RGB Products Show Enhanced Utility for Fog Monitoring

It was a “typical” post-rain foggy morning for portions of the Appalachian region this morning.  When looking at the suite of SPoRT satellite products this morning, I noticed the usual fog in the GOES and MODIS imagery, but what caught my attention was the early detection of fog by the Nighttime Microphysics RGB product.  Image 1 below shows the GOES-MODIS 10.8-3.9 µm product currently created by SPoRT and available through the Southern Region LDM to collaborating offices.

Image 1. GOES-MODIS 11-3.9 µm hybrid image valid May 16, 2012 0331Z.




















In this standard color scheme, the yellow colors generally correspond to low clouds and/or fog while the blue colors represent high clouds.  Notice that low clouds and fog can be seen in portions of the Smoky Mtns region in North Carolina and East Tennessee, from around Waynesville, NC to Johnson City, TN.  Also, areas of fog and low clouds can be seen in portions of West Virgina and western Virgina.  Now, take a look at the Nighttime Microphysics RGB below (Figure 2)…

Figure 2. SPoRT Nighttime Microphysics RGB product valid May 16, 2012 0334Z.

Notice in the RGB image that the areas of fog mentioned above show up as the light aqua colors. However, notice the very light aqua colors that show up in the Cumberlands and Alleghenys to the west. In this area, generally from Livingston, TN northeastward through eastern Kentucky and into western and central portions of West Virgina, fog shows up fairly well in the narrow valleys of the Cumberland/Allegheny Plateau region. I was surprised to see this much difference between the two products, but the enhancement of the RGB product and the ability to discern the shallow fog and low clouds from the terrain background can be helpful to forecasters. This is possible with the more complex “recipe” of the RGB Nighttime Microphysics product (Red: 12.0-10.8 µm, Green: 10.8-3.9 µm, Blue: 10.8 µm). In this case, it would have alerted the forecasters to the early development of valley fog. Given a continuation of favorable conditions (which did occur), the fog would likely spread and become more dense with time overnight. See the RGB image below valid at 0746Z, which indicates the rapid expansion of the fog.

Figure 3. SPoRT Nighttime Microphysics RGB valid May 16, 2012 0745Z.
Notice the aqua colors have spread markedly across the valleys of this region over the ensuing 4 hour period. Most of the NWS offices with forecast responsibility in this region (Morristown, Blacksburg, Jackson (KY)) issued dense fog advisories during the early morning hours for their affected counties. These advisories came several hours after the early detection of fog by the RGB Nighttime Microphysics product, and most forecasters are not going to issue these products until its evident dense fog is going to form anyway (and speaking from experience, that doesn’t often come easily). Of course, most of these offices do not get these types of satellite products yet, but they do certainly show utility in the future in these types of cases. With pattern recognition, the early detection of fog amidst favorable conditions might suggest that dense fog would eventually form. Had forecasters been able to see the locations of fog development relatively early (as shown in the 0334Z RGB product), it could have increased their confidence in the development of widespread dense fog, which could have been reflected properly in Area Forecast Discussions or other advisories or statements during the late evening.

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