Regions of Kentucky

Louisville sits at the Falls of the Ohio, the one place the river was not navigable, which is why the city is there and why the water is the story. The 1937 flood put seventy percent of it under; the levee and the floodwall that answered it are what stand between the Ohio and downtown now. It is also the warmest, most paved ground in Kentucky — the urban heat island runs several degrees above the farmland around it — and it sits at the northern edge of the corridor that put an F4 through Cherokee Park on April 3, 1974.

The Inner Bluegrass is a limestone plateau with almost no relief and almost no shelter, and the phosphate in that limestone is the reason the pasture grows the way it does. Weather crosses it unobstructed: this is where a squall line that has run all the way from Missouri still has its legs, and where a January ice storm coats four hundred miles of board fence in a night. Above Winchester the ground begins to break into the Knobs, and the forecast changes with it.

Northern Kentucky is the Ohio Valley proper — three counties of dense river-terrace city on the Cincinnati side of the water, and eight of farm country and river towns strung east along the bank. The valley walls hold fog on the river for days at a time, funnel the wind along the channel, and put the region on the cold side of nearly every winter storm that splits between rain and snow. It sits under the Wilmington office's warnings, not Louisville's, and it is the one part of Kentucky where the forecast is usually written from Ohio.

This is the ground where the Bluegrass gives way to the Knobs and then to the cave country, and the forecast changes twice across it. The Ohio River counties on the north edge take the same flooding Louisville does; the sinkhole plain at the southern end drains underground and floods from below. Brandenburg was hit by an F5 on April 3, 1974 — one of the deadliest tornadoes of the Super Outbreak — and the same corridor still runs storms up out of the southwest after dark.

South-central Kentucky is karst: the rain does not run off here, it goes down. Mammoth Cave underneath it is the longest cave system in the world, and the sinkhole plain above it floods from the bottom up when the conduits fill faster than they drain. Above ground it is open, flat and unsheltered, the northern end of the corridor that brings Dixie Alley's overnight tornadoes up out of Tennessee — the December 10, 2021 track crossed the Barrens on its way to Bowling Green, where it killed seventeen people in one subdivision.

The western coalfield is low, wet ground between two rivers — the Ohio along the top of it and the Green cutting through the middle — and it is the part of Kentucky that floods most readily and drains most slowly. It is also the corridor the December 2021 quad-state tornado tracked straight up: Bremen and Dawson Springs were both destroyed that night, seventy miles apart on the same continuous track. The January 2009 ice storm centered here too, and left much of the region dark for two weeks.

Far western Kentucky is where four rivers meet and where the ground itself is not settled: the New Madrid seismic zone runs under the Purchase, and the 1811–12 earthquakes reversed the Mississippi here. It is the flattest, warmest and least sheltered corner of the state, the first ground a spring squall line reaches, and the December 10, 2021 tornado came ashore on it — an EF4 that ran 165 miles and took most of downtown Mayfield with it. Paducah's own NWS office writes the warnings for four states from the middle of it.

The southern Cumberland Plateau is where Kentucky starts to stand up. Lake Cumberland fills 100 miles of drowned river gorge behind Wolf Creek Dam, and the ridges above it hold cold air, freezing rain and fog long after the Bluegrass has gone over to plain rain. I-75 climbs through it from the Tennessee line, and the same escarpment that ices the road drops flash floods into the hollows below it in the space of an afternoon.

Nowhere else in Kentucky does a rain gauge total mean so little and the terrain mean so much. The mountains here are not high but they are steep and closely spaced, and every town sits in the bottom of a hollow with a creek running through it. Four inches of rain on that ground is not a flood advisory, it is a wall of water: July 2022 killed 45 people across Breathitt, Knott, Perry and Letcher counties in a single night. Black Mountain above Harlan is the highest ground in the state at 4,145 feet, and it holds snow the rest of Kentucky never sees.

The northeast corner is the Tri-State — Kentucky, Ohio and West Virginia inside twenty miles of each other where the Big Sandy meets the Ohio — and it forecasts like the Ohio Valley rather than like Kentucky. The river bottoms hold fog and cold air; the ridges behind them are the first of the Appalachians and take upslope snow off a northwest wind. Warnings here come out of Charleston, West Virginia, and the flooding comes from two directions: the Ohio backing up from below and the Little Sandy and Tygart coming down from above.