In yesterday’s forecast, I mentioned the possibility of cloudiness for Sunday afternoon. Several of the models have low cloudiness moving in on an easterly flow Sunday afternoon.
The model blend statistical treatment shows about 40% mean (average) cloudiness, but the standard deviation (a measure of the spread in the models or it can be interpreted as uncertainty) is as high 45-50%, especially west of Philadelphia Sunday afternoon by 3 PM.
The high resolution NAM-NEST shows low level cloudiness moving in, with a mix of high and middle level clouds further to our west—
So, there’s uncertainty in the degree of cloudiness for Sunday afternoon, but I’m thinking it might be significant by 3 PM.
High temp Sunday 63.7º with a high confidence of 0.8º standard deviation. (The standard deviation can be thought of as 67% of the time, the temperature will fall with ± 0.8º of the mean temp 63.7º)
Last night’s model runs show a somewhat earlier approach of the rain Sunday afternoon, now expected between 2 and 5 PM, earlier far southwest of Philadelphia.
Indeed, current observations (Real Time Analysis) in West Virginia and Virginia show a larger swarth of rain now than had predicted by most of the models. The model blend has moved the precipitation earlier.