Winter Storm Sunday & Monday -An Early Look

While there is still time to view this storm system we wanted to get the word out about it since this system has the potential to create some travel issues along with the potential for power outage issues. Those power outage issues essentially apply to south of the PA /MD border where colder air is going to be trapped in against the mountains at the surface often referred to as Cold Air Damming or CAD..

A brief look at the guidance and we see the GFS is among the warmest of the guidance ..

What we see is high pressure in prime position located to the north of Maine..However..that high pressure begins to slide to the east as the storm system tracks up towards the Lakes region. A secondary does pop along the coast ..however..it never becomes stronger then the primary. As long as the primary tracking to the lakes region remains the strongest it causes a strong push of WAA or Warm Air Advection precipitation across the region. With cold air at the surface thanks to the high pressure ..precipitation starts as snow...with the mid and upper levels warming which we will show on the ECM from 12 Z ...this snow turns over to Ice and eventually to rain. The amount of ICE will depend on how fast or slow the cold air erodes at the surface..

Looking at the ECM we are just going to look at 96 hrs as this is when the heaviest precipitation is across the region.

And the temperatures ..

The ECM is arguably colder then the GFS. Tracking is quite similar with a primary towards the lakes and a secondary developing. However ..the ECM is a higher resolution so it is able to pick up on the CAD sig better then the GFS. So on the ECM you have snow that changes over to ice and a longer duration ice event. Matter of fact in locations such as ABE for example the ECM is all frozen.

The GGEM is similar with what it shows to the ECM..

So the GGEM shows a forecasting nightmare with snow and ice across the region with the only real change over to rain coming in at the end and along the coast. 

We find it best in these type of scenarios to take a blend of the models and factor in climo into the forecast as well along with experience. When you have a track to the west with a stronger primary ...and a secondary that develops...two things usually happen.. One the precipitation arrives earlier then forecasted and secondly.. the WAA is stronger then modeled. 
So we have come up with the following scenario map based on the guidance over the last couple days..

The red shading is where we expect primarily ice to occur and this is where we think that region could end up with power outage problems. 

The next area which is pink is the winter mix zone where we expect precipitation to start off as snow /sleet and change to ZR or freezing rain but as warmer air filters in aloft we think that a changeover to plain rain will occur. Noteable exceptions to this could be NE PA and NW NJ and as far south as the Lehigh Valley where colder air could stay trapped at the surface and keep the precipitation as ice longer. To the north of that we have lighter snows ..mainly because the heaviest precipitation on the ECM looks to go east northeast from the frame that we have posted. And finally along the coast...plain rain..It could start as snow or sleet but a quicker transition to rain should occur there as temperatures are warmer.

We will update this should it become necessary!