Sunday, November 27, 2016

Stuck in a Fog

Anyone else feel like they were in a fog Sunday afternoon?  If so, it could have been because it was so foggy outside most of the day.  At times during the afternoon, visibility dropped under a mile prompting a Dense Fog Advisory for some.  The fog also had an impact on our high temperatures leaving most of us in the 30's.  Temperatures will slowly rise through the overnight as rain from Iowa increases.

The image to the left is a 'snap shot' of the atmosphere Sunday morning from the Quad Cities National Weather Service.  It's called a Skew-T diagram and shows the temperature, dew point, wind speed and direction from the surface up to where the jet stream is located.  Every morning and evening National Weather Service offices launch weather balloons to help gather information of the atmosphere above our heads.  This information is then fed into our weather computer models that help meteorologists predict the weather.

The red line is the air temperature and the green line is the dew point temperature.  When the two lines are close to each other, the atmosphere is pretty saturated.  When the lines are apart the surrounding air is dry.  On the bottom of the graph (the X axis) are temperatures in degrees Celsius and on the left ( the Y axis) are heights.  Notice what happens to the temperature as it goes further up into the warms!  This is called an inversion.  Inversions occur when the temperature aloft warms faster than the surface temperature.  This happens quite often in the summer and spring, and can limit thunderstorm growth.  In the fall and winter an inversion can keep fog stuck at the surface.  The inversion this morning trapped moisture near the surface of the earth.  And since the sun angle is reaching it's lowest point as we approach the winter solstice, the air was unable to mix keeping the fog around longer.

Incoming rain from the south and west will actually allow some of the fog to dissipate this evening, which will help with visibility.

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