Dense Wildfire Smoke, Severe Weather, and Flooding in June

July 13, 2023 // Article by: Steven Weinstein

The month of June and official start of summer marked the return of very active conditions and severe weather across the Northeast. Prominent weather stories throughout the month included instances of flash flooding and continued bouts of dense Canadian wildfire smoke that dramatically reduced air quality, visibilities, and made for some rather apocalyptic and 'martian-like' scenes across many Northeastern cities. Despite drought conditions growing slightly, heavy rainfall across parts of the region (especially during the latter part of of June) began to quench the driest areas. This drought was the byproduct of an abnormally dry May and well below normal 60 day precipitation departures. In fact, portions of Maryland and eastern Pennsylvania were in moderate to even severe drought categories. Furthermore, despite the drastic temperature swings throughout the month, temperatures were cooler than normal.

Despite the first few days of June starting off rather toasty with many New England climate sites setting daily record highs in the mid 80s to low 90s, there was a pattern change evolving. A series of upper level disturbances passed overhead, which caused temperatures to run as much as 7 - 15 degrees below average throughout the first week of the month. This cool down was felt most across portions of New England, that saw temperatures drop as much as 30 - 40 degrees between the 2nd and 3rd! Other weather events during the first week included some stronger storms that trekked across portions of New Jersey / Pennsylvania and into New England on the 2nd and 6th, leading to spotty wind damage, downed trees, and localized large hail. This pattern ultimately provided the ideal conditions for a plume of dense Canadian wildfire smoke to dive down and traverse the Northeast on the 6th - 7th, significantly hindering visibilities and air quality. In fact, this led to some of the worst air quality in decades, as many cities experienced a distinct rubbery/campfire smell. As a testament to this, Air Quality Index (AQI) values skyrocketted into the 300s and 400s for a time, well into the 'Hazardous' category, meaning that everyone was at risk of experiencing adverse health effects from the poor air quality.

The second week then picked up on the same cool note as temperatures continued to run a bit below average. Consequently, many Northeast climate sites set daily record lows during the first week or two of June, most notably Mt. Pocono which dropped to a chilly 34 degrees during the night of the 8th. Outside of isolated showers and storms across the Northeast, two systems were prominent during this time. The first was a widespread system on the 12th which produced heavy rainfall across portions of Pennsylvania and northern Delaware, with areas seeing 2-4"+ of rainfall and some localized flooding. The other was an upper level low on the 14th which brought a few strong storms to New Jersey / Pennsylvania and New England, resulting in some downed trees and powerlines.  

Timelapse from NWS New York showing a dense plume of Canadian wildfire smoke overtaking New York City on June 7th, 2023.

As we headed past the midway point and into the latter half of June the weather trended even more active with instances of more summer-like heat and humidity increasing. As such, afternoon and evening pop-up showers and storms and localized torrential downpours and flash flooding were the frequent headlines, though wildfire smoke aloft still made for occasionally hazy skies across the Northeast. All this available moisture helped fuel a more signficant bout of severe storms on the 16th across Southeastern PA, Southern NJ, and much of Virginia, which led to scattered wind damage. Additionally, two brief tornadoes resulted from this line, 1 EF-1 in Chester County PA and a brief EF-0 tornado in Burlington County, NJ. Further south in Virginia, the damaging wind and hail reports (of up to 2" in diameter) were more widespread as a result of storms. The next several days were much quieter for the majority of the Northeast with the bulk of any shower / storm activity suppressed off to the south in association with multiple systems across Maryland and Virginia. Otherwise, the 23rd brought renewed unsettled conditions to the entire Northeast as widespread showers and storms traversed the region. There were also pockets of significant flash flooding that occurred under torrential and repeated downpours during this event, particularly across Northern DE and on either side of D.C. where locally 3-5" of rainfall fell in a short while.

The very active pattern continued into the end of the month with an upper low producing some scattered downed trees and powerlines across New Jersey and Pennsylvania on the 25th. The 26th then brought the most signficicant event of the entire month as a slow moving system and multiple rounds of heavy thunderstorms, flooding, and severe weather moved across portions of the Hudson Valley, New Jersey, and Pennsylvania. Widespread damaging wind and hail reports were again notable across much of the Mid-Atlantic with a widespread swath of 2-5"+ of rainfall falling northwest of the I-95 corridor in New Jersey and Pennsylvania. Consequently, numerous poor drainage, roadway, and stream / creek flooding resulted which led to many water rescues and road closures. Lastly, a few confirmed tornadoes also occurred on this day, 1 EF-0 in northeastern Northampton County, PA (the county's first since 1997), and an EF-1 rated tornado in Northern Somerset County, NJ. Even the following day brought rounds of locally heavy rainfall across much of the Mid-Atlantic with some scattered strong and gusty storms. The last few days of the month then finally trended much quieter and drier, althought the summertime heat and humidity was in full swing. 

Tweet from NWS Mt Holly showing estimated totals and widespread heavy rainfall from storms on June 26th, 2023.

Overall, temperatures generally ran 1-2.5 degrees below average for the month even with the swings in readings. Precipitation wise, anomalies were widely variable across the Northeast owing to the localized nature of many of the heavy rainfall events. As such, while many areas across the Mid-Atlantic finished 0.5-2" above their normal monthly precip, there were other regions that ran slightly below normal for the month, most notably across Connecticut and Long Island where anomalies finished 1.5-2" below normal. Moreover, the jackpots for precipitation resided across Southeastern VA and Northern DE / Southeastern PA, that saw a surplus of 3-4"+ of rainfall!