Break from tropical downpours to be short-lived in Northeast
By
Alex Sosnowski, AccuWeather senior meteorologist
Updated Jul 16, 2021 8:08 AM EST
The same weather pattern responsible for excessive humidity and relentless downpours is likely to continue into next week over much of the northeastern United States, according to AccuWeather meteorologists, and that means more rounds of dangerous flash flooding and uncomfortable conditions are expected.
"The wet weather in the Northeast so far this July has been the result of a northward bulge in the jet stream in the West with a compensating southward dip in the jet stream centered on the Midwest," AccuWeather Senior Meteorologist Brett Anderson said.
Northward bulges in the jet stream are associated with heat and dryness in the summer, while southward dips in the high-speed river of air result in cool and wet conditions.
"That southward dip in the jet stream in the Midwest has created a south to southwesterly breeze in the eastern third of the nation, which has been loaded with moisture from the Gulf of Mexico and the Atlantic Ocean," Anderson said.
The moisture has delivered many days filled with high humidity that is more typical of Florida, as well as the summertime downpours that accompany that humidity. Light steering winds have not only allowed the showers and thunderstorms that have erupted in the heat of the midday and afternoon hours to reach miles up into the atmosphere, but they have also allowed them to only move at a snail's pace and unload copious amounts of rain in the process.
Following a drier June than average for a significant part of the region, the first half of July has been just the opposite.
During June, rainfall in Boston was about 70% of average with 2.57 inches of rain. It rained on nine of the 30 days, which was about average. However, it has rained every day during the first 13 days of July in Beantown, with nearly 9 inches of rain resulting in a departure of seven times that of normal.
It has been a similar story in New York City which recorded a June rainfall total of about 59% of average. The Big Apple has already received 8.49 inches of rain through July 14, compared to an average of 2.09 inches.
Parts of the Philadelphia area have also received excessive rain so far this month. The rain was boosted significantly by a deluge during late Monday afternoon where 5-10 inches of rain poured down in the northeastern suburbs.
Philadelphia International Airport has already received 4.35 inches through July 15, which is typically what falls during the entire month of July. At Northeast Philadelphia Airport, about 14 miles from Center City Philadelphia, nearly 8 inches were recorded from July 1-15. The normal for all of July at the airport is 5.17 inches.
Rainfall has been less extreme farther south along the I-95 corridor, but many areas over the central Appalachians and the eastern part of the Great Lakes region have had more rainy days than dry ones.
This image shows seven-day rainfall for the United States as of Thursday morning, July 15, 2021. (NWS/AccuWeather)
While downpours equal in magnitude to what fell in the northeastern Philadelphia suburbs on July 12, as well as part of New York City from last week may not be repeated, the ground remains saturated over a broad part of the region and may not take nearly as much rain to trigger flash flooding.
In some cases from Pennsylvania and northern New Jersey to parts of upstate New York and central New England, a mere 1-2 inches of rain in an hour can be enough to trigger rapid runoff and flooding of yards, low-lying areas and small streams.
By Monday, July 19, many areas in the region are likely to pick up another 0.50 of an inch to 1 inch of rain, but some locations may receive 2-4 inches of rain with the potential for even higher amounts in a couple of areas.
The saturated soil may allow trees to topple more easily in moderate winds when compared to more typical dry July conditions.
Commuters should be prepared for travel disruptions in much of the Northeast during this time. Some roads may rapidly become impassable as downpours erupt and crawl through some neighborhoods.
People living along small streams should keep a close eye and be prepared to move to higher ground should a deluge develop in their area.
There is some good news in the short term for those not only sick of the daily downpours but also the high humidity.
Many areas have a shot at being free of rain from into Friday morning. Some people over the interior Northeast, such as the Appalachians, may notice a subtle drop in humidity levels as well. There can still be a couple of random, pop up thunderstorms.
The break is likely to be short-lived, however.
As the next jet stream dip reloads over the Midwest Friday afternoon, showers and thunderstorms may begin to re-populate the sky over the eastern Great Lakes and central Appalachians. Although storms may hold off over parts of the I-95 zone and the beaches Friday, the heat and humidity are another story.
The temperature at Philadelphia International Airport broke into the low 80s on Thursday morning while temperatures around Baltimore nearly made it to 90 degrees. Highs Friday are forecast to range from near 90 in Boston and New York City to the mid-90s in Philadelphia, Baltimore and Washington, D.C.
Showers and thunderstorms are likely to expand over much of the Northeast Saturday, with perhaps the exception of some of the mid-Atlantic beaches and northern Maine, according to Anderson.
With more extensive cloud cover over the weekend, high temperatures are forecast to trend lower into the 80s, but the nights will be quite warm and muggy with lows mainly in the 70s.
"It is possible that enough dry air filters in from Canada to lower humidity levels and turn off the downpours from parts of the eastern Great Lakes and northwestern New England on Sunday," Anderson said.
Much of the balance of the region is likely to remain unsettled with high humidity.
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Many areas in the mid-Atlantic experienced dew point temperatures in the middle 70s F this week. The dew point is the temperature to which the air becomes saturated when cooled. The higher this number, the more humid the air is and the slower perspiration evaporates from the skin and clothes. Typical dew point temperatures for July range from the middle 60s to the lower 70s. Above this level, the air is considered to be very humid, even for midsummer standards in the Northeast.
"Many areas in the mid-Atlantic are likely to experience more mid-70-degree dew point temperatures this weekend to early next week," Anderson said.
The forecast for next week in the Northeast is still coming together, with multiple scenarios in play.
In one scenario, the southward dip in the jet stream may push to the Atlantic coast. In this case, temperatures may further ease down in the Northeast thanks to a weak push of drier, less humid air that could expand southeastward from Ontario and Michigan.
In another scenario, the southward dip in the jet stream may stall over the Midwest. This would allow the south to southwest flow of moisture with high humidity, showers and thunderstorms to continue in the Northeast.
One thing for certain during the middle of July is that weather systems generally do not move quickly and big blasts of cool air with low humidity are rare, especially over the Eastern Seaboard. Intense sunshine tends to override any cool starts to the days and makes for sweltering afternoons.
Either way, a totally dry week in the Northeast is unlikely with at least a couple of days where showers and thunderstorms will likely roam the region.
Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.
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News / Weather Forecasts
Break from tropical downpours to be short-lived in Northeast
By Alex Sosnowski, AccuWeather senior meteorologist
Updated Jul 16, 2021 8:08 AM EST
The same weather pattern responsible for excessive humidity and relentless downpours is likely to continue into next week over much of the northeastern United States, according to AccuWeather meteorologists, and that means more rounds of dangerous flash flooding and uncomfortable conditions are expected.
"The wet weather in the Northeast so far this July has been the result of a northward bulge in the jet stream in the West with a compensating southward dip in the jet stream centered on the Midwest," AccuWeather Senior Meteorologist Brett Anderson said.
Northward bulges in the jet stream are associated with heat and dryness in the summer, while southward dips in the high-speed river of air result in cool and wet conditions.
"That southward dip in the jet stream in the Midwest has created a south to southwesterly breeze in the eastern third of the nation, which has been loaded with moisture from the Gulf of Mexico and the Atlantic Ocean," Anderson said.
The moisture has delivered many days filled with high humidity that is more typical of Florida, as well as the summertime downpours that accompany that humidity. Light steering winds have not only allowed the showers and thunderstorms that have erupted in the heat of the midday and afternoon hours to reach miles up into the atmosphere, but they have also allowed them to only move at a snail's pace and unload copious amounts of rain in the process.
Following a drier June than average for a significant part of the region, the first half of July has been just the opposite.
During June, rainfall in Boston was about 70% of average with 2.57 inches of rain. It rained on nine of the 30 days, which was about average. However, it has rained every day during the first 13 days of July in Beantown, with nearly 9 inches of rain resulting in a departure of seven times that of normal.
It has been a similar story in New York City which recorded a June rainfall total of about 59% of average. The Big Apple has already received 8.49 inches of rain through July 14, compared to an average of 2.09 inches.
Parts of the Philadelphia area have also received excessive rain so far this month. The rain was boosted significantly by a deluge during late Monday afternoon where 5-10 inches of rain poured down in the northeastern suburbs.
Philadelphia International Airport has already received 4.35 inches through July 15, which is typically what falls during the entire month of July. At Northeast Philadelphia Airport, about 14 miles from Center City Philadelphia, nearly 8 inches were recorded from July 1-15. The normal for all of July at the airport is 5.17 inches.
Rainfall has been less extreme farther south along the I-95 corridor, but many areas over the central Appalachians and the eastern part of the Great Lakes region have had more rainy days than dry ones.
This image shows seven-day rainfall for the United States as of Thursday morning, July 15, 2021. (NWS/AccuWeather)
While downpours equal in magnitude to what fell in the northeastern Philadelphia suburbs on July 12, as well as part of New York City from last week may not be repeated, the ground remains saturated over a broad part of the region and may not take nearly as much rain to trigger flash flooding.
In some cases from Pennsylvania and northern New Jersey to parts of upstate New York and central New England, a mere 1-2 inches of rain in an hour can be enough to trigger rapid runoff and flooding of yards, low-lying areas and small streams.
By Monday, July 19, many areas in the region are likely to pick up another 0.50 of an inch to 1 inch of rain, but some locations may receive 2-4 inches of rain with the potential for even higher amounts in a couple of areas.
The saturated soil may allow trees to topple more easily in moderate winds when compared to more typical dry July conditions.
Commuters should be prepared for travel disruptions in much of the Northeast during this time. Some roads may rapidly become impassable as downpours erupt and crawl through some neighborhoods.
People living along small streams should keep a close eye and be prepared to move to higher ground should a deluge develop in their area.
There is some good news in the short term for those not only sick of the daily downpours but also the high humidity.
Many areas have a shot at being free of rain from into Friday morning. Some people over the interior Northeast, such as the Appalachians, may notice a subtle drop in humidity levels as well. There can still be a couple of random, pop up thunderstorms.
The break is likely to be short-lived, however.
As the next jet stream dip reloads over the Midwest Friday afternoon, showers and thunderstorms may begin to re-populate the sky over the eastern Great Lakes and central Appalachians. Although storms may hold off over parts of the I-95 zone and the beaches Friday, the heat and humidity are another story.
The temperature at Philadelphia International Airport broke into the low 80s on Thursday morning while temperatures around Baltimore nearly made it to 90 degrees. Highs Friday are forecast to range from near 90 in Boston and New York City to the mid-90s in Philadelphia, Baltimore and Washington, D.C.
Showers and thunderstorms are likely to expand over much of the Northeast Saturday, with perhaps the exception of some of the mid-Atlantic beaches and northern Maine, according to Anderson.
With more extensive cloud cover over the weekend, high temperatures are forecast to trend lower into the 80s, but the nights will be quite warm and muggy with lows mainly in the 70s.
"It is possible that enough dry air filters in from Canada to lower humidity levels and turn off the downpours from parts of the eastern Great Lakes and northwestern New England on Sunday," Anderson said.
Much of the balance of the region is likely to remain unsettled with high humidity.
CLICK HERE FOR THE FREE ACCUWEATHER APP
Many areas in the mid-Atlantic experienced dew point temperatures in the middle 70s F this week. The dew point is the temperature to which the air becomes saturated when cooled. The higher this number, the more humid the air is and the slower perspiration evaporates from the skin and clothes. Typical dew point temperatures for July range from the middle 60s to the lower 70s. Above this level, the air is considered to be very humid, even for midsummer standards in the Northeast.
"Many areas in the mid-Atlantic are likely to experience more mid-70-degree dew point temperatures this weekend to early next week," Anderson said.
The forecast for next week in the Northeast is still coming together, with multiple scenarios in play.
In one scenario, the southward dip in the jet stream may push to the Atlantic coast. In this case, temperatures may further ease down in the Northeast thanks to a weak push of drier, less humid air that could expand southeastward from Ontario and Michigan.
In another scenario, the southward dip in the jet stream may stall over the Midwest. This would allow the south to southwest flow of moisture with high humidity, showers and thunderstorms to continue in the Northeast.
One thing for certain during the middle of July is that weather systems generally do not move quickly and big blasts of cool air with low humidity are rare, especially over the Eastern Seaboard. Intense sunshine tends to override any cool starts to the days and makes for sweltering afternoons.
Either way, a totally dry week in the Northeast is unlikely with at least a couple of days where showers and thunderstorms will likely roam the region.
Additional weather news:
Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier, Spectrum, FuboTV, Philo, and Verizon Fios.
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