It has been a while since we have been able to confidently back off on winter weather potential; in a season which has featured an absolutely tremendous amount of snowfall events and a staggering amount of over-performers. With the upcoming midweek storm, the winter weather potential was fairly clear from the get go. A southern stream disturbance meandering near the Mississippi River, some cold air in place to start, and an energetic northern stream disturbance racing southeastward from Canada to the Great Lakes. The summation of all of these parts usually results in a winter weather event somewhere in the Northeast US, and this situation likely will end no differently. But a delicate evolution of events is likely to produce a warmer situation in our local area.
The evolution of the system begins well to our west, over the Rockies and International Border in the Northern US. As mentioned earlier, a southern stream disturbance will eject from Mexico into the Southern United States (likely providing a fairly significant amount of moisture) while a disturbance from the northern stream slides southeastward to phase with it. At the time of the interaction, a lack of high latitude blocking (over the Northwest Atlantic and Greenland) will allow for height rises over the East Coast, and warmer air intrusion ahead of the developing system. This will be less of a concern over New England, but all models agree that the warm air will likely warm both the mid levels and the surface and help to keep the thermal gradient to our north — meaning more rain than snow in much of the area.
The low pressure system is eventually forecast to develop from the Mid Atlantic states to a position near or just south of our area. As you may well know by this point, a low pressure system tracking over our area from the southwest has little or no chance to produce winter weather nearby. So with an antecedent airmass that is warm, we would need the low pressure system to track far south of our area. Forecast models, at this point, are in good agreement that it will track too far north for snow or wintry weather in much of Southern, Central NJ and NYC, with the exception being the northern suburbs where a period of wintry weather is possible at the start and finish of the event. Those are details which we will have to iron out as the event draws nearer.
While confidence is increasing that the system will track too close to our area to provide a significant winter weather event, the potential for heavy rain and gusty winds seems to be coming into better focus. As the system moves northeastward from the Tennessee Valley and Mid Atlantic, a strengthening low level jet is forecast to develop. With moisture streaming northward, aided by the southern stream shortwave phasing into the trough over the Mid Atlantic states, heavy rain is likely to develop near or just south of the thermal gradient. The strengthening winds aloft are also likely to provide gusty winds, especially near the area shores and beaches.
The axis of heaviest rain remains uncertain and will likely come down to the intricate details of the phasing systems and, accordingly, the development and placement of the warm front. So while our confidence is increasing in an event which will feature more rain/gusty winds than snow in our area, the details remain somewhat foggy and forecast models aren’t providing much increased confidence at this range. Over the next few days, models should begin to hone in on those details and we should be able to get a better feel as to exactly what kind of impacts the midweek system will bring to our area.