The large blocked high pressure system that has given us the unseasonably mild temperatures will move east allowing a frontal boundary to move through.
On Saturday, look for increasing cloudiness with showers by evening. (The daytime hours should be dry. ) Mild temperatures continue with highs in the low 60s despite the cloudiness.
Update; This morning’s models have the rain today (Saturday) starting as early as 2-3 PM
The models diverge a bit for Sunday, with the GFS having showers ending early morning with just lingering cloudiness and cooler temperatures. The NAM model has the front stalling closer to PHL with showers continuing into early afternoon Sunday. High 56.
There has been a lack of continuity with the current blocked upper air pattern, so this Sunday’s forecast is lower than usual confidence. I suspect the NAM’s handling of the frontal showers continuing into the day Sunday may be correct.
The latest NAM run is similar to the GFS model– rain ends early Sunday morning and skies clear in the afternoon.
High pressure brings sunny skies for Saturday. Highs 55
A cold front moves through before daybreak Sunday. There’s a slight chance of a sprinkle before daybreak Sunday and as the front moves through, some cloudiness early Sunday morning. Winds pick up and the clouds break for sunshine during the mid morning. Sunny, windy and chilly for the rest of the day. High 49
Low pressure developed along the stalled front on Sunday, prolonging the cloudiness for PHL and allowing showers to develop in NJ
There are many past winter storms where there have been large differences between the GFS and NAM models regarding QPF (amount of precip).
By definition ( if not by other measures) tomorrow’s rain is not a winter storm, but the models differ significantly with the amount of precipitation forecast. The NAM has been advertising 2 inches of rain for PHL, while the GFS has a light rain, less than 0.50 inches total. That’s a giant difference.
When dealing with snowfall, the differences are obvious when a heavy precip forecast goes bust. It will be interesting to see if the NAM or the GFS model verifies tomorrow. Something to consider for later in the season when we likely see divergence in forecasts.
