Widespread precipitation-related impacts can be expected for the rest of the week over the eastern half of the nation. Areas of heavy rain and snow will have impacts on water resources, both from too much precipitation resulting in flooding to welcome drought relief.
There will be three areas of interest: (A) Midwest Heavy Snow Event, (B) Southeast U.S. Rain and Flood Event, and (C) PNW Enhanced Precipitation.
Midwest Winter Storm
A Midwest winter storm will dump over a foot of snow over portions of Oklahoma, Kansas, Nebraska, Missouri, and Iowa over the next few days. Sleet and freezing rain will occur along the southern edge of the system, mainly in Oklahoma, Arkansas, and Missouri.
Heavy Rain and Strong Storms
A broad swatch of 3- to 4-inch rainfall can be expected from Louisiana, across southern sections of Mississippi, Alabama, and Georgia, and into South Carolina. Mississippi and Alabama have been wetter than areas further east so the potential for runoff and flooding is heightened in this area. Still, due to recent heavy rainfall even in the core of drought in Georgia, flooding is also possible in that area. Isolated higher amounts, exceeding 5 inches, are possible over the next 7 days.
Despite recent rainfall, and most likely due to longer-term soil moisture deficits, runoff threshold values within most of this region are close to 3 inches. In a very general sense, and depending on the rate of rainfall, about 75 percent of this next episode of rainfall will tend to go towards soil moisture recharge, with 25 percent tending to be excess, leading towards heightened runoff, river rises, and flooding.
Of course, the rate of rainfall in thunderstorms will be more localized and higher and result in the potential for urban and flash flooding.
Relationship to the Drought
I have outlined with a white line the core of drought over the Midwest and Southeast U.S. and overlaid the next 7-day rainfall forecast. Significant amounts of precipitation are expected over areas of drought, and very well will moderate drought impacts.
Note that3 or 4 inches of rain is forecast over the core of drought in Georgia and along the middle and lower Savannah River Basin. While this likely will not end the drought in this region, it will result in a significant reduction of drought intensity. Considering recent heavy rainfall in this area, this week’s rain event also will tend to recharge upper soils and enhance runoff into river systems, including tributaries to the Savannah River.
While amounts are not as great in the Midwest, and precipitation will be in the form of snow — it will be quite welcome from a drought relief standpoint. Around 1 inch of water equivalent can be expected over a large area of severe drought. From a drought relief perspective, while this event will not end the drought it will have several benefitual aspects.
- Snow water equivalents will be widespread covering over 60 percent of the core of severe drought.
- Melting snow is very effective in recharging upper soils due to (generally) more manageable runoff.
- While it is too early to say, to end this drought, there must be a break in the “feedback” of continued dry weather. While a widespread 1-inch precipitation event has a long way to go to end the drought, it might represent a “first-step” in breaking this feedback loop.