HeatwaveReady

El Niño calculators

Four El Niño season calculators, each one job, each showing its working. Size an air conditioner, size an evaporative cooler, check the heat index, work out battery hours. No sign-up, nothing sent.

How long will my battery run this?

A strong El Niño winter raises the odds of storms and power cuts across the southern tier. This is the arithmetic every power-station spec sheet is doing behind the scenes, with the loss allowance stated instead of hidden.

Power-cut runtime

Enter the battery size in watt-hours (it is printed on the unit) and the load in watts. The result is a planning figure, not a guarantee.

Where this number comes from

hours = watt-hours x 0.85 / watts. The 0.85 is a working allowance for inverter and conversion losses, which is the range most manufacturers quote for their own units. It is arithmetic, not a measurement of your battery. Cold weather, battery age and start-up surge all cut it further, and a battery run flat repeatedly will not hold its rating for long.

What size air conditioner do I need?

Air conditioner sizing

Open the calculator

Two questions; sized with ENERGY STAR’s table, then the unit here that fits.

Where this number comes from

A sizing guide built from ENERGY STAR’s published table, not a full Manual-J load calculation. For odd rooms (lots of glass, top floor, extreme climates) an HVAC pro’s load calc is worth it.

Evaporative cooler: how many CFM?

Evaporative cooler sizing

Open the calculator

Room volume in, CFM out, by the US Department of Energy formula.

Where this number comes from

Formula, the 20–40 ACH range and the wet-bulb ≤70 °F effectiveness threshold are the US DOE Building America Solution Center (PNNL)’s own — validated against its Salt Lake City worked example (16,000 cu ft × 20 ACH ÷ 60 = 5,333 CFM).

Heat index right now

Heat index and humidity check

Open the checker

Enter temperature and humidity: the feels-like heat index, the NWS level, and whether evaporative cooling helps.

Where this number comes from

Heat index uses the National Weather Service Rothfusz regression. Live readings come from api.weather.gov (US only, public domain) and stay in your browser — we don’t store your location. Not medical advice.

My state's El Niño winter odds

This is the one figure on the site nobody else has joined up: what December to February precipitation actually did in each of the 9 strong El Niño winters since 1958, state by state, against the 1901-2000 mean. It is a small sample, so it gives odds, never a forecast. Temperature is left out on purpose because the record warms across the period, so every recent winter reads warm whatever El Niño is doing.

StateWetter than the baselineBaseline winter rainPage
Utah 6 of 9 winters 3.54 in Utah winters
California 7 of 9 winters 11.73 in page not published yet
Indiana 3 of 9 winters 7.81 in page not published yet

Every other US state: not computed yet. Method: NOAA NCEI Climate at a Glance statewide December-February series. Each analog El Nino event is matched to the December-February winter its peak season falls in. Anomalies are against the 1901-2000 mean. Precipitation is the usable signal; temperature is trend-confounded and must not be presented as an El Nino effect. Source: NOAA NCEI Climate at a Glance, generated 2026-09-02.

Back to the station map or read the dated NOAA update log.