Much of Indiana and Ohio have increased probabilities of severe weather between 8 a.m. EDT tomorrow (Sat., July 26) and 8 a.m. EDT Sunday, according to the “Day 2 Convective Outlook” that the National Weather Service Storm Prediction Center issued at 2:05 a.m. EDT. Some areas have twice as much probability of severe weather, as compared to the “Day 3 Convective Outlook” the SPC issued yesterday.
All of Indiana and Ohio have a slight risk (a probability of at least 15 percent) of some form of severe weather within 25 miles of a point on Saturday, but a large part of Indiana and Ohio — including most of IMO SKYWARN quadrant two — now have a 30 percent probability, which is on the high end of “slight risk” criteria. When you consider that normal severe weather probabilities in these areas are probably 1 percent or less, a 30 percent probability essentially means that severe weather is approximately 30 times more likely than normal. Read more about how to interpret outlook probabilities.
For readers who might have trouble seeing the map above, within quadrant two, the 30% probability area includes southern Whitley County, extreme southern Allen County (Ind.), extreme southwestern Putnam County and all of the Indiana counties of Huntington, Wells, Adams, Blackford and Jay and the Ohio counties of Van Wert and Allen.
Day two outlooks do not provide probabilities of specific types of severe weather, so the probabilities above refer to one or more of the following: tornadoes, damaging straight-line thunderstorm winds or gusts of 58 mph or higher or hail of one inch or more in diameter.
Saturday meteorology
Here’s what meteorologists expect to happen Saturday: A cold front will travel quickly eastward across Wisconsin and Upper Michigan and then become stalled southwestward across northern Illinois, Iowa and northern Missouri and Kansas through evening. A broad belt of southwesterly winds in the low levels will develop and bring substantial moisture northeastward ahead of the front with dew points in the 70s into Illinois and Indiana by late afternoon. The greatest severe wind potential appears to be during the evening and overnight, from central Illinois eastward across Indiana, northern Kentucky and Western Ohio. Computer models are in good agreement, showing a corridor of strong storms.
A large complex of severe thunderstorms, which could persist for several hours, is possible (a severe mesoscale convective system, for readers who are weather geeks). Changes of wind direction and speed with altitude, which are required to sustain a severe thunderstorm (wind shear) will also increase overnight. Significant wind gusts will be possible. In addition, large, discrete rotating thunderstorms (supercells) are possible if the storms that form do not meld together as quickly as expected. If that happens, a couple tornadoes could occur.
Sunday
Slightly more than half of Indiana and all of Ohio have a slight risk of severe weather between 8 a.m. EDT Sunday, July 27 and 8 a.m. EDT Monday, according to the “Day 3 Convective Outlook” that the SPC issued at 3:30 a.m.
All of IMO SKYWARN quadrant two — including all of Allen County, Indiana — have a 15 percent probability of severe weather within 25 miles of a point. More importantly, the entire quadrant has a 10 percent or greater risk of significant severe weather, which the NWS defines as one or more of the following: tornadoes capable of producing EF2 or greater damage, damaging straight-line winds with speeds greater than 65 knots (75 mph), or two-inch-diameter or larger hail. Obviously, significant severe weather is even more rare, so 10 percent represents well more than 10 times the normal probability.
As with Saturday, Sunday’s severe weather will most likely happen late in the day. Meteorologists expect that by late afternoon Sunday, low pressure will settle over Lower Michigan, while a cold front extends southwestward from Indiana into southern Missouri. Ahead of the front, a very moist and unstable air mass will exist within an environment that has enough wind shear (see above) to support severe storms. Afternoon storm development will most likely happen first along the cold front, from northern Indiana into northern Ohio and extending northeastward across western New York. Supercells (see above) will be the dominant storm mode with very large hail and a tornado or two possible.
It would be a good idea to check today to make sure you have a reliable way to receive weather warnings and watches, especially in the middle of the night Saturday, while you’re sleeping. As always, I recommend a weather alert radio, which you can buy today for around $30 at many local retailers, including Walgreens and Kroger. If you have planned any outdoor activities Saturday afternoon or evening or Sunday afternoon or evening, determine now how you’ll know if a warning is issued while you’re out and where you will take shelter. If you are a SKYWARN storm spotter, be prepared for activation Saturday and Sunday.
The outlooks described above are subject to change (they could get more or less serious as the days they describe approach). Our next look at the outlook for Saturday comes when the SPC updates its “Day 2 Convective Outlook” by 1:30 p.m. EDT. After that, the next look at Saturday comes in a “Day 1 Convective Outlook” due out by 2 a.m. EDT tomorrow. Out next look at the outlook for Sunday comes in Saturday’s “Day 2 Convective Outlook” also due by 2 a.m. EDT tomorrow.
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