Apr. 14th, 2012

eponymous_rose: (Weather | Radar)
Because hey, I worked as an operational forecaster for a while, there:

This is going to be a big one. Check here to see if your region is likely to be affected, and what type of severe weather to expect.

Note that, if you live in south-central Nebraska, there is a 45% chance that a tornado will occur within 25 miles of your position. This is extreme - to put that into perspective, major outbreaks typically present with a 10% probability. Odds are also good that the tornadoes that form will be EF-2 or higher, which means winds of upwards of 180 km/h (and I wouldn't be surprised if they break 300 km/h for an EF-5 or two). Straight-line winds between 50 and 65 kt are also a concern along a band to the east as the squall line develops, though really extreme (>65 kt) straight-line winds aren't expected. In terms of hail, the same region as for tornadoes is likely to see hail larger than 2 inches in diameter (in some cases, much larger) - to put that into perspective, one-inch hail is the size of a quarter. Picture someone standing on a tall building flinging quarters down at you. Now picture someone standing on a tall building flinging rock-solid grapefruits at you. Yeah.

If you're in Nebraska, Kansas, Oklahoma, western Iowa or Missouri, or just east of the Texas panhandle, keep an especially close eye on the weather today. Stormy weather is indeed a possibility across much of this region, so if you find yourself just outside the warning areas, stay alert.

The possibility of major loss of life today is high - there are lots of well-populated cities in the path of this weather. Keep emergency supplies on hand and don't take chances when it comes to taking shelter. If you're out stormchasing or trying to get pictures (...I really, really hope you're not), stay the heck away from cities, go the heck home if it starts getting dark, obey traffic laws, and do not under any circumstances leave your car in a position to block the path of emergency vehicles. Remember that while we don't warn for lightning, it's not something to mess around with - the risk of lightning persists up to 30 minutes after a storm has passed (the "bolt from the blue" is a real phenomenon).

Convective initiation has begun and a tornado watch is already in place over Kansas - a watch means that conditions are favourable for tornadoes to develop in this specific region, whereas a warning means that tornadoes are currently on the ground, or will be within the next fifteen or so minutes. If you'd like to monitor the situation (and watch live streams from chasers in the region), visit this site.

What to do if a tornado is headed your way:

In a house:
- If you have a proper storm shelter (or have access to one - the National Weather Center in Norman, Oklahoma has a massively reinforced auditorium-sized shelter that it opens to the public when those sirens start blaring, and yes, you can bring your pets), go.
- If you have a basement that is completely underground, go.
- If you have a basement that is partially underground, find a spot as far from the windows as possible, and if it seems likely that said windows will break, find something solid like a mattress to hide under to shield yourself from debris.
- If you do not have a basement, find a room with no walls connected to the outside world and stay low. If you don't have such a room, find the one with the smallest windows (usually the bathroom), stay low to the ground as far from the windows as possible (say, the bathtub), and drag a mattress over you to shield yourself from debris.

In an apartment:
- If you're on an upper floor, get down. If your building has a laundry room or some similar common area, stay low, stay away from the windows, and shield yourself. Note that unlike hurricanes, where people tend to take shelters in large, wide-open spaces, tornado shelters should be small and cramped to minimize the area where debris can fly around. A small closet or something similar is also acceptable. Just drag that mattress along and hide under it to shield yourself from debris.
- If you're on an upper floor and there is no common area downstairs, and there is a truly dangerous situation occurring, knock on doors. Tell people there's a storm coming (they should know at this point), explain that you're from an upper floor, and ask whether you can take shelter with them, if they have a room with no windows.
- If you're on the lowest floor and have a room with no windows, see the description of what to do in a similar situation in a house.
- If you're on the lowest floor and don't have a room with no windows, find a hallway (generally connecting the apartments) and bunker down there. Again, your mattress is your friend.

In an auditorium or a stadium:
- Get. Out. Find a sheltered room downstairs somewhere (they should open these to the public, but don't rely on event planners knowing what they're doing).

In a car:
- If you see a tornado and it's far enough away, drive at right angles to the tornado to escape. Obey traffic laws, and keep in mind that others may not be as conscientious as you - the worst thing to happen is to get into a car accident with a tornado heading straight for you. If the tornado doesn't seem to be moving, keep in mind that it is likely moving directly toward you.
- If outrunning is not an option, the best possible thing to do is to abandon your car (at least pull onto the shoulder so you don't cause a pile-up), get far enough away that it won't roll on you, and lie flat in the ditch. This reduces your odds of getting struck by lightning or hit by debris, but you have to keep in mind that flash flooding is a possibility with these things - be prepared to move if the ditch fills suddenly with water.
- DO NOT, repeat DO NOT seek shelter under an underpass. Never. Never ever. It can cause a wind tunnel, debris can still blow underneath, and what's more, you're highly increasing the odds of blocking traffic, including emergency vehicles. DO NOT SEEK SHELTER UNDER AN UNDERPASS. You're in even greater danger, and you're putting others in danger at the same time.

In an open field:
- The rule is to stay low to avoid being hit by lightning or debris. If you're in a wooded area, get out - those trees will become projectiles. Do not go to you car - it can become a projectile, too.

Wherever you are:
- Watch the radar. Listen for warnings and tornado sirens. Have an emergency plan in place. Stay safe.
- Once these storms are really up and running, strong winds will be running a considerable distance ahead of the storm itself, so you can take a sudden massive gust as a sign to seek shelter. The storm may have a circular or "mothership" look to it due to strong rotation. Also keep in mind that these are likely to be high-precipitation supercells, so any tornadoes could be wrapped in rain or hail and be very difficult to see. Trust the warnings.

Please, stay safe and pay attention to what's happening. Don't underestimate the destructive power of these storms.

Edit: The first tornado warnings have been issued, near Concordia, KS

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