NOAA Office of Satellite and Product Operations


On Tuesday, December 1, at approximately 1330 UTC (8:30 a.m. EST), a planned system failover test for up to 8 hours will result in delayed, inconsistent, stale or missing data on the GOES and SPSD web sites and an outage of the OSPO web site. Please monitor for additional information. The failover test may be delayed or suspended if there is a critical weather event.

As a reminder separate from the failover test, GOES-13 Sounder IR data is not available. All products from GOES-13 (GOES-East) Sounder IR data have been halted and distribution has been stopped. Engineers are investigating the problem.

GVI - Precipitable Water Index

The Precipitable Water Index (PWI), otherwise known as the brightness temperature difference, is the difference between AVHRR channels 4 and 5. PWI is a measurement of how much water vapor is in the atmosphere (lower K values denote higher concentrations of water vapor). Since AVHRR channels 4 and 5 are volume sampled from the top of the atmosphere to the surface, PWI, to an extent, measures the total column precipitable water in the atmosphere (Steve Olson, 1997).

GVI Precipitable Water Index image

Regions on display include North America, South America, Alaska, Europe, Asia,
British Isles, Africa, and Oceania.

Please note that PWI is not the same as relative humidity, which measures the percentage of water vaper over the amount of water vapor needed for saturation at a given temperature.