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Fairfax County faces a marginal risk of flash flooding from Hurricane Ian (via NOAA)

(Updated at 11:20 p.m.) An October weekend once filled with fall events is starting to clear out, as Fairfax County braces for Hurricane Ian.

The storm that devastated Florida after making landfall on Wednesday (Sept. 28) is expected to weaken as it heads north, but its rain and winds could still prove dangerous, the Fairfax County Department of Emergency Management and Security (DEMS) warns.

According to the department, remnants of Hurricane Ian are projected to arrive tonight (Friday), bringing scattered flooding and strong winds:

  • Scattered localized flooding is possible from rain. Overall, we are not expecting significant flooding impacts from this event. The rainfall totals are expected to be between 1″-2″ with a high end of 3″ over the three day period of Friday through Sunday. A rumble of thunder may enter the area early Saturday morning, but no significant thunderstorm threat is expected.
  • Winds will be sustained at 15-20 mph with gusts between 20-30 mph throughout the weekend.
  • Tidal anomalies of 1-2 feet are possible, but no significant tidal flooding for Fairfax County is expected.

Gov. Glenn Youngkin declared a State of Emergency earlier this week, giving the state authority to mobilize resources in preparation for the storm.

Several events planned across the county for tomorrow (Saturday) have already been canceled or rescheduled, with organizers citing the impending inclement weather. Others are still monitoring conditions before making a determination.

The McLean Project for the Arts pulled the plug on its annual MPAartfest on Wednesday, though the 2022 McLean 5K is still on for now.

“This is a rain or shine event, we have no plans to cancel,” McLean Community Center General Programs Director Mike Fisher said. “If we do cancel, that decision will be made in the moment as a result of on the ground conditions at the event site.”

Reston Community Center’s first-ever Silent Dance Party at Reston Station has been postponed to 5 p.m. on Oct. 9, while Reston Association announced yesterday (Thursday) that its popular Reston Community Yard Sale has moved to next Saturday, Oct. 8.

This morning, the Town of Vienna officially canceled tomorrow’s Oktoberfest, which drew more than 35,000 visitors last year. The Fall Native Plant Sale has been bumped to Oct. 8.

Both Fairfax County Park Authority events set for tomorrow have been altered. Bug Fest at Lewinsville Park in McLean has been postponed to Oct. 22, but Buktertoberfest at Burke Lake Golf Course has been canceled.

In Fairfax City, the Out of Darkness Walk to raise awareness about suicide and mental health impacts is currently still a go, but the American Foundation for Suicide Prevention says it will provide an update by 5 p.m. if that changes.

Map via NOAA

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Rain collects around a storm drain (staff photo by Angela Woolsey)

Fairfax County is considering making all existing and future development built to lessen flooding risks from huge, 100-year event storms, as opposed to a 10-year storm.

The risk of flooding in the county is rising due to climate change, staff told the Fairfax County Board of Supervisors environmental committee late last month. While preventing flooding is impossible, its impact can be mitigated, they said.

Under the staff proposal, the county would require all future development to have proper drainage, pipe conveyance, and safety measures to accommodate a 100-year storm event adjusting for climate change.

The proposal is part of the county’s Community-wide Energy and Climate Action Plan, which was approved last September.

A “100-year storm event” is defined by the U.S. Geological Survey as one that “statistically has a 1-percent chance of occurring in any given year.” It brings about 8 inches of rain over a 24-hour period, according to the latest data.

With climate change expected to produce stronger storms and increased flooding, that figure is likely to be adjusted in the future.

Part of the proposal is that new development would be required to be built to adjust for predicted sea level rise and severe weather risks.

Currently, all developments must accommodate a 10-year storm event, which is the 10% chance of 4.5 inches of rain falling in a 24-hour period.

In the last decade, Fairfax County and the D.C. region have experienced several flood-level storms. In 2011, Tropical Storm Lee dumped 7 inches of rain in three hours. In 2019, nearly 5 inches came down in some parts of the county, and just last month, nearby Montgomery County experienced extreme flooding from more than 5 inches of rain.

For existing structures, like houses, the plan is to “mitigate” flooding through regulation, public infrastructure projects, and recovery programs.

“There’s no right answer about what flood risk is acceptable because there’s no such thing as zero risk from flood,” Department of Public Works and Environmental Services Deputy Director Ellie Codding said. “What we can do is design infrastructure to a reasonable point and to educate the public and be ready with resources for recovery.”

With water typically passing through residential properties from upstream, a channel or flood path blocked by a fence, debris or an unpermitted addition can exacerbate flooding, preventing water from flowing where it was designed to go.

Almost all flooding in the county happens in basements, Codding said, so understanding and preventing this is a shared responsibility of residents and the county.

“With participation from residents and businesses, the county alone can’t achieve a meaningful level of flood risk reduction,” she said.

Of course, all of this will come with a cost, one that might be supplemented by increased taxes.

While board members agreed with the overall assessment, several noted that educating homeowners will be an important and more cost-effective component.

Chairman Jeff McKay said homeowners associations or community groups that own and manage stormwater facilities and common areas (like ponds) may not know how to maintain those.

“I’m increasingly concerned about the smaller subdivisions and lack of information, assistance, and oversight to even maintain stormwater facilities that they put in with their development,” McKay said.

Braddock District Supervisor James Walkinshaw noted that some responsibility needs to fall on contractors, who might be doing home renovations or repairs. They are either not educated themselves on good practices or not passing that knowledge on to their clients.

With the board’s consent, county staff are expected to present a “proof-of-concept” study with cost estimates next spring, followed by a flood mitigation plan later in 2023.

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The National Weather Service issued a Severe Thunderstorm Watch in the area through 10 p.m. (via National Weather Service)

Fairfax County and areas nearby are under a Severe Thunderstorm Watch this evening.

The National Weather Service issued a Flood Watch earlier today (Monday), cautioning flooding may occur this evening, and a Severe Thunderstorm Watch is in effect until 10 p.m.

“Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations,” the Flood Watch reads. “Afternoon to evening showers and thunderstorms may produce very heavy rainfall capable of flash flooding. This could include multiple rounds of storms which would enhance the flood risk. Rainfall rates may reach 1 to 2 inches per hour, locally higher in spots. The D.C. and Baltimore metros will be the most susceptible given recent heavy rainfall the past couple of weeks.”

The National Weather Service advises residents to monitor forecasts and be prepared in case of flash floods.

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Rain collects around a storm drain (staff photo by Angela Woolsey)

A Flood Watch has been issued for Fairfax County and the rest of the D.C. area.

The alert will be in effect from 11 p.m. today (Friday) through 2 p.m. tomorrow (Saturday), according to the National Weather Service, which warns that “excessive” rainfall may lead to flash flooding.

Rain levels are expected to range from 1 to 7 inches, depending on the exact location.

Here is more from the NWS:

* WHEN…From 11 PM EDT this evening through Saturday afternoon.

* IMPACTS…Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations.

* ADDITIONAL DETAILS…
– Showers are expected with scattered thunderstorms late this evening into midday Saturday. Average rainfall amounts around 1 to 3 inches are expected, but localized amounts around 4 to 7 inches in heavier showers and thunderstorms. Rainfall amounts around 1 to 3 inches within an hour or two are possible in areas where the heaviest rainfall occurs. The best chance for the heaviest rainfall will be overnight into Saturday morning.

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A Flood Watch has been issued for the D.C. area on July 6 (via National Weather Service/Twitter)

Updated at 2:25 p.m. — The Flood Watch has been extended to 5 a.m. tomorrow (Thursday), per Fairfax County.

Earlier: A Flood Watch is on the horizon for much of the D.C. area, including Fairfax County.

The National Weather Service issued an alert at 5:20 a.m. today (Wednesday), warning that storms may lead to flash flooding starting around 3 p.m. The watch is currently set to remain in effect until 3 a.m. tomorrow.

Here is more from the alert:

* IMPACTS…Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Creeks and streams may rise rapidly out of their banks. Flooding may occur quickly in poor drainage and urban areas.

* ADDITIONAL DETAILS…

– Multiple rounds of scattered to numerous showers and thunderstorms are likely this afternoon and tonight. The most likely time period for thunderstorms producing heavy rain and potential flash flooding is this evening, but thunderstorms could develop as early as this afternoon, and may linger well into the night. Several inches of rain is possible in a short period of time, which would cause rapid rises of water.

Despite the risk of rain, the region’s usual July heat and humidity are out in full force, with temperatures potentially reaching the low 90s. The heat index is expected to peak near 100 degrees, according to the Fairfax County Fire and Rescue Department.

“If possible, make sure to stay hydrated and in shaded or air-conditioned places. Also check on your friends and neighbors,” the department said.

Symptoms of heat-related illnesses include fainting or dizziness, muscle cramps, and nausea or vomiting.

Image via National Weather Service/Twitter

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Fairfax County’s interactive climate map shows heat and flooding conditions (via Office of Environmental and Energy Coordination)

As Fairfax County finalizes its first-ever plan to address the future effects of climate change, community members can see how the phenomenon already affects them with a newly released interactive map.

Launched last week, the climate map depicts heat and flooding data that can be viewed in conjunction with maps of the county’s population and infrastructure, including roads, utilities, and public facilities.

“The Fairfax County interactive climate map is a dynamic tool showcasing some of the best available data we have to date on climate impacts in our community,” Matt Meyers, the climate planning division director for the Fairfax County Office of Environmental and Energy Coordination, said. “The map is meant to inform and empower county residents, business owners, and community leaders to actively prepare for and participate in resilience efforts on a local level.”

The map offers a clear illustration of the heat island effect, showing that average daytime temperatures are higher in more populated and developed areas along major highways, like Tysons, Reston, the Fair Lakes and Fair Oaks area, and the Route 1 corridor.

Flooding appears to be most intense in the southeast part of the county, with waters from the Potomac River and Occoquan Bay overflowing onto Belle Haven, Lorton, Mason Neck, and Fort Belvoir. If sea levels rise a foot, Mason Neck will noticeably shrink. If they rise three feet, the Route 1 ramps to I-495 at the Alexandria border will be submerged.

Mason Neck with a 1-foot rise in sea level (via Office of Environmental and Energy Coordination)

The OEEC developed the map using information gathered through its Resilient Fairfax initiative, which started last year to establish a Climate Adaptation and Resilience Plan intended to reduce and prepare the county for the damages that will come with a rapidly warming Earth.

So far, the initiative has produced:

The Climate Adaptation and Resilience Plan will be finalized and presented to the Board of Supervisors for acceptance this fall, according to OEEC spokesperson Ali Althen.

The climate map uses the same data that went into the projections report and risk assessment, but it’s narrower in scope, focusing on current flood and heat information with some indicators of future conditions, such as “projected sea level rise and coastal storm surge,” the OEEC says.

With marginalized communities facing the most severe consequences from climate change, the map also incorporates data from the county’s Vulnerability Index, which scored different areas based on residents’ income, education, homeownership, and other socioeconomic factors.

The OEEC says it’s important for residents to understand what climate hazards are in store for the county so they can get involved in efforts to address those impacts. In Belle Haven, for instance, the U.S. Army Corps of Engineers has already proposed building a wall to mitigate flooding.

“Awareness is the first step toward climate readiness, and we hope this tool will allow users to grow in their understanding of the risks facing Fairfax County now and in the years to come,” Meyers said.

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Flooding on Old Courthouse Road in Vienna (file photo)

Fairfax County is under a Flood Watch until midnight.

The National Weather Service issued the watch this morning, noting flash flooding caused by excessive rainfall is possible after 3 p.m.

Showers and thunderstorms are expected later this afternoon into the evening, according to the National Weather Service. There will be heavy rainfall at times, with predicted rainfall amounts of 1 to 3 inches within the span of a couple of hours, according to the Flood Watch.

A Hazardous Weather Outlook in the county states damaging winds and hail are also possible.

Showers and thunderstorms are likely, mainly between 3 PM and 11
PM. A Flash Flood Watch for potential flash flooding is in effect
near and west of Interstate 95 during this time. Isolated
instances of flooding can`t be ruled out further east.

In addition, a few storms may become severe with damaging wind
gusts and large hail. An isolated tornado can`t be ruled out.

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A map depicts the location of a proposed floodwall in Belle Haven (via U.S. Army Corps of Engineers)

A floodwall in the Belle Haven community could help address Northern Virginia’s flood risk.

A recent study looked at the west bank of the Potomac River from Arlington to Prince William County for solutions to improve resiliency and reduce risks to human health and safety, economic damages, and disruption of critical infrastructure, according to a presentation.

While there were multiple options, the U.S. Army Corps of Engineers found a 5,600-foot-long floodwall in Belle Haven and a 2,500-foot-long floodwall along the Arlington Water Pollution Control Plant on S. Glebe Road were the most feasible.

The total cost of both would be $52.6 million, which includes a 45% contingency on costs, and is estimated to reduce about $66 million in potential damage.

The proposed Belle Haven floodwall would begin around Golf Course Square and extend down Boulevard View before turning west. Then, an earthen levee would be constructed and end near Westview Dog Park, according to the Feasibility Report and Environmental Assessment by Army Corps of Engineers, Baltimore District, and the Metropolitan Washington Council of Governments.

A map shows the potential flooding of Belle Haven by 2030 (via U.S. Army Corps of Engineers)

A map of Belle Haven shows that by 2030, the flood risk could extend to the Belle View Shopping Center, Belle Haven Country Club and other parts of the community.

The Belle Haven floodwall would have permanent aesthetic and recreation impacts, as well as stream impacts, according to the presentation. The floodwall would be about 6 feet tall on average.

During construction, there would also be temporary stream impacts. Mitigation would be required for permanent stream impacts.

A rendering shows what a 6.5 foot floodwall could look like in Belle Haven (via U.S. Army Corps of Engineers)

The public can comment on the study through Thursday, June 30, by emailing the project team at DC-Metro-CSRM-Study@usace.army.mil. The Corps of Engineers will respond to comments and revise the report between July and September, determing if this is the preferred option by November.

After further study, design — which hasn’t been funded yet — wouldn’t begin on the project until at least 2024.

The study was conducted as Northern Virginia has seen damaging storms over the years, to include the Chesapeake and Potomac Hurricane of 1933, Hurricane Agnes (1972), Hurricane Fran (1996), Nor’easter (1998), Hurricane Floyd (1999), Hurricane Isabel (2003), Hurricane Irene (2011) and Hurricane Sandy (2012).

Hurricane Isabel resulted in extreme water levels and caused millions of dollars of damage to residences, businesses and critical infrastructure, according to the study.

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A map shows areas across Virginia and the D.C. region under a tornado watch (via NWS Baltimore-Washington/Twitter)

(Updated at 12:55 p.m.) Tornado and storm warnings briefly usurped earlier weather alerts for Fairfax County as the National Weather Service noted potential dangers and hazards across the region.

“Damaging winds will cause some trees and large branches to fall. This could injure those outdoors, as well as damage homes and vehicles,” NWS said in a Severe Thunderstorm Warning alert. “Roadways may become blocked by downed trees. Localized power outages are possible. Unsecured light objects may become projectiles.”

An NWS Baltimore-Washington news feed noted just before noon that a Tornado Warning was in effect for parts of Reston and Great Falls until 12:15 p.m. today (Friday). A watch means tornadoes are possible, whereas warnings mean that they are spotted or indicated by radar.

Fairfax County and surrounding areas were also subject to a Severe Thunderstorm Warning until 12:30 p.m. today.

Previously, the National Weather Service issued a Tornado Watch around 6:20 a.m. today that’s in effect until 2 p.m. for Fairfax County and the D.C. region.

Tornadoes, damaging wind gusts and large hail are possible, the NWS said in the earlier alert.

The NWS Baltimore-Washington said on Twitter that scattered gusts could possibly reach 70 mph.

The NWS also issued a Flood Watch at 4:33 a.m. for the county and surrounding areas from 11 a.m. through 11 p.m. today. A NWS meteorologist warned that flash flooding is possible due to excessive rainfall.

“Multiple rounds of thunderstorms producing heavy rainfall may lead to scattered instances of flash flooding,” the NWS said.

Due to the storm risks, the county is under a Hazardous Weather Outlook, per the Fairfax County Office of Emergency Management:

Multiple rounds of showers and thunderstorms are likely starting this morning and continuing through this evening. Localized rainfall totals of 1 to 3 inches are expected, though locations that experience multiple rounds of thunderstorms could exceed 3 inches.

If you’re driving, don’t pass through flooded roads. Turn around, don’t drown. Also, keep children away from creeks and streams that may rise rapidly.

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Rain with hail in Vienna (staff photo by Angela Woolsey)

Updated at 7:25 p.m. — A Flood Warning has now been issued for Fairfax County, with an additional half to 1.5 inches of rain possible until 1:15 a.m. Monday. The Severe Thunderstorm Warning has also been extended to 8 p.m.

Earlier: A Severe Thunderstorm Warning is in effect for Fairfax County.

The National Weather Service issued the alert shortly after 5 p.m., warning of 60 mph wind gusts and quarter-sized hail:

IMPACT…Damaging winds will cause some trees and large branches to fall. This could injure those outdoors, as well as damage homes and vehicles. Roadways may become blocked by downed trees. Localized power outages are possible. Unsecured light objects may become projectiles.

Moving eastward, the storm has already made its way through Herndon and just passed the Town of Vienna, bringing a couple minutes of intense rain, thunder, and hail that ended as quickly as it began.

This is the second thunderstorm with hail to hit the D.C. area within the past week, and it came a day after temperatures hit a high of 92 degrees, according to NWS data.

While the warning is set to end at 6 p.m., a Severe Thunderstorm Watch is currently in effect until 9 p.m.

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