Greetings! A real tricky forecast continues for many areas as we sit 3-4 days prior to the window of interest for a developing East Coast Low this weekend.
What we know: Someone on the east coast is going to see a decent snow storm from this. The area of highest confidence in that is within a zone from northern Virginia up into the Washington DC metroplex.
Other areas in play: Anywhere from the Carolinas to Southern New England should monitor the progress of this storm.
In situations with high uncertainty, ensemble forecasting is key. One of the major questions for impacts up here in Connecticut is the northward extent of the precipitation shield. Two primary factors impact that: the eventual (1) track and (2) strength of the developing storm. A weaker storm further south would have a more condensed, lighter, and perhaps mostly offshore precipitation field. A stronger storm further north would have a more expansive precipitation field with more widespread impacts.
A closer look at The GEFS has shown mixed signals, –the probability of 1″ of QPF getting into coastal SNE hovers around 30%
The evolution of the upper level low has a lot to say about the above. Its position in the operational GFS has been stronger and more north, while the ECMWF has been weaker and further south. Confidence in a particular solution will become more clear over the next 24 hours as the associated wave of energy moves into the west coast tonight. This does look like a major snowstorm in the Mid Atlantic region with a still existing potential for it to be more widespread into Southern New England. Stay tuned.