As mentioned in my “Outlook” post a few days ago, the models were maintaining a nose of high pressure that seemed to block shower activity from reaching our area.  However, the trend was for this high pressure blocking  to be decreasing.  Such is the case today, as high pressure is now expected to retreat eastward, allowing showers to move in as early as Sunday afternoon.

For Saturday, mostly sunny and hot, with a  slight chance of a scattered thundershower later in the afternoon.  High 89

Significant moisture from a semitropical system off the southeast coast will move in on Sunday giving us an increasing chance of showers in the afternoon.  Sunshine in the morning with clouds, showers and thunderstorms likely during the afternoon.  High 82 and much more humid.

Monday looks to be cloudy with rain, possibly heavy.  Warm and quite humid. High 78

Note- The forecast has changed considerably over the past two days.  The effects of a tropical system will throw another monkey wrench into this current forecast.  Expect further changes. 

The GFS model has been consistently predicting low pressure to approach our area from the southwest and bring heavy rain to PHL for Saturday, as a coastal low forms over the Delmarva area.   (For the record, the European Model had it moving south and missing us until recently.)

Saturday will be cloudy with rain, fairly heavy, beginning about 8-9 AM and continuing through the day. High 63.

An upper cyclonic flow over our area on Sunday, with an area of vorticity rotating through during the day will keep mostly cloudy skies for most of Sunday (maybe some bright spots) with a persistent chance of scattered showers, especially during the afternoon.  (Any sunshine will be of the self-destructive form, due to instability.)  High 67.

10pm update:  latest NAM has most of the rain holding off until afternoon on Saturday.

A cold front approaches and moves through our area Saturday afternoon.  Saturday morning and early afternoon will be sunny, but clouds roll in about 2-3 PM.   High 72.   Becoming breezy mid afternoon.  Showers and thunderstorms likely by around 4 PM and move through by 7 PM as the cold front moves through.   Temperatures drop.

Sunday, we’ll be under the influence of an upper air cyclonic flow.  It will be windy and cool.  High temps 61. 55.    Sunshine will be broken by instability cloudiness during the afternoon due to the upper level pool of cold air.

Sat 9 AM Update:  Thunderstorms are likely today between about 4-5 PM in near western suburbs and moving through PHL between 5- 7PM.