Latency of Radar Images

Generally, you should find that the timestamp on the latest image and the actual time, the “latency,” should be within a range from four to thirty minutes or more depending on the station and the mode (composite and local) you’re looking at.

Example of low latency: four minutes.

For local mode, where the radar imagery from a single radar station is being viewed, the more weather there is in the area, the faster the refresh rate and the lower the latency for the radar. Conversely, if there is no weather in the area, the radar station might publish one image every thirty minutes or more. Sometimes they seem to switch the station into a standby mode when there is no weather, especially at night. I’ve seen the latest image as old as forty-five minutes on an operating radar station. Once an image is published, it can take a further two to even six minutes for the image to be available in RadarNow!.

For composite mode, where the entire screen is filled with radar imagery, a new image layer (aka tile layer) is published about once every ten minutes or so. This image is itself composited from the local station’s data so is subject to that latency as well. Please see our blog post “The RadarNow! Advantage” for more on that topic. The publishing time is more or less random and doesn’t occur on the ten minute mark on the clock.

Possible issues with apparent latency

If one local radar station’s latest radar image seems to be older than thirty minutes, it is very possible that the station itself has developed a fault somewhere in the line from producing the image to publishing on the internet. Generally, the National Weather Service (NWS) makes every effort to return the station to active service. Once the station is returned to service, the imagery will be picked up automatically by RadarNow!.

When the timestamp of the latest image, regardless of the radar station you’re looking at, seems to be an even hour off, the problem can usually be traced to the device’s system time setting set to something other than “Auto”. This setting can be found in the device’s settings apps, under “Date and time” (depending on your OS version). Changing this setting to “Auto” allows RadarNow!’s time calculations to be made from a reliable source.

Occasionally, and this is actually quite rare, a major server for the NWS will go offline and data will stop flowing to the internet. NWS usually restores service quickly for these events.