More Locally Heavy Rain May Aggravate Flooding in Texas, Oklahoma, Louisiana (FORECAST)

April 20,2016
Flood-weary parts of Texas, Oklahoma and Louisiana, including the Houston metro area, aren't yet done with rain, but there is a light at the end of the tunnel.
(MORE: Is Houston America's Flood Capital?)

Flood Alerts

Rivers and bayous have either crested, or are cresting now in the Houston metro area after 10 to 20 inches of rain inundated the north side of the metro area on April 18.
Hundreds of water rescues were reported and numerous subdivisions encountered flooding.
The governor of Texas has also declared a state of emergency in nine counties due to the deadly flooding. For the latest on impacts from the flooding, see our full news story at the link below.
(LATEST NEWS: Destructive, Deadly Houston Flooding)
Below are more details on the severe weather and flood threats the next few days. At the bottom of this article you can find a full recap on the severe weather caused by this same storm system since Friday.

Flood/Severe Threat Forecast

Wednesday

• Following a morning line of t-storms in central and east Texas, clusters of slow-moving thunderstorms are again expected in central and southeast Texas, Louisiana, Arkansas, Mississippi and west Tennessee, including the Houston metro area in the afternoon and evening.
• While not as heavy as Monday's event, additional flash flooding is possible, and locally heavy rainfall may slow the fall of already flooded rivers, creeks and bayous in southeast Texas.
• Once again, an isolated severe t-storm is possible with a brief strong wind gust and hail possible.
• Wednesday night, some t-storm clusters are possible from the Texas panhandle into southern Oklahoma and central Texas

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

Current Radar with Watches and Warnings

Thursday/Friday

• Clusters of thunderstorms should sweep from the Red River southeastward toward the Texas and Louisiana Gulf Coast Thursday.
• Drier weather will finally arrive by Friday behind a cold front.

(MORE: Drier Pattern Ahead)
The map below is a general view of the area where we're expecting the heaviest rain through Thursday.

Rainfall Outlook Through Thursday

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