More Rain, Possible Severe Storms For South-Central States (FORECAST)

April 21,2016
More rain and thunderstorms will continue to rumble across the south-central states Thursday, but thankfully a drier weather pattern is expected take hold for late week.
(MORE: Is Houston America's Flood Capital?)
A few of the storms today could turn severe with large hail and damaging winds. In addition, locally heavy rain could be a potential hazard.
Below are more details on the forecast for Thursday.

Current Radar with Watches and Warnings

Flood/Severe Threat Forecast

Thursday Night

• Clusters of thunderstorms will impact locations from Texas to Louisiana and Mississippi.
• A few severe thunderstorms are possible from southern and central Texas to the lower Mississippi Valley. Isolated flash flooding is also possible.
• Isolated severe storms are also possible farther north in Illinois and adjacent parts of Indiana and Missouri.

(INTERACTIVE: Get Your 7-Day Severe Weather Outlook)

Rainfall Outlook Through Thursday

Friday

• Drier weather will finally arrive by Friday behind a cold front.

(MORE: Drier Pattern Ahead)

Flood Recap

Impressively, April 18 was the second wettest calendar day on record for official reporting stations in Houston, dating to 1888, with 9.92 inches of rain measured at Bush Intercontinental Airport. Only one other calendar day was wetter, June 26, 1989 (10.34 inches). This was also almost exactly three times the average rain for the entire month of April (3.31 inches).

Roads were also closed Monday night by high water in Shreveport, Louisiana, where over 6 inches of rain fell. April 18 was the second wettest April day in Shreveport. In March, they had their top two wettest March days on record.
(FLASHBACK: Massive Louisiana March 2016 Flood)

Hardest hit was Cypress Creek through the north Houston metro area, cresting just one inch shy of its all time record crest from October 1994 near Cypress, Texas on April 19.
Incredibly, this was just under 10 inches higher than the crest there during the Allison flood of June 2001, though it should be noted metro area rainfall totals during Allison were up to double what they were in this event.

Elsewhere, flood levels were over five feet higher than the May 2015 on the Colorado River at Columbus, Texas, three feet higher on the Navidad River at Sublime, Texas, (second highest crest over a short period of record) and over eight feet higher on Spring Creek near Spring, Texas.
(FLASHBACK: May 2015 Houston Area Flood)
Other mainly minor to moderate river flooding was observed in parts of central and north Texas into southern Oklahoma. East Cache Creek near Walters, Oklahoma, surged into major flood status early on April 19, reaching levels that would put some county roads under 6 feet of water, according to the National Weather Service.
In some parts of the High Plains, the average rainfall for April was doubled in just a couple of days this past weekend. This includes Dodge City, Kansas, which picked up 4.98 inches of rain Saturday into Sunday, more than doubling their April average of 1.82 inches. Northeast of Dodge City in Ellis County, a few roads were washed out by flooding.

Here is a list of notable rainfall totals by state through Wednesday morning, April 20:

• Arkansas: 4.48 inches near Fouke
• Kansas: 6.52 inches near Elkhart; 4.98 inches in Dodge City
• Louisiana: 6.70 inches at Shreveport Regional Airport
• Nebraska: 6.25 inches near Riverdale; 5.50 inches in Kearney
• Oklahoma: 7.87 inches in Frederick; 6.13 inches in Tipton; 4.69 inches in Okla. City
• Texas: 10-20 inches on north and west side of the Houston metro; over 10 inches of rain was also reported west of the Austin metro in Fayette county

What's Causing the Heavy Rain?

Sometimes, winds at jet-stream level don't simply flow generally west to east (in the northern hemisphere), but rather take large north-south (or south-north) meanders. When this happens, weather systems producing rain or snow slow down.

Upper-level pattern forecast for Sunday, April 17, 2016, featuring an omega block in the East, trapped low in the Rockies, and deep moisture into the Plains states.

A southward dip in the jet stream over the Rockies has become trapped for a while from a so-called "omega block" of high pressure over the East and Great Lakes, responsible for a much-welcomed warm-up in those areas.
(MET 101: "Omega Block" Brings Welcomed Warm-Up)
With high pressure both to the northwest and northeast of the stuck low, there's nowhere for the closed low to go fast.
On the east side of that swirling, slow-moving low, deep moisture is in place in the central states.
In general, the slower the trapped upper low moves, the greater the potential for heavy rain over the same areas over multiple days.
This stagnant pattern with a deep plume of moisture in place is a prime setup for flooding rainfall, even despite parts of the Plains being rather dry, recently (more on that below).

MORE: Flooding Hits Houston Metro