What I have done here is laid side by side the last 3 runs of the GFS model with regards to total precip forecast from the next weather system that approaches on Tuesday. We are going to get showers and thunderstorms from this but we mentioned in yesterday’s piece the fact that models have underperformed in this regard by showing us a substantial rain only to back off considerably as reality approaches. Indeed this seems to be the case with the overnight model runs which have done just that. The map above is from Saturday’s morning run.





Now notice what has happened in the last 2 runs. The Saturday afternoon run increased the rainfall amounts to put a large part of our area in the 1-2 inch rain only to have the late Saturday night/early Sunday run cut the amounts in half just about everywhere! Looking at the dynamics it seems that the changes are subtle.

gfs66 gfs72


The major difference here is subtle but substantial in that the front on the new models is a little faster and perhaps a little less deep. More energy seems to be focused around the deeper low in the Saint Lawrence Valley then on the front itself. It could be a timing issue in that a faster front by even a couple of hours can make a huge difference regarding how much energy is available due to daytime heating. Or it could be a simple matter of the dynamics just being a shade less dynamic! I still think the potential is here for a good 1 to 2 inch rainfall as it seems everyone is going to get something out of this. Lawns are browning everywhere and some areas are seeing rainfall deficits of 6 inches or more. Even if we wind up with the 1 to 2 inches forecast we are going to need 3 of these kind of fronts over the next few weeks to pull even. Guess what? This might be the last one like this for a little while as we are seeing another pattern shift for the second half of August. Joestradamus will cover that later today.

Meanwhile today and Monday look good especially today. No rain and plenty of sunshine for Today and a mix of sunshine and arriving clouds on Monday. No rain is forecast for Monday as thunderstorms will hold off probably until late Monday night in most areas though in Northeast Pennsylvania downpours will probably arrive sooner than that…probably the chance for stray downpours Monday evening and then heavier ones after midnight. The coast will see the bulk of this on Tuesday during the day.