Weather apps are built to answer "what will the weather be?" But when you're standing in the hallway with your keys, that's not your question. Your question is: "should I leave now, in twenty minutes, or should I have left twenty minutes ago?"
Those are different questions, and the second one is far more useful — because on most rainy days, when you travel matters more than whether you travel.
Rain is bands, not blankets
The hourly forecast trains us to think of rain as a state: "raining from 8 to 11." Radar tells the truth: rain moves through in bands, with gaps. A morning summarized as "rain: 8–11 AM" is often three showers with two 30-minute dry windows between them.
If your trip takes 15–45 minutes — a commute, a school run, a ride to the gym — those gaps are big enough to hide your entire journey. Getting wet or staying dry is frequently a 15-minute decision.
How to make the call manually
- Open the radar, not the hourly view. Loop the last hour of radar so you can see which way the cells are moving and how fast.
- Find your window. If a band is 20 minutes away and takes 30 to pass, your options are "leave right now" or "leave in ~50 minutes." Leaving in 20 is the one wrong answer.
- Sanity-check the tail. Behind one band there's often another. Make sure your window is long enough for the whole trip, not just the start of it.
- Decide with the exposure in mind. In a car, a marginal call costs you nothing. On foot or on a bike, wrong-by-ten-minutes means soaked — take the conservative window.
Two more timing rules worth internalizing:
- Leaving earlier is usually better than later. Fronts more often accelerate than stall, and traffic gets worse in rain — the later window shrinks from both ends.
- Thresholds, not icons. A drizzle icon at your departure time is not a reason to shift; under ~0.5 mm/h barely registers. Shift for real intensity, not for pixel art.
The problem: this only works if you do it
The radar-loop routine takes three focused minutes. The reason people still get soaked isn't that the method fails — it's that nobody does it at 7:40 AM while finding a missing shoe. Timing decisions need the information to arrive before the decision point, without being asked.
Briefings at decision time
That's the design idea behind Waycast. You save a trip — route, travel mode, departure time, one-off or recurring — and it watches the forecast along your route for your exact time window. At your alert lead (say, 45 minutes before departure), it sends a briefing that answers the hallway question directly: "Shower passing until 8:10 — leave 15 late and you're dry," or "Dry window now, heavy rain from 8:30 — don't delay."
Running late anyway? Push the departure back in the app and it re-checks the new window. If the forecast shifts materially after your briefing, you get one update — not a feed to monitor.
It's free for up to three trips, no card required. Save the trip you time most often — for most people that's the commute — and let the "when should I leave?" answer show up on its own.