Good evening! This post will cover tomorrow’s heavy rain threat.
Wednesday Heavy Rain Threat
First, it needs to be pointed out that this is only a threat of heavy rain and not all locales will see said heavy rain. Nonetheless, showers and storms are likely late tomorrow morning into the afternoon. An area of showers and storms exists in eastern Ohio and western Pennsylvania ahead of that short wave that will move NE overnight and reach the area late tomorrow morning: (radar courtesy NWS)
There is a distinct possibility that the cluster will expand, and the HRRR portrays this nicely as the area moves in late tomorrow morning and early afternoon (last frame is at noon tomorrow, this is the 1Z HRRR, courtesy of Weatherbell):
Again, moderate to isolated heavy rain is possible with the cluster but the larger heavy rain threat is behind it. Later in the day, dependent on how much clearing occurs, there is a chance of showers and storms forming. With high dewpoints and high PWAT values, heavy rain is likely in any storm that forms – PWATs over 2″ are likely in much of southern New England and all of New England sees greater than 1″ PWATs (as depicted with the 0Z 4km NAM at 2 PM tomorrow, courtesy Pivotal Weather):
The shortwave acts as a trigger, and high humidity gives some instability as dewpoints rise into the 60s and low 70s. There is a question of how much clearing does occur – lots of clouds, hindered storm development but even in that situation at least a few storms should form given marginal instability, and once you have a storm in such a highly juiced atmosphere, heavy rain becomes a risk, with localized urban flooding possible. In the afternoon heavy rain will be hit or miss as with any storm threat but the more clearing there is, the more likely it is that storms form. Additionally, strong winds are possible in the strongest storms, and the risk is increased a little bit if there is more clearing to equal more instability. Wind shear of 30-40kt in the 0-6km layer supports a strong wind threat in the strongest storms (0Z NAM at 2 PM tomorrow, courtesy of Accuweather Pro):
The threat will be dwindling by the evening hours.
More tomorrow morning on this threat, and the heat to come.
-Nathan
