Snow Potential In Jacksonville

A unique forecasting challenge is coming up this week for the potential of winter precipitation on the First Coast.

An unusual long lasting Arctic outbreak of air is holding over Jacksonville all week. A series of freezes is in the forecast.  These charts from Sunday represent the potental for sleet over southern Georgia Friday morning. The top two maps show temperatures and wind at 850 mb which is about 5000 ft. The first map is 1 am with the freezing isotherm on the state line. The second map shows the freezing level moving south by noon over Orlando. This is the new cold air pushing south behind Friday's front. If this were earlier it would be certain to snow in Jacksonville.  But the warmer air in advance of a cold front will cause the boundary layer or air within 3000' of the ground to be warmer earlier in the morning.  The next map is 7 am with the freezing isotherm on the state line.

The bottom two charts are a key tool for determining the type of precipitation in the winter.  Thickness charts like these represent the depth of each layer in the atmosphere.  Colder air makes the air  contract and is less thick.  Warmer air increases thickness.  Snow is a good bet if the last blue line is over your forecast location. This is the 540 thickness line. You can see it is almost over Tampa early in the week on Monday night at 1 am.  The green represents rain.  It is cold and dry in Jacksonville during this time period and temperatures are in the low to mid 20s at the surface. 

But by Thursday night when the rain arrives, the thickness increases over Jacksonville.  This is why the forecast is tricky.  This GFS forecast model run indicates the green over coastal Georgia would be snow.  Sleet is more likely due to possible warmer air just above the ground in northeast Florida.  The accuracy of computer models in pinpointing exact temperatures in the vertical layers of the atmosphere is a challenge that can bust a forecast. 

Super strong cold advection which is the cold air moving south is shown by the parallel black pressure lines (isobars) at right angles perpendicular to the blue thickness dashed lines.  This means cold and windy conditions Friday as the reinforcing new blast of arctic air keeps freezes going into the weekend.