Heavy Rain & Severe Storms Possible Thursday

Flash Flood Watch in effect for Thursday.


Meteorologist Trent Okerson

Thursday Midday Update:

The first half of our Thursday certainly has been soggy, with parts of the Bootheel & TN already picking up 2-3" or more of rainfall.  For a link to the radar estimated precipitation totals, click here.

Not much has changed as far as the rainfall portion of this storm system is concerned.  Here is a look at the latest rainfall forecast map, which continues to show totals of 2-5" across western KY, northwest TN, and parts of southeast MO:




As I mentioned in the original post below, even though it makes for a soggy, gloomy day, this rainfall is actually just what the doctor ordered in terms of ongoing drought conditions.  (Click here for the latest U.S. Drought Monitor).  The real issue as far as a flash flooding potential will be later this evening and tonight when more showers and thunderstorms arrive...possibly producing more rainfall than the ground can soak up.  This morning's Flash Flood Guidance estimates that the ground can handle rainfall rates of about 1.5" in an hour, 1.8" in three hours, or 2.3" in six hours.  Anymore than this will lead to some problems of standing water and rapid rises on smaller creeks and rivers.  With that in mind, a Flash Flood Watch continues through late tonight for roughly the southern 2/3rds of the area....highlighted in the darker shade of green on the map below:

As for the severe threat today, the moderate risk currently includes much of western KY, the southeastern most sections of MO, and all of northwest TN.  Areas north of this, up to around Route 13 in IL are included in a slight risk.  Here is the latest SPC outlook:

While there is likely to be a bit of a break with the action this afternoon, a deepening area of low pressure will pass directly over the region this evening, and areas along and south of that low will be fair game for strong to severe storms.  Specifically, it would appear that the threat will extend from around 6PM through midnight, with a line of storms moving across at least the southern half of the region.  The main concern with these storms will be damaging winds, but large hail and isolated tornadoes are also possible.

Be sure to stay with the Weather Authority this evening for the very latest.

Original Post:

Our weather over the past several days has felt a lot more like spring, however, as we turn the corner toward spring, we know that also means dealing with storms...which is what our attention is focused on for Thursday.

The weather picture for Thursday is somewhat complicated, so here's a summary of what we're expecting.  An area of low pressure will be taking shape tonight out over the Plains states, with lots of Gulf of Mexico moisture surging north into the region.  Fairly widespread showers should begin breaking out tonight, especially after midnight, as a warm front approaches from the southwest.  This warm front will be draped across our region tomorrow, serving as a focus for more showers and thunderstorms during the course of the day.  A southwest-to-northeast oriented front, along with mid and upper level flow that is parallel to the front will encourage showers and storms to move over the same areas, what is called "training" of storms.  This will lead to the threat of locally heavy rainfall.  Tomorrow night will be when we're expecting the heaviest rainfall, and perhaps the threat for some localized flash flooding.  By the time this system moves out of here overnight tomorrow, parts of the region may receive anywhere from 2-4" of rain.  Here's a look at the latest rainfall forecast from the HPC:

As far as these rainfall amounts are concerned, there could be good and bad news here.  First, for the good news.  We really need this rain!  As I wrote last week, parts of KY, MO, & TN need between 9-12" of rain to break out of what is becoming a long-duration drought.  These rainfall totals will certainly make a dent.  The thing we'll have to watch is exactly how fast this rain comes down.  If we can pick up an inch every few hours, then this will actually turn out to be a very helpful rain.  The bad news is the concern that rain will come down in buckets, especially Thursday night.  Flash flood guidance (minimum amount of rain for a specified time needed to produce flash flooding) for most of the area is about 1.7" in one hour, 2.1" in three hours, and about 2.7" in six hours.  With this concern, the NWS has issued a Flash Flood Watch through late Thursday night for all of western KY, northwest TN, and parts of southern IL & southeast MO.  Here is a look at the watch area (shown in dark green):


In terms of thunderstorms, the main event will be tomorrow night as the surface low moves over the region.  As this low lifts through the region, areas that stay to the north of its track will continue to deal with a steady rainfall......but parts of the area along and south of the low is where there will be a concern for severe storms.  So, needless to say, determining the track of the low is key in determining the northern extent of the severe weather threat.  As of the latest forecast model runs, it looks like the low will track along or just south of the Ohio River, putting at least parts of KY, MO, & TN under the gun for some strong to severe storms.  Here is a look at the latest severe weather outlook from the SPC:

As you can see, areas along and south of the Ohio River need to be on alert for severe weather, but the greatest threat will be across the MO Bootheel & northwest TN, where a Moderate Risk exists.  With these storms, tornadoes and damaging straight-line winds will be possible.

As you drive to and from work tomorrow, be alert for standing water on roadways, and remember to never attempt to drive across a flooded roadway.  Also, make sure to review your severe weather plan with your family tonight, and be sure your weather radios are ready to go!