1194. This week, we look at weather forecast terminology, including why "mostly sunny" and "partly cloudy" aren't the same thing, what "oktas" are, and how terms like "breezy," "scattered," and "likely" are officially standardized by the National Weather Service — even if your favorite TV meteorologists adds their own spin.
1194. This week, we look at weather forecast terminology, including why "mostly sunny" and "partly cloudy" aren't the same thing, what "oktas" are, and how terms like "breezy," "scattered," and "likely" are officially standardized by the National Weather Service — even if your favorite TV meteorologists adds their own spin.
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Grammar Girl here. I’m Mignon Fogarty. This week, we're talking about weather words.
by Karen Lunde
Before you head out for the day, do you check the weather forecast? Let's say you see "Mostly sunny with a high of 78." Sounds great! But what exactly does "mostly sunny" mean? Is the report just hedging, unwilling to commit to a fully sunny day? And what about "partly cloudy"? Aren't partly cloudy and mostly sunny pretty much the same thing? "Mostly sunny" sounds more optimistic than "partly cloudy," so you might even wonder if meteorologists are trying to manipulate our emotions (just a little) with those different terms.
The answer to the emotional manipulation question is "no." But also a little bit "yes." Weather forecasts may sound casual and conversational, but many of the terms forecasters use are actually standardized technical language. Still, meteorologists absolutely do "read the room" when they're giving forecasts, leaning into language they think will connect better with their audience.
So, let's look at that "mostly sunny"/"partly cloudy" difference first. The National Weather Service and NOAA in the United States actually do define official weather terms around cloud cover. But to understand the terminology, we have to learn about "oktas."
Meteorologists have traditionally divided the sky into eight segments called "oktas." One okta is one eighth of the sky. When one or two oktas have cloud cover, that's mostly sunny. Partly sunny or partly cloudy? That's three to five oktas. Six or seven oktas is mostly cloudy. And if there’s not a trace of blue, that’s just plain cloudy.
Just don't get the spelling wrong! Okta is spelled O-K-T-A, with a K instead of the C you might expect. “Okta” comes from the Greek word "okto," meaning “eight,” and meteorologists kept the Greek-style K spelling instead of the more familiar Latinized O-C-T spelling we see in words like “octagon” and “octopus.”
So, the meteorology world was decisive about the spelling of "okta," but it's been pretty indecisive about how to measure clouds. Early weather observers often used tenths, so that's where we started. Then, international meteorologists and aviation experts standardized things into eighths because they worked neatly in coded reports. Now, thanks to computers, public-facing forecasts, and even weather apps, forecasters have drifted back toward tenths again. It makes percentages easier. If three tenths of the sky is covered, that's 30 percent cloud cover. And one clarification: Those high thin cirrus clouds you see on sunny days? They don't really block the sun, so they don't officially count as making a day "cloudy" at all. No respect!
This standardized language doesn't just apply to clouds either. The National Weather Service also has terms for the probability of rain, wind speed, timing, and even the wording used around storms. The goal is to make forecasts feel consistent whether you're in southern California or northern Maine, even though the climates themselves are wildly different.
Here are a few examples:
"Breezy" may sound like an adjective forecasters lean into because it sounds good, but it actually refers to winds of 15 to 25 miles per hour. If it's windy and cold, meteorologists might use the term "blustery," instead. Winds of 30 to 40 miles per hour are called "very windy," and sustained winds over 40 miles per hour are referred to as "strong" or "dangerous," which means you'll likely see a "high wind" warning on your weather app. So, although you might hear variations, the terminology around wind isn't purely based on vibes.
Even the wording around the "probability of precipitation" — or "POP" in meteorologist shorthand — is standardized. Just a 10 percent chance of rain? Your local meteorologist might use "isolated," as in "isolated showers." A 20 percent chance is designated as a "slight chance" or "widely scattered." A 30 to 50 percent chance can be called a chance of rain or scattered rain, and a 60 to 70 percent chance gets you into precipitation "likely" territory. And anything above that? Well, you're probably going to get rained or snowed on whether you like it or not.
Even though these terms are standardized and laid out by the National Weather Service for official government forecasts, that doesn't mean meteorologists are strictly required to use them. They tend to, because they usually get their data from National Weather Service sources, but if you've ever had a favorite TV meteorologist, you know that broadcast weather is also about personality. That creates a little room for… not spin, exactly, but a shifting of the emotional tone and connecting with a local audience by using the same sort of language they might use.
In a more Wild West sort of environment, amateur and professional storm chasers seem to have a language of their own, and it's a mix of insider lingo and more scientific terms. (Worth mentioning: Meteorologists absolutely use these terms, too.)
A "wall cloud" is when there's a lowering cloud base beneath a thunderstorm. That lowering can signal a tornado forming if it starts to rotate. Storm spotters have to learn to differentiate wall clouds from "scud," which is really just low, ragged cloud fragments that people often mistake for tornadoes or wall clouds. (One meteorologist I know calls scud "SLCs" for "scary-looking clouds.")
If you're a fan of weather radar, you might be familiar with "hook echoes." That's when a hook appears on storm-tracking radar. It's often a strong sign that a storm is rotating, which could mean a tornado has formed. But forecasters also rely on "ground truth" — intel from storm spotters who are looking at the actual storm and not just an image on radar.
The "dryline" is a boundary that separates moist and dry air masses, especially across the U.S. Great Plains, where severe weather tends to set up. "Inflow" is the warm moist air that flows in to "feed" a storm system and make it grow, often into a "supercell." That's a large thunderstorm with a rotating updraft.
So, weather forecasts may sound casual, but behind all those “slight chances,” “breezy afternoons,” and “partly cloudy skies” is a surprisingly precise little language all its own: a carefully calibrated mix of science, standardization, and meteorologists trying very hard not to ruin your weekend plans. If you'd like to check out more weather terms on your own, the National Weather Service has an online glossary you can visit at forecast-DOT-weather-DOT-gov-SLASH-glossary-DOT-php.
That segment was by Karen Lunde, a career writer, and former Quick & Dirty Tips editor. [She also spent many years chasing scary looking clouds as a trained storm spotter.] She writes I'll Go First, a Substack where she shares personal essays and memoir, then hands you a weekly writing prompt and a metaphorical pen. Find her on igofirst.org.
Finally, I have a familect story from Marcus, a great a producer I've worked with many times at WOSU public radio in Ohio:
"Hi, Mignon. In my family, when we find something hilariously inappropriate, we say not only is it wrong, it's R-O-N-G wrong."
Thanks, Marcus. I love this because it really captures and emphasizes the wrongness of something. It's so wrong, it's R-O-N-G wrong!
Grammar Girl is a Quick and Dirty Tips podcast. Thanks to Holly Hutchings; Nat Hoopes; Morgan Christianson; Rebekah Sebastian; Dan Feierabend; Steven Schapansky; and Maram Elnagheeb, who often misspells the word "library" on the first try, forgetting the first R in the word.
And I'm Mignon Fogarty, better known as Grammar Girl.
That's all. Thanks for listening.