A colder regime is setting up into early next week

That's right folks, a colder regime is setting up and will presist into early next week. A potent ULL is currently tracking eastward from out of the Plains states, as its associated surface low, at 997mb at 00Z and its cold front is treking eastward into the OH Valley.

The 12Z GFS/NAM have trended drier with the frontal passage. Why? The upper level forcing will be north of the NYC area. A warm front, clearly shown on the WV imagery at 850mb in the mid levels is trying to trek to the NE at this hour. That will bring an increase in clouds in SW low level flow. A couple of things play against the warm front clearing the NYC area to the north: the surface low is still well to the west, chilly ocean waters, and a developing LLJ at 850mb not overspreading the region until morning. The front should clear southern portions of the NYC area. However, the best lifting and convergence is to the north.

However, there is a chance for thunderstorms. First, theta e ridge will advect in to create marginal to moderate levels of instability, however elevated in nature because the warm front should not make much progress northward and those north of the front will be stuck in a stable, cool airmass. Remember, the airmass is not all that humid and moist. Shear is impressive in the low levels as well as deep layer shear is impressive. Could see some convection fire by daybreak in the vincinity of the warm front. Then the warm front tries to lift through by 12Z.

Looking for an afternoon frontal passage after blending the ECMWF/GFS/NAM. Should see plenty of cloud cover, and that will inhibit destablization of the atmosphere. However, if skies clear faster, then watch for a line of low topped thunderstorms moving W to E with the cold front with strong mid level forcing, strong deep layer shear, and enough of a mid level wind profile. Damaging winds will be the main threat if those low topped thunderstorms develop.

After the frontal passage, strong CAA will commence, and winds will increase as the stacked low intensifies in the Gulf of Maine and Candian Maritimes and High Pressure builds out of Central Canada eastward to the Mid-Atlantic. Winds could advisory level criteria tomorrow evening on Long Island. Temps will rapidly drop into the 40's most areas tomorrow night. Sunday will be a cool day with cyclonic flow aloft. Temperatures will struggle to get to 60 degrees. The high continues to build overhead on Monday, and the low turns more anti-cyclonic. Still, temperatures will struggle into the lower 60's. Tuesday and Wednesday, a warm front tries to approach from the southwest, bringing a chance of showers, with moderating temperatues to near normal levels.