Onshore flow and Unsettled Weather Remains, but Light at the End of the Tunnel

Good evening, everyone! Unfortunately, the onshore flow and unsettled regime from the past several weeks has re-entrenched itself across the area, giving our area plenty of clouds, fog, drizzle, as well as scattered showers and thunderstorms. But as we mentioned in our premium article on Saturday night, there would be some subsidence in the area between a departing coastal storm and the core of a mid-level disturbance well to the northwest. This is why our area is not seeing any rain right now. However, plenty of deep onshore flow will keep a lot of low-level clouds and moisture around, which will lead to drizzle and fog continuing for the night. Some of this fog could be dense along the coast, as this moisture will get trapped underneath a strong inversion aloft. Temperatures will generally remain in the low 60s for most of the overnight, and any rain and thunderstorms associated with the main mid-level disturbance will mostly remain in Orange and Dutchess counties and northward. But as the mid-level disturbance slowly pivots southeast, storms will gradually get triggered a bit further south as the overnight goes on.

This means that parts of Northern New Jersey may have some pop up small thunderstorms during the late overnight hours that could bring brief periods of heavy rain as well as loud thunder and lightning. But generally speaking, any areas south and east of N NJ will still be too far removed from the mid-level disturbance and still embedded in large-scale subsidence from the departing coastal system, and thus it should remain mostly dry except for the aforementioned drizzle and fog. However, a decaying cluster of showers and thunderstorms could make it to E NJ, NYC, and parts of LI during the early-morning hours on Tuesday, as a vort max may break ahead of the main mid-level disturbance to trigger just enough lift for its formation.

Monday afternoon’s NAM model valid for Tuesday afternoon shows a potent 500mb low approaching the area, bringing very cold temperatures aloft.

As Tuesday goes on, the coastal disturbance will be departing and the 500mb low will be getting closer. This will greatly increase the mid-level instability, as it will provide a very impressive cold pool — 500mb heights of 558dam are impressively low for this time of year. And although the vorticity is somewhat strung out, there is a nice core of a vort max at the base of the 500mb low, which will be moving into the area and providing some positive vorticity advection. That, combined with the good jet dynamics should be enough to trigger several areas of showers and thunderstorms with relatively large coverage across the area. With a very stable layer at the surface, we do not expect any strong wind gusts with these storms, but some heavy rain, thunder and lightning are possible. It will not be raining all the time, as the lack of low-level lift will lead to breaks in the action and some scattered areas that do not get much rain at all.

Monday night’s 3km NAM model valid for 1:00pm on Tuesday shows a cluster of showers and thunderstorms in N NJ, moving into NYC (Tropical Tidbits).

Later Tuesday night, the 500mb low will open up and weaken, and thus coverage of showers and thunderstorms will wane. But continued onshore flow will keep things very chilly. In fact, as the coastal storm moves to our east and northeast winds thus strengthen on Tuesday, temperatures may actually fall throughout the day into the upper 50s — extremely chilly for the middle of the day in June. And on Tuesday night, temperatures will fall into the low to mid 50s, with continued clouds, fog, and drizzle.

Monday afternoon’s NAM model valid for Wednesday afternoon shows a high pressure to the north and a low pressure to the south, allowing for more onshore flow and chilly weather.

On Wednesday, the departing coastal storm will be replaced with an area of high pressure to the north, and a new coastal disturbance will be developing well to the south, which will again lead to onshore northeast winds. This will keep clouds and drizzle around, though the marine layer may not be as strong on Wednesday, so we may be able to pull off some very subtle peeks of sun and temperatures rising into the low to mid 60s. Notice the localized cool zone of 850mb temperatures in the Northeast, the developing low pressure in the Southeast, and the broad mid-level trough still over the area — all contributors to the continued chilly, unsettled weather.

This broad trough will actually turn into another cutoff low, but its associated surface low pressure system (the one in the Southeast in the above panel) should slide out to sea, and actually bring some subsidence to the area on Thursday as we will be away from the “lift” zone and thus in the adjacent “downward motion” zone. This may lead to more peeks of sunshine on Thursday and temperatures in the mid to upper 60s. We cannot completely rule out a scenario where that storm gets closer to the area, but we are not forecasting that right now.

Monday afternoon’s GFS model valid for Saturday afternoon shows southwest winds and temperatures in the upper 70s to low 80s!

And finally…some return southwesterly flow may move in on Friday behind that coastal storm and give us some sunnier and warmer weather with temperatures perhaps well into the 70s. The weather could become even warmer come Saturday. Some vorticity on the back side of the aforementioned cutoff low may help trigger some isolated scattered showers and thunderstorms on each day. It also looks like the warmth may stay around for at least several days!