Wrap Up for July 28-30 Rain Event
An anomalously strong upper-level trough sharpened over the Northeast this past week and caused heavy rain over a large portion of the Northeast including much of southern New England. An associated surface low pressure area intensified over southeastern New York and then slowly moved east to the southern Gulf of Maine. The various numerical prediction models provided reasonably helpful guidance with generally good consensus on the larger scale pattern but with greater variability in details as one might especially expect in a summertime event. A few models correctly captured the area of the heaviest rain that fell over portions of eastern New York State whereas other models focused areas of the heaviest rainfall elsewhere. The overall synoptic pattern looked to be quite favorable for periods of heavy rain in southern New England, especially across western and central areas. The Flood Watches issued well ahead of time by National Weather Service offices seemed well-placed. This system was characterized by a pattern more reminiscent of late fall through early spring but acting upon a very moist summertime air mass (noting that warmer air allows more water vapor to be available than cooler air).
The sharp neutral to negatively tilted trough set the stage for upper diffluent flow which created a broad region of fairly strong uplift of a very moist summertime air mass. That alone indicated the likelihood of significant rainfall. Another important factor was a SSE to SE to ESE moderately strong low-level jet which provided low level convergence that also enhanced uplift of the moist air mass (especially in conjunction with the upper-level divergence). Furthermore, that low level jet induced orographic uplift across the Berkshires, Worcester Hills, and the higher terrain of western CT as the upslope of very moist air added further impetus for the upward motion (the process needed to wring moisture out of the air). And in addition to these factors was atmospheric thermodynamic instability that enhanced the intensity of some of the rain bands. The convection resulting from atmospheric instability resulted in embedded thunderstorms with extremely heavy downpours. Given the strength of the upper trough, the system also moved very slowly to prolong the duration of these heavy bands of rainfall.
The National Weather Service has compiled reports of total rainfall across southern New England. Swaths of 3 to 6 inches fell across the western half of CT as well as the Berkshires and Worcester Hills in western and central MA. Generally, 1 to 3 inches fell across eastern CT, northwest RI, and southeast Worcester County in central MA. Elsewhere, including across most of RI and eastern MA, 1 to 2 inches of rain fell. A few of the higher rainfall totals included 4.99 inches in Newington, CT, 4.13 inches at Bradley International Airport outside of Hartford, CT, 5.12 inches in Shutesbury, MA and West Springfield, MA, 4.92 inches at the Worcester Airport, 5.95 inches in Paxton, MA, and an amazing 6.16 inches in Ashburnham, MA.
Even higher rainfall totals were reported in the mid and lower Hudson Valley and portions of the Catskills in eastern New York State where a general 4 to 8 inches fell with pockets of 8 to nearly 12 inches!
Looking ahead, most if not all of the weekend looks to be dry with at least partial sunshine and seasonably warm temperatures in the 80s for most locations. Another intensifying upper low pressure trough will move into the Ohio Valley late in the weekend and then probably weaken some as it crosses southern New England on Monday/Monday night. This system may bring areas of heavy rain to portions of the Midwest and Ohio Valley. There could be pockets of heavy showers across southern New England Monday and Monday night, but the amount of rain received with the last event is not expected at this time. Nevertheless, this system bears some watching should it be slower to weaken as it moves through our area and the fact that this past event has resulted in streams running high across western CT, the Berkshires, and the Worcester Hills.
Next Message
The next message will be the weekly significant weather outlook scheduled for Monday August 3.
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Message issued July 31, 2026 by:
Bob Thompson
Retired National Weather Service Meteorologist
Blue Hill Observatory and Science Center Board member
