Ottawa, IL Weather Forecast
LaSalle County, Illinois
Seven-day outlook
40–70°F across the weekThe week runs between 42° and 70°, with Tuesday the warmest day of it. There is no real trend across it: one day looks much like the next. Saturday is the wettest day, peaking near 70%.
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 Ottawa forecast
Ottawa sits at 41.3540°N, 88.8234°W in LaSalle County, Illinois. 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
- LaSalle County
- Coordinates
- 41.3540°N, 88.8234°W
- Population
- 18,752 · 2023 estimate
- Land area
- 14.895 sq mi
Place data from the US Census Bureau. Coordinates are the Census internal point for Ottawa, 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 Ottawa?
The nearest Doppler radar is KLOT (Chicago, IL), 42 miles to the ENE. 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 Ottawa its center is about 2,800 ft above ground. That is comfortably inside the useful range. The lowest scan passes low enough over Ottawa to show rotation in the part of a storm where tornadoes actually form. Ottawa is closer to its radar than 53% of US cities.
The closest instrument actually measuring the air is KVYS · Peru/Illinois Valley Rgnl on the ASOS/AWOS network, 17 miles away. Far enough that "current conditions" for Ottawa is an educated reading of somewhere else, worth knowing before you plan around a single temperature.
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 Illinois observing network as of this build.
Forecasts near Ottawa
- Marseilles, IL9 mi
- Oglesby, IL14 mi
- LaSalle, IL14 mi
- Streator, IL16 mi
- Peru, IL16 mi
- Spring Valley, IL19 mi
- Mendota, IL20 mi
- Morris, IL21 mi
Elsewhere in Illinois
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