Although a lot of the area has been able to salvage sunny skies for most of the day, clouds are on the increase and thunderstorms are forming in W NJ. The very warm and muggy airmass in association with a trough moving into the Great Lakes is the main trigger for these storms. The trough being quite far away also serves to keep wind shear quite weak. What this does is it prevents thunderstorms from becoming severe — but it also means that the storms move slowly. This, combined with the incredibly moist atmosphere leads to the potential for heavy downpours for a decently long period of time — thus the concerns for flash flooding. The strongest storms could have 40mph wind gusts and small hail — though that risk is more isolated.
As far as timing, the storms should move into Central New Jersey between 4:30 and 5:00pm, the NYC area between 5:00pm and 5:30pm, SW CT and Nassau County between 5:30pm and 6:00pm, and Suffolk County sometime after 6:00pm. Not everyone will get heavy downpours, but most of the area should see rain, with the potential for 1″ — with locally higher amounts. Definitely keep an eye on the latest radar and have the umbrella handy this evening.
Although the heaviest rain will probably fall within an hour of the storm’s arrival, showers and an isolated thunderstorm still cannot be ruled out for the rest of the overnight, and patchy fog may develop as well. Temperatures will remain in the 60s tonight with muggy conditions.
Wednesday: The showers and storms will clear the area by Wednesday morning, and the day should actually turn out to be decent, as a weak area of ridging will move in between the departing storm system, and another storm system coming for Thursday morning. It will be a bit cooler and drier than today, and skies should remain partly sunny, with temperatures in the upper 70s.
Wednesday night and Thursday: A disturbance and trough that is currently moving into the Central Plains — which will produce a significant outbreak of severe weather in those areas — will be moving eastward. Fortunately, we will not be seeing any tornadoes or derechos, but there is a relatively high probability of a complex of showers and embedded thunderstorms moving into the region on Wednesday night and Thursday morning. Yesterday’s article highlighted the chances for more significant severe weather, but it was dependent on the exact location of an associated frontal boundary. As of now, the front should stay far enough to our south to keep the highest instability for maintaining a line of severe thunderstorms confined to the Mid-Atlantic. If that front takes a trek north of forecast, we may have to watch for more significant severe weather. But as of now, heavy rain and embedded thunder is likely on Wednesday night and Thursday morning, with the potential for 1″ of rain in the localized heavy downpours.
As that batch of rain moves out, sunshine should briefly break out late Thursday morning and early Thursday afternoon, which may provide more instability for more scattered thunderstorms, in conjunction with a cold pool aloft. High temperatures should be in the upper 70s.
Weekend Outlook: The cold pool may linger on Friday, providing the chance for a few scattered showers and thunderstorms, though most of the day will have a mix of sun and clouds with temperatures in the mid to upper 70s. Saturday and Sunday look better as a ridge builds back in, and temperatures should be in the low 80s with little wind. Great conditions for the Belmont Stakes!