This afternoon’s NAM and GFS model runs continue the trend mentioned last night and this morning that the northward movement of the low pressure system will be blocked by high pressure, resulting in a delay for the snow to reach us.
The current models show snow starting during the evening Friday and getting heavy late Friday night through Saturday. Some of the model trends suggest a more southern movement of the low, so heaviest snow will be south and west of Philadelphia.
QPF values from the GFS are about 1.25 inches water, falling as snow. The GFS snow algorithm suggests 16-20 inches of snow possible by Saturday evening.
In addition to the delay in the snow onset, the other model trend has been for the snow to end earlier on Saturday night instead of lasting into Sunday, as the coastal low is expected to spin into two low pressure centers, transferring the energy to the further eastward low. This trend may result in lower storm snow totals if that transfer occurs earlier. Right now, the models say 16-20 inches, but that double barrel low pressure system is known to be handled poorly by the models. So the actual totals may be lower. Either way, have that snowblower ready.
I’ll update later tonight if thing change significantly. Otherwise check back Thursday morning.
10 PM -Tonight’s NAM model output just available shows a QPF of 2.54 inches water. That would translate into well over 30 inches of snow! The NAM almost always overstates the precipitation in this time frame, so I wouldn’t take this too seriously, If nothing more, it supports the likelihood of a big storm. Still starts early evening.