Several days of heavy downpours have already resulted in severe flooding in parts of the Northeast. While a brief reprieve from the rain is expected this upcoming weekend, long-term relief will not arrive for at least two more weeks. Heavy rains will continue to exasperate flooding woes into early August as an atmospheric river of tropical moisture remains steadfast over the western Atlantic Ocean into the eastern US. While rains will be heavy, tropical warmth will be associated with the moisture in the Northeast, keeping temperatures slightly above normal. Conversely, the pattern favors unseasonably cool temperatures to continue in the central and southeastern US.
The culprits behind the unsettled pattern are the seasonably strong Bermuda High over the western Atlantic Ocean and sequences of unseasonably potent upper-level low troughs positioning themselves over the central US. With high pressure to the east and low pressure to the west, air will be pulled northward between both systems from the Caribbean Sea into the eastern US. Given that it is the middle of summer, the strength of the hot Bermuda High over the subtropical Atlantic will overpower the southeastward progression of the cool upper-lows from the Canadian plains. This will cause the upper-lows to stop dead in their tracks over the Great Lakes and Ohio River Valley.
Model guidance has been in unusual agreement about the placement of the troughs and their associated cool air over the next few weeks. Recent runs of both the GFS, the ECMWF, and their ensembles were nearly identical in their positioning of the troughs. Both depict the base of the troughs and the fringes of the Canadian airmass extending southward to the Gulf Coast by the middle of next week and persisting through at least the end of the week.
There were minor differences in intensity of the Bermuda High and of the high pressure system currently broiling the West with record heat, however. Minor differences in jet stream placement and high pressure intensity contribute to more significant differences in precipitation in the East between the models, namely where the axis of heaviest precipitation will be and how much additional rain will fall.