A Flash Flood Watch is in effect for Arlington and the D.C. region and Arlington County just issued the following alert.

The National Weather Service (NWS) reports they are monitoring 3 weather related threats to the metropolitan DC area starting this afternoon and into the night; high winds, a line of thunderstorms, and rainfall accumulations.

The NWS predicts wind gusts around 35-40 MPH starting in the early afternoon hours. The NWS is also monitoring threats of a line of thunderstorms approaching from the west which is expected to reach the area between 7 and 10 PM. The storms have the potential to produce heavy rainfall and wind gusts up to 70 MPH. The National Weather Service reports this line of thunderstorms is fast moving and will last around 15 to 20 minutes with residual rainfall immediately following. The area should expect up to 2 inches of rainfall.

Wind gusts up to 50 miles per hour could make travel treacherous throughout the day and could result in downed trees and power lines, forecasters say.

…WIND ADVISORY IN EFFECT FROM 9 AM TO 6 PM EST THURSDAY…

THE NATIONAL WEATHER SERVICE IN BALTIMORE MD/WASHINGTON HAS ISSUED A WIND ADVISORY…WHICH IS IN EFFECT FROM 9 AM TO 6 PM EST THURSDAY.

* TIMING…THURSDAY MORNING AND AFTERNOON

* WINDS…NORTHWEST 20 TO 25 MPH WITH GUSTS UP TO 50 MPH.

* IMPACTS…DOWNED TREES AND POWERLINES WILL BE POSSIBLE FROM THE HIGHER WIND GUSTS.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

A WIND ADVISORY MEANS THAT WIND GUSTS OF 45 TO 55 MPH ARE EXPECTED. WINDS THIS STRONG CAN MAKE DRIVING DIFFICULT… ESPECIALLY FOR HIGH PROFILE VEHICLES.

County officials compared the dangerous conditions Arlington will experience over the next 24 hours to the heavy winds of the June 29 derecho, which lasted 24 minutes.

Already some power problems and falling trees and power lines have been reported. Dominion reported 423 customers without power in Arlington earlier this afternoon, but power has since been restored to most. Firefighters are currently on the scene of a large tree that fell on to a house on the 2900 block of N. Oxford Street, in the Bellevue Forest neighborhood. The house was unoccupied at the time and nobody was hurt.

In the following Arlington Alert, the county says they’re starting to receive reports of flooded roads. Long Bridge Drive has already been closed due to flooding.

Hurricane Sandy is about to get worse.

Think of the derecho storm with high winds in June that lasted 24 minutes. The winds we’re about to experience beginning this afternoon are like the derecho, but they will last for 24 hours.

To paraphrase: Instead of 24 minutes of dangerous winds, it will be 24 hours of dangerous conditions.

We need you to stay off the roads and indoors as travel will become extremely dangerous with winds and heavy rain beginning this afternoon.

Several inches of rain and potential flooding could start happening. We’re beginning to get reports of flooded roads.

Have your battery-powered radio available and make sure your phone is fully charged if you lose power. We will share any shelter openings and other updates via our information channels such as our Emergency Management Blog, County Web Page and Arlington Alert.

Separately, the county is advising residents to secure loose items outside, if that can be done safely, and to avoid driving into high standing water. “Please exercise extreme caution” in the storm, the county said.

As high winds approach, exercise extreme caution. For the safety of our employees, Arlington County will implement its high-wind policy. As the wind approaches sustained speeds of 30-40-45 miles-per-hour, we will pull crews off the roads and in to a safe place. This includes Parks staff, who will suspend responding to downed tree calls during these dangerous wind conditions. As winds approach very high, sustained speeds, police and fire personnel will respond only to life-threatening calls.

Please exercise extreme caution; emergency managers urge you to go a safe place and stay there. We also encourage you to remove/secure loose items from your yard, balcony, deck, etc., as these could become dangerous projectiles in high wind. Do this if you can do so safely.

Monday & Tuesday trash and recycling services are delayed until Wednesday. Bring your trash carts and recycling bins into your house/garage; do not leave them outside, as they could become airborne and dangerous.

Also, it’s a good idea to remove or secure loose items from your yard, balcony, deck, etc., as these could become dangerous projectiles in high wind. Do this if you can do so safely.

We are receiving reports of ponding on some roads. Standing water is deceptive; do not drive into standing water. Do not go out onto the roads if at all possible; we urge you to get to a safe place and stay there.

• Do not drive into standing water. If floodwaters rise around your car, abandon the car and move to higher ground if you can do so safely. You and the vehicle can be quickly swept away.
• Six inches of water will reach the bottom of most passenger cars, causing loss of control and possible stalling.
• A foot of water will float many vehicles .
• Two feet of rushing water can carry away most vehicles including SUVs and pick-ups.

The tree pollen level shot up to high today due to the warm and windy conditions.

Local doctors say typically the first couple weeks of April mark the start of heavy allergy season. That increases throughout the month as more trees release pollen spores, which can be seen blanketing the area.

This year, allergy sufferers have already been reporting symptoms for weeks, thanks to a mild winter. In fact, the Capital Weather Gang reports this has been the third warmest meteorological winter on record for the region.

Don’t worry, there is relief in sight. Lower temperatures and expected showers should push pollen back into the moderate level tomorrow.

Until then, here are some tips for lessening allergy suffering:

• Keep windows closed at home and in the car. Use the air conditioner if necessary, and be sure to change air filters.
• Stay inside on windy days.
• Avoid outdoor activity in the morning when pollen counts are highest, usually from 5:00-10:00 a.m.
• Change clothes after being outside. Take a shower to wash off pollen spores, especially before going to bed.
• Use a machine to dry laundry instead of hanging it outside.

The winds carry the possibility of blowing debris and downed power lines, among other hazards. From Arlington Alerts:

The National Weather Service has issued a Wind Advisory for Arlington County and other jurisdictions within the National Capital Region from 3 pm, Friday, February 24th, until midnight tonight. The strongest winds are expected to occur late this afternoon thru this evening with gusts up to 55 MPH. Winds this strong may make driving difficult, especially for high profile vehicles. Use extra caution

(Updated at 12:25 p.m.) Tropical storm-force winds from Hurricane Irene, combined with a steady, soaking rain, brought down at least 75 trees throughout Arlington last night, completely or partially blocking at least 35 streets, authorities said.

The falling trees blocked main roads, like Columbia Pike and westbound I-66, and knocked out power to various parts of the county. The 100 block of N. Liberty Street, Rock Spring Road and N. Wakefield Street, N. Quantico and N. 18th Street and N. Edison and Little Falls Road all remain blocked this afternoon, according to authorities and residents. County crews with chainsaws are helping to remove fallen trees and tree limbs from the roadway.

Some trees fell onto power lines and the roofs of houses, courtesy of wind gusts up to 59 miles per hour. A tree also fell onto the Blue Line tracks near Arlington National Cemetery, forcing Metro trains to single-track through the area.

Dominion was reporting more than 14,000 customers without power in Arlington as of 6:00 a.m. Numerous traffic lights were either dark or flashing as power flickered in many parts of the county overnight. The number of reported power outages dropped to just below 8,000 by noon on Sunday.

So far, only one minor storm-related injuries has been reported, according to Arlington County spokeswoman Jennifer K. Smith.

A steady, soaking, all-day rain and and gusty winds should make for an unpleasant Thursday. Officials are warning anyone who lives in low-lying or flood-prone areas to be “prepared to take action should flood develop.”

FLOOD WATCH REMAINS IN EFFECT FROM 6 PM EST THIS EVENING THROUGH THURSDAY EVENING…

THE FLOOD WATCH CONTINUES FOR

* PORTIONS OF NORTHERN AND EASTERN MARYLAND… THE DISTRICT OF COLUMBIA AND NORTHERN VIRGINIA… EAST OF THE BLUE RIDGE.

* FROM 6 PM EST THIS EVENING THROUGH THURSDAY EVENING

* PERIODS OF MODERATE TO HEAVY RAIN WILL MOVE INTO THE REGION AHEAD OF A COLD FRONT THIS EVENING INTO THURSDAY. BY THE TIME THE FRONT CLEARS THE AREA THURSDAY NIGHT… UP TO 3 INCHES OF RAIN WILL BE POSSIBLE.

* THE FORECASTED RAINFALL AMOUNTS LIKELY WILL CAUSE FLOODING OF LOW LYING AREAS… AS WELL AS CAUSE SMALL STREAMS AND CREEKS TO RISE OUT OF THEIR BANKS. THE RUNOFF WOULD THEN CREATE SIGNIFICANT RISES ON AREA RIVERS.

PRECAUTIONARY/PREPAREDNESS ACTIONS…

A FLOOD WATCH MEANS THERE IS A POTENTIAL FOR FLOODING BASED ON CURRENT FORECASTS.

YOU SHOULD MONITOR LATER FORECASTS AND BE ALERT FOR POSSIBLE FLOOD WARNINGS. THOSE LIVING IN AREAS PRONE TO FLOODING SHOULD BE PREPARED TO TAKE ACTION SHOULD FLOODING DEVELOP.

Steady rains caused some localized flooding in parts of the county. Police reportedly had to block off 11th Street at North Kennebec Street last night due to water in the roadway. A big pool of standing water also caused a traffic hazard on the northbound lanes of Glebe Road, just before Wilson Boulevard.

Local streams filled with fast-moving water as a result of the rain. This video shows a normally-peaceful section of Four Mile Run that turned into a raging rapid near Shirlington.

Elsewhere in Arlington, gusty winds brought down trees and power lines.

A brief period of sleet, meanwhile, made its way through the area around midnight. There was no noticeable accumulation in Arlington.

Numerous reports of downed power lines, toppled trees, dislodged traffic signs and blowing debris are coming in.

Among the reports we’re following right now:

• Downed power line on Four Mile Run Drive at George Mason Drive. Traffic is being diverted. Dominion is on the scene.
• Large tree down at 3700 North Harrison Street
• Awnings dislodged and glass broken at 3100 Clarendon Boulevard
• Compromised roof at 1300 South Arlington Ridge Road
• Updated at 5:05 pm. — Large tree down at 17th Street and North Utah Street
• Updated at 5:05 pm. — Wires down at 23rd Street North and George Mason Drive
• Updated at 5:05 pm. — Tree down at George Mason Drive and Four Mile Run Drive
• Updated at 5:05 pm. — Dominion is reporting 1,368 customers without power in Arlington
• Updated at 5:10 pm. – Wires down at 18th Street and South Edgewood Street

High winds have blown off part of the roof of the Virginia Department of Motor Vehicles building at 4150 South Four Mile Run Drive.

Firefighters report that a large section of the building’s metal roof blew off. The building has been evacuated. No injuries are reported.

A building inspector has been requested at the scene.