SKYWARN

Threat of severe weather today has increased

Products from the National Weather Service (NWS) this morning indicate increasing confidence of a significant severe weather event in Indiana today.

For starters, check out this multimedia briefing from the NWS northern Indiana weather forecast office:

The convective outlook that the Storm Prediction Center (SPC) issued at 8:36 a.m. includes almost all of Indiana in an area of moderate risk for severe weather. Only about 10 Indiana counties (two in the extreme northwest and several more to the extreme southeast) are outside the moderate risk area. In IMO SKYWARN’s quadrant two, all of the quadrant’s Indiana counties (Allen, Adams, Blackford, Huntington, Jay, Wells and Whitley) have a moderate risk, as do the western halves of the Ohio counties of Van Wert and Paulding. See the map below.

Covective outlook map

In case you’re unfamiliar with convective outlooks, the “categorical” view indicates areas of slight, moderate and high risk. In my experience, SPC rarely uses the high risk category. So even though the word “moderate” sounds, well, moderate, its use indicates a much stronger than usual probability of severe weather.

The probabilistic version of the convective outlook is even more interesting. In brief, most of Indiana has a 45 percent probability of damaging thunderstorm winds or wind gusts of 50 knots (58 mph) or higher within 25 miles of any point. That’s a much higher risk than exists on any normal April 18 (when the probability is probably less than two percent). And according to the Beaufort Wind Scale, such winds uproot trees and cause considerable structural damage.

On top of that, most of Indiana (including part of Allen County) has a 10 percent or greater probability of wind gusts of 65 knots (75 mph!) or greater within 25 miles of any point. Again, 10 percent seems like a small number, but if the probability of such winds on a normal April 18 is one percent, today’s risk would be 10 times greater than normal. And 65 knot winds are a big deal. According to the Beaufort wind scale, they can do “considerable and widespread damage to structures.”

Although damaging thunderstorm winds are the greatest threat today, there is a considerable threat of tornadoes, as well. Most of Indiana, including Allen County, has a 10 percent probability of at least a weak tornado within 25 miles of any point. In addition, the same area has a 10 percent or greater probability of EF2 – EF5 tornadoes within 25 miles of any point.

Perhaps the best summary of what to expect in the Fort Wayne area today comes from the Hazardous Weather Outlook that the northern Indiana NWS office put out at 4:03 a.m.:

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS MOST OF THE AREA TODAY AND TONIGHT. THE MOST LIKELY TIMEFRAME FOR SEVERE THUNDERSTORMS IS THIS AFTERNOON AND THIS EVENING. A LINE OF THUNDERSTORMS IS EXPECTED TO MOVE EAST ACROSS THE AREA THIS AFTERNOON AND THIS EVENING WITH WIDESPREAD WIND DAMAGE POSSIBLE AS THE STORMS MOVE THROUGH. ISOLATED TORNADOES MAY ALSO OCCUR.

SPOTTER ACTIVATION FOR SEVERE THUNDERSTORMS WILL LIKELY BE NEEDED THIS AFTERNOON AND TONIGHT. SPOTTER REPORTS OF ANY FLOODING TODAY AND TONIGHT WILL ALSO BE APPRECIATED.

What to do

Advice for the general public

  • Review the differences between weather watches (severe weather is likely) and warnings (severe weather is here, take shelter). See a definition page.
  • If you have a weather alert radio, make sure it’s on and working. Try to stay within earshot of it.
  • If you don’t have or won’t be near your weather radio, try to keep a local radio or television station on all day.
  • Consider signing up for free text message alerts. Most local TV stations offer them.
  • Prepare to cancel any planned outdoor activities.
  • Review how and where you’ll take shelter if a severe thunderstorm or tornado threatens.

Advice for spotters

  • Make sure your friends, family members, neighbors, etc. have the advice above.
  • Make sure all of your devices (radios, phones, tablets, computers, cameras, etc.) are working charged up and ready to go.
  • Watch the SPC site for mesoscale discussions, which give early notice that a watch is about to come out. At 8:25 a.m. EDT, the SPC had already issued mesoscale discussion number 0518, indicating an 80 percent chance of a watch in most of Indiana.
  • Review your spotter training (safety procedures, what to look for and where, what to report, what not to report, etc.).
  • Review your reporting procedures (Ham radio net procedures, Twitter procedures (use hash tag #nwsiwx if reporting to the northern Indiana NWS office), etc.)
  • If you have access to Twitter, set up a search for tweets containing the #nwsiwx hash tag, so you’ll see what others are reporting.

That’s it for now. If time permits, I’ll post additional blogs throughout the day. But I’ll also be working my day job, so time won’t always permit. Meantime, add a comment below with your thoughts, questions, plans, etc. Stay safe!