Thread by @MappingSupport

1/6 I’ve been volunteering to produce online wildland fire maps for about the last 10 years. The #1 thing to know is that any fire data you see on maps is **not real time**. There are 2 MODIS satellites and 2 VIIRS satellites. #GlassFire #GlassIncident #ZoggFire

2/6 The MODIS/VIIRS satellites make a total of 8 passes per 24 hours. For the West Coast very rough timing is midnight to 3am (4 passes) and noon to 3pm (4 passes). It takes NASA ~3 hours to process the raw data before it can be displayed on any map.

3/6 Usually by 7am pacific time the maps are showing all the MODIS/VIIRS data that is available until sometime after 3pm. Hotspot locations are approximate and sometimes the data is ‘false positive’.

4/6 The #GISsurfer fire map I produce displays any new MODIS/VIIRS data at the top of the hour. You have to re-open the map to see new data. I’m going to work on some code so the most recent hotspots use different symbols.

5/6 The #CalTopo fire map can display data from the GOES satellites. That data (large colored squares) is refreshed very frequently but the location is generalized over a much larger area compared to MODIS/VIIRS data.

6/6 Finally, never rely on any map to ignore an order to evacuate. The people in charge have more information than is available to the public, particularly in a fast moving event. HTH.