# 1606: Five-Day Forecast

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 Five-Day Forecast Title text: You know what they say--if you don't like the weather here in the Solar System, just wait five billion years.

A different user-made version for the picture using Celsius instead of Fahrenheit can be found here: Five day forecast in Celsius.

## Explanation

Weather forecasting is an extremely difficult task, even if it is only for five days. In numerical models, extremely small errors in initial values double roughly every five days for variables such as temperature and wind velocity. So most meteorologists only provide us with a five-day forecast.

In this comic Randall takes this to the extreme by first showing a Five-Day Forecast and then progressing to five-month, year, million, billion and finally trillion-year forecast, leading to weather patterns that we don't usually see on a regular basis.

Since the first weather symbol is the same in all six rows, we must assume this indicates the weather today (and not tomorrow or in a trillion years). It is first in the second panel that we have made the first jump according to the label. Consequently, the last column gives the predictions for four days, four months, ..., four trillion years from today.

When moving past the five days, the forecast is just a qualified guess based on the time of year. In a month it is Christmas as shown in the second panel of the second row. And then it is winter with January and February so snow is likely, but certainly not something that happens on all days of a winter month.

Looking at the five-year forecast, guesses are made as to what the weather will be like at the same time of year. For these first three predictions the weather symbols are all of the same three types. Sun, clouds and some kind of precipitation, rain or snow. And the temperature range from 21 to 44 °F (-6.1 to 6.6 °C), winter temperature.

Then we go into the far future, jumping a million years from panel to panel. But still the weather symbols stay the same. However, in 3 million years time aliens (or advanced humans) attack with energy beams from something looking like flying saucers. They are gone a million years later. The temperature range is still the same (except that it rises to 52 °F or 11.1 °C, a possible reference to global warming) in one panel. But then while the attack is going on the temperature rises to 275 °F (135 °C).

Once we get to the billion-year mark it actually becomes more meaningful to try to predict the "weather". Because now we reach the times when the Sun begins to change. Although the Sun will continue to burn hydrogen for about 5 billion years yet (while in its main sequence), it will still grow in diameter as it begins to exhaust its supply of fuel. The core will contract to increase the temperature, and the outer layer will then compensate by expanding slightly. This is what is indicated in panels two and three where the color of the Sun changes towards red as the surface becomes less hot as it expands away from the center of the Sun. The temperature will rise on Earth as indicated in the panels (105 °F = 40.5 °C and 371 °F = 188 °C). So in two billion years the temperature is hot enough that all the earth's oceans will have boiled away… Actually this will happen already in about a billion years.

Then once there is no longer enough hydrogen the Sun will truly expand into a red giant. This should not happen until five billion years from now,[citation needed] but in the forecast it is indicated to happen already in three. Maybe this is Randall taking liberties to show what happens during this phase, which would not fit into a five-billion-years forecast. Alternatively it is just indicating how uncertain these kinds of forecasts are, or a statement that we may not know for certain that it will take five not three billion years. Disregarding this, the fourth panel shows the temperature at Earth's position inside the red giant Sun. The color of the panel indicates that we are inside the Sun. The temperature is 71,488,106 degrees Fahrenheit (39,715,597 degrees Celsius). The current temperature of the center of the Sun is "only" 27 million degrees Fahrenheit (15 million degrees Celsius). And although that may rise by a factor of ten during helium fusion then that will only be at the very core and not out in the solar atmosphere reaching out to Earth Here the temperature would only be of the order of thousands of Fahrenheit, since the Sun's outer temperature decreases as it increases its diameter. So this panels temperature also makes little sense. It may involve some ambiguities regarding what the forecast means; the edge of the red giant Sun is predicted to be somewhere near the current orbit of Earth, but the position of the Earth could change. The most likely prediction at the moment is for Earth to move outward, but if the planet is engulfed by the Sun, it would spiral inward, and at some point fall apart. So in some sense "here" for the forecast could become a position deep inside the Sun, where core temperatures could reach 100 million Kelvin.

The red giant phase only lasts half a million years, so a billion years after the Sun has been a red giant its outer atmosphere will for sure have disappeared leaving only a white dwarf to cool down. Given Randall's version of this time schedule, then it will have had about a billion years to cool down, but would still likely be the brightest object in the sky as seen from where the Earth once was. It is not indicated in the last panel, where we just see other stars of the Galaxy. The temperature is down to that of the background radiation. Today this radiation has a temperature of 2.72548 kelvin = -270.4245 °C = -454.7641 °F. So this is a few degree F colder than what is shown in the comic which states the temperature is -452 °F = 4.26 kelvin. This higher temperature may have been chosen to reflect that even the star light from other stars would increase the actual temperature.

In the last panel with trillion years, we jump right past the Sun's Red Giant phase, to a panel looking much like the one after five billion years with only other stars. Over the next three trillion years the stars become fewer and fewer and dimmer and dimmer as they run out of fuel and fewer new stars form. After four trillion years the background temperature even decreases one degree to -453 °F as the universe keeps expanding and the wavelength of the radiation does the same, thus decreasing its temperature.

The title text is a play on comments referring to fast-changing weather on a more ordinary human timescale, such as Mark Twain's quip "If you don't like the weather in New England now, just wait a few minutes."

A ten days forecast was used in 1245: 10-Day Forecast. In 1379: 4.5 Degrees Randall looked at the weather over long periods of time as well.

## Transcript

[A grid with six rows of five columns, where each row is labeled to the left. For each of the 30 squares a temperature is given in Fahrenheit at the top left. The rest of the square represents the weather as in a weather forecast (or some other relevant items for the comic), mainly in bright colors. Below are the six labels given above each of their five weather symbols with temperature given below these symbols description.]
Your 5-day forecast
[A bright yellow sun.]
38°F
[A grey cloud.]
41°F
[A grey cloud with six lines of blue raindrops below.]
36°F
[A grey cloud in front of a yellow sun.]
40°F
[A bright yellow sun.]
44°F
Your 5-month forecast
[A bright yellow sun.]
38°F
[A green Christmas tree with red presents beneath it.]
29°F
[A grey cloud with four snowflakes below.]
21°F
[A grey cloud with four snowflakes below.]
24°F
[A grey cloud.]
35°F
Your 5-year forecast
[A bright yellow sun.]
38°F
[A grey cloud.]
25°F
[A bright yellow sun.]
36°F
[A grey cloud with six lines of blue raindrops below.]
37°F
[A bright yellow sun.]
41°F
Your 5-million-year forecast
[A bright yellow sun.]
38°F
[A bright yellow sun.]
52°F
[A grey cloud.]
40°F
[Two red flying saucers (with bright domes) are shooting energy beams downwards. One of the beams seems to impact with something at the bottom of the panel, which then explodes. Two plumes of smoke rises up from below, drifting to the right.]
275°F
[A grey cloud in front of a yellow sun.]
40°F
Your 5-billion-year forecast
[A bright yellow sun.]
38°F
[A larger orange sun.]
105°F
[A very large red sun.]
371°F
[A pale yellow panel with no drawing.]
71,488,106°F
[A night sky with many bright stars.]
-452°F
Your 5-trillion-year forecast
[A bright yellow sun.]
38°F
[A night sky with many bright stars.]
-452°F
[A night sky with many stars.]
-452°F
[A night sky with fewer not so bright stars.]
-452°F
[A night sky with few dim stars.]
-453°F

# Discussion

As far as I can figure out, -452 F is something like 4 K, which seems a bit too warm (above OTL microwave background). It probably should be -456 in the next-to-last row and -458 in the last row (-459 for the last column). --141.101.81.76 12:58, 20 November 2015 (UTC)

Inside a galaxy, it presumably is a bit warmer than CMB, since there are stars around to heat the interstellar medium a little. --Aaron of Mpls (talk) 05:40, 22 November 2015 (UTC)
If Randall is going to use Farenheit why don't we stick with Rankine, thus -452 F works out at about 8 R? (Saves all the messing about with multiplication and division) 162.158.34.147 13:15, 23 November 2015 (UTC)

Thanks for the conversions to degrees C as being a 58 year old Brit I have never understood degrees F (I know what they are just I have no idea whether 60F is cold, cool or comfortable). I have always used 5, 10 and 21, Winter, Spring and Summer sun - well works for Middle Brittan) RIIW - Ponder it (talk) 19:09, 20 November 2015 (UTC)

FYI 60 degrees F outside is quite pleasant, a little cool, but inside your feet get cold. 15.5 degrees C NotLock (talk) 09:12, 22 November 2015 (UTC)
Yes thank you for the conversions, _most_ readers of this comic use metric units: http://daretorant.com/wp-content/uploads/2010/06/metric-system.jpg Martin (talk) 21:52, 22 November 2015 (UTC)
As a younger Brit (56) I grew up with Farenheit, I'm not sure where in the UK our 58-year old grew up, but I don't remember a concerted effort to use SI units until the mid seventies. For me it's the other way 'round: 60F sort of OK as long as it isn't windy, 70F quite warm, 80F Phew! What a scorcher! All the centigrade equivalents are just too small! :) 162.158.34.147 13:15, 23 November 2015 (UTC)
Perhaps the original Brit is only 58F, and was born c. 2000.108.162.238.87 21:09, 1 December 2015 (UTC)

There will be ambient starlight in addition to the 2.7K background which should raise the temperature slightly. However, the 2.7K background will also redshift to a lower temperature as time goes on: T propto 1/a where a is the scale factor of the Universe. Would be a good assignment for a cosmology class. 173.245.54.48 13:07, 20 November 2015 (UTC)

Aha, what will last longer than stars etc is the silly Fahrenheits. 162.158.91.165 17:49, 20 November 2015 (UTC)

There are five columns. Either the first column is "today" and one should not speak of predictions after five (m/b/trillion) years (as is currently the case a couple of times), or the first column is "tomorrow (etc.)" and then the prediction of "A bright yellow sun; 38°F" for one trillion years would be very strange. Jkrstrt (talk) 18:39, 20 November 2015 (UTC)

Randall lives in a cold climate! 188.114.97.127 21:37, 20 November 2015 (UTC)

If the "red giant" temperature measures the sun's core, how do you explain the last panels showing decidedly non-white-dwarf temperatures? --199.27.130.234 03:48, 21 November 2015 (UTC)

Regarding the 5-year-predicion: It seems to me that the temperature is in average rising a bit across the year, maybe a reference to the slow process of global warming? This would not be the first time, there are even whole comics just about global warming, especially about the noticeable speed and the "in average"-importance (e.g. 1379, 1321) 162.158.92.118 (talk) (please sign your comments with ~~~~)

I don't believe so. Five years is probably too short a period for discussing global warming. Limit it to a single place and even more so. Limit it to a sample of one day per year, and I believe you can't bother looking at the p-values. --Ahyangyi (talk) 15:56, 29 March 2016 (UTC)
Image with °C

I hope someone will find my low-effort edited version useful: http://www.explainxkcd.com/wiki/index.php/File:five_day_forecast_Celsius.png --Asdf (talk) 18:15, 26 June 2017 (UTC)

Nice work. It's mentioned above the explanation section. I'm hoping the values are correct. ;-) --Dgbrt (talk) 18:39, 26 June 2017 (UTC)
Thanks, I thought it'd be forgotten. I rounded the last value down from -269.44... to -270 degrees C to keep the joke though.
Edit: Of course someone had thought of this before. See this Reddit thread to see a better image and conversion to kelvins. --Asdf (talk) 20:56, 26 June 2017 (UTC)

I’m thinking that maybe the flying saucers arrived to help us evacuate the planet (using tractor beams), before it was too late. Brenda (talk) 12:17, 21 May 2019 (UTC)