No sign of the 40's Monday with the dense fog

Ask any meteorologist what frustrates them the most with a forecast and I imagine many will say having different scenarios that could bust a forecast.  A good example of that was the fog Monday.

Fog and cloud cover can disrupt a forecast very easily.  Clouds clear earlier than thought, temperatures warm.  They don't clear fast enough, temperatures stay cool.  For us, low level moisture under a strong inversion was what kept the fog around through the afternoon and held high temperatures in the 30's all day!  Well below my forecast high of 43 degrees.

But you may have noticed that it's been pretty foggy the past several nights.  And there's a good reason for that.  Fog is a little more common during the cooler months because the days are shorter and the nights are longer.  The sun angle is lower and we just can't warm the lowest level of the atmosphere enough to 'mix' it out and get rid of the fog.  We also often see fog with a warm up following a recent snow.  But that hasn't been our case lately. 

Temperatures above the surface of the earth have been warming, but not as fast at the surface.  This creates what we call an 'inversion'.  Think of it like a lid on the atmosphere.  Above that lid, the air is dry but below the lid the is a lot of moisture.  When the lid is taken off, the air can mix.  Drier air is pulled down towards the surface, getting rid of the fog.  As we get closer and closer to the winter solstice, the shortest day of the year, there isn't enough daylight to fully warm the atmosphere.  And that's what we need to break the inversion.

Dense fog is redeveloping again Monday night where the visibility has already fallen to half a mile in a few spots.  Take it slow Tuesday morning.  An increasing wind and slightly drier air should help erode the fog a little faster than Monday.  But if it doesn't, then highs will stay in the upper 30's - just like Monday.