severe weather risk for Wednesday

The map below may look a bit overwhelming so let me break it down for everyone.

On Wednesday, high temperatures across the mid Atlantic will reach the low-mid 90s, with even a few upper 90s possible. Dew points are also expected to rise into the upper 60s to around 70, leading to moderate to high amounts of humidity. When combined with the hot temperatures, ample instability will develop (area outlined in brown). There will also be a belt of wind shear in the order of 25-40 kts across the northeast and mid Atlantic, which will overlap the area of instability across the mid Atlantic. The best overlap of these 2 favorable ingredients for severe weather is expected to occur across central/northern MD, central/southern PA, and NJ. To the west, a cold front will approach between 4 and 10pm, likely triggering thunderstorms along it. As they intersect this unstable airmass, they should become strong to severe. 

As of now, the SPC has expanded the slight risk (level 2/5) to include the entire area just as we were expecting. Model data on Monday came into better agreement in more widespread thunderstorms occurring between 4pm and 10pm, leading to higher confidence. Scattered to numerous strong/severe thunderstorms seem like an increasingly likely possibility. If confidence in more widespread thunderstorms increases, then an enhanced risk (level 3/5) may be issued, but confidence is too low at this time.

The main hazards for Wednesday will be damaging winds that could reach or exceed 60-70mph. Model data shows a favorable environment for some pretty substantial wind gusts in any severe storms that develop. Some hail is also possible, but it should not exceed the size of quarters. The chance of tornadoes does exist, but its a very low risk and confined mainly north of the MD/PA state line where there will be stronger wind shear. Heavy rain is likely with any storm along with frequent lightning. 

There are some similarities with this event to July 12th 2022. But while this has potential to be a notable severe weather event, there are some things that could go wrong with the forecast leading to a lower risk of severe weather. 

1: Cloud cover left over from thunderstorms in the Midwest may leak over the mountains into our area sometime Wednesday morning. If this occurs and they don't dissipate in time, we miss out on peak heating which will lower instability greatly reducing our severe weather threat. 

2: Deep mixing of the lower atmosphere during the afternoon drops the dew points too low, inhibiting the development of robust thunderstorms and dropping the instability low enough to where the storms are weaker.

3: Scattered showers and storms form well ahead of the cold front between 2 and 4pm and drop our temperatures and leave behind a lid over the atmosphere known as convective inhibition. This would prevent any additional storms from becoming severe with the actual cold front.

With that said, this certainly bears watching, but is not something to be overly worried about and I certainly wouldn't cancel any plans. Just keep an eye on the forecast and watch for changes and updates.

​Senior Forecaster Jack