The Bay Area midsummer is heralded by the arrival of a monolithic, tempestuous atmostpheric phenomenon known colloquially as 'Karl the Fog'. It is massive and beautiful, charging up San Francisco's western slopes and through the Golden Gate in the late morning, erupting vertically into mist from Twin Peaks in the afternoon, and on hotter days cascading down the City's eastern slopes late in the day. From the east bay, it can occlude the city entirely, giving the impression that there is no San Francisco at all; from the inverted perspective of the City, there is no outside.
This phenomenon is caused by the geography and weather patterns of the area. California's interior forms a sprawling and continuous valley in which summer temperatures regularly climb into the triple-digits. As this hot air rises, it acts to draw new air in to replace it, from the ocean and through the mile-wide Golden Gate. It is the condensation of this cooler water that gives shape to Karl. Given this relatively simple model for how Karl forms, it may be possible to forecast the fog (thus, Karlcast) using weather data from the Central Valley. This data could be combined with historical fog data, for example from the geostationary satellite GOES-16, to uncover the relationship between heat in the central valley and the movement and growth of Karl. To begin to approach this problem, I've written some python to collect real-time and historical weather data from the Darksky API. This code is available as a jupyter notebook on my github. Below are some visualizations using bokeh of the weather data that I've collected. The first plot is of the last 120 days of hourly temperature and humidity data from Stockton, the endpoint of the SF Bay system. The second plot shows the relationship between temperature and humidity during this time. As could be expected, these are negatively-correlated: more humid days are cooler.
3 Comments
5/14/2019 08:34:10 pm
I would like to commend the author for using the scattered graph. This graph is usually used for this kind of information. Based on what I read, this fog is really a phenomena. It will actually cover or block the entire San Francisco! Thankfully, your blog is very informative, you even included graphs. The readers, especially those who are from San Francisco, will definitely understand this well. Instead of panicking, they will prepare for this phenomena. Keep safe everyone!
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5/16/2019 02:00:12 am
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3/10/2020 01:11:44 am
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