Thursday, March 28, 2013

Signs of Spring

Another beautiful morning is yet again finally showing a sign that spring is going to show up after all.  Here is how this morning looked a little before 9 AM.  Blue skies and sunshine!

Now for some forecasting fun.  Did you notice the puffy looking cumulus clouds develop Wednesday afternoon?  That's likely to happen again and here is why.  The sun angle this time of the year is much greater and stronger.  This provides more energy to the lower atmosphere that will eventually fuel spring storms and summer heat.  Here is a diagram of the atmosphere later this afternoon in the form of something called a Skew-T model.  I'll point out two things, first a very steep lower level lapse rate that will allow air to freely rise this afternoon and secondly available lower level moisture. 

I also look closely at what is known as the Convective Temperature (ConvT).  This is the surface temperature that has to be reached for pure convection, or rising air to occur.  At this point, the sunny start to the morning will quickly be dotted with "fluffy" looking cumulus clouds developing.  This explains how a morning (stable atmosphere) can start off clear and sunny only to be followed by clouds that seem to develop out of the blue.  It is important to note there must be sufficient lower level moisture for the clouds to actually develop.  Later this season, this very process is the same one that often leads to afternoon showers or scattered thunderstorms.