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Tule fog in California

By Scott Bachmeier •


The tweet shown above was issued by the NWS forecast office in Hanford, California — using an image of the GOES-15 Low Instrument Flight Rules (LIFR) Probability, a component of the GOES-R Fog/low stratus suite of products — to illustrate where areas of dense Tule fog persisted into the morning hours on 31 January 2017.

AWIPS II images of the GOES-15 Marginal Visual Flight Rules (MVFR) product (below) showed the increase in areal coverage of Tule fog beginning at 0600 UTC (10 pm local time on 30 January); the fog eventually dissipated by 2030 UTC (12:30 pm local time) on 31 January. Note that Lemoore Naval Air Station (identifier KNLC) reported freezing fog at 14 UTC (their surface air temperature had dropped to 31º F that hour). In addition, some of the higher MVFR Probability values were seen farther to the north, along the Interstate 5 corridor between Stockton (KSCK) and Sacramento (KSAC) — numerous traffic accidents and school delays were attributed to the Tule fog on this day.

GOES-15 MVFR Probability product [click to play animation]

GOES-15 MVFR Probability product [click to play animation]

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GOES-15 MVFR Probability and Aqua MODIS Infrared Brightness Temperature Difference (BTD) products [click to enlarge]

GOES-15 MVFR Probability and Aqua MODIS Infrared Brightness Temperature Difference (BTD) products [click to enlarge]

Legacy infrared Brightness Temperature Difference (BTD) products are limited in their ability to accurately detect fog/low stratus features if high-level cirrus clouds are present overhead. This is demonstrated in comparisons of GOES-15 MVFR Probability and BTD products from Aqua MODIS (above) and Suomi NPP VIIRS (below). Again, note the Interstate-5 corridor between Stockton and Sacramento, where the extent of the fog was not well-depicted on the BTD images (even using high spatial resolution polar-orbiter MODIS and VIIRS data).

GOES-15 MVFR Probability and Suomi NPP VIIRS infrared Brightness Temperature Difference (BTD) products [click to enlarge]

GOES-15 MVFR Probability and Suomi NPP VIIRS infrared Brightness Temperature Difference (BTD) products [click to enlarge]

Daylight images of GOES-15 Visible (0.63 µm) data (below) showed the dissipation of the Tule fog during the 1600-2200 UTC (8 am – 2 pm local time) period. The brighter white snow pack in the higher elevations of the Sierra Nevada was also very evident in the upper right portion of the satellite scene.

GOES-15 Visible (0.63 µm) images [click to play animation]

GOES-15 Visible (0.63 µm) images [click to play animation]

One ingredient contributing to this Tule fog event was moist soil, from precipitation (as much as 150-200% of normal at some locations in the Central Valley) that had been received during the previous 14-day period (below).

Total liquid precipitation and Percent of normal precipitation for the 14-day period ending on 31 January 2017 [click to enlarge]

Total liquid precipitation and Percent of normal precipitation for the 14-day period ending on 31 January 2017 [click to enlarge]

Categories: Aqua, Fog detection, GOES-15, GOES-R, MODIS, Suomi NPP, VIIRS