Category Archives: Weather Forecasts

Philly Weekend Weather Forecast

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Building cumulonimbus with altostratus  late Thursday
Building cumulonimbus with altostratus
late Thursday

A blocking pattern is causing high pressure near Nova Scotia to maintain an easterly flow of moisture, resulting in considerable cloudiness, cool temperatures and an ongoing chance of showers on Saturday.

This high pressure system is expected to build down over us later on Saturday, allowing a more northerly flow of drier air.  Clearing skies late Saturday should remain with us through Sunday.

The NAM has a much greater chance of showers during the day on Saturday than the GFS, but it has a tendency to overstate precipitation lately. Neither model has done very well with this blocking pattern over the past week and I have lower confidence in this forecast, especially for Saturday.

Sat 8/23: Mostly cloudy, a chance of widely scattered showers but mostly dry. Brightening skies late in the afternoon. High 77.

Sun 8/24: Sunny and warmer. Some fair weather clouds develop in the afternoon. High 83.

Philly Weather Update

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In some areas today, there was a large high cirrus cloud cover, even High level cirrus clouds with bat box in the foregroundan altocumulus congestus layer which kept temperatures down. There were more high level clouds than I had expected.

A weak frontal boundary will move through Sunday morning with cloudy skies early.  The models keep us dry.  Skies clear during the day as a dry northerly flow develops.

So for Sunday, clouds in the early morning with blue skies and billowy fair weather clouds in the afternoon.

Philly Weekend Weather Forecast

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A cold upper air cyclonic flow will allow mostly sunny skies for Saturday, with perhaps some fair weather cumulus developing in the afternoon. A weak upper air disturbance and front will rotate through Sunday morning and will be offshore Sunday evening.

Sat 8/16: Sunny and beautiful. High 83.

Sun 8/17: Cloudy, in the early morning with a chance of a shower. Skies clear during the afternoon. High 84.

Philly Weekend Weather Forecast

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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.