The showers never materialized anywhere near Philadelphia yesterday. Except for an isolated shower near Reading, the entire area was dry. So much for the HRRR model, (which has been very good, but clearly not perfect.)
A cold front is moving towards us this morning, but its passage around noon will be dry, maybe with a few clouds. Cooler and low dew point air will be filtering in during the afternoon. Too dry aloft even for instability clouds. So it will be sunny and breezy. High 83.
The NAM lifting index and vertical velocity now support showers and thunderstorms for Saturday afternoon, but the line of showers moving through may be broken up and scattered.
The highest probability of thunderstorms is north and west of PHL into central NJ.
The HRRR shows showers/thunderstorms moving into far northern/western suburbs by 2 PM and moving through Philadelphia between 3-4 PM.
The line sinks south and east with additional scattered showers possible through 8 PM. Note that the GFS-based LAMP forecasts show a lower chance of showers/thunderstorms somewhat later, between 4-7 PM.
The probability of thunderstorms is not very high (as compared to this past week’s storms), but high enough to plan for the possibility.
7PM Update: Not a single shower in the Philadelphia area! It wasn’t expected to be a high probability event and it wasn’t.
The models, particularly the GFS, over-estimated the chance of precipitation on Saturday. When I looked at the NAM-based HRRR model (High Resolution Rapid Refresh) yesterday, it did seem to keep the precipitation to our north and west. The GFS-based LAMP forecast was very off with precipitation forecast yesterday.
This morning, there are scattered light showers, mostly far north and west of the city.
Looking at the short-range models, the HRRR brings widely scattered showers into the general PHL area by about noon. The real action (possible severe thunderstorms, possible heavy rain) develops to our west between 1-2 PM and moves through from 2-7 PM. Any breaks of sunshine late morning or early afternoon will only fuel the thunderstorms.
We’ll see if the severe weather develops. The NAM instability indexes for PHL aren’t forecast to be that impressive, enough for heavy thunderstorms, but not necessarily severe. But the NWS has been forecasting severe weather and I’ll defer to the NWS for their forecast here.
4PM update- Not the rainy day that had been expected a few days ago. This weather “event” will basically be a frontal passage with heavy rain and strong thunderstorms, starting in PHL about 5:30 to 6:30 PM . Best chance of severe weather looks to be in Delaware and areas of NJ around Delaware Bay.