How Uncertain Is the Forecast? — Four Fires

Multi-Fire MC Comparison

Arrival Spreads Across Four Fires

For each fire, the chart shows the P10–P90 arrival time spread for representative communities. Wide bars mean high uncertainty. The "never reached" percentage shows how many MC draws never reached the community at all.

P10-P90 Arrival Spread by Community (Hours from Ignition)

MC Uncertainty Summary — All Communities

Fire	Community	P10	P50	P90	Spread (P90-P10)	Never Reached
Kincade	Geyserville	29.3 h	38.5 h	51.7 h	22.4 h	38.0%
	Healdsburg	37.0 h	44.0 h	54.0 h	17.0 h	36.0%
	Windsor	45.7 h	51.0 h	61.3 h	15.6 h	36.0%
Camp Fire	Paradise	27.0 h	30.0 h	33.1 h	6.1 h	0%
	Magalia	18.0 h	20.0 h	22.1 h	4.1 h	0%
	Concow	11.9 h	14.0 h	16.0 h	4.1 h	0%
Dixie	Greenville	50.0 h	54.0 h	60.0 h	10.0 h	1.5%
	Quincy	37.0 h	40.0 h	44.0 h	7.0 h	1.5%
	Indian Falls	27.0 h	32.0 h	37.0 h	10.0 h	1.5%
Marshall	Louisville	49.0 h	54.0 h	59.0 h	10.0 h	0%
	Superior	36.0 h	41.0 h	46.0 h	10.0 h	0%
	Broomfield	42.0 h	46.0 h	50.1 h	8.1 h	0%

Fire Character

Aggressive vs. Uncertain

Camp Fire: P10-P90 spreads of only 4–6 hours. 0% never-reached. The fire is so aggressive it always arrives regardless of weather perturbation. Kincade: spreads of 15–22 hours. 36–38% never-reached. The fire's behavior is fundamentally more sensitive to weather conditions.

Camp Fire vs. Kincade: Never-Reached Rate (%)

Finding

Fire character determines MC uncertainty more than model parameters. Camp Fire has tight P10–P90 spreads (4–6 hours, 0% never-reached) because the fire is always aggressive. Kincade has wide spreads (15–22 hours, 36–38% never-reached) because weather perturbations can redirect the fire entirely. Dixie and Marshall fall between: low never-reached (0–1.5%) but moderate spreads (7–10 hours).

Different fire types, different MC value. For aggressive fires like Camp Fire, the MC ensemble confirms what you suspected — every draw says "evacuate now." For uncertain fires like Kincade, it reveals something the deterministic run hides: 36% of draws never reach communities the single-point forecast threatens. In both cases, MC adds information you'd act on differently. The mechanism is just different.

Same code, 200 runs instead of 1. The deterministic CA says "fire arrives at hour 27." The MC ensemble says "somewhere between hour 20 and 34, and there's a 36% chance it never arrives at all." Camp Fire's ensemble confirms urgency. Kincade's ensemble shows the deterministic forecast is dangerously overconfident. The question shifted from "when does fire arrive" to "how confident should we be in that number" — and answering it took 200 runs of the same model.

Model: Rothermel cellular automaton, 50×50 grid, 200 Monte Carlo draws per fire. Weather perturbation: wind speed ±30%, direction ±20°, humidity ±15%. Runtime: ~240 seconds per fire.

← Previous Q2: How Far, How Fast? Next → Q4: When to Pull the Trigger?

How Uncertain?

Arrival Spreads Across Four Fires

Aggressive vs. Uncertain