Range85-100
High confidence
Strong setup. Set the alarm and plan around it.
The Science Behind the Score
How Fog-Index turns atmospheric data into a single fog probability — the algorithms, the honest report card, and where the model is headed next.
Quick summary
Fog-Index helps photographers decide if an upcoming morning is worth the alarm, where to shoot, and what kind of fog scene to expect. Planning Context translates weather data into practical choices for viewpoint and composition.
Focused on the Light that Matters
Running advanced predictive models against global weather data is computationally expensive. To keep Fog-Index accessible and sustainable, the processing power is concentrated where it counts most for photography.
The Sunrise Window
The model actively analyzes conditions during the morning Sunrise Window: Blue Hour at civil twilight (-6°) through the end of Golden Hour (+6°).
Exact local times vary by date and location.
Civil Twilight Start
Blue Hour begins at -6°.
Sunrise
Sun crosses the horizon at 0°.
Golden Hour End
Morning golden light wraps at +6°.
Fog Score ranges, at a glance
This is the core Fog-Index scale. Every forecast score lands in one of these four color tiers.
Range70-84
Favorable
Good odds. Worth the drive with a backup angle.
Range60-69
Watch
Borderline. Keep plans flexible and scout-ready.
Range0-59
Low confidence
Long shot. Stay in bed if you want fog.
Planning cues come after this score to help with composition and positioning. They add context, not points.
From Fog Likely to Shot Ready
Fog-Index doesn't stop at “fog likely.” It helps you decide what the air will feel like, where to stand, and what light to expect. When a morning scores high, Planning Context translates meteorology into shot strategy — fewer blind alarm clocks, more intentional choices.
Fog Density
A surface-level read at your saved spot. It helps answer the in-the-soup question: barely there, cinematic layering, or full white-room risk.
Subtle MistUseful atmosphere, but light separation may still feel thin
Cinematic LayeringThe sweet spot for depth, trunks, shorelines, and background fade
White-Room RiskVery limited visibility, best for close textures and minimal scenes
Fog Height
An approximate fog-top altitude built from vertical atmospheric structure — pressure levels, humidity/cloud continuity, and inversion context. Your location's elevation is compared against the estimate to produce a viewpoint verdict.
AboveYou're likely above the fog deck
UncertainCould be in or above — have a backup plan
In FogYou're likely in the layer — moody atmosphere
Sky Above
Estimates the light quality above the fog deck by reading only mid- and high-level cloud cover. Low cloud is intentionally excluded because it's often the fog layer itself.
OpenClear sky above — best light-break potential
FilteredThin mid/high cloud — soft glow likely
BlockedHeavy overcast — lower odds of dramatic light
How it works under the hood
- Fog Density is a surface-level read at your saved spot, combining visibility, humidity, dew-point compression, weather code, and wind stability to estimate whether conditions feel subtly misty, beautifully layered, or fully socked in.
- Fog Height is derived from vertical atmospheric structure — pressure-level humidity, cloud-layer continuity, and inversion context — then confidence-gated before surfacing.
- Sky Above reads mid-level (≤ 30% = open) and high-level (≤ 40% = open) cloud cover independently. Low cloud is excluded because it is often the fog deck itself.
- Viewpoint verdict compares your saved location's elevation against the estimated fog top with a safety margin, and downgrades to “uncertain” when confidence is low or stacked low-cloud contamination risk is high.
- Signal confirmation (ICON, Tomorrow.io, NWS) boosts confidence in the Fog Score when independent sources agree, and can floor weak raw scores upward.
Two Photographer Workflows
Start with a high-score morning. Then choose the workflow that matches what you want to make.
In the Soup
Above the Fog
In the Soup
For forests, lakeshores, creeks, and intimate scenes where atmosphere and depth are the goal.
- Read Fog Density first. Cinematic layering is the sweet spot; white-room risk favors close, minimal compositions.
- Use Sky Above to judge whether light can leak through or if the whole scene will stay flat.
- Keep Fog Height secondary here. It is mostly an exit plan if the layer looks too thick.
- Arrive early and adapt: when the fog thins, go wider; when it thickens, simplify.
Above the Fog
For peaks, ridges, lookouts, and city overlooks where the plan is to climb above the layer.
- Read Fog Height and the viewpoint verdict first to decide whether your spot is likely above the deck.
- Check Sky Above and the cloud split to judge sunrise and light-break potential.
- Use Fog Density as context for how the world may look if you stay inside the layer instead.
- Always keep one backup location at a different elevation band.
Born in the Pacific Northwest
Every region has a unique atmospheric fingerprint. Fog-Index works worldwide today, and was originally tuned and tested in the Pacific Northwest. The Fog Potential Map currently covers the continental US, while broader regional tuning and support for more fog regimes continue to expand. The algorithm runs two dedicated scoring pathways in parallel — one for radiation fog, one for advection (coastal) fog — and automatically picks the best fit for conditions at your location.
The Algorithm Report Card
I believe you should know exactly where the model excels and where it's still learning.
| Fog Type | Current Algorithm Fit | The Honest Truth (Notes) |
|---|---|---|
| Radiation Fog | 🟢🟢🟢🟢🟢Excellent | The primary target. The model is perfectly tuned to detect the high-saturation, calm-wind, clear-sky cooling that creates these classic sunrise layers. |
| Valley Fog | 🟢🟢🟢🟢🟡4.5 / 5 | A core strength. Valley terrain bonuses, inversion-layer detection, and winter stagnation persistence make the model highly effective at predicting deep, persistent valley events. |
| Advection Fog | 🟢🟢🟢🟢🟡4.5 / 5 | Strongly improved in v2.3.0. The model now uses sea-surface temperature (air-sea delta) plus an upwind 3-ray marine fan with onshore/offshore wind checks. Remaining gap: performance still depends on marine data availability and sparse coastal sampling. |
| Upslope Fog | 🟠🟠🟡⚪⚪2.5 / 5 | Improved in v2.5.0. A conservative upslope mode now activates for ridge fallback transport when moisture and wind support lift, and it bypasses ridge and inland fallback penalties. Remaining gap: still heuristic and not yet a full terrain-relative forced-ascent model. |
| Precipitation Fog | 🟠🟠🟠⚪⚪Developing | Improved in v2.3.0 with a frontal fog gate (recent rain + rapid moistening + gust guardrail). Still heuristic: it captures many rain-driven setups but not full frontal dynamics. |
| Steam Fog | 🔴⚪⚪⚪⚪Poor | Requires data that isn't available yet: the specific temperature difference between cold air and warm water. The model will likely miss these localized events. |
Why One Model Can't (Yet) Predict the World
Atmospheric physics change drastically based on geography. A model perfectly tuned for Seattle's stable valleys will fail wildly in a tropical environment.
| System Type | PNW, USA | Costa Rica |
|---|---|---|
| System Type | Stable Stratiform & Marine (Current Focus) | Dynamic Convective (Future Focus) |
| Wind | Calm (valley fog) or moderate onshore (marine fog) | Strong wind (pushing upslope) |
| Temperature | Cold ground temperature | Warm ocean air |
| Cloud Type | Flat, uniform cloud layer | Tall, puffy cumulus clouds |
| Formation | Valley fog needs calm, stable air and clear skies (radiative cooling). Marine fog needs onshore wind pushing moist ocean air over cold water. | Comes from unstable air, rapid uplift, and intense convective activity — fundamentally different physics. |
Conclusion: Even with our parallel pathways for marine fog, tropical and convective fog systems remain outside the model's reach. Conditions like orographic lift and warm-ocean convection that cause fog in other regions still need dedicated tuning.
The Essential Fog Types
The Photogenic Six: Understanding Your Target
Clear-sky cooling
Radiation Fog (Ground Fog)
The classic "morning mist." Forms overnight on clear, calm ground. Hugs valleys and burns off quickly after sunrise.
Cold-air pooling
Valley Fog
A sea of clouds. Cold air drains into basins, creating thick, persistent layers that can last for days in winter inversions.
Marine transport
Advection Fog (Coastal Fog)
The coastal blanket. Warm, moist air rolls over cold water. Thick, persistent, and driven inland by wind.
Terrain lift
Upslope Fog
The mountain capper. Moist wind forced up terrain cools and clings to peaks and forested slopes.
Warm water, cold air
Steam Fog (Sea Smoke)
Sea smoke. Wispy vapor rising from warm water into biting cold air. Surreal, fleeting, and distinct.
Rain-driven saturation
Precipitation Fog
Frontal fog. Forms when warm rain falls through cold air, saturating it. Widespread, soft, and moody.
The Horizon: What's Next
This model is forever being honed. With radiation, valley, and marine fog now covered, here's where we're headed next.
DONE
The Foundation
Radiation & Valley fog tuned for the US. The baseline algorithm that started it all.
DONE
The Marine Layer
A dedicated Advection Fog pathway now runs in parallel, scoring coastal marine fog with wind direction, onshore flow detection, and summer seasonality.
NEXT
Mobile Experience
Native iOS and Android apps for robust push notifications and location-based alerts on the go.
FUTURE
International Expansion
Expanding beyond the US to fog-rich regions worldwide — from the UK moors to the coastal valleys of Portugal and beyond.
LONG-TERM
Community Tuning
The ultimate vision: allowing trusted users to "verify" fog events, feeding real-world ground truth back into the model.
Ready to stop missing foggy mornings?
Join other fog-loving nature photographers and cinematographers who trust Fog-Index to alert them when conditions align.
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