Multiple rounds of heavy rain likely in the Northeast this week

An expansive and multi-faceted storm system will develop throughout the United States during the early and middle part of the upcoming week. Multiple pieces of energy will move from the Plains through the Mississippi and Ohio Valley’s and eventually towards the Northeast — each disturbance aiding in the development of heavy rain over a relatively large area. While wintry precipitation and severe weather are both possible in the Central United States, the main focus in the Northeast will be periods of heavy rain — much needed in many areas.

While uncertainty does exist given the multiple disturbances and intricate interactions between fronts, confidence has increased in the heavy rain threat over the past 24 to 48 hours. Forecast model and ensemble guidance has come into much better agreement on the storms overall evolution, with two separate rounds of rainfall likely in the Northeast US from Tuesday through Thursday.

Forecast models suggest the development of a large, expansive storm across the US this week.

Forecast models suggest the development of a large, expansive storm across the US this week.

One main takeaway from all the disturbances is this: There is plenty of moisture to work with in the atmosphere. With each disturbance providing sufficient lift for precipitation, that moisture will be tapped in to — resulting in the potential for heavy rain over a relatively large area.

The first disturbance moves towards the Northeast US on Tuesday afternoon and evening. From the southwest will come an area of “Warm Air Advection” or the movement of warmer air towards a certain area (that’s us) in multiple levels of the atmosphere. With this warm air comes moisture, and not-coincidentally, with the warm air and moisture comes lift. A period of heavy rain will shift northeastwards from the Mid Atlantic through New England — with rainfall totals of near 1″ possible across a large area.

Behind this disturbance will come an area of sinking air, or “subsidence”, where conditions dry out. But a large-scale disturbance will still be lingering back to the west, with more moisture surging up the East Coast on Wednesday. By Wednesday afternoon and evening, lift will again increase and rains will move from the Mid Atlantic through New England again.

Forecast models suggest the development of heavy rain in the Northeast US on Wednesday afternoon.

Forecast models suggest the development of heavy rain in the Northeast US on Wednesday afternoon.

This round is likely to feature periods of very heavy rain, near and along a cold front which will be pushing eastwards towards the coast from the Ohio Valley. This front will push through the Northeast US on Thursday, with drier air surging eastward and ending the rainfall on Thursday morning or early afternoon, depending on where you are located.

Rainfall totals are likely to exceed 2″ in some areas, but confidence in those numbers being widespread is not currently high. Still, beneficial rains are likely for a relatively large area this week. The heavy and rapid nature of rainfall at times could cause localized flooding, which could be problematic in poor drainage areas or areas that typically flood easier than others.

Over the next day or two, details should come into even more focus, with timing and intensity becoming more of an hour-by-hour forecast. Stay tuned for more premium posts and details as the event approaches.