The very mild weather that will be with us through Friday will come to brief end later Friday as a cold front moves through.
As in recent months, the cold front precipitation dynamics move to our north as a wave develops on the front to our south. That gives us a windy day, but low rain probability to the frontal passage late Friday.
The current dry pattern seems deeply entrenched for our area. Indeed, the upper air pattern that has been with us since August is a marked departure from the pattern of the past two years. It suggests a much milder winter and possibly a much drier winter. More about that in a upcoming post regarding my Winter Weather Outlook.
Back to this weekend…the wave of low pressure may bring cloudiness to our area on Saturday, but it appears that the rain will stoy just to our south, affecting southern NJ and DE.
For Sunday, cooler high pressure builds in for sunny and seasonably cool weather.
The first significant dip in the jet stream for this fall/winter season will occur this weekend for the northeastern US. A cyclonic flow of cool/colder air will bring temperatures down to about 40 or less at night and the 50s during the day.
While the predicted upper air jet pattern has been consistent, the models have shown great variation with the possibility of upper air disturbances embedded in the flow. What this means is that it’s not a certainty how much sunshine we’ll get with these cooler temperatures.
Periods of sun and cloudiness looks to be the best bet, and there’s a slight chance of a quick sprinkle during the afternoon on Saturday and even moreso later Sunday afternoon and evening, as the upper flow changes to the southwest. A brief snow flurry Sunday night isn’t out of the question.
Numerous tropical models show tropical storm Joaquin becoming a hurricane, possibly Category II, over the next day or so and many of those models suggest a track into the east coast, anywhere from the Carolinas to Delaware over the weekend.
In the past, my preferred model for hurricane paths was the Navy NOGAPS model, now called the NAVGEMS
The NAVGEMS has Joaquin hitting pretty far south, near South Carolina. Numerous experimental models show the path of Joaquin hitting the east coast further north.
The GFS model has the storm further intensifying at sea and hitting the east coast around Virginia over the weekend. Hurricanes are tough to forecast and their presence along the coast often affects the forecast accuracy of non-tropical systems in the regular daily forecasts.
This storm needs to be watched, since it beginning to appear that it will affect PHL in some way (heavy rain potential and winds) over the weekend.
The blocking pattern that has given us the extended mild and dry pattern will weaken a bit but continue to block the progress of a frontal boundary and will likely also block the northeast movement of tropical storm Joaquin.
Heavy rain for tonight (Tues) will likely be more focused west and north of Philadelphia, but we will still receive some moderate to heavy rain, tapering Wednesday afternoon.
The front stalls to our south and areas of low pressure move along the front, bringing more rain Thursday into Friday.
Tropical storm Joaquin may strengthen to hurricane status before moving into the Carolinas or even Delaware sometime between Friday and Sunday. This situation needs to be watched, since heavy rain and high winds are possible.