Daily Archives: September 16, 2015

Cloud Thickness and Dissipation Time


Dissipation time as a function of GOES-R Cloud Thickness

The chart above shows the relationship between the last pre-sunrise GOES-R Cloud Thickness product and Fog Dissipation time.  Observations of the last pre-sunrise GOES-R Cloud Thickness (developed from an empirical relationship between 3.9 µm emissivity and sodar-observed cloud thickness of the west coast of the USA) can be related to the dissipation time relative to the last observation of Cloud Thickness.  The scatterplot was developed using data mostly over the southeastern part of the USA, but also over the Great Plains.  However, it does have value in other geographic regions too, as shown below.


GOES-R IFR Probabilities and GOES-R Cloud Thickness, 1100 UTC 16 September 2015 (Click to enlarge)

On 16 September, river fog developed over the Ohio River and its tributaries in Ohio, West Virginia and Pennsylvania. The toggle above shows GOES-R IFR Probability and GOES-R Cloud Thickness fields at 1100 UTC on 16 September.  This was the last pre-sunrise GOES-R Cloud Thickness over West Virginia (Indeed, the leading edge of twilight — where GOES-R Cloud Thickness is not computed — is apparent at the extreme eastern edge of the image, from Virginia up into central Pennsylvania). The GOES-R Cloud Thickness fields show largest values — around 800 feet — in/around the Ohio River between West Virginia and Ohio. The chart above suggest rapid dissipation. The best fit line (blue) suggests dissipation in about an hour, although there is considerable spread to the values, from 30 minutes up to almost 2-1/2 hours.

Almost two hours later (1245 UTC), fog is still present in isolated patches near the river, and GOES-R IFR Probability fields are suggesting fog is still present as well.  The horizontal extent of the GOES-R IFR Probability field is greatly reduced because visible imagery can be used after sunrise to screen out clear regions (Cloud-clearing in the algorithm is more effective).  By 1415 UTC (bottom), three hours after the GOES-R Cloud Thickness imagery above, all fog has evaporated.


GOES-R IFR Probabilities and GOES-13 Visible Imagery (with a low-light enhancement), 1245 UTC 16 September 2015 (Click to enlarge)


GOES-13 Visible Imagery, 1415 UTC 16 September 2015 (Click to enlarge)