Tuesday, August 15, 2017

All day fog event in SFO - model solutions and satellite verification

It was an interesting day at the SFO desk to start off the second week of the Summer Experiment within the AWT. A trough moving across the West Coast made forecasting any clearing times even more of a challenge than usual, pitting the mesoscale fog climate with synoptic scale forcing.

The HRRR had ceilings clearing out by 16Z, while the GLAMP held onto them until at least 21Z. The UKMET kept ceilings around even later, through 23Z, and only suggested a partial clearing, if at all.
1400 UTC run, 2200 UTC forecast of HRRR ceiling height (top left), GLAMP ceiling height (top right), and UKMET cloud cover (bottom).
Satellite observations around the time of the 1400 UTC run, however, suggested that ceilings were not clearing quickly at all, meaning the HRRR forecast wouldn't be accurate and possibly ruling out the GLAMP forecast as well. In fact, the high spatial and temporal resolution of GOES-16 showed some of the fog actually building back in by 1600 UTC.
20170814 1437 - 1637 UTC GOES-16 high resolution imagery over SFO with winds, ceilings, and ASDI flight tracking overlaid
20170814 1437 and 1537 UTC GOES-16 visible imagery with winds, ceilings, and ASDI flight tracking overlaid. The yellow dashed line and orange arrows indicate where the layer of stratus was receding, while the green circles shows an area building back in behind.
GOES-16 imagery has been heavily relied upon during the experiment for both situational awareness and model verification, providing a 5-minute temporal refresh along with much better resolution than the legacy GOES-15. Check out GOES-15 imagery at the same time below:

20170814 1430 - 1630 UTC GOES-15 imagery with winds and ceilings overlaid
Compared to GOES-16, GOES-15 has only a 15 minute refresh. That along with the lower resolution did not reveal the detail in the stratus layer as it did in GOES-16. Additionally, participants were able to see the movement of stratus building back in much earlier than they did in GOES-15.

In the end, ceilings never really cleared out, though the UKMET high resolution model did have the closet solution to reality.

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