3:00pm Update: Showers and embedded thunderstorms continue to approach the area, now in Western New Jersey and shifting eastward. While radar presentation isn’t necessarily eye-grabbing, the winds just above the surface that are mixing down to the surface are impressive.
Philadelphia International Airport recently gusted to 71 miles per hour as thunderstorms passed through. Multiple gusts over 45 miles per hour have been reported in Eastern Pennsylvania. As storms continue to shift eastward toward the axis of more favorable instability and lapse rates, expect these gusts to continue.
None of these storms are currently producing sustained severe-level winds, but we are continuing to monitor the situation. Stay tuned for future updates over the next few hours.
An approaching mid and upper level atmospheric disturbance will once again cause unsettled weather this afternoon. This time, showers and thunderstorms are expected to push from Pennsylvania through New Jersey during the late morning to early afternoon hours. As they do so, they’ll encounter a slightly more unstable environment — and will be able to strengthen and grow. Although surface instability relative to what often is experienced in late Spring and Summer is somewhat meager, it will suffice for the organization of these thunderstorms.
The main threat in stronger thunderstorms will be heavy rain, some lightning, small hail and gusty winds. Strong winds just above the surface could be mixed down by these thunderstorms as the move through. The weather looks to be pleasant until around noon, when clouds will increase. Southerly winds will bring temperatures into the 60’s, and storms will begin to approach from the west during the early to mid afternoon hours.
The potential threat for severe weather is expected to remain mostly marginal, but there is complicated meteorology behind it. Simplifying this meteorology helps to break down the potential threats for multiple types of hazardous weather, as mentioned above, which include small hail and wind gusts over 40 miles per hour.
In the mid and upper levels of the atmosphere, an energetic shortwave disturbance will swing eastward through Pennsylvania today. This disturbance will help to provide increased forcing and ascent for the development of showers and updrafts for thunderstorms. The stronger updrafts for thunderstorms may be initially hard to come by — as forecast models indicate that our area will be battling with a lack of instability. Essentially, the atmosphere is still recovering and rebuilding moisture in the column — so instability for thunderstorm development will be weaker than normal.
That being said, there is good agreement on the development of showers with embedded storms. As a weak axis of instability forms from Eastern Pennsylvania through New Jersey and southward to parts of the Mid Atlantic, storms could become slightly stronger on their progression east. In the upper levels, very cold air is present — which could aid in the development of both small hail and graupel in these stronger updrafts for thunderstorms.
Meanwhile, strong winds just above the surface near the cold front and mid level energy could also potentially mix down in these stronger storms. Forecast models, namely the NAM and RGEM, both agree on the potential for gusts of 40 mph or higher within this organized segment of showers and thunderstorms later this afternoon.
Accordingly, the Storm Prediction Center has placed our area in a “Marginal” risk for severe thunderstorms, with a 5% risk of severe hail and strong winds. As mentioned above, the risk for widespread severe weather is slim.
Stay tuned throughout the day — this thread will update at the top with additional information as it comes to us.