The National Blend of Models has a QPF of only 0.28 for PHL and really drops down to 0.20 for Blue Bell. This sort of edge condition with such a rapid taper is going to take a bite out the snow fall prediction accuracy.
The 4-7 is looking too high. 4-5 is more likely for the immediate PHL area.
The GFS model data is becoming available. The GFS has about 2 or so inches of snow by daybreak Thursday. But only an additional 2 or so inches during the morning hours.
The total GFS QPF is only 0.32 inches water, very consistent with earlier runs and the National Blend of Models.
With such differences between the NAM and GFS, the best guess usually is arrived at by averaging the two. With a high snow water ratio, I’ll have to revise the prediction to 4-7 inches, with 5 most likely in the immediate PHL area. Areas west will see less, areas east much more.
I guess we’ll see tomorrow!
11:30pm Update The National Blend of Models has a QPF of only 0.28 for PHL and really drops down to 0.20 for Blue Bell. This sort of edge condition with such a rapid taper is going to take a bite out the snow fall prediction accuracy. The 4-7 is looking too high. 4-5 is more likely for the immediate PHL area.
The latest NAM data has become available. The QPF is more in line with the GFS data from earlier today. The latest QPF is 0.46 inches water for PHL, increasing considerably eastward into NJ to almost 0.90 at the coast.
For Philadelphia, that QPF translates into 5-7 inches of snow. The NAM has the onset in the early morning hours before daybreak, with the heaviest snow during the morning, ending about 2pm. Areas in NJ may have snow totals in excess of a foot of snow.
The early GFS data becomes available 10:30 pm and I’ll update again after that time. (The GFS values are often lower.)
Reviewing additional NAM data, the snow may be minimal before 7 am with heavy snowfall after daybreak .
Some of the higher resolution models have lower QPF values, in the order of 0.30.
Waiting for tonight’s GFS data, but 5 inches is the most likely amount for the immediate PHL area based on averaging the data.
This afternoon’s model runs continue with an increase in QPF. NAM 0.70 and GFS 0.38 inches water. With a 1:13 snow ratio, it’s looking like 4-7 inches snowfall at least in PHL. Final models become available about 9:15 PM (NAM). I’ll update then.