This will be a very quick note. We could be seeing a multi-day severe weather event to end this week. It may start on Thursday with a chance for strong to severe storms Friday, Saturday, and Sunday. There is still some question about the timing and strength of these possible storms. I will update everyone as new information comes available. The following illustration is from Thursday morning to early Monday morning. Just wanted to give everyone a heads up.

For Thursday

 

A severe threat, with a potential for wind damage, large hail, and perhaps a tornado or two appears likely to develop on Thursday across parts of the mid to upper Mississippi Valley, Lower Ohio Valley and southwestern Great Lakes.

At the surface, a cold front will advance southeastward toward the western Great Lakes, providing a focus for convective initiation. A moist and unstable airmass will be in place ahead of the low across much of the Mississippi Valley extending eastward into the lower Ohio and Tennessee Valleys. Surface dewpoints across the moist airmass will generally be from the mid-60s to the mid-70s F. Scattered thunderstorms will likely develop across much of this airmass during the afternoon, with two or three clusters persisting into the early to mid-evening. MCS(Mesoscale Convective System) development will be possible. These are thunderstorms that act as a system. An MCS can spread across an entire state and last more than 12 hours. On radar one of these monsters might appear as a solid line, a broken line, or a cluster of cells. Like what we had on Sunday.

This environment will be favorable for supercells with large hail. Hailstones greater than 2 inches in diameter will be possible across much of northern and central Illinois, where the combination of shear and instability is forecast to become maximized.  Supercells are expected to be the favored mode early in the event, but a transition to linear mode may take place. Cold pool development would increase the wind-damage potential with any line segment that can become organized. A severe threat will be possible during the early to mid-evening across parts of the lower Ohio Valley.

For Friday

 

On Friday, thunderstorms associated with wind damage and hail will be possible in parts of the Ohio Valley. An isolated severe threat may also develop in the southern and central Appalachians. 

Model forecasts suggest that an MCS could be ongoing at the start of the period, with the MCS moving eastward across the Ohio Valley relatively early in the day. If this scenario pans out, then a wind-damage threat can be expected along the system's leading edge. Thunderstorm redevelopment will be possible in the wake of this convective system in the afternoon. Areas that are not impacted by the earlier MCS, could have a greater severe threat during the late afternoon and early evening, with wind damage and isolated large hail as the primary threats.

Just received the latest from the NWS-Louisville.

Quote

 

Good Morning:

Our active weather pattern is expected to continue for the remainder of the week and into the weekend. Multiple rounds of strong to severe thunderstorms may impact portions of the region beginning late tonight and continuing through the weekend. The timing and exact track of these rounds of storms remains a bit uncertain.

However, the best chances for severe weather on Thursday will be across southern Indiana and into portions of central Kentucky. The best chances of severe storms on Friday may shift a bit to the northeast and affect portions of southeast Indiana and northern and northeastern Kentucky.

The main threats with this activity will be torrential rainfall, damaging winds in excess of 60 mph, frequent lightning, and possibly some large hail.

Sincerely,

NWS Louisville, KY

 

 

Wednesday afternoon update:

Severe storms producing damaging winds and hail are possible across the region from Illinois to Kentucky. A couple of tornadoes may also occur.

 Areas of storms may be ongoing from eastern Iowa/northern Missouri southeastward into Illinois, Indiana, and parts of Kentucky, possibly producing damaging winds and aided by warm advection out of the west. Some of this activity could persist southeastward during the day into Kentucky and Tennessee, given the favorable conditions. In the wake of this activity, a very unstable air mass will remain in place. Conditionally, supercell profiles will exist with the potential for very large hail, damaging winds, and a few tornadoes assuming cellular storm mode. However, this is highly uncertain given the potential for widespread early storms. As such, the significant hail and tornado probabilities are conditional, but warranted given some of the forecast instability profiles. 

The Storm Prediction Center has a large swath of Kentucky under a level 2 Slight Risk Area. Most of the rest of Kentucky is under a level 1 Marginal Risk Area.