Tuesday: Death Blow or Hype?

With the ECMWF & GFS models continuing to forecast a significant coastal storm affecting the northeast Tuesday into Wednesday, rumors will no doubt be running rampant into the weekend. Here is what we know and what we don't know as of now (2:30 PM Friday).

1) With the medium range models remaining consistent in forecasting a significant storm to develop Tuesday, it is likely that this is going to happen. As of today, that storm does not exist.

2) As is always the case, the specific amount and type of precipitation that will fall where you are will depend on the exact track of the storm after it begins to form. It is too early too be confident about that yet.

3) These models are run as "ensembles". The "operational run" is the one you usually see displayed online or on TV. To gauge likelyhood, the model's starting conditions are changed slightly and it is run again. This is done 21 times for the GFS and 50 times for the Euro. If you keep getting the same solution after tweaking the starting conditions a bunch of times you will have a high level of confidence in the forecast. If every slight change results in a significantly different final solution, you will have little confidence in the forecast (operational run). In practice the results/confidence level are usually somewhere in-between. The operational run of the latest GFS and a number of its ensemble members bring mixed precipitation and a dry slot into our region during the storm (after an initial burst of snow). This would cut down on potential accumulations if it verified. You can view the GFS ensemble members here. If you look closely, you will see a red, dotted line labeled "540". That is very roughly where the snow/rain line would be.

4) The latest operational run of the European Model (ECMWF) pummels our region with a potentially historic type snow storm (can you say 2 feet plus in some places)? The image above is the Euro's current forecast for 7 PM Tuesday. Could this happen? Yes? Would I bet money that it would happen right now? Only if you gave me pretty good odds.

5) What's my best guess at this time? I'd expect shovelable snow and wind Tuesday that may or may not change to mixed precipitation and/or rain in parts of the region. If it doesn't amounts could be impressive. We will probably see some lingering light snow or snow showers into Wednesday with below average temperatures most of next week.