Johnston, IA Weather Forecast
Polk County, Iowa
Seven-day outlook
40–67°F across the weekThe week runs between 47° and 66°, with Sunday the warmest day of it. There is no real trend across it: one day looks much like the next. Monday is the wettest day, peaking near 83%.
Forecasts come from the National Weather Service's own computer models, and current conditions from the nearest reporting weather station. Both are served through the weather API. A forecast is guidance, not a warning, and anything the Weather Service has actually issued is on the live map.
The written summaries on this page are generated from the forecast data above, not by a meteorologist. Each sentence is a reading of the same numbers you can see, and no forecaster has reviewed them.
About the Johnston forecast
Johnston sits at 41.6919°N, 93.7245°W in Polk County, Iowa. The forecast above is drawn for that point from the National Weather Service's own computer models: a seven-day outlook, and a finer-grained one covering the next eighteen hours where it reaches, and the radar and alert panels show what the Weather Service has out over the area right now.
- County
- Polk County
- Coordinates
- 41.6919°N, 93.7245°W
- Population
- 24,640 · 2023 estimate
- Land area
- 19.49 sq mi
Place data from the US Census Bureau. Coordinates are the Census internal point for Johnston, and the forecast is for that location, not for every address inside the city limits, and a large city can have real weather differences from one side to the other.
How well can the network see Johnston?
The nearest Doppler radar is KDMX (Des Moines, IA), 2.7 miles to the N. A WSR-88D's lowest routine scan sits half a degree above horizontal, and the earth curves away beneath it, so by the time that beam reaches Johnston its center is about 130 ft above ground. That is about as close as radar coverage gets in the United States: the lowest scan is still near the ground when it reaches Johnston, so low-level rotation and the leading edge of a gust front show up on it. Johnston is closer to its radar than 99% of US cities.
The closest instrument actually measuring the air is KIKV · Ankeny Rgnl on the ASOS/AWOS network, 8.0 miles away. Near enough to be representative on most days, though a summer thunderstorm can soak one and miss the other entirely.
Beam height is the standard 4/3-earth approximation for the 0.5° scan and assumes normal refraction; it is where the center of the beam is, not its edges, and unusual temperature profiles bend it. Radar siting from the NWS WSR-88D network, station positions from the Iowa observing network as of this build.
Forecasts near Johnston
- Grimes, IA4 mi
- Urbandale, IA5 mi
- Windsor Heights, IA6 mi
- Polk City, IA6 mi
- Clive, IA7 mi
- Ankeny, IA7 mi
- Des Moines, IA10 mi
- West Des Moines, IA10 mi
Elsewhere in Iowa
Des MoinesCedar RapidsDavenportSioux CityIowa CityAnkenyAll Iowa forecasts →