(3:15PM) A developing late season winter storm continues to affect the southern half of the state this afternoon, with a mix of rain and accumulating snow.
As of mid-afternoon, snow has ended across Western Illinois. Further south, snow continues to fall across the St. Louis metro area, with moderate to heavy snow at times. Across the rest of Southern Illinois, rain is slowly transitioning to snow as dynamic cooling occurs. Periods of moderate to heavy snow will be likely once the transition occurs for most areas. Precip will slowly come to an end later in the evening, with a complete exit of the state by midnight.
This is a rapidly evolving situation. As is always the case with late season winter storms and dynamic cooling situations with surface temperatures at or above freezing, heavier precipitation rates are needed for the transition to snow to occur and for snow to accumulate. Snowfall accumulations that have occurred near the Illinois/Missouri border, in Eastern Missouri and into the St. Louis metro area have already exceeded what was shown on most model guidance, with an axis of 2-5″ of snow having fallen. With that said, we are bumping final expected snowfall accumulation amounts given a combination of model guidance and observed conditions at this time. An axis of final snowfall amounts of 2-5″ is likely across a good portion on Southern Illinois, with locally higher amounts in areas within the orange dotted lines on the TAM snowfall graphic below.