Today at the barn.

Add the air temperature in Fahrenheit to the relative humidity as a percentage. University of Minnesota Extension describes cooling as most effective under about 130, decreased between 130 and 150, and advises against riding over about 150, especially for horses not acclimated to heat. Over about 180 it warns the condition can be fatal if the horse is stressed.

This is a rough screen, not a heat index and not a measurement of your horse. It is arithmetic on two forecast numbers. Age, condition, coat, shade, water, acclimatization and how hard the work is all matter more than the total.

Below 70°F it is not shown at all. Adding humidity to a cool temperature does not describe a cooling problem, and a damp 50°F morning summed to 132 and used to display a heat warning here. Cold is assessed separately.

Montana is usually dry, which is why this number is usually low even on a hot day. That is real, not a fault.

Real runs of two or three consecutive forecast hours are tested, and every hour in a window has to clear every check before the window is shown. A window is rejected outright if any hour in it has an active severe weather alert, thunder or lightning in the forecast, an air quality index above 150, a hot-weather screen above 150, a temperature at or below 15°F, wind or gusts above the limits below, a 60 percent or higher chance of precipitation, or freezing precipitation.

Wind is read from the high end of a forecast range. "25 to 35 mph" is treated as 35, not 25.

If no window clears, the page says so. It does not fall back to naming the least bad hour, and it never calls a window "best", "safe" or "OK". The most it will say is that a window was the lowest risk in the forecast.

Hours are shown in the forecast location's own timezone, with its own sunrise and sunset, not your browser's.

It knows the sky and nothing else. It has never seen your arena, your gate, your footing or your horse, and it does not know that the river trail floods or that your gelding is unrideable on a windy Tuesday. Those you still have to supply.

The cold and wind limits used here are Lazy K's practical opinion, not published thresholds. A forecast at or below 15°F closes a window; at or below 38°F it prompts a longer warm up. Sustained wind at or above 30 mph, or gusts at or above 40 mph, close a window; 18 mph prompts a note. Say so out loud because they are judgment, not evidence.

If the overnight low is at or below freezing you get a reminder to check troughs, heaters and cords before bed. Reduced winter drinking is considered the main predisposing factor for impaction colic, and warming the water raises intake substantially. More in the winter guide.

Flagged when the low is at or below freezing and the following high is above it. That cycle turns churned ground into ruts and then into ice. Treat it as a prompt to go and look, not as a fact about your paddock. Every property drains differently and no forecast knows yours.

Rain flattens a winter coat and destroys its insulation, and wind strips the warm air off the skin. Cold alone is rarely the problem. Cold plus wet plus wind is, and that combination gets flagged separately from temperature.

The number shown is the US EPA Air Quality Index. Under 50 is good, 51 to 100 moderate, 101 to 150 unhealthy for sensitive groups, 151 to 200 unhealthy, 201 to 300 very unhealthy, and above that hazardous.

Above 150 this page closes the riding window rather than suggesting easier work. US Equestrian's air quality guidance recommends that organizers consider suspending or canceling competition when the index reaches 151 or above. Between 101 and 150 the page says to ease off hard work instead of stopping.

There is no horse specific AQI, and that matters. Research on horses and wildfire smoke is limited, so the human thresholds are the best available guide rather than a standard designed for a 1,100 lb animal breathing far more air than you are.

The air quality figure here is modeled, not measured. It comes from the Copernicus Atmosphere Monitoring Service model by way of Open-Meteo. It is not a reading from a United States Environmental Protection Agency monitoring station. For a regulatory monitor near you, check AirNow.

During smoke: limit strenuous work, keep water in front of them, and do not resume hard work the moment the number drops. Ask your veterinarian how long to wait after a heavy exposure. If you can smell it and see it, that is enough information to go easy.