A wet scenario will setup for this weekend. It’s a setup we’ve seen several times this summer season— an upper low pressure system is expected to close off to our west and a stream of moist unstable air will flow into our region.
Showers and thunderstorms are possible Friday evening, but the models have increasing chances of showers and thunderstorms throughout the daytime hours of Saturday into Saturday evening. Some of the showers could be heavy.
The skies will be mostly cloudy on Saturday, although some breaks or brightening skies are possible, especially mid-day hours. Highs about 81 with high humidity.
A similar situation is expected for Sunday, although the shower activity is expected to be lower than Saturday. Brighter skies and some sunny breaks possible on Sunday, but widely scattered showers possible any time, especially later in the afternoon. High again about 81,
Regarding forecast confidence, the GFS, ECMWF and the NBM are in good agreement. The NAM is significantly less robust with the shower coverage, especially for Sunday. I’ll update later.
A weak front will move through over the night time hours Friday into Saturday. Showers are expected tonight, with heavy showers just before daybreak Saturday.
The unsettled weather may linger into Saturday morning and clearing skies will be slow but brightening skies and some eventual sunshine should start by 10-11 AM. (Later, in areas east in New Jersey where showers may also linger.)
10:30 PM Update: Latest NAM data shows clearing skies occurring earlier, after 8 AM Saturday. Two weeks in a row, my late update using NAM data has been a problem and ruined an otherwise good forecast. Will look into this. The showers should be ending here about 10-11 AM and gradually clearing skies should follow by about noon.
By afternoon, Saturday will become hot and humid with highs near 89 and dew points remaining uncomfortable in the low 70s.
Somewhat drier but hot air moves in from the west for Sunday.
Sunday will be sunny, hot and humid with highs near 92 and dew points still high in the upper 60s.
Saturday morning’s NAM has backed off on the showers in eastern PA but has a slight chance for widely scattered showers in central NJ Saturday morning. Lingering periods of cloudiness in the morning still expected.
Tonight’s NAM data is just becoming available and it has the front lingering over our area during Saturday morning. This is a large change in the forecast. So there’s a chance of lingering light, scattered showers during the morning hours tomorrow, Saturday. Skies improve in the afternoon.
(GFS data not available until much later due to daylight saving time, so I can’t compare models at this time)
A weekend forecast that appeared high confidence, now appears to have some new uncertainty.
A front will move through Philadelphia late this afternoon and early evening (Friday) with showers and thunderstorms. Some storms are developing ahead of the front this afternoon in the warm, humid air. The dynamics suggest the possibility of heavy thunderstorms in PHL, although the strongest dynamics may move through to our north.
Updated 9 PM Fri: The heaviest storms were well north of the Philadelphia area. Rainfall was less than forecast. The sky appearance was impressive
By Saturday morning, the front will have moved off the coastline resulting in sunny skies with gradually falling humidity/dew points as the day goes on. Highs will be around 86 with a light wind out of the west.
For Sunday, some cloudiness very early, then partly to mostly sunny. Lower dew points in the 60s and highs around 85.
A return to unsettled weather and humidity for early next week.