Rare high risk of severe weather today, including tornadoes

Convective outlook map

All of Indiana, plus parts of Michigan and Ohio, including all 37 counties served by the northern Indiana National Weather Service (NWS) office, are at high risk of severe weather between 9 a.m. EST today and 8 a.m. EST tomorrow, according to the Day 1 Convective Outlook that the NWS Storm Prediction Center (SPC) issued at 7:59 a.m. today.

High risk areas in a convective outlook are not unusual in Oklahoma but it’s very unusual for the SPC to indicate a high risk in Indiana.

The outlook gives the following probabilities for the high-risk area:

  • Probability of a tornado within 25 miles of a point: 30%.
  • Probability of EF2 – EF5 tornadoes within 25 miles of a point: 10% or greater.
  • Probability of damaging thunderstorm winds or wind gusts of 50 knots (58 mph) or higher within 25 miles of a point: 45%
  • Probability of wind gusts 65 knots (74.8 mph) or greater within 25 miles of a point: 10% or greater.
  • Probability of hail 1″ or larger within 25 miles of a point: 15%

What do these percentages really mean? Read this excellent explanation on the SPC website.

A Public Severe Weather Outlook that the SPC issued at 3:49 a.m. EST captures the situation well in layman’s terms. You can read it below. I’m off to worship after I write this post but I’ll try to add additional information to this blog as time permits. Meanwhile, stay tuned to NOAA Weather Radio, and/or your favorite local broadcast station for any watches or warning. Also, the northern Indiana NWS office is putting out a constant stream of information on its Facebook page and Twitter feed.

0249 AM CST SUN NOV 17 2013


The NWS Storm Prediction Center in Norman, Oklahoma is forecasting
the development of a few strong, long-track tornadoes over parts of
the Mid-Mississippi and Ohio Valleys into Michigan today through
early tonight.

The areas most likely to experience this activity include:

Northern and Western Kentucky
Lower Michigan
Southeast Wisconsin

Surrounding this greatest risk region, severe thunderstorms will
also be possible from parts of Wisconsin, Iowa, Missouri, Arkansas,
Mississippi, Alabama, and Tennessee northeastward across much of the
Appalachians to the lower Great Lakes.

A potent jet stream disturbance with wind speeds in excess of 120
knots will sweep east across the central Plains today and across the
Ohio Valley and northern half of the Appalachians tonight. As this
occurs, a surface low now over the mid-Mississippi Valley will
rapidly intensify and accelerate northeastward, reaching northern
Michigan early tonight and western Quebec Monday morning.

East of the low, increasingly warm and humid air at the surface will
spread north across the Tennessee and Ohio Valleys, contributing to
very unstable conditions over a large part of the east central
United States. Coupled with daytime heating and ascent provided the
jet stream impulse, the environment will become very favorable for
severe thunderstorms --- especially along and ahead of fast-moving
cold front trailing southward from the low into the mid-Mississippi
and Ohio Valleys.

Given the degree of thermodynamic instability, and the strength and
character of the winds through the depth of the atmosphere, many of
the storms will become supercells. Some of these will be capable of
producing strong tornadoes --- in addition to large hail and swaths
of damaging surface winds.

The storms are expected to consolidate into one or two extensive
lines later today into tonight --- extending the threat for damaging
winds and isolated tornadoes eastward into the Appalachians by early

State and local emergency managers are monitoring this potentially
very dangerous situation. Those in the threatened area are urged to
review severe weather safety rules and to listen to radio,
television, and NOAA Weather Radio for possible watches, warnings,
and statements later today.