April 29: Heavy Rain & Strong Wind Approaching

Written on 04/29/2020
Jonathan Carr

Discussion: Another weather system featuring powerful upper-level dynamics should impact New Jersey tonight through Friday morning. Let’s break it down from top to bottom. 250mb jet analysis indicates a strong southerly jet streak for the E US coast on Thursday (120-130kts about 33k feet up). 500mb (about 18k feet up) analysis indicates a strong and broad W US ridge powering a narrow trough downstream currently over the C US. This trough will continue moving from W to E, with a near-neutral axis, eventually passing over New Jersey for peak impact conditions Thursday.

This should create a strong southerly Lower-Level Jet (LLJ) at 850mb (about 5k feet up) of about 60kts or 70mph) under the front-side of the narrow trough. With me so far? It means there will be a period of 70mph S winds at 5k feet up…starting tonight (Wednesday) and ending tomorrow night (Thursday). This does not however mean everyone on the surface will see 70mph winds.

A surface low should track with the trough through the Great Lakes and eventually transfer near NJ by Thursday night. It is then modeled to hang back over the NJ area on Friday as the frontal boundaries push through and occlude. All this adds up to very strong dynamics aloft with much uncertainty as to how much of these dynamics make it down to the surface. Down drafting (counter produced from lifting) and/or heavy downward rain columns could bring the 70mph jet to the surface but likely with some inhibited strength. That would mean some areas could see gusts of 50-60mph at times, especially during heavy downpours of rain and when embedded thunderstorms are nearby.

An area of high pressure in the Atlantic Ocean will aid in the S flow intensity. With that said winds should begin to strengthen this evening and ramp up by tomorrow morning. This places NJ in a strong warm sector Thursday until the front pushes through. You might see the sun poke through at times but it should feel like “a storm is coming.” A linear segment of precipitation should then slowly move through from W to E starting as early as Thursday afternoon and ending as late as early Friday AM. Because of the slow-moving nature of the front, flash flooding is very possible for areas of poor drainage, along creeks/streams/etc. As mentioned above the low then occludes and keeps some showers around Friday. The good news is that this sets up a beautiful weekend.

In English: S winds will continue to pick up tonight and really flex for Thursday. Thursday morning looks breezy-to-gusty with mostly cloudy skies and a few sunny breaks possible. It should have that “unstable feel ahead of a storm.” Clouds should then fill in by/around noon as a period of heavy rain, gusty winds and thunderstorms slowly passes through NJ from W to E between early Thursday afternoon and evening. Flash flooding is possible given how slow the line of rain is expected to move and how heavy the rainfall could be. The bottom line is that Thursday should be windy out of the S all day with heavy rain and thunderstorms possible during PM hours. The SENJ coast looks like the windiest area. NWNJ should still get breezy/gusty but not as much as SENJ. The main rain/storm/wind line then pushes off the coast by late-Thursday night/early-Friday AM. Lighter scattered rain showers could linger around Friday. We are then looking at sun and clouds with temperatures in the 60s and 70s for Saturday and Sunday. We just need to make it through the stronger storm/wind dynamics on Thursday and improving conditions by Friday night.

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