Snow analysis – 550 pm

As we mentioned earlier, this storm was stronger than the models anticipated, just like the last one.  A weak upper-level trough is located over Arkansas, and as air that is slowed down in that trough speeds up, divergence will occur aloft, pulling air up from below, creating upward motion and precipitation.  Also, we are in the right entrance region of an upper level jet maximum (see below).  As air tries to adjust to the higher pressure gradient in the jet, it initially flows toward low pressure (farther north).  This causes upper divergence in the right entrance region, and more upward motion.  So, we have two dynamic processes bringing us upward motion and precipitation over the next 5-8 hours.

As the main area of vertical motion moves over Alabama during the evening hours, expect precipitation to get heavier from west to east.  The temperature fell from 47 to 37 degrees in 2 hours at BHM, only due to some sleet and snow falling.  The dewpoint is still 24, so the wetbulb is now around freezing, and temperatures in the BHM area will fall to freezing once the heavier snow moves in over the next 2 hours.  Bridges could become icy very quickly, so any travel in the BHM area should be done now.  Travel is already discouraged in NW Alabama.

With the heavy amounts coming from some spots in Arkansas and Mississippi (some over 12″ in AR, some over 6″ in MS), there may be some convection involved, so snowfall amounts will vary greatly.  The averages James posted earlier are correct, it’s just that one spot may get 2″ while another 5 miles away gets 3″.

Category: Winter Weather