Relentless Storms and Flash Flooding in July

August 11, 2023 // Article by: Steven Weinstein

As summertime heat and humidity continued to build, the month of July saw an active pattern that brought numerous severe weather and flash flooding events to the Northeast. Activity was spread out throughout the entire month, with any prolonged dry stretches essentially nonexistent. While localized flooding issues were prevalent within frequent pop-up storms, it was the organized systems that produced more widespread and significant flash flooding, leading to a substantial amount of road closures and water rescues. As such, most climate sites recorded well above normal precipitation for the month. Additionally, July flipped the script from May and June, finally seeing above average temperatures.

The first week of July started out with many areas across the Northeast running above average temperature wise. Additionally, it was active with many rounds of afternoon showers and storms, sporadic severe weather / wind damage, and localized flooding. The most noteworthy days during this stretch included the 2nd, which brought gusty storms to parts of the Mid-Atlantic, with a few brief tornadoes also occurring along and mainly west of the I-81 corridor in PA. Repeated and heavy downpours also led to a swath of 2.5-3.5" of rainfall on this day, mostly along and north of the Mass Pike and down into Northern CT, leading to some flooding issues. Furthermore, after storms on the 3rd that led to scattered reports of downed trees and power lines across the Mid-Atlantic and Hudson Valley, hit or miss storms the following day put on damper on some 4th of July plans.

As we progressed into the second week of the month, the 9th brought a significant flash flooding event to Northern NJ / PA and the Hudson Valley in association with a robust system and stalled out frontal boundary. While sporadic wind damage also occurred, it was the life-threatening flash flooding that was the most significant. Torrential, slow-moving, and repeated downpours during the day led to widespread amounts of 3-5" in these areas, with a bullseye of 5-8" of rain falling across portions of the Lower Hudson Valley. As such, numerous poor drainage, roadway, and stream / creek flooding issues resulted. However, flooding was most significant in the lower Hudson Valley, where there were road closures, mudslides, collapsed bridges, homes filled with water, and many water rescues. Unfortunately, 1 person lost their life in the area after being swept away by the floodwaters. Much quieter and largely dry conditions then settled in for the next few days for the majority of the Northeast as high pressure briefly pushed in. The 13th and 14th then marked the quick return of storms across the entire Northeast as another system pushed eastward and then stalled out. Scattered wind damage and a few instances of larger hail occurred, particularly up into Northern NJ and New England where localized flooding issues were again prominent.

Radar loop from NWS Mt Holly showing the torrential and repeated downpours across the Northeast on July 9th, 2023.

Rainfall totals across the lower Hudson Valley from the life-threatening flash flooding that occurred on July 9th, 2023.

The blistering heat and humidity continued into the latter part of the month with temperatures generally running near to above average everywhere. This prime airmass in conjunction with a multitude of disturbances passing overhead continued to be a catalyst for an active pattern and frequent storms. Some notable events included the 16th, which saw tropical-like torrential downpours traverse many of the same areas (NJ / PA and New England) hit hard by previous heavy rainfall events. Additional swaths of 2-4"+ of rainfall fell, with renewed flooding issues. Isolated severe reports occurred once again with a brief EF-0 rated tornado also touching down in Worcester County, MA during the morning. The next prominent event fell during the early morning of the 21st, as a line of strong and gusty storms raced out ahead of an approaching cold front. While this activity weakened as it arrived to New England, it was able to produce a swath of spotty wind damage down into Southeastern PA and MD. However, New England would get in on the action later in the day as strong storms developed in the afternoon, leading to some wind damage and flooding.

The severe weather and flooding persisted all the way through the end of the month with four potent setups and events closing out a ridiculously active last week of July; the 25th, the 27th, the 28th, and the 29th. All these events lead to localized poor drainage / roadway flooding, and while the events on the 25th and 29th led to swaths of wind damage and downed trees / power lines across the entire Northeast, the 27th saw numerous strong wind reports mostly in New England, with widespread wind reports on the following day across all of MD. The storms on the 29th produced wind gusts as high as 84 mph near Washington D.C. and a brief EF-1 rated tornado in Norfolk County, MA. Otherwise, the passage of the system on the 29th ushered in a welcomed drier, cooler, and much less humid airmass to end the month. 

Tweet from NWS Boston showing recorded rainfall totals throughout the month of July at various climate sites.

Overall, high and low temperatures largely ran 1-3 degrees above normal for July across the entire Northeast. While the oppressive humidity often made it feel much worse than it actually was, a few daily record highs were set during the month, most notably during the last week of July with many climate sites recording highs in the low to upper 90s. Conversely, the cooler airmass that finally settled in to finish the last few days of the month even allowed for some daily record lows in the 50s and 60s across many areas. Precipitation wise, most places ran well above normal. While many areas in the Mid-Atlantic up through NJ / PA were 1-3" above normal for the month, it was into Northern NJ, the Hudson Valley, and throughout much of New England where there was a surplus of 3-7"+ for the month! In fact, Hartford, CT recorded a total of 13.93" in July, which is a staggering 9.91" above the 30 day normal, making for the wettest July on record! Incredibly, there were some very spotty exceptions to this where areas actually ran slightly below average, most notably in Western MD and Western Long Island.