Smog is simply fog with an excess of particulates, and it happens when fog stays in town too long. You should start worrying if you have travel plans or - more ominously - when fog becomes smog. They call it a "nuisance" more than anything else. Should I be worried? It's nearly Halloween, and the climate feels like it's coming apart at the seams, and now all this creepy fog.īefore you hyperventilate, remember that 1) localized weather patterns don't necessarily indicate shifting climate patterns, 2) October is always a great time for fog-spotting, and 3) even climate-concerned scientists we spoke with aren't worried about it. But even then, fog doesn't always appear with temperature shifts.Ĥ. To make predictions, forecasters will monitor the difference between the current temperature and the dew point, which allows for accuracy "certainly within a degree," Bond says. are good at getting large-scale pressure patterns, and things like winds over large areas, but not really the local effects." "Right now the computer models that we have. "If we had continuous measuring every 100 feet up we could probably do a lot better," he says.
Weather instruments are essentially non-existent in the troposphere (the section of air between the ground and seven miles above us), which makes evaluating weather near the surface difficult. How meteorologists handle that in weather modeling is part of the problem, too, Bond says. and in the atmosphere column above the ground, not just at the surface." It turns out you need just a little bit of wind. "The problem with fog forecasting is that subtle details can matter," Bond says. "It’s a very tricky problem. Modern meteorology can help you gauge in general if you need to ride bikes with extra caution tomorrow morning, but it can't tell you exactly what time or where. Fog is a special beast because the humidity that helps precipitate it can be highly localized, and fog appears and dissipates very quickly under mercurial, Goldilocks-exact conditions. "This time of year, before storms start rolling in with depressing regularity, we have a lot of calm, settled weather conditions like we’ve had the last few days and things come together, and suddenly it turns foggy."ģ. Why can't you just tell me when fog will appear and dissappear? Which brings us to seasonal fog: Crisp, calm, cool fall air enhances fog conditions, Bond says. Once shed from the air, homeless droplets condense around particulates and become fog, aka Ground Clouds.īecause warm air is less dense than cold air, the layers of fog “invert” below the moisture-free warm air layer and stay trapped at ground level until the temperature between layers evens out. When the sky is clear and the temperature drops below the dew point (the temperature at which water vapor condenses into liquid), moisture can get too heavy for cold air molecules to contain. There are a few types of fog, but all of them depend on a phenomenon known as a weather inversion.
If you forgot your elementary meteorology, basically it's "cloud formed at the surface," says Burg.
To understand why October weather patterns really lend themselves to our current murky conditions, it's good to first get a handle on what fog is. "But usually, we’d have at least a few weak storms come in and clear things things up." "We have had some months with much more settled weather than usual in the past few years, that happens from time to time anyway," says Washington State Climatologist Nick Bond. Right now, we're clocking seven days of dense fog, and 16 total days with at least some fog. (The October record is eight straight days.)īut that historical average doesn't speak to streaks, which makes the recent spate of fog weird, to say the least. In perspective, the streak can be disconcerting. October sees more densely foggy days on average (seven) than any other month in the Pacific Northwest, says Johnny Burg, a Seattle-based meteorologist with the National Weather Service. The citizen journalists of Seattle social media were right to marvel at the weather. While climatologists I spoke with told me that the five-day streak of heavy fog (defined as 'fog impairing visibility to a quarter-mile or less') isn't unprecedented, it is unusual. Is this normal for Seattle? It doesn't feel normal.
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