Yes. Fog is a stratus cloud resting on the ground, which means walking through fog is walking through a cloud. It behaves like the rest of its family: gray, featureless, and capable of drizzle at most.

Does a halo around the sun or moon guarantee rain?

No. It reports that a thin veil of ice crystals is overhead, which often runs 12 to 24 hours ahead of rain or snow, per the NWS cloud chart. Often is not always, which is exactly what the one-week cloud log is for.

What is a mackerel sky?

A high field of small white ripples, cirrocumulus, that looks like fish scales. It is usually fair, brief, and better at being pretty than at forecasting anything.

Are the white lines behind jets clouds?

They are. Contrails are ice-crystal clouds made by aircraft exhaust in cold high air. Ones that vanish in seconds mean the air up there is dry; ones that linger and spread mean it is moist, which can itself be an early hint of change on the way.

Why does this page keep saying usually?

Because a cloud is a witness, not a contract. Each one reports on what the air is doing where it lives, and the sky can change its plans. Keeping score for a week, with the log, is how you learn what your own sky's hints are worth.

The Weather Journal / Explainers

Know Your Clouds

By the rock. August 26, 2026. Grounded in National Weather Service definitions; suitable for classrooms and other curious humans.

The short version

There are ten basic clouds, and each one is a hint about what the sky does next. Wisps and veils up high mean change may be a day out, and a halo around the sun or moon often runs 12 to 24 hours ahead of rain or snow. Gray sheets mean steady rain on a schedule. Heaps tell you about the afternoon: flat-bottomed puffs are fair weather, puffy rows on a sticky morning hint at late-day thunderstorms, and a tower with an anvil top is a thunderstorm now. This page is the spotter's guide; how clouds form is the flagship lesson's job, and how much sky they cover is sky-cover's.

How to read a sky

Before any names, stand outside and ask the sky three questions. Is it wisps, sheets, or heaps? Can I still see the sun through it, and how clearly? And is it growing, right now, while I watch? Nearly everything a cloud has to tell you is an answer to one of those three.

Two things this guide deliberately leaves to other pages. Why clouds form at all, and why their names sort into families by height, is the how a cloud forms lesson's whole subject. And how much of the sky is covered, the difference between partly and . More cloud than sun.">mostly cloudy, has its own page. This one is strictly the field guide: what you are looking at, and what it usually means next. Usually. Clouds are witnesses, not contracts, which is exactly why the experiment at the bottom keeps score.

The first sorting question. Wisps are ice way up high, sheets are layers, heaps are rising air caught mid-climb. Everything below is one of these three in a costume.

The wisps and veils: messages from a day out

Cirrus. Thin white curls and streaks, very high, like the sky was combed. Fair weather today, but cirrus are often the first riders ahead of a change, so if they keep thickening through the day, pay attention to what arrives behind them.
Cirrocumulus. A high field of tiny white ripples, sometimes called a mackerel sky for its fish-scale look. Pretty, fleeting, usually fair. Enjoy it; it rarely stays long.
Cirrostratus. A milky veil so thin you may only notice it by its signature: a pale ring, a halo, around the sun or the moon. That halo is light bending through ice crystals, and it is the best free forecast in this guide: per the National Weather Service cloud chart, rain or snow often arrives within 12 to 24 hours. A halo tonight is a question about tomorrow.

The gray sheets: rain on a schedule

Altostratus. A gray sheet across the sky with the sun still visible through it, dim and fuzzy, like a flashlight behind frosted glass. Steady rain is often gathering. This is a middle chapter of the long cloud schedule a , sliding up a long shallow ramp over the cooler air ahead. Its clouds arrive high and thin as much as a day early, then lower and thicken into steady, patient rain.">warm writes, which the fronts page reads start to finish.
Nimbostratus. Dark, gray, wet-looking, and no longer hinting: it is raining, steadily, and the sheet says settle in. This is all-day rain, not a passing shower.
. A low gray blanket, featureless, sometimes close enough to flatten the whole day's light. at most. Fog, for the record, is stratus resting on the ground, which means you have walked through a cloud and survived.

The heaps: the afternoon's mood

. White cauliflower puffs with flat bottoms, drifting on a nice day. The fair-weather cloud. The one thing worth watching is ambition: a cumulus that grows taller than it is wide, and keeps going, is changing careers.
Stratocumulus. Low lumpy gray-and-white rolls, patchy, with blue gaps. Rarely more than a moody afternoon; little rain comes of it.
Altocumulus. Puffy white patches and rows in the middle of the sky's height. The cloud chart's famous tip, verified and worth memorizing: on a warm, sticky morning, altocumulus hints at by late afternoon. It is the sky mentioning, casually, at breakfast, what it is considering for dinner.
. The tower. A dark base, a hard cauliflower climb, and up top a flat spreading anvil. This is the thunderstorm, fully built, and everything about how it works lives in the thunderstorm recipe. From you it asks only one thing: admire it from indoors. When thunder roars, go indoors, every time.

The one-week cloud log

The guide above is full of usually and often, and the only way to find out what the sky over your house means by those words is to keep score. This experiment runs on whatever sky is actually up there, today and for the next six days. No forecast allowed: your eyes, then the wait, then the verdict.

Rule a sheet of paper into four columns. Column one: the day, and what the morning sky looks like: name the cloud with this guide, or draw it if the name will not come. Column two is the whole game, the guess column: what will this sky do by dinner? Commit in the morning, in ink. all day. Gray by lunch, rain by dinner. Storm by late afternoon. Whatever the clouds are hinting, read the hint and write the bet.

Column three, at dinner: what actually happened. Column four: the grade. Give the morning sky a hit or a miss, and be honest, because a miss is where the learning lives. A halo that delivered rain the next day is a lesson. A mackerel sky that came to nothing is also a lesson, arguably a better one.

After seven days, read the whole card and hold court. Which clouds kept their promises? Which sky fooled you, and can you catch what it was hiding? A question for the grown-up to ask at the end of the week, no right answer attached: which cloud this week was the biggest liar, and what do you want to watch for next time it shows up? The rock, which has been logging skies since before paper, reports that the sky is honest on average and shifty in the particulars, much like everyone else it knows.

Words in this lesson

Every marked word above is here in full, because a definition that only appears on hover is no use to somebody reading on a phone, printing the page, or listening to it.

Air mass: noun say it: AIR mas; A huge body of air, hundreds of miles across, that has sat in one place long enough to take on that place's temperature and moisture. Most day to day weather is the story of air masses shoving each other around.
Sunny: adjective say it: SUN-ee; Zero to one okta of cloud. Full sun.
Cumulonimbus: The thunderstorm tower, anvil top and all.
Cumulus: noun say it: KYOO-myuh-lus; A heaped, cauliflower cloud built by rising air. Given enough moisture and lift it can grow into a shower or a thunderstorm.
Drizzle: noun say it: DRIZ-ul; Fine drops under 0.02 inch across, usually from stratus. Light, moderate, and dense grades.
Front: noun say it: FRUNT; The boundary where two air masses of different temperature and moisture meet. Air gets lifted along a front, which is why most of a map's clouds and rain queue up on one.
Mostly cloudy: adjective say it: MOHST-lee KLOW-dee; Six to seven oktas. More cloud than sun.
Okta: noun say it: OK-tuh; One eighth of the sky. Sky cover is counted in oktas, from zero for clear to eight for overcast, which is why the familiar sky words are really just bands of a number.
Stratus: noun say it: STRAY-tus; A flat, featureless layer cloud that forms in stable air. It brings drizzle rather than downpours.
Thunderstorm: noun say it: THUN-der-storm; Any storm producing thunder and lightning.
Warm front: noun say it: WORM frunt; The leading edge of an advancing warm air mass, sliding up a long shallow ramp over the cooler air ahead. Its clouds arrive high and thin as much as a day early, then lower and thicken into steady, patient rain.

Definitions in this explainer follow the National Weather Service. The rock checked twice. The rock always checks twice.