15 May 2014

Can You Think Like A Forecaster??

Posted by Dan Satterfield


Image from NASA Terra Satellite. Click for larger version.

Image from NASA Terra Satellite. Click for larger version.

Any ideas?? Pretend you’re a forecaster, and you need to make a short term forecast for the area I have delineated. Will you forecast it to stay clear? I’ll post the answer below tomorrow! Fellow meteorologists, you are NOT allowed to guess! (you should immediately know the answer!).


Answer below, but think about it for a few mins. What could have been happening before. What kindof clouds are you seeing north of it and south of the clear slot?


Answer to why the skies are clear in this area:
First of all, What is going on here? A deck of low clouds/ and fog covers the Delmarva Penn. and eastern Va. due to a deep marine layer over the area. The fog/low cloud began burning off around the edges by late aftn.

The clear area was covered by cloud earlier but it’s sunny now. The ground is still cool however, so bubbles of warm air are not yet rising and forming cumulus clouds like you see just south of the clear slot..

Where the skies are clear, the air near the ground is still cooler than the air above it, so it sinks down, once the sun warms the ground, it warms the air and eventually bubbles of buoyant air rise until they cool and condense, forming puffy cumulus clouds, and in some cases a thunderstorm. Like the one on the SW corner of the clear slot.

What temp. is required for those cumulus clouds to form? How warm will it have to be for thunderstorms to develop and how high will the clouds get before they are colder than the air surrounding them? What time of day will those cumulus clouds to the south develop and what height will they be??

These are all answerable if you know the temperature and humidity structure of the atmosphere, but that gets into maths and thermodynamics. Which is why you study physics and calculus to really understand the atmosphere.