April 20: Thunderstorms Approaching

Written on 04/21/2021
Jonathan Carr

Discussion: We’ve had a nice run of non-disruptive weather conditions. Tomorrow (Wednesday) that will likely come to an end with a stormy frontal passage. Low pressure will track through PA into New England (just to the NW of NJ) on Wednesday. Right now (late Tuesday night) we’re in the warm sector ahead of the low (mild and moist SW flow). This gave us our warmer Tuesday and likely a warm start to Wednesday. The front will then push through Wednesday afternoon before colder air mass invades for Wednesday night through at least Thursday.

Let’s talk details for tomorrow. Until the storm front arrives, expect a mild and breezy day (out of the SW). The more clouds around, the weaker the afternoon thunderstorms will be. If skies are clearer, then diurnal instability will swell and likely produce a stronger thunderstorm outcome…suns out guns out. The storm front itself is modeled very thin so it should be a quick in and out event that approaches WNJ around noon and clears ENJ by 4pm or earlier.

I would expect a ~10-20 minute downpour with gusty winds and possible lightning. Isolated-to-scattered areas along the storm front could reach severe thunderstorm criteria for wind gusts and/or hail diameter. There is adequate wind shear to aid in wind gust potential. This could be a broken storm line meaning some will get missed while others get hit to the N and S. Otherwise expect a completed linear segment of storms along the front which is more inhibitive of tornado formation. We’ll know that tomorrow morning. The cold front will then push in and significantly drop temperatures and humidity through sundown Wednesday evening.

This colder air mass invasion will be driven by low pressure in SE Canada and high pressure in the SE US…the pitching machine wheels effect…straight NW flow for us from a cold Canadian air tap. With that said, Thursday morning is going to be a cold shock especially with wind chill factors.

In English: Expect milder breezy conditions until about noon on Wednesday. From noon to 4pm on Wednesday, a brief period (half hour or less) of rain and thunderstorms should push through from W to E (starts around noon for WNJ and ends by 4pm for ENJ). Temperatures should then plunge colder for Wednesday night and Thursday. I imagine lots of frost/freeze warnings. Temperatures should then moderate back for the weekend. Have a great Wednesday and please be safe! JC