Some new developments since my earlier post this morning. SPC has upped damaging wind probabilities from 15% to 30% for New York City, New Jersey, Eastern PA and the Lower Hudson Valley. Probabilities for large hail and tornadoes remain lower and unchanged: 
The 12z OKX sounding from a balloon launch by the National Weather Service, showed a cap inversion layer around 900mb. Also a 500-850mb lapse rate of 6.4 C/km and 37kts of 0-6km bulk shear . As a result, with enough sunshine, we will be able to destabilize at faster pace than yesterday. Before more forcing arrives to overcome that cap. Hence the forecast SBCAPE at 2016 J/kg (click on image to see clearer): 
Also, the threat for isolated tornadoes increases. For example, the 12z HRRR from the College of Dupage website shows also 2500 J/kg- 3000 J/kg SBCAPE with low-level winds backing to SE late this afternoon over NE NJ/NYC area, These parameters combined along with low LCL and high helicity results in significant tornado parameter greater than 3.0 over that area. Which is very substantial for the local area: 
This may not played out as precisely as this models shows. But the potential is worth monitoring today. I might have other updates through the day today, if there are major changes or new developments.
Year: 2014
Possible Tornado in Southern NJ… More Flooding and Severe T-Storms Likely Today
Yesterday t-storms produce mostly heavy rains with only some widely scattered reports of damage or strong winds. However, radar detected strong rotation and winds with thunderstorm over near Permberton,NJ last night around 8:30pm. A storm chaser on twitter took this picture of a possible tornado that hit near that town. A weak low forming yesterday over Southern NJ, enhanced low-level directional shear that may of produced tornado. The National Weather Service will likely go out and survey the area today. I may have another post about it, when the survey is completed. Update: NWS confirms straight-line winds. No tornado.
Meanwhile, the Storm Prediction Center has slight risk for the entire tri-state area again today. In my last post I discussed, that the severe weather threat may be reduced today with more showers and thunderstorms through the day, keeping instability lower. However, models still show moderate instability with SBCAPE values 1500 J/kg to 2500 J/kg and liifted Index values between -3 and -6, by this afternoon. 0-6km bulk shear is also 30kt to 40kts this afternoon. Those parameters support organized severe thunderstorms, in some locations. Especially over NYC, New Jersey, the Lower Hudson Valley . A southerly wind off the water, will likely keep parts of LI and South CT less unstable. Damaging winds from thunderstorms are still biggest severe weather threat. However, cold upper-level low a little closer to area to today, the threat for large hail is little higher than yesterday. Model soundings also indicate a backing of low-level flow this afternoon. So an isolated weak tornado cannot be ruled out.
The National Weather Service has also issued a flash flood watch for the entire area. Flooding still appears to be bigger threat than severe weather, as only marginal instability is needed for t-storms with heavy rainfall this afternoon and evening. With precipitable water values near 2.00″ any storm produce between 1″ – 3″ of rainfall in short period of time, resulting in flooding of poor drainage areas or small rivers and streams. Showers and thunderstorms will likely continue overnight and into Wednesday morning, as the cold front with system, slowly moves through the area. With the of loss diurnal heating, instability will diminish. So the threat for more severe thunderstorms will be over. But threat for heavy rainfall will continue. After the cold front passes, clouds will likely break for sunshine tomorrow afternoon. Sunshine, low humidity and seasonable temperatures are expected for Thursday and Friday.
Severe Weather & Flooding Threats Monday & Tuesday 7/14- 7/15
An anomalous cold closed upper-level low swinging over the Great Lakes, will cause another period of stormy weather early this week, in Northeast and Mid-Atlantic. A deep southwesterly flow ahead of this system, will provide moisture feed out the Gulf of Mexico and Atlantic. The Storm Prediction Center has again issued a slight risk for the local tri-state area on Monday. That means they are anticipating some organized severe thunderstorms. But not widespread in coverage and violent in intensity.
The main threat, from any of these storms Monday will be flash flooding, damaging winds Large hail is possible. But poor mid-level lapse rates and high freezing levels shown on model forecast soundings, will keep this threat lower. A warm frontal boundary will develop over the local region on Monday. This will cause winds the low-level winds to back from south-southeast at the surface to southwest aloft. For areas near the coast, including NYC, there will be more of marine influence that may keep thunderstorms under severe levels. But areas further inland, may heightened risk for isolated weak tornado. Especially over the Lower Hudson Valley.
On Tuesday, as the upper-level low moves further east, shear and lifting will increase. Without much capping in the atmosphere, showers and thunderstorms could be more widespread and frequent through the area. But this may also act to keep instability lower across the area for thunderstorms to become severe. Flash flooding is likely to be a bigger threat. Very high precipitable water values and some unidirectional shear will causes thunderstorms to train and produce torrential downpours in parts of the area. Stay tuned for another update tomorrow for this threat.
Miguel Pierre Weather 