Daily Archives: April 6, 2021

IFR Probability fields over the Bering Sea

GOES-17 IFR Probability from 1220 – 1710 UTC on 6 April 2021 (Click to enlarge)

GOES-17 IFR Probability fields, above, show a large region of high probabilities to the south and west of Alaska over the Bering Sea. This region of low clouds is encroaching onto shore and demonstrates how the field could be used to predict the onset of lower ceilings. The Night Fog brightness temperature difference animation, below, spanning the same times, documents how high clouds can make mask the satellite detection of low clouds. The animation also shows how the signal changes when the Sun rises (mot noticeable after about 1600 UTC). The Night Fog Brightness Temperature difference field is a component of the Nighttime Microphysics RGB; if the Night Fog Brightness Temperature difference cannot detect low fog because of high clouds, then the Nighttime Microphysics RGB similarly will not detect low clouds.

GOES-17 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) fields, 1220 UTC – 1710 UTC on 6 April 2021 (click to enlarge).

The toggles below of Night Fog Brightness Temperature difference and GOES-17 IFR Probability at 1400 UTC (below) and 1620 UTC (bottom) underscore how the IFR Probability field can give useful information in regions underneath high clouds. If you were scheduled to be on a boat in the Bering Sea on this day, for example, would you expect any visibility?

Toggle between GOES-17 IFR Probability and GOES-17 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) fields, 1400 UTC on 6 April 2021 (click to enlarge). Surface observations of ceilings and visibilities at 1600 UTC are also plotted.
Toggle between GOES-17 IFR Probability and GOES-17 Night Fog Brightness Temperature Difference (10.3 µm – 3.9 µm) fields, 1620 UTC on 6 April 2021 (click to enlarge). Surface observations of ceilings and visibilities at 1600 UTC are also plotted.

The imagery below, from webcams at Togiak (at 1700 UTC) (source), show the low clouds along the coast.

Webcam image from Togiak AK, 1715 UTC 6 April 2021, looking north
Webcam image from Togiak AK, 1715 UTC 6 April 2021, looking west