Category Archives: Weather Forecasts


This weekend’s weather will be the nicest we’ve had in many weeks and the forecast  will be easier as well —  a  far cry from the boundary conditions with a stalled front  we’ve had to deal with over past weekends.

Both Saturday and Sunday will be sunny.  High on Saturday 84 and high on Sunday 90!

Sat AM Update: High temperatures have shifted a bit higher for Saturday 86 and Sunday 91.

We’re finally entering a summer-like weather stretch. Monday’s high is expected to be 96-98 with increasing dew points.

By the way, the NWS announced today an expected major update in the GFS model. The new GFS model, to be referred to as the FV3-GFS,  will become operational in mid January 2019, in time to improve snow forecasts.

From what I could infer from reading about the new model, its improvement is in part due to changes in the geometry of how the globe’s atmosphere  is broken down into a 3 dimensional mathematical grid.

The new geometry, a Finite Volume Cubed Sphere, (hence FV3) allows for better computation at the edges of each cubed grid, and reduces approximations where some of the physics would ordinarily result in infinite mathematical series or unsolvable equations.  This should result in better forecasts .

The pre-release version of this new model was used for this forecast’s high temperatures. We’ll see if the highs on Monday really reach 96+.


Fri 11pm Update: Tonight’s NAM shows showers before 8am Saturday, then dry until later in the afternoon with  showers  from PHL and south. Tonight’s NAM also keeps Sunday dry until Sunday evening. 

This weekend’s weather is going to depend greatly on your location— a weak front will move south through PHL late Saturday and will orient west to east just south of Philadelphia.  Like the past few weekends, high pressure will nose in from the northeast on Sunday— an easterly wind will keep temperatures cool on Sunday.

Currently the models are in somewhat reasonable agreement that most of the disturbances riding along the boundary this weekend, especially Saturday, will be in Delaware and Maryland and may just reach into extreme southern Pennsylvania and southern NJ.  Those are the areas where widely scattered showers and thunderstorms are expected.  Areas north of PHL—  Bucks County and Upper Mongomery county look to be relatively rain-free.

So Saturday will be a mix of sun and clouds;  showers will develop late afternoon, mostly to our south.  High 83.


NAM Forecast
NAM Forecast for 5 PM Saturday.   

For Sunday, the NAM keeps our area dry with a mix of clouds and sun; the north-south dichotomy will remain.  An easterly wind will keep temperatures cool; with a high of 74.

BUT, there are large differences with the model forecast for Sunday. The GFS pushes more precipitation into our area on Sunday into Sunday evening while the NAM shunts it south into Delaware and Maryland. With such LARGE differences, we’ll have to wait to make a better call.


This weekend’s weather is shaping up to be somewhat similar to last weekend’s Sunday-Monday forecast.  Less than perfect weather for the start of June.

Low presssure developing near the Delmarva coast along with the moisture remnants of Tropical Storm Alberto will bring rainy conditions for much of Saturday. It will be warm and humid, with high temperatures in the low 80s.  There may be some sun mid-day.

Sunday afternoon
Fri PM updated outlook for Sunday afternoon

Like last weekend, high pressure will nose down from the northeast on Sunday suppressing rain to our south.  An easterly flow will bring cool, mostly cloudy and damp conditions but much of the day Sunday will be rain-free. High temperatures 68.

Friday 11PM Update: Tonight’s NAM shows showers returning late morning on Sunday; Sunday doesn’t look dry as previously forecast .

There’s the chance of showers returning Sunday evening.


The Philadelphia area forecast for this weekend has clarified a bit more.

Saturday will start sunny; high dew points in the 60s and high temperatures in the mid to upper 80s will make it an appropriate start of the summer season.

Unfortunately, moisture will also move in as mid-level cloudiness between 2 and 4pm.  There’s a high chance of showers and thunderstorms between 4 and 6 pm and the showers will likely continue into the evening.

The stream of moisture,  instability and cloudiness  are firmly entrenched by Sunday.  The GFS maintains showers throughout Sunday BUT the NAM holds off most of the precipitation  until later in the afternoon Sunday.  So there’s uncertainty about timing of showers on Sunday. I’m betting on the NAM here at this time. Any showers will be heavy.  High 78.

11pm update: Sunday possibly looking better in the afternoon as a backdoor cold front noses in from the northeast.
High pressure noses in Sunday afternoon 

Monday starts off cloudy, but expect some sun by late in the afternoon.

I’ll try to nail down the timing of the showers with updates.