Philly Weekend Weather Forecast

The forecast has clarified for this weekend, and it’s looking very wet, especially according to the NAM model.

The upper air trough providing the cooler than average weather will remain entrenched aloft as high pressure in the northern Atlantic tries to build westward. As a result, an easterly/southeasterly flow from the ocean will converge with the dry, cool upper flow of the trough over us, creating a retrograding coastal warm front for the next few days.

The Shore and areas south appear to be in the maximum convergence zone and will have the most clouds and rain. The GFS has depicted areas west of Philadelphia to be among the dryer areas, although the exact placement of the moisture convergence is difficult to determine.

Sat 8/2: Heavy rain during the morning ending late morning. Some brightening skies afternoon with a chance of a shower. High 79.

Sun 8/3: Cloudy, some bright spots mid-day with a chance of showers especially afternoon. Humid. High 81.

Philly Weekend Weather Outlook

GFS outlook Sunday afternoon
GFS outlook Sunday afternoon

Our string of beautiful weekends appears to be ending this coming weekend.

The upper air trough providing the cooler than average weather will remain entrenched aloft as high pressure in the northern Atlantic tries to build westward. As a result, an easterly/southeasterly flow from the ocean will converge with the dry, cool upper flow of the trough over us, creating a retrograding coastal warm front for the next few days.

The Shore and areas south appear to be in the maximum convergence zone and will have the most clouds and rain. The GFS has depicted areas west of Philadelphia to be among the dryer areas, although the exact placement of the moisture convergence is difficult to determine.

So will the weekend be a total washout? Perhaps at the Jersey Shore, but not necessarily in Philadelphia or areas west.

At this time, all we can say is that more clouds and chances of showers are possible throughout the weekend. Yet, the models did poorly last weekend predicting the cloud cover and showers, and were equally wrong about the cloudiness this past Tuesday. So it’s clear that the models have had trouble with this anomalous trough providing the cool weather.

 

Sat 8/2: A mix of clouds and maybe some sun at times. More humid. Chance of showers, especially during the afternoon. High 81.

Sun 8/3: Continued cloudy, possible bright spots and sun, with a chance of showers. Humid. High 82.

 

Philly Weather Update

Uncertainty in Sunday’s forecast was a known issue.  But clearly there’s uncertainty in today’s forecast.  An upper disturbance, ahead of the front has moved into our western suburbs and will cause showers and possibly a scattered thunderstorm as it moves through Saturday morning.

A rule of thumb in weather forecasting- if the models are incorrect in the short term forecast, it suggests even more uncertainty in the longer range (Sunday in this case).

Philly Weekend Weather Forecast

Uncertainty in the forecast this weekend, especially with the amount of cloud cover on Sunday. The NAM is much wetter on Sunday with a chance of showers both morning and late afternoon. The GFS is dryer, more sun.

An interesting pattern change starts setting up over the weekend, as an amplified jet stream trough begins to develop over the Great Lakes and weak disturbances begin to rotate through our area as a cold front slowly advances. This amplified pattern is something we usually start seeing late August, not July, but it’s been a somewhat consistent feature of our cooler weather this entire year.

The timing and intensity of the these upper air disturbances around this developing trough are difficult to model and that’s where there is great uncertainty in this weekend’s forecast. That said, the GFS has done better than the NAM in recent weeks, so I’m thinking that Sunday will be drier and warmer than depicted by the NAM.

This amplified trough will eventually bring cooler temps and lower humidity to our area next week.

 

Sat 7/26: Cloudy in the morning, then bright spots, breaks of sun around noon, then increasingly cloudy with a chance of a shower or thunderstorm. High 84.

Sun 7/27: Mostly cloudy, some bright spots mid-day, then increasingly cloudy with showers by evening. Warm and humid. High temp will depend upon amount of sunshine…85 possibly warmer to 89.

Storm Forecasts & Other Things "up in the air".

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