Tuesday, May 5, 2015

Potential Drought Relief in Plains Also Brings Flood Threat (FORECAST)

Jon Erdman
Published: May 5,2015





 
In stark contrast to the dominant pattern early in the year, a stagnant jet stream pattern will continue to deliver locally heavy rain to much of the Plains into Mother's Day weekend.
Interestingly, this persistently wet outlook is actually both good and bad news in the nation's heartland.
The upper-level setup for repeated heavy rain through at least the weekend in the nation's heartland.

Rainfall Forecast Through Monday

Bad News: Flood Threat
















Monday provided a good example of the threat over the next several days.
Significant flash flooding was reported in Manhattan, Kansas, Lubbock, Texas, and Seagraves, Texas. Monday was the third wettest May day on record in Lubbock (3.42 inches), and Manhattan, Kansas, picked up over 4 inches of rain.
(MORE: Monday's Heavy Rain Pounds the Plains)
Through the weekend, the jet stream will feature a prominent southward dip in the West and at least a slight northward bulge in the East.
This setup will tap deep Gulf moisture and send it northward through the Plains, and will also send a steady stream of upper-level disturbances providing lift for rain and thunderstorms.
Each day, thunderstorm coverage may be a little more in some parts of the Plains, and a little less in others.
Through next Monday, we expect the corridor of heaviest total rainfall to stretch from parts of Iowa, Nebraska and eastern Colorado to north, central and West Texas. Many of these areas have a high chance of picking up at least 2 inches of rainfall through the period.
(MAPS: 7-Day Weekly Planner)
However, the potential exists each day for slow-moving thunderstorm clusters to stall in a given area, quickly wringing out several inches of rain in 1-3 hours.
(INTERACTIVE: Radar Loop | Flood Alerts)
These rapid rain rates may quickly trigger flash flooding, particularly in areas that may have received heavy rain the previous days. Local flash flooding may also occur even in areas that had been rather dry recently.
(MORE: Your Vehicle...Biggest Flood Danger)
There is also the threat of severe thunderstorms in this pattern each afternoon and evening through the weekend. For more details on this threat, check out our severe weather tracker page.
We expect this wet pattern to finally clear the Plains by later next Monday or Tuesday, as a cold front finally sweeps through.

Late April/early May Drought Monitor analysis from 2011 through 2015. Brown box denotes area in southern Plains of most persistent drought since 2011.

Three-month change in the Drought Monitor analysis ending April 28, 2015. Green shading indicates areas where the drought has improved. Yellow and orange shadings indicate areas with worsening drought.
(USDA/NDMC/NOAA)

Good News: Optimal Spring Drought Relief

While California is getting much of the nation's attention on the drought front, another long-term drought continues in the nation's heartland.
Parts of the southern and central Plains have been struggling in drought since fall 2010.
According to the Texas Water Development Board, most reservoirs in northwest and west-central Texas, as well as the Texas panhandle, are still running at less than half of capacity.
O.C. Fisher Lake, a secondary drinking water source for San Angelo, Texas, is still at only 0.5 percent of capacity. About 10 other reservoirs in northwest and western Texas are also running at less than 10 percent capacity.
The news isn't all bad in the Lone Star State. Most reservoir levels generally along and east of I-35 from the Red River to Austin are running at least 80 percent of capacity.
Also, 2015 has been wetter in the southern Plains. Above-average precipitation has fallen in Amarillo, Abilene and San Angelo. Near-average precipitation has been recorded in both Oklahoma City and Wichita Falls, Texas.
While it will likely take at least one, if not multiple wet years to fully recharge still-depleted southern Plains reservoirs, the wet pattern over the next several days is about as lucrative for a short-term drought dent as you can draw up in the middle of spring.
(FORECAST: Dallas | Okla. City | Amarillo | Wichita)
Drought relief is easier to come by in the spring compared to the summer, when the jet stream migrates well to the north, leaving the southern Plains often subject to hot, dry high-pressure aloft, evaporating water from reservoirs.
In the absence of a remnant tropical cyclone, it's difficult to get widespread, significant drought-denting summer rain in the southern Plains.
Interestingly, a dry winter has left parts of the northern Plains and Upper Midwest in moderate to locally severe drought, according to the April 28 Drought Monitor analysis.
The recent warmth and dry weather has allowed farmers an early start on spring planting. However, rain is needed in parts of the Dakotas, Minnesota and Wisconsin.
While not as high a flood threat, some locally heavy rain is also expected to spread into these areas in the Wednesday-Thursday and weekend timeframes.

MORE: Wettest Place on Earth

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