A Move to the Middle. Monday Storm Picture Becoming More Clear

As expected, the operational models are trending further south with the precipitation shield for Monday's event. You'll remember that yesterday, I posted a discussion on how we can use ensemble models to predict an inevitable squeezing of the heaviest snowfall to the south of New England.

In that discussion, I noted the relatively high uncertainty on two main atmospheric features, the position of polar vortex's southern edge and the strength of the upper level storm. Less than 24 hours later, the ensemble average is coming into better agreement, with greater than 70% agreeing on a greater intrusion of the polar vortex, which results in cold and dry air squeezing the storm southward.

The image below represents a "relative measure of predictability" for the forecasted position of the PV on Sunday night. The darker orange shading, highlighted by the circle, implies that 70% of the individual ensemble members agree on the position of the PV.  70% is certainly not perfect, but its a high enough value at 48 hours out to place confidence in a southward trend.

Interestingly enough, we can still see a high uncertainty in the strength and placement of the upper level storm, which suggests low confidence in the actual surface storm track. This uncertainty is of more importance to our friends in the mid-Atlantic, as New England's fate in this storm has all but been decided.

Watch for forecasted snowfall totals around these parts to continue to fall tonight.