An ice storm consisting of sleet and freezing rain continues to impact portions of the Mid Atlantic today. The National Weather Service’s Storm Prediction Center (SPC) as issued a Mesoscale Discussion about an area of concern involving this storm from Virginia to New Jersey.

“Areas of freezing rain and occasional sleet will impact much of the Mid-Atlantic through early afternoon,” the SPC writes.  “A broad area of ascent/isentropic lift atop a shallow cold airmass continues to contribute to widespread freezing rain at this time. The freezing rain is reportedly mixing with sleet at times across the DC / Baltimore, MD areas, though a transition to more freezing rain should occur in that area over time as models indicate warm advection…”

Precipitation types are based on the thermal profile of the atmosphere from the ground to the tops of clouds where precipitation first falls. When that vertical distance is completely below the freezing mark, snow falls. When there’s a layer of milder air for the precipitation to fall through, precipitation that starts as snow melts but re-freezes into an ice pellet, which hits the ground as sleet.  But when only the surface or the area immediately above is it frozen, the precipitation only re-freezes upon contact, leading to an icy glaze.

 

The SPC says, “Precipitation rates may approach 0.05 inch/hour at times beneath heavier precipitation bands. The general regime should persist through early afternoon, with a general northeastward expansion of the precipitation shield toward Delaware / southern New Jersey and the Philadelphia area over the next couple hours or so.”

Ice is extremely difficult to walk or drive in, especially on untreated surfaces. It is recommended that people stay put until the threat of ice has passed and outdoor conditions improve. It is nearly impossible to get any traction on untreated surfaces and even vehicles with four wheel drive can slide uncontrollably on roads covered with only a light glaze of ice.