Severe weather threat growing for southern New Jersey

4:15 PM

The dynamics appear to be coming together for the potential for strong to severe thunderstorms over southeastern Pennsylvania and southern New Jersey.  

As discussed this morning, a warm front will move through the forecast area tonight to producing a steady, heavy rain over the entire region.  Currently, an area of heavy rainfall associated with the warm front is over western Virginia and North Carolina, which will continue to move northward through the afternoon and into the forecast area by tonight.  

Notice the difference in precipitation though, the warm front is currently over the South Carolina/North Carolina boarder.  Precipitation to the north of the warm front is a steady moderate to heavy rainfall which is a more stratus-precipitation.  The precipitation over western South Carolina and Georgia is south of the warm front and more convective.  The thunderstorms over the Southeast are strong to severe with strong winds, large hail, and even a few isolated tornadoes.  

By tomorrow morning, the warm front will begin to stall over central New Jersey and just south of Long Island.  An occluded front will form over northeastern Pennsylvania and a cold front will begin to push through southeastern Pennsylvania.  

The combination of a strong low level jet stream at 850 MB (45 to 60 KT jet streak over New Jersey coast), significant lifting via the frontal structures, and a veering wind profile over the Philadelphia metro and central/southern New Jersey will support an environment for low-top severe thunderstorms.  These thunderstorms will be capable of strong wind gusts and even an isolated tornado.  I don’t think tornadoes will be a significant issue, however the potential is still obviously present.  

Meanwhile, locations to the north of the warm front will have very heavy rain.  The process of lifting the low level jet stream, which will supply the forecast area with plenty of moisture from the Gulf of Mexico and Atlantic, along with significant lifting via upper level dynamics will support wide spread heavy rainfall over the northern Philadelphia metro and almost all of the New York City metro.  Small river and urban flooding will be an issue in these areas and caution will need to be taken when driving tomorrow morning.  

So while cloudy to partly cloudy skies can be expected through the rest of the day, a very active period of weather can be expected late tonight through early tomorrow morning with the potential for flooding, severe thunderstorms, wind damage, and even an isolated tornado.