A fast moving disturbance will bring rain about daybreak on Saturday.  Much of the morning will be wet, but the rain stops early afternoon and clearing is expected by mid afternoon .  High 49.

Christmas Eve will be dry and clear with lows in the mid 30s.

A zonal flow jet stream will keep temperatures above average for Sunday, Christmas Day and the next several days after. Sunday will be sunny and mild. High 51.

Look for things to become much colder and stormier next weekend, around New Year’s Eve.

Latest NAM FOUS data just became available. This will be mostly an ice storm rather than a snow event.

Temperatures in the upper atmosphere become too warm for snow before daybreak.  Light snow starts after midnight but changes to sleet and freezing rain by daybreak in PHL.

Heavy freezing rain, likely with temperatures remaining near or below freezing at the surface, continues until late morning with a significant “cold air damming” effect.  A significant ice storm is possible with heavy precipitation causing dynamic cooling, prolonging the freezing rain event.  

Difficult travel during much of the morning, especially north and west of the city.  Temperatures rise above freezing by the late morning or early afternoon as the precipitation tapers off.

Friday 4 PM Update: Latest NAM data maintains ‘cold air damming ‘ in the immediate PHL area.  A more significant ice storm is possible before the changeover to rain.  The next NAM data available about 9:40 PM and I’ll update around that time.

Here’s the latest trends for tomorrow morning’s winter weather–

The trend has been for temperatures in the upper atmosphere and the surface to warm a bit faster.  The latest NAM shows temperatures near the surface to be above freezing by 7 AM in Philadelphia.

So, for Philadelphia, it’s looking like less snow, that quickly turns to sleet and freezing rain before daybreak. It will probably be all rain by daybreak in the city, so any small accumulation of sleet and snow  will be slush early.

Areas to the immediate north and west will get less snow and more freezing rain. Significant icy conditions possible for several hours  after daybreak before changing to all rain by mid to late morning.

The rain will be heavy in the morning, tapering and ending early afternoon.

I’ll update about 9:40 this evening, after this evening’s NAM FOUS data becomes available.

As mentioned last week, the models continue to advertise a warm up around X-mas