A series of LightningCast Probability plots from this RealEarth-powered website, below, shows increasing probabilities of lightning over the South Pacific to the south of American Samoa’s Manu’a Islands. The 75% contour (magenta) appears at 0530 UTC; the first GLM observation is shown at 0620 UTC. LightningCast is the probability that a GLM observation will occur within the next 60 minutes, so this is a good case showing its efficacy.

The WSO forecast office in Pago Pago was using this product to advertise the danger from lightning, as shown in the screenshot below for their Facebook page (direct link to the image). The time of the image below (ca. 0826 UTC) is after the end of the animation above; the lightning with this convective complex continued for several hours.

GOES-18 Level 2 products below (Lifted Index, left, scaled from -5 to 10 and Total Precipitable Water, right, scaled from 1 to 2.5 inches) show that the convection developed in a region where TPW and instability were both increasing to the north. Knowledge of the distribution of these level 2 products in concert with the development of LightningCast probabilities is a good indicator that convection will develop. The convection that developed eventually overspread Tutuila; the airport at Pago Pago received more than 0.5″ of rain.

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