Harvey will roll across the Ohio Valley, before racing across the mid-Atlantic states with rain during part of the Labor Day weekend. While Harvey is not expected to bring damage anywhere close to the disaster in Texas, enough rain is likely to fall to bring isolated flash flooding hundreds of miles north of the Gulf of Mexico coast. This is due to its increase in forward speed as it transitions to a tropical rainstorm. Nevertheless, Harvey will remain an efficient producer of rain for several more days, a general 2-4 inches is likely to fall near and just north of its path over the Ohio Valley.
The Ohio Valley gets a lot of its weather from the Gulf of Mexico during the summer months, but why do these weather patterns race up parallel to the Mississippi River then swing east along the Ohio River?
Looking at historical tracks of hurricanes shows a connection between hurricanes hitting the Texas Gulf Coast and the Great Lakes region. Hurricanes hitting the Gulf Coast in a similar spot to Hurricane Harvey often drift north into Arkansas, Missouri and the Ohio River Valley. The remnants of these hurricanes frequently move into the southern Great Lakes region. The map just below shows all of the tropical systems of any strength to hit the area where Harvey came ashore.
You can see two common paths of hurricanes making landfall similar to Hurricane Harvey. One path often takes hurricanes westward into west Texas, northern Mexico and New Mexico. There is also a common track that brings remnants into the Ohio Valley and eventually the Great Lakes region. Three former hurricanes took a track through Missouri, Illinois, Indiana and Ohio. Centers of former hurricanes tracking into Ohio mean Michigan gets some rain that surrounds the circulation. Notice one tropical system barreled north, right through Michigan.
Just where is the Ohio Valley? Technically a river valley would just be a few miles wide but we tend to broaden our definition. As it turns out, that definition is quite broad. The center of the valley is, of course, the Ohio River, but the term encompasses a lot of land north and south of the Ohio and several states, too.
Loosely defined it includes a good portion of Ohio, Indiana, Kentucky, extreme southwestern Pennsylvania, extreme northwestern West Virginia, and down to the junction of the Ohio and Mississippi rivers. The Ohio River stretches nearly a thousand miles from Pittsburgh to its junction with the Mississippi River in Cairo, Illinois. It follows, for the most part, a west-south-westerly course.
So while the actual river valley may only be a few miles wide, the term encompasses the lower half of the state of Ohio along with much of northern and western Kentucky, southeastern Illinois and southwestern Indiana.
The Ohio River Valley can affect the weather because weather systems tend to follow the Ohio River Valley. In fact, it seems to be a preferred storm track because it's the path of least resistance and winds can channel into the low area. Moisture associated with the Ohio rRver plays a role in thunderstorms that cross the broad Ohio Valley region.
Ohio Valley weather is the equivalent of a meteorological Las Vegas with many days a potential crap shoot. In the Spring there may be three or four days in the 70s and lower 80s interspersed with frost, thunderstorms, flooding, sleet, temperatures in the 30s, more rain, hail, high winds and overnight snow that melts away before noon the next day, and tornadoes.
In the Ohio Valley, March is always miserable...two fairly pleasant days then the thermometer will start dropping. Then a rain shower that will rapidly deteriorate into a snowstorm, dumping three inches on the area. The following day will feature a wind-chill factor of minus 10. The last week of March features temperatures ranging from 20 to 80. There will be tornado warnings. Some days will be balmy before a cold driving rain sets in.
In mid-June spring weather will officially arrive in the Ohio Valley and by the end of the month the temperature will hit the 80s or 90s and every day will be hazy, hot, and humid.
There will be two nice weeks in October sandwiched between lots of rain. November and December will be cold, but usually not too bad. January and February will feature rain, snow, sleet, fog, ice, and an average temperature of 37 degrees, an ideal temperature for spawning 63 different types of viruses. There will be 13 days of sunshine.