The next few days will be a roller-coaster weatherwise.
First, the Tuesday through Wednesday timeframe should be nothing like this past Sunday’s icestorm. This upcoming storm on Tuesday will be much warmer and wetter. While precipitation may start as snow, it will quickly turnover to sleet and then rain. Some sleet buildup, but it should not be a major concern long term.
Unlike yesterday, temperatures at the surface will rise above freezing and the entire atmospheric vertical column will be much warmer. So a turnover to heavy rain is expected Tuesday evening and the rain should continue into Wednesday. There should not be the extensive ice buildup we have just experienced.
Rain continues Wednesday, as the low pressure system moves through to our north, and a cold front will move through sometime later Wednesday. Timing uncertain.
Temperatures will be in the 40s on Wednesday, not likely in the 50s as had been previously thought.
Wednesday night into Thursday, the GFShas the front stalling just to our south as a wave of low pressure develops and moves along the front. The final stalled position of the front is uncertain, but the GFS is pumping out some significant snow late Wednesday into Thursday (4-8 inches) right now. Too soon to really know at this time. Stay tuned.
So the only really impactful event may be Wednesday night into Thursday.
This morning’s NAM has backed off from the heavy freezing rain this evening and has the precipitation ending about midnight. Both the NAM and the GFS have total QPF values about 0.35 inches water, with the GFS correctly predicting this morning’s earlier onset.
Both models (for PHL) keep surface temperatures at freezing, with the upper atmosphere warming by late afternoon.
So a transition from snow to sleet/freezing rain still looks correct, with greater snow totals north and west of Philadelphia.
Accumulations will be difficult to predict, still 1-3 inches likely, but the concern is the amount of icing will we get. The unknown will be the actual rise in surface temperatures, both later today and especially tomorrow morning. The NAM keeps us at freezing, the GFS brings us just above freezing.
Latest NAM and GFS models show light snow starting mid to late morning with a changeover to sleet and freezing rain during the late afternoon. The NAM has much heavier rain/freezing rain in the evening. Not much in the way of accumulations, but significant icing conditions possible, especially north and west of the city.
The precipitation ends after midnight. Temperatures may remain just around freezing, making things slippery for the early Monday morning commute.
The latest NAM and GFS model data has become available. Here are the trends: Both models have the precipitation arriving earlier than previously predicted on Sunday.
The snow will start in the early afternoon.
As always, the NAM has a higher QPF than the GFS, with almost 0.47 inches water falling. The NAM is also colder than previous model runs. The NAM has done well with temperatures, but has been over-stating QPF.
So there is the possibility of accumulating wet snow Sunday afternoon into Sunday evening before a changeover to sleet and freezing rain during the evening. 1-3 inches snow possible. It’s difficult to determine accumulations- higher sun angle this time of year, so roadway surfaces tend to not develop as much accumulation during the day.