Green area: Non-severe thunderstorms. Yellow: Slight risk of severe weather. Red: Moderate risk of severe weather.

The risk of severe weather today — the 40th anniversary of the 1974 tornado super outbreak — appears slightly lower than today’s risk appeared yesterday, according to the Day 1 Convective Outlook issued at 1:58 a.m. EDT by the National Weather Service (NWS) Storm Prediction Center (SPC). Most of Indiana continues to have a slight risk of severe weather between 8 a.m. EDT today and 8 a.m. EDT tomorrow and a moderate risk continues in the Mississippi Valley, but the risk of significant severe weather covers a smaller area in today’s day one outlook than it did in yesterday’s day two outlook.

Specifically, today’s day one outlook no longer indicates significantly severe weather in any part of Indiana.

Indiana and Ohio Counties
In northeastern Indiana, the slight risk area continues to include Huntington, Wells, Adams, Blackford and Jay Counties, as well as counties to the west and south of them. It does not include Allen, Whitley, DeKalb or Noble Counties or counties to the north and west of them. In northwestern Ohio, the slight risk area barely clips the southwestern corner of Van Wert County and excludes Allen County. It includes, however, Mercer and Auglaize Counties and essentially the southwestern fourth of Ohio.

Meanwhile, the very southwestern tip of Indiana, including Evansville, has a moderate risk of severe weather. The moderate risk area also includes western Kentucky and Tennessee, southern Illinois, most of the southern half of Missouri, most of Arkansas and the northwestern portion of Mississippi.

Hail, wind and tornado risk
For most of Indiana, the greatest risk is hail, with a 15 percent to 30 percent probability of at least one-inch-diameter hail within 25 miles of a point.

The probability of damaging thunderstorm winds or wind gusts of 50 knots (58 mph) or higher within 25 miles of a point ranges from five percent north of Indianapolis to 45 percent in the Evansville area.

And the probability of a tornado within 25 miles of a point ranges from less than two percent north of Indianapolis to 10 percent in the Evansville area.

Remember that all these events are generally rare, so probabilities as low as 10 percent indicate much more risk than on a normal day. Read more about severe weather probabilities.

Significantly severe weather in Mississippi Valley
The most remarkable risk in this morning’s outlook is for tornadoes capable of producing EF2 to EF5 damage (See an explanation of the enhanced Fujita scale). The probability of such significant tornadoes within 25 miles of a point is at least 10 percent in parts of southern Illinois, southern Missouri and northern and eastern Arkansas.

The outlook also indicates a 10 percent or greater probability of two-inch-diameter hail within 25 miles of a point in parts of Missouri, Arkansas, Oklahoma and Texas.

Timing for northern Indiana
Regarding timing, any severe storms in northern Indiana will most likely not occur until tonight and will mostly be south of U.S. 30, according to a Hazardous Weather Outlook issued by the northern Indiana NWS office at 5:11 EDT. That outlook also indicates that heavy rainfall today and tonight could result in flooding, especially along and south of U.S. 24.

The Hazardous Weather Outlook indicates that SKYWARN storm spotter activation might be needed tonight, so spotters should check their gear and be ready to report severe weather, especially hail and damaging winds.

Next update
The SPC will update its Day 1 Convective Outlook at approximately 12:30 p.m. EDT and again at approximately 4 p.m. This link will take you to the latest version at any time of day.

Probabilities of severe weather with 25 miles of a point, 8 a.m. EDT April 3 to 8 a.m. EDT April 4. Hatched area: 10% or greater probability of significant severe weather (see text below) within 25 miles of a point.

Tomorrow is the 40th anniversary of a super outbreak of tornadoes … an outbreak that caused massive damage in Monticello, Indiana and Xenia, Ohio, among many other places.

Ironically, some of the same areas that were affected by the 1974 outbreak have either a slight or moderate risk of severe weather, including tornadoes, on the anniversary.

Most of Indiana has a slight risk of severe weather between 8 a.m. EDT tomorrow (April 3) and 8 a.m. EDT Friday, according to the Day 2 Convective Outlook that the National Weather Service Storm Prediction Center (SPC) issued at 1:58 a.m. EDT today. The slight risk area also includes parts of Ohio and several states to the south and west. The slight risk area includes all or part of the Indiana counties of Huntington, Wells, Adams, Blackford and Jay, as well as other Indiana counties to the west and south of those. It also includes part of Van Wert County, Ohio. As of this morning, the slight risk area does not include the Indiana counties of Allen or Whitley, or counties to the north and west of them.

As you can see on the probabilities map above, north central and northeastern Indiana counties in the slight risk area have a 15 percent probability of severe weather occurring within 25 miles of a point. You can see an excellent explanation of severe weather probabilities on the SPC website. Day two outlooks lump all types of severe weather together, so these probabilities indicate that any of the following could occur: large hail, damaging wind, or tornadoes.

What’s particularly interesting about this morning’s day two outlook is that it indicates an area in which there’s a 10 percent or greater risk of significant severe weather. The SPC defines “significant severe weather” as two-inch diameter or larger hail, 65 knot (75 mph) or stronger winds or tornadoes capable of producing EF2 or greater damage. Because there’s less than a one percent probability of any of these events on a normal day, a 10 percent or greater probability represents a much greater risk than normal.

The area with increased risk of significant severe weather is indicated on the map above by the black loop and hash marks. It includes much of central and southern Indiana, including the Indianapolis, Terre Haute and Evansville areas. It also includes the southern halves of Illinois and Missouri, western halves of Kentucky and Tennessee, northwestern Mississippi, and all of Arkansas.

Here’s a summary of what SPC meteorologists wrote in the textual part of this morning’s Day 2 Convective Outlook: The potential exists for numerous severe storms Thursday with damaging wind, large hail and tornadoes possible, especially from the lower- to mid-Mississippi Valleys into the western Tennessee and Ohio valleys.

Surface-based thunderstorms will probably form across the lower- to middle- Mississippi Valley Thursday afternoon. These storms may initially be discrete in character, and conditions will become increasingly favorable for supercells capable of large hail and tornadoes. This activity will eventually spread eastward into western portions of the Tennessee Valley during the evening and overnight with a continued severe threat.

In the Ohio Valley region (including Indiana), the primary severe threat should develop Thursday afternoon and again overnight as deep layer winds strengthen ahead of a mesoscale convective system that is expected to evolve upstream across the mid-Mississippi Valley region. Damaging wind and a few tornadoes will be the primary threats

Our next look at the severe weather picture for tomorrow comes midday today, when the SPC will issue an updated Day 2 Convective Outlook. Even more specific information will appear in a Day 1 Convective Outlook due out early tomorrow morning.

Convective outlook for the period 8 a.m. EDT April 3 to 8 a.m. EDT April 4. Green area: Non-severe thunderstorms. Yellow area: Slight risk of severe thunderstorms.

Most of Indiana has a slight risk of severe thunderstorms between 8 a.m. EDT Thursday and 8 a.m. EDT Friday, according to the Day 3 Convective Outlook that the National Weather Service (NWS) Storm Prediction Center (SPC)  issued at 3:29 a.m. EDT today. The slight risk area includes Huntington, Wells, Blackford and Jay Counties of northeastern Indiana. It does not currently include Whitley, Allen or Adams County, Indiana or any of the Ohio counties served by the northern Indiana NWS office.

The potential exists for a widespread severe event Thursday — with damaging wind, large hail and tornadoes possible — especially from the lower-and mid-Mississippi Valley into the western Tennessee Valley, according to the Day 3 Convective Outlook. Meteorologists anticipate that they might need to upgrade the risk level from “slight” to “moderate” in portions of the above-described area in later outlooks.

The main threat for Indiana will be overnight Thursday into Friday morning, as storms develop along an advancing cold front. Meteorologists expect the storms to grow into one or more mesoscale convective systems.

Much could change between now and Thursday but this is a good time for SKYWARN storm spotters to make sure their equipment is ready to go and to keep an eye on subsequent convective outlooks.

Others, especially anyone who has planned outdoor activities Thursday, should prepare to change their plans as the day draws closer.

We’ll get our next outlook for the period early tomorrow morning, when the SPC issues a Day 2 Convective Oulook.

Professional photographer James Langford got this shot of a supercell near Allen, Tex. March 27, 2014. Visit Langford’s webiste.

Want more info on the Atlantic storm? Give @NWSBoston and @NWSCaribou a follow for some great tweets!

— NWS Northern Indiana (@NWSIWX) March 26, 2014

The National Weather Service recently reported that the May 31, 2013 tornado that killed four storm chasers presented a deceptive appearance that might have impacted chaser and spotter safety decisions. Well-known tornado scientist Tim Samaras was one of the four chasers who died, despite his reputation for caution.

Below is an excerpt from the NWS Service Assessment: May 2013 Oklahoma Tornadoes and Flash Flooding:

   Several storm chasers reported the visually-deceiving nature of the El Reno storm and its apparent width. Data received, and used with permission, from a chaser compares the visible width of the tornado condensation funnels to the actual width based on RaxPol (Rapid-scan X-band Polarimetric Radar). Although the tornadic circulation was evident on radar, many chasers did not realize they were in, or as close to, the large circulation (W9LW highlighting). During the time of rapid intensification, the forward motion of the circulation increased from approximately 35 mph to more than 50 mph. This speed increase, combined with a sharp left turn and intense inflow winds, made driving away from the tornado difficult (Figures 18–20).

Figure 18:  Analysis from Gabe Garfield showing “visible vs. actual” tornado width. Red markers approximate visible tornado width and blue markers approximate actual width of the tornadic circulation. Source: Skip Talbot, via NWS service assessment.

Figure 19: Visible vs. RaxPol-derived El Reno tornado width. Source: Gabe Garfield via NWS service assessment

Figure 20: Estimate of the El Reno tornado speed. Source:  Gabe Garfield and Jeff Snyder via NWS service assessment

This information should provide impetus for all SKYWARN storm spotters to reevaluate their safety procedures as the 2014 storm season approaches. It should serve to remind us all that:

• Tornadoes can and do make drastic direction and speed changes (don’t expect them to travel in a straight line).
• Life-threatening conditions can extend well beyond the visible condensation cloud and/or debris cloud, especially in the largest and most powerful tornadoes.

The authors of the service assessment recommended that all future SKYWARN training sessions “reinforce spotter safety and the rules outlined in NWSI 10-1807, The Skywarn® Weather Spotter Program.” That document contains the “10 Golden Spotter Safety Rules,” summarized below (the original 10 rules provide significantly more detail about each rule):

No spotter report or storm data is worth any person’s life. Please share this post with anyone you know who participates in storm chasing and/or SKYWARN storm spotting. Buttons below allow convenient sharing on social networks.

For several years, a Web-based weather reporting system called “eSpotter” has been available to trained SKYWARN storm spotters. They could obtain accounts from their local National Weather Service (NWS) offices and then used the special website to make any kind of SKYWARN spotter report. The report would be relayed immediately to the appropriate NWS staff member. That system is coming to an end this month, according to a Web page on the northern Indiana NWS website.

As a result of the pending termination of eSpotter, the NWS is no longer creating new accounts on the system. Spotters who already have accounts may continue to use eSpotter until it goes off line, but the NWS is encouraging them to begin using alternative reporting methods in preparation for the termination of eSpotter.

The IMO SKYWARN quadrant two net has used eSpotter in the past to relay reports from ham radio-equipped spotters when the ham radio station at the northern Indiana NWS office (WX9IWX) was not staffed. Over the past year, most quadrant net control station operators have obtained accounts on an internal NWS chat room service called, “NWSChat.” In the future, therefore, if WX9IWX is not staffed during a severe weather event, net control stations can relay hams’ reports via NWSChat. NWSChat accounts are not available to all spotters. They are only available to staff members of the NWS and its government partners, broadcasters and members of the emergency management community (including public safety officials and SKYWARN net control station operators).

For those spotters who are not eligible for NWSChat accounts and who prefer to use an Internet-based reporting method, below are the best alternatives. (This list is focused on the northern Indiana NWS office. To learn how to send tweets, Facebook messages, etc. to other offices, contact those offices):

Of course, non-Internet reporting methods remain available, including ham radio (for licensed operators) and telephone, using the special toll-free number that the NWS provides to spotters when they attend training (if you attended training but don’t have the number, use the email address above to request it).