A blocking pattern with high pressure over the Atlantic will allow a southerly flow of warm air to be with us over the weekend. The same blocking pattern will impede the northern movement of tropical storm Ana, although there is always uncertainty with the movement of these systems.
A weak warm front will move through Friday night and some cloudiness will linger into Saturday morning as dew points rise. Skies should break to sunshine in the afternoon with temps getting to 80. It will be more humid on Saturday.
The overall dry pattern will continue for Sunday, but some moisture from tropical storm Ana may introduce some cloudiness Sunday afternoon. Mostly sunny with some cloudiness in the afternoon. High 83 and humid.
I just want to emphasize that tropical storm Ana affects the models and introduces some increased uncertainty in this forecast.
Surface low pressure and associated upper low will depart Friday night. Cloudiness associated with this system will move away Friday night.
High pressure builds in for Saturday giving us mostly sunny skies, although a weak front will move through late Saturday afternoon resulting in some clouds. Temperatures will be near 70 as the winds will be from the northeast for much earlier part of the day.
For Sunday, high pressure will control, with mostly sunny skies and above average temperatures. Highs expected to be about 79.
There are greater uncertainties forecasting the weather during the springtime as large scale weather determinants become increasingly influenced by smaller scale (mesoscale) effects.
Such is the case this weekend, with the NAM and GFS models having different forecasts, especially for Sunday. Basically, cold high pressure moves off to the east, allowing low pressure to approach from the west. The GFS allows this low pressure to give us a chance of showers on Sunday, especially to our south. The NAM suppresses the low pressure system to our south, keeping us dry in Sunday.
The NAM model has done well lately and I’m going to go with that model. Saturday has a mix of sun and clouds. High 62. Sunday has mostly cloudy, some breaks of sun. High 65. If the GFS verifies, then Sunday will be much cloudier with a chance of very light showers, especially south of PHL.
Saturday AM update: The GFS has joined the NAM in keeping the rain to our south on Sunday. Sunday will be partly sunny/partly cloudy with temps near 65. There remains uncertainty about the amount of cloud cover for both Saturday and Sunday.
