San Bernardino Heat Window Planner

Paste hourly conditions you already have. The planner calculates the NWS heat index and finds the contiguous window with the lowest peak apparent heat.

Your day, measured hour by hour

Load the sample or paste consecutive observations to compare every possible outdoor window with the same published calculation.

Drink water even before thirstLimit activity during the hottest hoursWear lightweight light-colored clothingNever leave children or pets in parked vehicles Drink water even before thirstLimit activity during the hottest hoursWear lightweight light-colored clothingNever leave children or pets in parked vehicles

Read the result, not just the number.

The selected interval is lower only relative to the rows you supplied. It is not a medical clearance or a promise of safe conditions.

How the NWS heat index is computed

The engine first checks the NWS simple formula. When its averaged result reaches 80 F, it uses the Rothfusz regression and applies the published low- or high-humidity adjustment when its conditions are met.

HI = -42.379 + 2.04901523T + 10.14333127RH − 0.22475541TRH − 0.00683783T² − 0.05481717RH² + 0.00122874T²RH + 0.00085282TRH² − 0.00000199T²RH²

Why the planner minimizes the peak first

Every possible contiguous window is evaluated. The window with the lowest hottest member ranks first; the lower average and earlier start break ties. This prevents one unusually hot slot from disappearing inside an average.

What direct-sun upper bound means

NWS notes that direct sunlight can increase apparent heat by up to 15 F. The tool can add that maximum to every supplied hour as a conservative comparison. It does not predict that the full increase will occur.

What the calculation cannot see

Heat index is shade-based and is not WBGT. Wind, radiant load, clothing, work intensity, hydration, acclimatization, medication, age, pregnancy, and health conditions can all change risk. Follow current official alerts and stop activity if symptoms appear.