Beginning this morning at 7 am local time anyway and the watch runs until Thursday night.
Here is the NWS statement in it's entirety:
...FLASH FLOOD WATCH REMAINS IN EFFECT FROM 7 AM CDT WEDNESDAY THROUGH LATE THURSDAY NIGHT...
THE FLASH FLOOD WATCH CONTINUES FOR PORTIONS OF KANSAS AND MISSOURI- INCLUDING THE FOLLOWING (COUNTIES) AREAS:
IN KANSAS: JOHNSON KS-LEAVENWORTH- LINN KS- MIAMI AND WYANDOTTE.
IN MISSOURI: BATES- CARROLL- CASS- CLAY- COOPER- HENRY- JACKSON- JOHNSON MO- LAFAYETTE- PETTIS- PLATTE- RAY AND SALINE.
* FROM 7 AM CDT WEDNESDAY THROUGH LATE THURSDAY NIGHT*
A COLD FRONT OVER THE NORTHERN PLAINS WILL MOVE INTO NORTHWEST MISSOURI EARLY THIS MORNING AND SHIFT SLOWLY SOUTHWARD INTO EAST CENTRAL KANSAS AND CENTRAL MISSOURI TODAY THROUGH THURSDAY. AT THE SAME TIME- A SLOW MOVING UPPER LEVEL LOW PRESSURE SYSTEM OVER OKLAHOMA WILL DRIFT NORTHEAST TOWARD MISSOURI.
AS THE FRONT AND UPPER LEVEL DISTURBANCE INTERACT WITH MOISTURE OVER THE REGION- SEVERAL ROUNDS OF HEAVY RAINFALL ARE EXPECTED TO DEVELOP. WIDESPREAD ACCUMULATIONS IN EXCESS OF TWO INCHES ARE POSSIBLE BY THE END OF THE DAY THURSDAY. LOCALLY HIGHER AMOUNTS OF UP TO FIVE INCHES WILL BE POSSIBLE WHERE SEVERAL HEAVY BANDS OF RAIN MOVE THROUGH.
THIS HEAVY RAINFALL WILL LIKELY LEAD TO FLASH FLOODING ACROSS THE WATCH AREA. ADDITIONALLY- WHILE LOCAL AREA RIVERS AND STREAMS WILL BE ABLE TO TAKE A CONSIDERABLE AMOUNT OF WATER TO BEGIN WITH- THE EXPECTED LENGTH OF THIS EVENT WILL LIKELY LEAD TO RIVER AND STREAM FLOODING BY THURSDAY.
A FLASH FLOOD WATCH MEANS THAT CONDITIONS ARE FAVORABLE FOR HEAVY RAIN ACROSS THE WATCH AREA- WHICH MAY LEAD TO FLASH FLOODING.
IF YOU ARE IN THE WATCH AREA- CHECK YOUR PREPAREDNESS REQUIREMENTS- ESPECIALLY IF YOU HAVE INTERESTS ALONG AREA RIVERS.
KEEP INFORMED- AND BE READY FOR ACTION IF FLOODING IS OBSERVED OR IF A FLASH FLOOD WARNING IS ISSUED.