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.
It was supposed to be a dry frontal passage this morning, but that hasn’t panned out. The models show as little as a 4% chance of showers this morning, but the short range models (GFS-LAMP) have increased the chances s bit. Nonetheless, radar shows that an area of fast-moving showers is passing through.
NEXRAD Radar PHL 9:25 AM today
Interestingly, the NAM model was updated and enhanced this past Tuesday, but I see little improvement in the precipitation forecasts since then.
For the balance of the day, broken clouds, showers early morning , then clearing in the mid-afternoon.
In some areas today, there was a large high cirrus cloud cover, even an 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.
