[su_box title=”Weather Update Fri 11 PM” box_color=”#defcdc” title_color=”#000000″]Tonight’s NAM and WRF models have scattered thunderstorms as early as 3 pm Saturday. In the immediate Philadelphia area, it seems that the most activity and the strongest dynamics will be between 5-8 pm.

Sunday may have significant cloudiness, as mentioned below.[/su_box]

Today’s thunderstorms did materialize and dissipated as expected about 8 PM.

The heat will be with us through Saturday. A front will move through on Saturday, the result of an upper low pressure system dropping down over the New England coastline.

There are significant differences between the GFS global model and the mesoscale models regarding showers and thunderstorms Saturday afternoon. The GFS has the showers remaining in the  northwest suburbs and dissipating before reaching the immediate Philadelphia area.

The mesoscale models (NAM, WRF and the HIREF ensemble) have showers and thunderstorms moving through Philadelphia late Saturday afternoon and evening.

The mesoscale WRF and HIREF models did well today and I’m leaning towards their forecast, but the discrepancy between the GFS and these models can’t be overlooked.  So confidence in the chance of showers in Philadelphia Saturday is below average.

Most models are forecasting high temperatures Saturday 92-94 with high clouds and increasing lower level cloudiness during the afternoon. It will be humid. If the WRF and HIREF are correct, showers are likely far northwest suburbs mid afternoon and they move through Philadelphia between 4-8 PM.

Sunday will have a mix of sun and some clouds. The upper low cyclonic flow may result in more clouds than currently forecast. It will be breezy. High temps 86.

I’ll update later this evening after 11pm when the new model runs come in.

Just a quick update that last night’s models showed a much higher chance of thundershowers this afternoon and Saturday afternoon.   Today’s showers and thunderstorms will be the ‘pop-up’ variety; they will dynamically form in position and fall apart without moving much.  Some areas won’t see any; other’s might have a significant quick downpour.  The showers may pop up anywhere and anytime after 1 PM  Friday and persist popping up until about 8 PM.

Here’s the High Resolution Ensemble Forecast (HIREF) for 5:30 PM today showing accumulated precipitation:

(These accumulated Precip maps as well as the TV “future tracker” stuff can’t be taken literally in terms of exact timing, position and intensity. They just give a general idea about timing and the mostly likely areal coverage. That said, the HIREF model depiction isn’t bad for these things.)

Saturday’s showers and thunderstorms will be associated with a weak front moving through.  Some of the models keep these mostly to our west and barely make it into Philadelphia.   Will have to see.  I’ll update tonight.