Wind Chill

This program calculates the wind chill temperature in degrees Fahrenheit using the traditional Siple-Passel formula. It prompts the user for an ambient temperature in Fahrenheit and a wind speed in miles per hour, then applies the formula WC = 0.0817 × (3.71 × √S + 5.81 − 0.25 × S) × (T − 91.4) + 91.4. A guard clause at line 80 handles the meteorological convention that wind chill is undefined below 4 mph, simply returning the ambient temperature in that case. After displaying the result with a long PAUSE of approximately 40 seconds, the screen clears and the program restarts automatically.

***

## Program Analysis

### Program Structure

The program follows a simple linear input–calculate–output loop across three phases:

1. **Input** (lines 10–60): Prompts for temperature `T` and wind speed `S`, echoing each value back after entry.
2. **Calculation** (lines 70–80): Applies the wind chill formula and handles the low-wind edge case.
3. **Output and restart** (lines 90–120): Displays the result, pauses, clears the screen, and loops via `RUN`.

Lines 9998–9999 are utility lines outside normal execution: `SAVE "WINDCHIL%L"` saves the program (the `%L` represents an inverse-video ‘L’ in the filename), and the trailing `RUN` restarts immediately after loading.

### Wind Chill Formula

Line 70 implements the Siple-Passel empirical wind chill formula:

`WC = 0.0817 × (3.71 × S^0.5 + 5.81 − 0.25 × S) × (T − 91.4) + 91.4`

This is the classic pre-2001 formula expressing wind chill in degrees Fahrenheit, where `S` is wind speed in mph and `T` is air temperature in Fahrenheit. The constant 91.4°F represents normal skin temperature. The `**.5` exponentiation is used to compute the square root of wind speed rather than a dedicated `SQR` function, which is mathematically equivalent.

### Notable Techniques

- **Tab-comma formatting**: The double commas (`,,`) in `PRINT` statements at lines 10, 40, and 90 advance the print position to the third print zone, centering the prompts on the display.
- **Input echo**: Lines 30 and 60 print back `T` and `S` respectively. On this platform, `INPUT` accepts values without leaving them visibly confirmed on screen in all modes, so this serves as user feedback.
- **Long PAUSE for display**: `PAUSE 40000` at line 100 holds the result on screen for roughly 40 seconds (at 50 Hz) before auto-clearing, avoiding the need for a keypress to continue.
- **RUN as loop**: Using `RUN` at line 120 rather than `GO TO 10` restarts from scratch, clearing all variables — a clean but slightly heavier-weight approach to looping.

### Edge Case Handling

Line 80 checks whether wind speed is below 4 mph:

`80 IF S<4 THEN LET WC=T`

This correctly replaces the formula result with the ambient temperature, as the Siple-Passel model is not valid at very low wind speeds (the formula can produce values higher than the ambient temperature at near-zero wind, which is physically nonsensical).

### Variable Summary

| Variable | Purpose |
| --- | --- |
| `T` | Ambient temperature in degrees Fahrenheit |
| `S` | Wind speed in miles per hour |
| `WC` | Calculated wind chill temperature in degrees Fahrenheit |

## Source Code

```
  10 PRINT ,,"TEMPERATURE (F)? ";
  20 INPUT T
  30 PRINT T
  40 PRINT ,,"WIND SPEED (M/HR)? ";
  50 INPUT S
  60 PRINT S
  70 LET WC=.0817*(3.71*S**.5+5.81-.25*S)*(T-91.4)+91.4
  80 IF S<4 THEN LET WC=T
  90 PRINT ,,"WIND CHILL = ";WC;" DEGREES."
 100 PAUSE 40000
 110 CLS 
 120 RUN 
 9998 SAVE "WINDCHIL%L"
 9999 RUN
```