Trapped under cloudy skies, central Indiana in the grips of a "temperature inversion"

Weather Blog
Data pix.

There’s been an awful lot of clouds around this month and we continue a stretch of sun-free days this upcoming week.  For the past two days the clouds have been trapped in place by what meteorologist call a temperature inversion.

These occur more often in the cool weather months and refers to a reversal in how temperatures are typically distributed, warmer at the surface while cooling with height.  The setup is for temperatures to remain cool through the first 3000 feet then warm through the cloud layer at or about 5000 feet above the surface.  For example, today’s high of 34° was recorded while 5000 feet up (less than a mile) the temperatures were rising.

When an inversion develops, moist air is trapped at the surface with little or no wind, cancelling any attempts to mix with drier air thus breaking the overcast and warming up.  The warming layer aloft traps the clouds and these clouds are reluctant to go.

Another result of the inversion is the haze and fog.  Tiny water droplets remain suspended and with relative humidity’s nearing 100%, visibility has been reduced especially in the nighttime hours.

The persistent cloud cover has been noted here with only 21% possible sunshine this month, the normal is 40%.  This is the cloudiest January in three years.

So what does it take to break the inversion?  An increase in winds associated with a front or approaching storm system will get those stronger winds aloft to mix down and break the lower clouds thus “mixing out” the inversion.  After the passing front or storm all layers of the atmosphere are drying out with brightening skies to follow.  Stay tuned and be patient, Sunshine has been in short supply as of late.

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