Instrument Flight Rules (IFR) Probability from GOES-17

April 7th, 2022 |

Instrument Flight Rules (IFR) are rules and guidelines put in place by the Federal Aviation Administration that govern conditions in which “flight by outside visual reference is not safe”, whether by low clouds or fog. Cloud and reflectance data from geostationary satellites GOES-16 and GOES-17 provide a satellite IFR Probability product, by detecting fog and low stratus. More information on this product can be found here.

An example of GOES-17 IFR Probability is shown below in Southern California on April 7, 2022 at 1546UTC, displaying GOES-17 IFR Probability, IFR advisories issued by the Aviation Weather Center, and GOES-17 red band reflectance.

GOES-17 IFR Probability, IFR advisory, and GOES-17 Band 2 (0.64µm) reflectance on April 7, 2022 at 1546UTC.

The full domain of GOES-17 IFR Probability may be useful for ocean prediction. GOES-16/17 IFR products are available on RealEarth.

The GOES-17 IFR Probability and Band 2 reflectance for the full GOES-West “CONUS” domain, April 7, 2022 at 1546UTC.

Detection of fog during a fatal crash in Florida

March 3rd, 2022 |
GOES-16 Band 7 Shortwave Infrared (3.9 µm) imagery, 0546 – 0731 UTC 3 March 2022

A combination of fog and smoke reduced visibilities along I-95 S in southern Volusia County Florida. A series of fatal crashes (news report; this tweet suggests the accident was near Florida State Route 442; second tweet). News report suggest the smoke that helped seed the dense fog resulted from controlled burns. The Band 7 imagery (3.9 µm) above, does not show strong evidence of burns (the Fire Detection and Characterization Algorithm — FDCA — similarly showed no information in Volusia County), nor of the fire that occurred at the crash scene as vehicles burned. The first crashes occurred around 0630 UTC.

The Nighttime microphysics RGB is often used to highlight regions of fog. On this day, however, no obvious signal of fog (fog typically appears as a color between cyan and yellow, as noted here) is apparent.

Nighttime microphysics RGB, 0501 – 7031 UTC on 3 March 2022 (Click to enlarge)

The Night Fog brightness temperature difference (the ‘green’ component of the RGB above) also can be used to detect fog. GOES-R IFR Probability fields use satellite data (and model data) to outline regions of fog. The toggle below includes the night time microphysics RGB, the night fog brightness temperature difference, and the IFR Probability fields at 0631 UTC, near the time of the crash. Satellite data provided little detection for this very thin combination of smoke and fog. For this case, it would be better to rely on things like webcams.

GOES-16 Band 7 (3.9 µm), Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm), Night time Microphysics RGB and IFR Probability fields, 0631 UTC on 3 March 2022 (Click to enlarge)

There was a very timely Suomi-NPP overpass as shown below. The timestamp is at 0632 UTC, which is when the satellite first was broadcasting data to the Direct Broadcast antenna at CIMSS; the satellite was viewing central Florida around 0642 UTC, based on this orbit calculation (from this site). The slider does suggest a small temperature difference as might be caused by fog over southern Volusia County. (Click here to see a toggle — and here to see a very fast toggle).

A brightness temperature difference field between I05 and I04 on this date was created using McIDAS-V in this blog post.


A similar incident of fog — possibly enhanced by smoke — causing a multi-vehicle accident occurred in Osceola County (not far to the south of Volusia County) Florida on 13 March 2007. In that case, higher-resolution MODIS imagery was a bit more helpful in helping to highlight an area of nocturnal fog formation.

Gridded NUCAPS over the ocean and IFR Probability

March 1st, 2022 |
Gridded NUCAPS estimates of low-level (1000 mb) dewpoint, and (CONUS) GOES-16 IFR Probability, 2100 UC on 28 February 2022 (Click to enlarge)

The image above (from 2100 UTC on 28 February 2022) and below (from 0930 UTC on 1 March 2022) toggle between low-level estimates of 1000-mb dewpoint and GOES-16 IFR Probability fields. Is there a general relationship between the two? At first blush, it does seem like the IFR Probability fields are affected by the strong gradient in low-level temperature, where the dewpoint drops from the teens (oC, grey/blue to cyan in the enhancement) to the single digits (purple and white in the enhancement). Note that SSTs in the region where the 1000-mb dewpoints are in the single digits are between 10 and 14 C at both ~2100 UTC 28 February and ~0930 UTC 1 March (ACSPO SSTs at the link are derived from Direct Broadcast data from CIMSS and are available via an LDM feed).

Gridded NUCAPS estimates of low-level (1000 mb) dewpoint, and (CONUS) GOES-16 IFR Probability, 0930 UC on 1 March 2022 (Click to enlarge)

The toggle below compares gridded NUCAPS estimates of 1000-mb relative humidity with Low IFR Probability fields. There again seems to be a relationship. How robust that relationship is is to be determined. This is the first in a series of blog posts that compares these two fields, as part of a way of better forecasting fog over the oceans.

Gridded NUCAPS estimates of low-level (1000 mb) relative humidity, and (CONUS) GOES-16 Low-IFR Probability, 0930 UC on 1 March 2022 (Click to enlarge)

AWIPS imagery in this blog post was created using the NOAA/NESDIS TOWR-S AWIPS Cloud Instance.

GOES-17 IFR Probability Fields now available in RealEarth

December 1st, 2021 |
RealEarth depiction of GOES-17 IFR Probability fields, 1200-1230 UTC on 1 December 2021 (Click to enlarge)

RealEarth has added GOES-17 IFR Probability Fields to its product suite (GOES-16 IFR Probability fields have been available in RealEarth for some time). They can be accessed most simply by entering ‘IFR Probabilty’ in the RealEarth search box. At present only the ‘PACUS’ domain (the GOES-17 equivalent of the GOES-16 ‘CONUS’ domain) is available, at 5-minute time-steps. An example over western Washington and offshore waters is shown above.