Tuesday, February 4, 2020

Prolonged rain threat to increase flood risk across eastern US

SEVERE WEATHER Updated Feb. 4, 2020 2:47 PM




A series of storms will make their way across the country and result in an expanding flood threat across a wide swath of the eastern United States during the middle to latter part of this week. One of the storms in the series also brought damaging wind gusts to the Southwest, accumulating snowfall to the Rockies and will bring along a multitude of other threats as it tracks eastward in the coming days.
Temperatures more commonly observed in early spring graced much of the eastern United States on Monday and will linger past the middle of the week in parts of the East. This above-average warmth will allow ample amounts of moisture to surge northward out of the Gulf of Mexico.
As the energy in the jet stream slides eastward into the southern Plains into Tuesday night, the lower part of the atmosphere will respond with an expanding area of drenching rain. The lower Mississippi Valley and portions of the mid-South will be targeted first. Area creeks and streams will rise as a result of the rain.
This same area has already observed well above-average rainfall amounts through the month of January and as the first full week of February progresses, the trend is expected to continue.
Because of the wet start to the year already, rainfall rates will not need to be exceptionally high to produce a flash flood risk.
The flash flood risk will likely be maximized across Dixie Alley where severe thunderstorms are expected. Because of the nearly saturated soil across the region, rainfall rates of less than 1 inch per hour could lead to flash flooding.
While rainfall rates may not be as high farther north, the risk for flooding is still present. Rather than a widespread flash flood risk due to heavy rain and thunderstorms, area streams, creeks and rivers will be on the rise as their entire basins receive moderate rainfall for a more prolonged period of time. A general 2-4 inches of rain is forecast with an AccuWeather Local StormMax™ of 6 inches.
The threat for the heaviest rain will slide eastward into Wednesday and Thursday, targeting the Deep South, Tennessee Valley and Southeast. Similar to what is expected into Tuesday night, a heightened flash flood risk is expected across the Deep South and Southeast as potentially severe thunderstorms track through the region, while river and creek flooding will be the primary threat for areas farther north.
"Many southern cities, such as AtlantaCharlotte and Nashville, recorded higher-than-average rainfall totals for the month of January," AccuWeather Meteorologist Mary Gilbert said. "Atlanta recorded 8.01 inches of rain in January, which nearly doubled the typical total of 4.20 inches."
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The storm system is expected to take a jog northeastward late week, expanding the area of potentially heavy rainfall farther to the north up the Appalachians and East Coast.
Many locales across the mid-Atlantic could experience a long-duration rainfall event as the storm system tracks up the Atlantic coast late week. Depending on the exact track and the amount of cold air in place, accumulating snow and ice could lead to travel problems in parts of the Northeast.
While it has been a relatively quiet start to the month across the Southeast and East Coast, this storm system will likely bring a change of pace.
The expansive area of rain expected across the southern states will generally clear out in a west-to-east fashion late week as a cold front sweeps through the region to end the week. As the cold air filters in, a few snowflakes may even mix in across portions of the mid-South and southern Appalachians before the dry air mass takes over.
Keep checking back on AccuWeather.com and stay tuned to the AccuWeather Network on DirecTV, Frontier and Verizon Fios.

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