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PhotoWeather

Trend Rules

Your forecast app shows fog at 6 AM. You live 30 minutes from your favorite woodland location. Do you make the drive?

With instant-only weather conditions, you’re gambling. That fog could burn off in 15 minutes, leaving you with gear in hand and no shot. Or it could linger for hours, perfect for those moody forest scenes you’re after.

Trend Rules answer the question that actually matters: “Will this weather persist long enough to be worth my time?”

How Trend Rules Work

Section titled “How Trend Rules Work”

Instead of checking weather at single moments, Trend Rules evaluate conditions across time windows. You set how long conditions need to persist, and you only get alerts when weather is stable enough to plan around.

Rolling Sum Operator

Section titled “Rolling Sum Operator”

The roll_sum operator totals a weather parameter over your chosen time window. Think of it as “accumulated conditions” rather than “current conditions.”

Real-World Examples:

Persistent Morning Fog:

fog_probability > 70 (rolling sum over 3 hours)

Translation: Fog probability above 70% for at least 3 consecutive hours.

This is the difference between fog that’s gone by the time you arrive and fog that’ll hold steady while you compose and shoot. For a 30-minute drive, 3-hour windows give you confidence to commit.

Heavy Snowfall Events:

snowfall > 5cm (rolling sum over 6 hours)

Translation: At least 5cm of accumulated snow within a 6-hour period.

Not “light flurries right now,” but actual accumulation worth photographing. Fresh snow on branches, unspoiled trails, that pristine landscape look that lasts maybe an hour after it stops.

Extended Golden Hour:

golden_hour_potential > 80 (rolling sum over 2 hours)

Translation: High-quality golden hour light persisting for 2+ hours.

Some evenings the light is magic for 20 minutes. Other times you get extended golden hour that lasts through sunset into blue hour. This rule catches the latter.

Creating Trend Rules

Section titled “Creating Trend Rules”
  1. Open the rule builder
  2. Select your weather parameter (fog_probability, snowfall, cloud_cover, etc.)
  3. Choose “Rolling Sum” as your operator
  4. Set your time window in hours (1-12 hours typically)
  5. Define your threshold value
  6. Enable at your locations

The system evaluates weather forecasts across your time window and only alerts when conditions hold for your specified duration.

Why Duration Matters

Section titled “Why Duration Matters”

Single-moment rule: fog_probability > 70 What you get: Alert at 6 AM. Fog is at 75%. By 6:30 AM, it’s clearing. You’re halfway to your location when the fog burns off.

Trend rule: fog_probability > 70 (rolling sum, 3 hours) What you get: Alert at 6 AM. Fog is at 75% and will hold until at least 9 AM. You have time to make the 30-minute drive, scout, set up, and shoot for 2+ hours before conditions change.

That’s the difference between “weather detected” and “weather you can plan around.”

Single-moment rule: snowfall > 2cm What you get: Alert. Light snow this hour. Might accumulate, might not. Drive out to find barely dusted ground.

Trend rule: snowfall > 5cm (rolling sum, 6 hours) What you get: Alert. Heavy, sustained snowfall. Accumulation guaranteed. Fresh powder on everything. The shot you drove out for actually exists.

Which Parameters Work Best

Section titled “Which Parameters Work Best”

Trend Rules shine with parameters that accumulate or need to persist:

Excellent for Trend Rules:

  • fog_probability - Needs to persist for composition and light quality
  • snowfall / rainfall - Accumulation matters more than rate
  • cloud_cover - Stable cloud conditions for light planning
  • golden_hour_potential - Extended quality light windows
  • wind_speed - Calm conditions need to hold for long exposures

Less useful for Trend Rules:

  • temperature - Usually changes gradually anyway
  • solar_elevation - Predictable; doesn’t need time-based analysis
  • moon_phase - Changes too slowly to need time windows

Use Trend Rules where stability or accumulation directly impacts whether a shoot is viable.

Upcoming Operators

Section titled “Upcoming Operators”

Additional operators are planned for future releases:

  • Rolling Average (roll_mean) - Average value over a time window
  • Rolling Delta (roll_delta) - Change in value over a time window
  • Rolling Trend (roll_trend) - Detect increasing or decreasing patterns

These will enable rules like “temperature dropping by 10°C over 3 hours” or “cloud cover steadily increasing” for tracking weather transitions and trends.

Subscription Requirements

Section titled “Subscription Requirements”

Pro subscription required

Trend Rules are exclusive to Pro subscribers. This includes the roll_sum operator and all future operators.

Next Steps

Section titled “Next Steps”