A large area of weak low pressure will move up northeastward into New England tonight as its associated front lingers back across our region tonight through Saturday night.
Showers and thunderstorms are expected this evening (Friday), although the heaviest dynamics will pass to by to our west and north.
Fri 10pm update: The thunderstorms went with the dynamics Friday evening and remained west and north of Philadelphia. With the near range forecast so far off, it suggests that the models, especially the GFS, may not be handling the stalling front very well this weekend. The forecast below for Saturday was based mostly on the NAM and it appears to be on track for mostly dry conditions before 3 pm Saturday.
On Saturday, the lingering frontal boundary remains through Pennsylvania and into West Virginia. This will allow low pressure to develop along the frontal boundary in Maryland as it sags to our south later on Saturday afternoon and evening.
Saturday may have some brief scattered showers in the mid-morning, but much of the day before 3 PM will dry. With a mix of clouds and some sunshine, high temperatures may reach 86. It will be humid.
With the low developing on the front to our southwest, there will be an increasing chance of showers and thunderstorms after 3 PM into Saturday evening.
The showers may linger into early Sunday morning, but as the low pressure moves off the Delaware coast, drier air should move in during the day on Sunday, according to the NAM. However, the GFS maintains a chance of showers throughout the day on Sunday. I’ve been mislead by the NAM on recent past weekends, but we’ll see what happens. Sunday may remain mostly cloudy with some brightening skies later in the day. Highs near 81 with lower humidity
Saturday Noon Update: Heavy rain is falling around the shore in NJ at this hour and much of the activity was east of PHL this morning. Sunshine has broken out in PHL (more than forecast) and the rain in PHL was over-forecast for the morning.
Current short-range analysis has a significant bullseye of deep moisture convergence in the immediate PHL area.
Showers and thunderstorms should re-develop this afternoon in the immediate PHL area.
A wet Saturday appears to be a certainty, as even the NAM has joined the other models with significant rain. The details were outlined in this morning’s early edition post.
Rain and showers are expected on or before daybreak Saturday and should become heavier in the afternoon. It will be warm and humid with highs near 83 and dewpoints in the 70s.
There’s still some uncertainty about the amount of rain and showers on Sunday, but the current thinking is that showers will be more widely scattered with more breaks than Saturday. Highs near 85 and continued humid.
That said, the latest GFS shows quite a bit of rain for Sunday. I’ll need to update over the weekend.
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.