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Sunday Forecast Update
Posted Sunday 07/05/26 @ 8:38 AM —For today, the big question is the amount of cloud cover and how early any thunderstorms will develop. (A slowly moving front is moving south over us tonight with the edge of the heat dome (760 thickness line) moving to somewhat south of us.
Based on the latest RRFS, I’m going with clouds thin for sunshine by late morning or early afternoon. While a few isolated storms will form as early 2 PM, the RRFS shows much of the area dry through 5-6 PM with the exception of southern NJ Cape May county, which may have more numerous scattered storms late afternoon.
Widespread heavy rains/thunderstorms develop and move down from the north and west between 7 PM and 9 PM and continue through much of the night. Expect some severe thunderstorm warnings this evening.
With the edge of the heat dome right over us, expect plenty of clouds Monday with scattered showers and storms especially with daytime heating.
Lightning or Fireworks?
Updated Saturday 07/04/26 @ 5:47 PM — A quick update. The latest radar shows a series of storms on a path towards Philadelphia.
The latest RRFS and HRRR show this area of storms reaching us by 9 PM (RRFS) or 10 PM (HRRR). The storms dissipate as they move through and may end in the city by 11 PM.
This is another “out on a limb” forecast, but I guess that’s why you read this blog- to get a different perspective on the weather.
Posted Saturday 07/04/26 @ 10:01 AM — Today looks to be very hot again with the model blend high temperatures returning to 102º ± 2.4º for Philadelphia (KPHL). Just to the west of the city, as shown in last night’s temperature map, it will likely be ‘less hot’. (I can’t use the word ‘cooler’ here and dew points will be near 70º at times.)
The big question is the rain and thunderstorm threat for the afternoon and evening. Several models suggest that the immediate PHL area will be in a relative doughnut hole of precipitation/storms this evening.
The NAM-NEST shows strong triggered ‘forcing’ of storms to our west but the 700 mb wind flow may take it just north of the city and south of the city—
Trying to predict thunderstorms is like trying to predict where boiling water will create its first bubble at the bottom of a large sauce pan. This week’s thunderstorm forecasts timing and forecast tracks haven’t been very accurate.
Supporting the relative calm for Philadelphia this evening with the city being in-between main forecast tracks is the current water vapor image.
So, in summary, (and I’m going out on a weak limb here), fireworks in Philadelphia beginning around 9-10 PM may escape the onset of natural fireworks (lightning). I’ll try to update later this afternoon.
When it comes to lightning, always listen to the latest official NWS forecasts and warnings.
Originally Posted Fri 8:21 PM —
Another hot day is expected on Saturday while a high pressure system tries to move southward, slowly pushing the extremely hot air mass (with the heat boundary defined here as the 760 thickness line) to our south—
Numerous showers and thunderstorms will break out during the day to our west and by 5-6 PM, they will be moving in to the Philadelphia area. These storms are not the result of a fast moving cold front and as such, they will develop , re-develop and linger for much of Saturday evening. Nature will be producing its own fireworks.
By Sunday evening, the 760 thickness line is just south of Philadelphia causing many showers and thunderstorms. Exact details to follow in my Weekend Updates.
Saturday
Sunny with some high thin cirrus clouds for much of the day. Storms develop and move in between 5 and 8 PM. Model Blend Highs: Blue Bell- 99º Philadelphia 101º ±1.9º (average sd, average uncertainty)
Sunday
Considerable cloudiness. Plenty of showers and thundershowers around beginning about 2 PM. Highs (Model Blend): Blue Bell- 91 º Philadelphia 93º ±4.7º Humid! Very high sd and high uncertainty in this forecast.
