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NOTE: This diary will be updated as a liveblog for as long as I can stay awake. New updates are above the squiggle, the original diary is below.


UPDATE 4 150AM ET: The derecho is starting to weaken a bit as it hits the rain-cooled, stable air left behind by the thunderstorms that occurred earlier this evening. There are still numerous warnings on the storm for 70+ MPH winds. I have to turn in for the night, as I have to get up in 5 hours (ha!). You can keep track of the derecho's progress by using this link to Wunderground's great weather radar. Just click the little + closest to where you live.

Buenas noches. Stay safe.

UPDATE 3 125AM ET: The north end of the derecho is winning out. The south end -- as per normal with mesoscale convective systems -- is orienting itself on an east-west axis, taking the "oomph" out of its winds and turning into a flash flood threat.

The north side of the derecho, with a more north-south orientation, is powering along with 70 MPH winds. People all across Ohio, West Virginia, and Pennsylvania need to watch how this storm develops over the next few hours.

UPDATE 2 107AM ET: The derecho is moving into Central Ohio right now with 70+ MPH winds. The cold pool is starting to move ahead of the line a little bit on the south end. Hopefully this trend keeps up, but everyone under the watch needs to stay alert.

INITIAL UPDATE 1216AM ET: First note is that all times will now be ET, since the derecho has left the central time zone and is completely in the eastern time zone.

To answer the most pressing question on a lot of people's minds right now, we don't know if the derecho will hit the Washington DC area. The models say YES, around the morning rush, but it won't be as severe as it is right now. The problem with mesoscale convective systems (MCS, or organized lines of storms) like this is that there's not a very accurate way to predict when they will dissipate. Sometimes they last for hundreds of miles, sometimes they dissipate without warning.  

To get technical about it, the MCS dies off when the cold pool runs too far out ahead of the convection and chokes off the inflow, killing the convection. We don't know when that will happen. We know the environment all the way out to at least the Appalachian Mountains is favorable for cold pool maintenance, but stuff happens. We just have to watch the radar and look for signs of the cold pool beginning to outrun the convection.

No sleep tonight. This is an emergency situation for people who live in eastern Indiana and pretty much anywhere in Ohio. This is the derecho that we've promised for the last couple of days. It's happening. If you live in the area, you need to keep the local news on, set your weather radios to go off when a warning is issued, and wake your friends/family up so they don't get caught off-guard by this powerful system.

A PARTICULARLY DANGEROUS SITUATION Severe Thunderstorm Watch has been issued for parts of Indiana, Ohio, West Virginia, and Pennsylvania in anticipation of the derecho holding together and blowing through during the overnight hours. 80 MPH winds and large hail can be expected with the derecho as it comes through. These are destructive winds that will down large trees, power lines, and do damage to structures.

Here's the radar image as of this diary's posting around a quarter after 11 Central. The NWS warnings (yellow boxes) are for "destructive winds in excess of 80 MPH." The Doppler Radar out of Fort Wayne is measuring winds of 96 MPH 5000 feet off the surface, and if a downdraft pushes it to the surface, it could translate into sustained winds (or gusts) over 100 MPH.

This has the potential to be extremely dangerous, even more so since people are sleeping and may be unaware that the storms are coming. Please do what you can to alert your friends and family that this extremely dangerous line of storms is on its way. People can yell at me for editorializing and making this diary "emotional," but sometimes you have to call a spade a spade -- this is a very dangerous situation.

See my diary from yesterday for a comprehensive overview of derechos.

Prepare, but don't panic. Secure all loose items outside, as they will easily blow around in winds. Grills, patio furniture, garden gnomes, and whatever else you've got should go inside a shed, come inside, or get tied up against a sturdy object.

Make sure your cell phones are charged and you've got gas in your car.

Wear sneakers/tennis shoes/whatever you call them tomorrow in case you have to walk through broken glass or debris outside.

Make plans in case you lose power for an extended period of time.

Keep a very close eye on the Storm Prediction Center and your local National Weather Service office. Like I said, it'll happen very quickly once the storms form and the line(s) develop. People closer to the Appalachians will have more time to react than people in Illinois or Indiana.

Hopefully a derecho will not happen, but the risk exists, and it's better to be informed than scared by the news stations that can't be bothered to do in-depth reporting.

I'll continuously post updates tonight and tomorrow on my Facebook page regarding this and all other major severe weather outbreaks. Most other weather weenie pages are hyping this up as much as possible for their own personal gain. You won't find hype here or on my Facebook page -- hype doesn't help. 

Remember to only make decisions based on what the National Weather Service says.

Stay tuned to the weather and stay safe.

GET A WEATHER RADIO

National Weather Service Main Page
National Weather Service -- Wilmington OH
National Weather Service -- Charleston, WV
National Weather Service -- Pittsburgh PA
National Weather Service -- State College PA
National Weather Service -- Baltimore/Washington DC
National Weather Service -- Blacksburg, VA
National Weather Service -- Wakefield, VA
National Weather Service -- Philadelphia, PA
National Weather Service -- New York City NY

Storm Prediction Center Main Page
Storm Prediction Center -- Current Severe Weather Watches
Storm Prediction Center -- Convective (Severe Weather) Outlooks
Storm Prediction Center -- Mesoscale Discussions
Storm Prediction Center -- Storm Reports
Storm Prediction Center -- Mesoscale Analysis Pages

Wunderground's Detailed Radar (click the + nearest to you to see your local radar)

NOAA Weather Models

iMapWeather Radio App for iPhone/iPod Touch (costs $9.99 but well worth it)

Follow me on Facebook for updates on this severe weather outbreak and other weather news.
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