Just a quick update,based on tonight’s NAM model data that just became available.
Much of what I wrote about earlier today still holds. While the lower levels of the atmosphere remain below freezing for an extended period on Thursday due to “cold air damming”, the upper levels of the atmosphere are forecast to be too warm to support snow Thursday.
I believe this will be a sleet event, eventually changing to sleet and rain; rain possibly heavy in the afternoon. While some early snowflakes are possible, it should quickly change to sleet.
I’m sure there are forecasts out there for snow, based on preset precipitation type algorithms. But thermal profiles have worked well for my forecasts in the past and I’m going to stick with it this time. This forecast is for Philadelphia and immediate suburbs. Areas far north and west may have more freezing rain and sleet accumulating.
The scenario with the upper low enhancing a secondary surface low Thursday night into Friday morning is also supported by tonight’s NAM. However, it’s looking less likely that enough cold air will allow a changeover to snow .
Things will clarify by tomorrow evening.