Plains Flood Threat Underway From Unusual April Multi-Day Heavy Rain Event (FORECAST)

Jon Erdman
Published: April 16,2016
A stalling storm system will produce several days of heay rainfall over a broad swath of the Plains, triggering potentially serious flash flooding in parts of Texas, Oklahoma, Kansas and Nebraska.
In some parts of the High Plains, rainfall totals over a 4-5 day period through early next week could approach all-time monthly records for the month of April.
Friday night, 3 to 5 feet of water inundated roads between Stratton and Bethune, Colorado, and many county roads were flooded in Morton County, Kansas.
A CoCoRaHS station near Elkhart, Kansas, picked up 6.52 inches of rain as of Saturday morning, while Dodge City, Kansas picked up almost twice their average April monthly rainfall in just 2 hours.
(INTERACTIVE: Where the Heavy Rain is Now)

Flood Setup

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 will 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 will be in place from Texas as far north as the southern Canadian prairie.
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).
Flood watches have been issued for periods of heavy rainfall for portions of the southern and central Plains from west Texas northward into central Kansas. The heavy rain may cause roads, as well as streams and rivers to flood, especially in flood prone areas.

Flood Alerts

The map below is a general view of the area where we're expecting the heaviest rain into Tuesday. Keep in mind locally much heavier amounts may fall where bands of rain or thunderstorms stall for a few hours at a time.

Rainfall Outlook Through Tuesday Night

In general, many areas of the Plains from Texas to parts of South Dakota could pick up at least 3 inches of total rainfall through Tuesday night.
Parts of Kansas, Oklahoma and Texas could tally 5-8 inches or more of total rainfall over a four-day period.
(MAPS: 7-Day Rainfall Forecast)
This would be on par with existing April, even May monthly precipitation records in North Platte, Nebraska, and could threaten some April, or even all-time three-day precipitation records in parts of western Kansas and southwest Nebraska.

North Platte, Nebraska, Record Monthly Precipitation (Data: NWS)

	Monthly Precipitation Record (inches)
April	7.10 (1915)
May	8.01 (1962)

This potential multi-day rainfall would be roughly equivalent to the combined average April-May precipitation total in North Platte.

Slow-moving clusters of t-storms will rumble across parts of Oklahoma and Texas from Satruday night Sunday morning through at least Monday, if not Tuesday, giving rise to a high threat of flash flooding, there.
(FORECASTS: Okla. City | Dallas | Austin | San Antonio | Houston)
If that wasn't enough, a threat of some severe thunderstorms with large hail, damaging winds, and perhaps a few tornadoes will be in play in these areas.
(FORECAST: Severe Weather Threat Through Monday)
Heavy, wet snow will also pound parts of the High Plains and Rockies, with over a foot possible in some areas.
(FORECAST: An April Snowstorm Ahead)

Drought monitor animation from March 1 through April 5, 2016, illustrating the developing drought (light tan contour) in the Plains.

Yet Another Bizarre Flip-Flop

Over the past several weeks, a flash drought, one which develops quickly, has spread across parts of the Plains states.
Garden City, Kansas, hadn't seen any measurable rain or snow in over two months since Groundhog Day, until they picked up almost three-tenths of an inch of rain Monday.
The combination of this complete lack of precipitation with persistently warm and windy weather this spring has led to several large wildfires, including the largest fire on record in Kansas, hopping across the border from Oklahoma in late March.
(RECENT FIRES: Imagery of March Wildfire | Early April NW Oklahoma Fire)
Finally, a wetter pattern more typical of early spring will take shape, however, its extremely stagnant nature will lead to extreme precipitation totals in the High Plains, as we mentioned earlier.
Thanks to this sluggish, blocked pattern, Garden City, Kansas, could pick up perhaps twice the average April monthly precipitation, potentially even topping the average wettest month of the year, June.

MORE: Largest Wildfire in Kansas History (March 2016)