I didn’t have a chance to make this post last week when the imagery were more time-relevant. Nevertheless, I wanted to point out another example of the usefulness of MODIS and VIIRS imagery over current GOES imagery and show the usefulness of exciting products and imagery to come! First, let’s take a look at the color-enhanced GOES-IR image below from the morning (0715 UTC) of June 20th.
I’ve placed the yellow circles in the image for a reason, which you’ll see below. Further down, I’m going to show areas of fog displayed in the MODIS and VIIRS imagery, and granted, this is not the standard GOES channel difference (11-3.9 µm) typically used for making fog assessments. However, this post is meant to show current (MODIS / VIIRS) and future capabilities (GOES-R / JPSS) that will make fog detection and cloud differentiation much more easy for the operational forecaster. So, in the image above, fog is nearly unidentifiable as it was in the 11-3.9 µm channel difference image that morning (not shown). Mainly high cirrus clouds can be observed scattered across the region. Now, let’s take a look at the MODIS “fog” product, or channel difference (11-3.9 um) product valid at about the same time (Image 2).
Notice that in the same areas we can now begin to see low clouds (indicated by yellow colors) scattered around the valleys of the southern Appalachian region. While the GOES-East imager is capable of detecting larger scale fog often in the valleys in the eastern circle, fog in the valleys in the western circle present challenges for the current GOES-East instrument, and is often not shown very well (even in the standard 11-3.9 µm channel difference). Next, let’s take a look at a VIIRS Nighttime Microphysics RGB valid at about the same time.
In the RGB imagery it is much easier to detect the extent of the fog, making the operational forecast process much more effective. Notice also that it is possible to see the fog through the higher clouds around the TN/GA/NC border region. Not only does the resolution of the VIIRS and MODIS instruments allow for superior fog detection, but the RGBs in particular offer tremendous operational advantages. As a user of RGBs for about 2 years now, I am convinced that this type of imagery has a relevant and needed place in future operational forecasting. Of course, it will take time for forecasters to become accustomed and adjust to the new imagery, but it will happen.