The changeover to sleet, freezing rain and rain has occurred in PHL and the immediate surrounding suburbs and this precipitation type will continue fairly heavy until about 1-2 PM today.  What you see is what you’ll get….If you haven’t received heavy snow, you’re not going to.  

Winds will pick up with temperatures at or below freezing early, but rising during the morning. Slippery conditions still exist, but roadways may be less impacted than usual with solar insolation through clouds reducing icing on dark asphalt as we approach noontime.  A brief changeover to  snow at the end of the storm won’t add much accumulation.

When the TV people try to explain what happened to their 10-12 inch forecasts from last night, don’t believe them.  The “track of the storm” didn’t change.  They simply didn’t interpret the data properly.

Ok , I’m still up.   It’s 11:45 and the GFS has almost identical QPF as the NAM and a bit colder.  It’s looking like at least12 inches  in PHL and  immediate surrounding suburbs north and west.

The latest NAM data has become available and it has reverted back to a somewhat warmer, but more intense storm.

Latest QPF value has increased to 1.30 inches water.

For the Philadelphia area and immediate suburbs, it shows about 6-8 inches by daybreak, BUT it shows that temperatures in the upper atmosphere warm up so that a several hour mix of sleet and freezing rain is possible in PHL and immediate suburbs, from 6 am to 9 am before a return to all snow, ending about 1-2 pm.

The GFS model data won’t be available tonight until after my bedtime  🙂

Still too early to try to pin down storm totals. I’ll be updating tomorrow, so check back.

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.