Day 32: Persistent Fog
(Note: Clicking on the above picture may take awhile to load the image. It is quite large.)
In the image above, areas circled in yellow have clear skies which allows for the satellite’s sensors to “see” the white snow on the ground. Because the satellite can’t distinguish between snow and clouds, the snow on the ground gets displayed on the resulting image. One way a meteorologist can distinguish snow from clouds on a visible satellite image is by looking at the details. Unless a lake or river is completely frozen (which doesn’t happen very often in the south), the lake and river won’t have snow on it. Thus a visible satellite image would show a dark spot in the middle of the bright white snow cover. If you look in the areas circled in yellow, you can easily see how splotchy the white looks and the occasional “crease” that runs through the white. The splotches and creases are the lakes and rivers standing out against the white backdrop of the snow.
Contrast these areas with the areas over central Oklahoma, eastern Kansas, and Nebraska. Notice how smooth the white looks; these are clouds. Lakes and rivers are on the surface, beneath the clouds, so there are no splotches and creases to stand out. Those of you living in Oklahoma, particularly the central part of the state, may be wondering why it has been so foggy lately. After all, weren’t we supposed to warm up and see some sun by now? Ironically, the mechanism by which we were supposed to warm up has produced a lot of low clouds and fog which has hampered our warm up.
A shortwave tough (upper-low) has been slowly moving across the northern United States. As this shortwave trough was moving to the north of Oklahoma, it was trying to draw northward into it the relatively warm, moist air from Texas. In order for the warm, moist air to reach the shortwave trough, it has to move over the cold ground (thanks to the fresh snow cover) in Oklahoma. As it does this, the warm, moist air is cooled by the ground until the air because saturated, and a cloud forms. We call this cloud that forms on the ground “fog”. So, in other words, because warm, moist air is trying to move through Oklahoma, fog continues to be created. The thicker the fog becomes, the less sunlight is able to reach and warm the ground.
For the past few days, the models were accurately predicting a warm up because of this warm, moist air moving through our area. Unfortunately, the models underestimated the amount of snow Oklahoma received last Friday and therefore handled the ground temperatures rather poorly. Because of this, the models weren’t predicting the fog that developed. Because the models weren’t predicting the fog, the models have been forecasting higher temperatures than we’ve been having. As long as we continue to have warm, moist air moving through Oklahoma, and there is snow on the ground, we will continue to have fog. As such, we will continue to to be colder than the models predict. The shortwave trough responsible for drawing the warm, moist air northward should move off to the east by tomorrow and this should lessen the amount of warm, moist air being drawn northward. If this happens, we might see some sun tomorrow afternoon. Unfortunately, a new shortwave trough will begin approaching the area late tomorrow. As this shortwave trough approaches, the warm, moist will once again resume moving northward through Oklahoma – and the cloud/fog should return. Thus, tomorrow afternoon will be our best chance for sun over the next few days…or until a majority of the snow melts.
The NWS is forecasting a high of 45 in Norman, OK tomorrow, along with some sunshine. If we don’t see the sunshine, I’m willing to bet we will remain in the 30s. By this time tomorrow night, we’ll know what happened…
