The budding warmth overspreading the eastern half of the US this week comes at a striking cost. A building contrast between the arctic and the Gulf of Mexico will culminate in two days of flooding downpours and thunderstorms over the Ohio River Valley and lower Mississippi Valley between Wednesday morning and Thursday night.
High temperatures Wednesday and Thursday in the Ohio Valley will soar into the 60s to near 70°F . This warmth comes just one week after an arctic blast delivered punishing subzero low temperatures across the Midwest. But winter won’t be far away. The region will reside along the boundary between winter and spring. High temperatures will only be in the 30s closer to Lakes Michigan and Erie.
Unfortunately, winter-weary residents of the Ohio and Middle-Mississippi River Valleys will have little opportunity to enjoy the reprieve. The clash of the two air masses will produce heavy rainfall along the boundary between them. The rain will be enhanced by a steady influx of moisture from the Gulf of Mexico. As it is only February, winter will ultimately win the battle, but not without an extended two-day skirmish.
Rain will first develop late Tuesday night ahead of a decelerating cold front along a corridor from central Missouri to southwestern New York. North of this zone of rain, ice and snow will return to portions of Upper Midwest as the warmth glides over the arctic cold. A moderate snowfall of 3-6″ will inconvenience motorists from Upper Michigan to southern Minnesota. Closer to the boundary between the clashing airmasses, up to a quarter inch of ice could grind travel to a halt through Wednesday morning between northern Missouri and southern Michigan.
The cold front will become stationary Wednesday morning. Rain will intensify and become more widespread across the Ohio River Valley Wednesday and afternoon and evening as the first of several disturbances rides along the boundary between the two air masses. Intensifying flow from the Gulf of Mexico will simultaneously nudge temperatures above 60°F while pumping copious quantities of moisture toward the arctic boundary. The cold front is expected to remain stationary until pushed southward by a large-scale trough of low pressure Friday morning.
Rain will moderate late overnight Wednesday into Thursday morning ahead of a second, more intense low pressure system expected to bring the heaviest rain of the event Thursday afternoon and evening. This low will lead the trough that will eventually suppress the warmth. Several hours of blinding downpours are likely from northeastern Arkansas to Ohio, the most intense of which will develop along the Ohio River and near its confluence with the Mississippi River. Thunder and isolated gusty winds capable of severing tree branches cannot may be associated with these downpours.
The cold front will finally push eastward Thursday night. The torrential rain may be followed by a brief period of snow before precipitation finally clears Friday morning with the return of seasonal winter temperatures. Up to a half foot of rain may fall near the Ohio River, with 2-4″ of rain likely elsewhere in the region.
The copious rainfall along with recent snow melt further north will likely contribute to minor to locally moderate flooding of the Ohio River and its feeding tributaries. Floodwaters will not crest until late Friday, after the rain stops. Cities like Cincinnati, Louisville, and Evansville are all at risk for flooding from this event.
The low pressure system responsible for Thursday’s rain will trek to the Northeast Thursday night through Friday. It will gradually become severed from the Gulf of Mexico’s moisture feed, resulting in much less rainfall for the East Coast than the Ohio Valley.