GOES Imagery has long been a valuable tool for fog detection and tracking, both during the day and night. With GOES ABI, forecasters are able analyse low clouds and fog in even better detail, spatial and temporally. Further, the additional spectral bands allow for more insight into the features through the generation of multispectral products such as RGBs.
NWS Bismark, ND forecasters leveraged GOES-East ABI Imagery in tandem with area webcams and surface obs to analyze fog evolution prior to and after sunrise on 09 Nov 2021, informing their forecast decision-making. While GOES imagery provides a great look at the spatial extent of low clouds and fog and their evolution with time, the webcams and surface obs allow the user to determine actual surface conditions associated with the satellite cloud feature. At 1213 UTC, the forecaster issued an update to the Area Forecast Discussion that read: “GOES Nighttime Microphysics shows extent of fog in southwest North Dakota, possibly nudging into the south central this morning. Based on cameras and coverage depicted on satellite imagery, coverage is somewhat patchy, but has lowered visibility at Hettinger down to 1/4 mile. An SPS was issued to address fog this morning for this area. Fog will gradually dissipate mid-morning as boundary layer mixing increases after sunrise.”
The Nighttime Microphysics RGB imagery that goes with the above discussion captures the low clouds and fog as a light orange/light brown/yellow color, compared to the pink clear-sky land background, blue/magenta bodies of water, and red (thick) to black (thin) high clouds (Figure 1). The imagery shows the development and northward surge of low clouds and fog from beneath exiting upper level cloud cover over a 5-hour period ending just prior to sunrise. The webcams (and METARs) confirmed conditions beneath the suspected low clouds, per the discussion.
Forecasters continued to analyze satellite imagery and webcams after sunrise to inform their decision-making, as the low clouds and fog hung around. At 1505 UTC, Forecasters wrote: “Latest satellite and webcams indicate fog over the southwest and south central is beginning to dissipate. We did extend the areas of fog farther east and extend the SPS for fog through 16 UTC. Otherwise no changes to the current forecast.” During the daytime, multispectral products such as the Day Cloud Phase Distinction (Fig 2) and Day Snow Fog (Fig 3) RGBs may be utilized, in addition to visible imagery (Fig 4). In the three hour period following sunrise, these animations show the fog and low clouds dissipating through the morning hours, with surface conditions confirmed by webcams and METARs.
Bill Line, NESDIS and CIRA