How to Read a Snow Forecast

What does a 70% snow chance mean? Learn to read hourly snow percentages, expected snowfall in cm or inches, and snow depth, plus why forecasts change.

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What the percentage means

A snow percentage is a chance, not a promise and not a share of your town. A 70% chance means that in 10 weather setups like this one, about 7 produced snow. It does not mean 70% of your street gets snow, and it does not tell you how much will fall.

On our forecast pages we use simple bands so you can decide at a glance:

• Under 25%: probably no snow. Keep an eye on it if the number is rising.
• 20 to 50%: flurries or a nearby shower are possible. Good time to check again later.
• 50 to 80%: snow is likely. Plan for slow travel and cold gear.
• Over 75 to 80%: get ready. Find your gloves, charge your phone, and expect a snow day routine.

The icons follow the same bands. Light snowflakes turn into a snowman as confidence grows, while rain and mixed icons warn you that precipitation may fall as liquid instead.

Which view to use

Every place page has three views of the same storm, and each answers a different question.

The next 6 hours

Use the hourly strip when you ask, will it snow today, what time will it start, or should I leave now. It shows the snow chance hour by hour with a small icon. Look for the first hour above 20%, then see if later hours climb toward 70%. A line that rises from 10 to 60 to 85 is a storm arriving. A line stuck at 15 is just a cold cloud passing by.

Yesterday and tomorrow chart

The chart shows snow chance as lines and snowfall in millimeters as columns for the past 24 hours and the day ahead. Hover any hour for the exact chance of snow, rain, and new snow. This is the best tool for, what time will it stop, or did I miss the peak. If the columns shrink while the line stays high, expect flurries with little buildup.

Upcoming days

The 7-day list shows the peak chance per day plus expected depth in millimeters. Depths over 0 appear in parentheses next to the day, for example (12mm). Use it for planning the week, not for exact timing. Beyond 3 days treat the numbers as a trend. A day moving from 20 to 45 to 60 across updates means growing confidence.

Snow, rain or sleet

We start from the official hourly chance of precipitation, then weigh it against temperature, dew point, and precipitation type. Cold air high in the cloud must be at or below freezing (32F or 0C) for flakes to form, and the flakes must survive the fall without melting.

• Snow: air stays cold all the way down. Best chance when temperatures sit below freezing for several hours.
• Rain: air is too warm, even if precipitation chance is 100%. High precip with low snow chance usually means rain.
• Sleet or freezing rain: a warm layer sits above cold ground. The forecast may show moderate snow chance with a rain icon. Treat this as icy travel even with little snow depth.

If snow is already falling, we raise the chance to match what you can see outside. Models can lag reality by an hour, and eyes beat equations for now.

How much snow will fall

Chance answers will it snow. Amount answers how much will I shovel. Keep the two apart.

• Snowfall is new snow in a period, shown in millimeters on the chart and daily list.
• Snow depth is what sits on the ground, shown in the 24-hour summary as centimeters or inches.
• Trace shows as under 1 cm (or under 0.5 in in the US) rather than 0 cm, so you know flurries are possible with no real buildup.

We quote inches in the US and centimeters in the UK, Canada, Australia, and everywhere else, matching how local forecasts are published. Ten millimeters of snowfall is about 1 centimeter, or just under half an inch. A 90% chance with 0 mm means flurries with no buildup. A 50% chance with 150 mm means a major storm is possible and worth preparing for.

Common questions we see in search: how heavy is the predicted snow, how much snow are we supposed to get, how many inches tomorrow, snow accumulation today. All of them are answered by the depth line in the 24-hour summary plus the daily totals, not by the percentage alone.

Why forecasts change

Snow lives in a narrow window. A shift of 1 degree, a storm track 50 miles east, or dry air eating the first flakes can turn 80% into nothing or 30% into a surprise. That is normal, not broken.

• 6 hours out: most accurate. Trust hourly order and timing.
• 24 hours out: very useful. Trust the peak and the depth range.
• 3 to 6 days out: trend only. Watch direction (rising or falling), not exact numbers.

Re-check the morning of the event and enable a snow alert so a late speedup still reaches you. If the percentage climbs across updates while depth holds, prepare. If percentage holds while depth falls, expect pretty flakes with little shoveling.

One more rule of thumb: the heaviest snow usually falls just below freezing, when the air is cold enough for flakes but still warm enough to hold plenty of moisture. Very cold air is dry air, which is why the deepest storms often arrive at temperatures only a few degrees under 0°C.

FAQ

How much snow are we supposed to get?

Read the 24-hour summary depth plus the daily totals in millimeters. Chance without depth means flurries. Depth without high chance means a short heavy burst is possible.

What time will it start snowing?

Find the first hourly block above 20%, then confirm the next blocks keep rising. The chart hover gives the exact hour for snow, rain, and new snow.

Why did an 80% forecast produce no snow?

80% means 8 in 10 similar setups snowed. Warm ground, a faster storm, or dry low air can erase the other 2. Short-range updates catch most of these shifts.

Is snow measured in inches or centimeters?

Both. Our US pages use inches and all other pages use centimeters, matching local practice. Trace reads as under 1 cm or under 0.5 in.

When is the most accurate time to check?

Within 24 hours, and within 6 hours for timing. Further out, follow the trend rather than the exact number.