Here we go again, with the same model dilemma. The Americans might have won the revolutionary war, but when it comes to the battle of the weather models, the Europeans seem to still have the edge.
This morning I am looking at a European model which brings plowable, (over 2 inches) of snow to areas from about metro Boston southward later Saturday and overnight. The westward extent of the snow would put it roughly at Route 495. On the other side of the coin, the American model has this same storm, but keeps it further out to sea bringing just a chance of some snow to eastern Massachusetts with metro Boston seeing just a few flurries.
The two images below show the forecast position of the storm at 7PM Saturday. The first is the American model, the second the European. Notice how much closer the storm (L) is on the Euro model. The storm is quite large and has the potential to bring lots of precipitation and wind if it comes close enough. A difference of 75 to 100 miles would make an enormous difference in my forecast.
I’ll be updating the forecast here and on Twitter @growingwisdom. Please follow me there for more details.
What’s really disconcerting about this scenario isn’t so much the difference between the models, we’ve seen this before, it’s the fact, in spite of a major upgrade to the GFS, it’s still the case. Now, it may turn out that the Euro positions the storm further out to sea with each successive rendition aka “run” of the model. We will get a new version of each later today and early tomorrow. Perhaps, in the end, the GFS will come out on top.
However, there are other factors, which at least today, makes it more likely the scenario portrayed by the Euro is going to be closer to the actual solution on Saturday.
One of these factors is the ensemble models which also point towards a snowier solution Saturday night. Think of ensembles as the Cooks Illustrated of weather. If you’ve never heard of the magazine, they basically take a recipe and tweak how they put it together. The scientists at Cooks vary things like ingredient order, cooking time and even types of baking pans. In the weather world, ensemble forecasting takes the same model and then runs it with slightly different starting conditions. If you end up with the same result each time, your confidence grows in the forecast.
The ensemble mean forecast of the European model is also pointing towards accumulating snow later Saturday and overnight. We have the same tool for the GFS. The image below shows many of the GFS ensemble forecasts. Remember, this is the same model, just compared essentially with itself. Most what you have likely seen on a television weather forecast shows different models compared with one another, not the ensembles.
Ensemble forecasting is the next generation of forecasting and will only become more prominent over the coming years. As we add more and more computing power we will be able to get an even better picture of the atmosphere and thus a more accurate forecast.
Today is of course only Wednesday and we are talking about a forecast for Saturday into Sunday, 3-4 days in the future. The accuracy of the forecast becomes much greater inside 60 hours, when some of the other models can also work on the solution to where this storm will go.
Looking even further out in time another storm will threaten the area Tuesday. All the prominent longer range models are forecasting another storm to move up along the coastline with the track and intensity the critical pieces to what we see.
It does appear more than likely the days of bare ground are about to come to an end.