Wed 05:43 PM Update — It’s not just snowstorm forecasts that change. It’s just more obvious when a snow forecast has gone astray with a 10:1 ratio making the error more obvious.   

This afternoon’s models have moved the heavy rain south and eastward into N.J.  Here’s the latest NAM-NEST model—

Wed 08:40 AM Update — The models have moved the axis of heavy rain today and tonight  just to the south of the immediate PHL area.  Current RAP has the axis of heavy rain as shown—

The ICON and early morning Canadian models have the axis even further to our south.     So there remains uncertainty about total rainfall  from PHL and north.   Likely closer to 0.8-1.0″ 

from last night…

The models have begun predicting an increasingly heavy rain event for Philadelphia, from Wednesday afternoon into daybreak Thursday. Rain starts about noon on Wednesday and tapers early Thursday morning. The heaviest rain will occur Wednesday evening, towards midnight.

Previous model runs had an axis of heavy rain to the south of our area, through southern Delaware.

Today’s model runs, specifically the the ICON model and the Canadian High Resolution model (HRDPS) have the axis of heavy rain through the Philadelphia area.

(The ICON model did particularly well predicting the heavy rain in advance of  last week’s storm.)

This afternoon’s HRRR and NAM models are moving in the same direction with total rainfall in the 1-1.8″ range for Philadelphia.

The heaviest rain will occur Wednesday evening, towards midnight. There remains some spread as to where the rain axis will be heaviest. The NAM is slightly south of Philadelphia, while the Canadian models are slightly north.

This event is still more than 24 hours away, but the trend towards heavy rain has been consistent.