The models have been remarkably consistent predicting the nor’easter that’s expected to develop over the Delmarva coastline this coming Monday night into Tuesday.

As mentioned, an upper air vorticity moving in from the northwest in the jet stream flow will interact with an inverted coastal front along the southeastern states late Monday and spawn an intense nor’easter over the Delmarva area  Monday night into Tuesday.

All global models, including the ECMWF (European), the CMC (Canadian), the NAVGEM (Navy) and the GFS (US Global Forecast System) have been onboard with this development.

What is uncertain is the exact position of the storm early Tuesday, with a 25-50 mile discrepancy between the NJ coastline and the Delaware Bay resulting in either a major snowstorm  or a snowfall that mixes with rain for Philadelphia.  (Areas to the north and west are expected to have all snow at this time.)

As of the current time, it appears that snow will start Monday evening and become heavy after midnight, giving us a heavy snowfall by  daybreak Tuesday.  The snow will either continue or mix with rain in Philadelphia.   Last night’s GFS model had 18 inches of snow for PHL.

If this verifies, it would be the first time this season that an extended range forecast didn’t self-destruct a day or two before the event.   So despite the overwhelming forecast evidence, it’s too soon to be definite about this.