Tracking areas of stratus and fog can be somewhat difficult using traditional satellite images along with METAR observations...particularly on a day with a variety of low and high level clouds. Sky conditions across the Great Lakes during the afternoon of November 6th is a good example. Below are infrared and visible GOES images along with plotted METAR ceilings and visibilities:
 |
| GOES Infrared |
 |
| GOES Visible |
Note how conditions are evident at point locations, but it is difficult to discriminate areal coverage across the region. For the purpose of issuing and updating TAFs, it would be very useful to better visually display areas of lower ceilings and visibilities, increasing situational awareness and improving the ability to track and forecast improving or deteriorating conditions. Fortunately, GOES-R fog and low clouds products are proving quite useful in filling this need. Below are images of GOES-R IFR probabilitly and LIFR probability:
 |
| GOES-R IFR Probability |
 |
| GOES-R LIFR Probability |
The IFR product does a very good job of showing the area of ceilings that are less than 1000 feet, particularly for values above 60 percent. Though LIFR percentages are not very high, the highest percentages do coincide pretty well with some of the lower ceilings and visibilities in the region. Something that was immediately useful was observing a loop of the IFR image, which showed that the eastern edge of the lower ceilings had temporarily stalled across eastern Wisconsin. This might lead to delaying the arrival of IFR ceilings in eastern TAF sites.
Another likely use of the GOES-R fog and low cloud products would be tracking stratus or fog advecting into Wisconsin off of Lake Michigan. Using an example off the California coast, note that GOES infrared and fog images will give you an idea of where there is cloud cover, but will not give and immediate idea of what type of conditions are moving into the area:
 |
| GOES Infrared |
 |
| GOES IR Fog |
While the traditional fog product above does give a clue that you're looking at either fog or stratus...the GOES-R IFR and LIFR products confirm this and also give an indication of how low the ceilings and/or visibilites are:
 |
| GOES-R IFR Probability |
 |
| GOES-R LIFR Probability |
It is immediately clear the conditions are at or below IFR for much of the area of fog/stratus...with a pretty good probability of LIFR conditions over a large portion of the area. This is quite useful...as ceiling and visibility observations are very limited over bodies of water. Hopefully the use of this product will help in troublesome situations where poor conditions can sneak onshore... particularly when somewhat obstructed by other cloud decks.
In summary, GOES-R fog and low cloud products can be very useful in tracking areas of fog and stratus. In contrast to using a combination of surface observations and traditional visible/infrared products, the GOES-R products can give a very quick and fairly accurate representation of where IFR or worse conditions are located. Being able to track these areas will hopefully lead to improvements in TAFs.
Denny VanCleve
NWS Milwaukee/Sullivan
