R to O: Low Cloud and Fog... a forecaster's perspective

It never ceases to amaze me how sitting over a forecaster's shoulder really changes your perspective on things. Earlier this morning I shadowed the FA West desk and was shown all the quirks and tricks to issuing AIRMETs, particularly those for low ceilings along the West Coast. I was also able to give an impromptu GOES-R FLS training session to the forecaster, after which time we discussed the product at great length and came across the example below.

Shown here is the IFR probability (top), the nighttime 'visible' imagery (middle), and the cloud thickness (bottom), all taken this morning (120712) at 0545 UTC. Note the circled area, in this case giving a very good example of the fused method of the FLS algorithm. The 'visible' image at this time (which is really the IR 11 and 3.9 micron BTD) shows a small hole within the low stratus deck (the darker gray spot) as well as an area of higher clouds just to the north of this hole (the black areas). IFR probabilities for this same time picked up on these areas; in both cases the modeled RH profiles still indicating a higher likelihood for IFR conditions, while the satellite predictors were indicating a weaker response due to the hole in the clouds and the higher cloud contamination.

120712 0545 UTC IFR probabilities

120712 0545 nighttime 'visible' imagery

120712 0545 UTC Cloud Thickness

The cloud thickness imagery also correlates to the what the nighttime 'visible imagery showed; the higher clouds to the north contaminating the image, not allowing for any data in that area, while the hole in the clouds was noted as a much thinner cloud layer (purple) than the surrounding area.

This example shows the utility of this product as an excellent situational awareness tool for forecasters, particularly for those issuing AIRMETs along the West Coast. In this case, there was likely still a stratus deck beneath the higher clouds, while the hole indicated clearing conditions. This fused fog detection approach allows for a dual sided perspective of current conditions, one that incorporates both satellite data as well as environmental characteristics, and gives forecasters greater confidence in their assessment of low ceiling conditions.