The unusual cool pattern for June continues. The upper air cyclonic flow and the dip in the jet stream relaxes on Saturday, allowing a warm front to approach Saturday. It currently appears that much of the dynamics and moisture will lift to our north. Much of Saturday will be dry.
For Sunday, low pressure over eastern Canada intensifies, and the associated upper air flow again becomes cyclonic, following a cold front passage. Unsettled and cooler weather is likely again for Sunday. A mix of clouds and sun with a possible shower and windy, as upper air vorticities rotate around the Canadian surface low. Again, mostly dry.
This cool weather, unstable, upper air cyclonic pattern really continues on and off for much of June, with short-lived warm ups. The medium-long range forecast for the next two weeks or so doesn’t show much of a Bermuda high pattern typical of late spring and summer. Expect cool weather, mostly dry but with instability allowing shower-formation for the next few weeks.
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.
The models seem to be consistent and in fairly good agreement with this weekend’s weather forecast.
Saturday will have a damp, humid, southerly flow maintaining mostly cloudy skies, with some brightening and maybe some sun midday. Clouds return in the afternoon and there’s a chance of showers moving in from the west by 4-6 pm. High 80.
Rain develops Saturday night and continues through Sunday. There may be a lull in the rain during the morning but heavy rain and possible thunderstorms developing Sunday afternoon ahead of a cold front. High 79
A poorly defined series of disturbances will affect our weather during the first part this coming weekend. A stronger system brings rain likely for Sunday.
Friday will likely have showers at some point during the day, but the GFS and the NAM differ about QPF, with the GFS wetter than the NAM.
Saturday will likely be a mix of clouds and some sun. The NAM is again drier than the GFS and I’m leaning towards the drier NAM.
Both models predict heavy rain for Sunday, especially in the afternoon. (But that sort of forecast didn’t pan out this past Monday, as most the rain moved east into NJ, predicted by the NAM.)
Will update late Friday.