No Stratus, No Problems

Another focus of the experiment this summer was looking at high-resolution ceiling and visibility (C&V) model data over the San Francisco airport (SFO).  The airport utilizes a parallel runway system that requires pilots to be able to physically see each other as they make their landing approach.  When low ceilings are present (< 3000ft), the use of parallel approaches is restricted, causing decreased arrival capacity and increased delays. 

The UK Met Office and the ESRL Global Systems Division (GSD) HRRR group both provided high-resolution nests over SFO for this experiment.  The UK Met model nest has 330m grid spacing, with the experimental HRRR nest set at 750m horizontal grid spacing. 

As luck would have it, during the week of the experiment SFO was stratus free!  So instead, participants kept busy by looking at how the various model guidance handled the clouds and other phenomena in the area within the nests.  Focus was also given to Monterrey bay some days, which is just south of SFO.  In addition to the high-resolution nests from the UK Met model and the HRRR, participants also compared with experimental versions of the LAMP and RTMA.

In the above example, the HRRR 750m nest looks to best represent the cloud structure seen in the GOES 17 imagery west of Monterrey bay.  Another example below shows how the HRRR experimental starts to clear out the cloud cover inland of the bay by 15Z, where the experimental RTMA 3-D continues to keep the clouds at 15Z, which is later verified by satellite imagery.

In addition to clouds from the models, participants also looked at winds, the NDFD sky cover and how it compared to the guidance, as well as how RTMA and LAMP interpret observations into their analysis and forecasts.  So even without stratus, valuable information on the various guidance products was gained.

Thankfully, partners at both GSD and the UK Met office have agreed to continue producing the experimental nest data for a few more weeks so that AWC researchers can continue to evaluate the data when stratus is in fact present over SFO.