Commute weather

Two trips, one word each: dry, damp, wet or ice. Here is how the page picks the word.

What this lens tells you

The Commute lens reads the forecast for the trip in and the trip home. Each trip gets one of four words: dry, damp, wet or ice. The headline says both. The "What to wear" card prints the two words with a temperature each, writing ice as "icy", and the day chart marks the trips that fall today.

The "Why we say that" box under the headline gives a temperature for each trip and, when the forecast has one, a chance of precipitation. Both are the forecast for the first of the two hours the lens reads for that trip, so a trip can read wet while the box shows a low chance.

Use it when the question is the trip and not the day. Open the forecast with the Commute lens on.

Which hours it looks at

The trip in is 7:30 AM and the trip home is 5:15 PM, by the clock of the place the forecast is for. Those two times are fixed in our code. They are not your hours, and the page has no setting to change them. The lens uses them every day of the week, weekends included. If you travel at other times, the day chart on the same page shows the whole of today.

The forecast comes in whole hours. For each trip the lens reads two of them: the hour that holds the time half an hour before the trip, and the hour that holds the time half an hour after. Where the clock is a whole number of hours from UTC, which covers every time zone in the United States, those are the 7 AM and 8 AM hours for the trip in and the 4 PM and 5 PM hours for the trip home. We call the two hours the trip's window.

It also reads the stretch before: the forecast hours that start more than half an hour and no more than three hours before the trip. On the same clock those are the 5 AM and 6 AM hours for the trip in and the 3 PM and 4 PM hours for the trip home. We assume a road stays wet for a while after the rain stops.

Once a trip is more than 20 minutes behind you, the lens moves that trip to tomorrow. After the morning trip the headline is about tomorrow morning, and says so. The trip home stays today's until it is more than 20 minutes past as well, and after that both trips are tomorrow's. In between, the headline pairs tomorrow morning with today's trip home. If both are dry it says "Dry both ways tomorrow", and the trip home in that line is still today's.

Will it rain on my commute?

The lens calls a trip wet when either forecast hour in its window counts as a wet hour, unless the ice rule below applies first. What counts is our rule, the same one the rest of the forecast page uses:

• The forecast says rain, drizzle, thunderstorms, snow or a wintry mix, and the chance is at least 40 percent or the expected amount is at least 0.5 millimetre (about 0.02 inch). If the forecast gives no chance at all, the word alone is enough.
• The forecast says anything else, and the chance is at least 60 percent with at least 0.3 millimetre (about 0.01 inch) expected.
• In the United States there is one step before either rule: an hour the Weather Service gives a chance under 25 percent is read as cloud whatever word it uses, so it falls under the second rule.

For a wet trip in, the headline says wet. For a wet trip home it says "Rain on the way home", whatever kind of wet the forecast names, and gives a time. That time is the start of the first wet forecast hour in the window, or half an hour before the trip if that is later. Rain that began at noon gets the same time, so read it as wet by then, not as the minute it starts.

If the trip itself does not count as wet but the stretch before it does, the lens says damp. In the headline that is "roads are still wet" for the trip in and "clear but damp" for the trip home.

Will the roads be icy in the morning?

The page cannot see a road. What it can say is "Ice is possible", and it says so when two things are true of a trip at once:

• The air temperature in the first forecast hour of the trip's window is at or below about 35°F (1.5°C).
• There is moisture about: the trip is wet, or the stretch before it was, or an hour in the window has at least a 30 percent chance of precipitation.

That is an inference from the air temperature and the precipitation forecast. It is not a road temperature, and it is not a report from the road. The lens runs the same check on the trip home.

The rule has gaps. It reads the temperature of the first hour only, so a colder second hour is not counted. It needs the moisture listed above. Without it a cold morning reads dry, however cold it is. Frost, and melt that froze again overnight, are outside the rule. A dry reading here does not mean the road is clear of ice.

For the road itself, ask your state or local road agency.

The rule, in order

The lens tries these from the top and takes the first that fits.

Do I need an umbrella for the drive home?

The "What to wear" card shows one kit for both trips, so the umbrella can be for either. The kit looks for a trip the lens called wet: the trip in first, then the trip home. A trip called ice does not count as wet here, even when rain is in its forecast. For the trip it picks, the kit reads what the forecast calls the sky in the first hour of the window:

• Snow: no shell and no umbrella. The coat rules below apply.
• Thunderstorms or a wintry mix: a rain shell and no umbrella.
• Anything else: a rain shell and a compact umbrella.

It reads that first hour only. If thunderstorms arrive in the second hour, the kit does not see them and can still show the umbrella.

The line under the shell names the first wet hour in that trip's window, so you can tell which trip it is for.

What to wear and carry

The kit dresses you for the colder of the two trips, by the feels-like temperature in the first hour of each window. When there is no rain shell, the top layer is the first line here that fits:

• Gloves in the cold, shell or no shell.
• Footwear is the first of these that fits. Boots with grip when ice is possible on either trip, or when the sky word the kit read is snow or a wintry mix. Water-resistant shoes for any other wet trip. Shoes with grip when a trip is damp. Everyday shoes otherwise.
• A rain cover for the pack, and spare socks, when either trip is wet or damp.
• Bike lights if you ride, and something reflective, when the forecast marks the first hour of either trip as night.

What the page does not know, and who does

• Your road. A forecast cannot see a particular road. The page does not know which bridge, shaded stretch or untreated side street is on your way. It does not know what has been salted, cleared or closed either. For that, ask your state or local road agency.
• Traffic. Nothing here knows about traffic.
• Warnings. Official warnings come from the National Weather Service. The page shows them at the top in the Weather Service's own words. When the Weather Service marks a warning as immediate, it replaces this headline and the "What to wear" card is put away. For anything urgent, follow weather.gov and your local officials. Outside the United States the page has no official alerts yet, so check your own country's weather service.

Ask it another way

An assistant can ask the same service directly, about your hours instead of ours. It has no fixed trip times. It answers for the stretch of hours you name, and it does not sort a trip into these four words. The page for agents says how.

The other lenses

• Run and ride: the best hour for it, or a plain no.
• Hunt and fish: pressure, light and storms.
• Home and yard: freezes, mowing and watering.
• Build and finish: which day suits stain or paint.
• Methodology: where the data comes from, and where it can be wrong.