WX Alert: Flood WarningWXD Alert: Active Discussion, Observations
Rounds of rain and showers will be the common theme right into May for the Eastern third of the nation. This will be accompanied by cooler than normal temps for most areas as a series of cold fronts move through with each passing disturbance. Severe weather is a threat in southern areas as well as the upper Mississippi Valley into the Ohio River Valley. Brief surges of warmth and tropical humidity preceding these disturbances will set the stage for heavier rain and Thunderstorms as well. With the ground saturated and rivers and streams swollen from previous rain, flooding is likely and dangerous conditions could be intensified by any additional rain.
Severe thunderstorms capable of damaging winds, large hail, and a few tornadoes will be likely Thursday into Thursday night over the Deep South and northern Gulf Coast. In addition, heavy rain may produce flash flooding of low lying areas. The severe weather and heavy rain threat will shift to the Mid Atlantic and Southeast U.S. on Friday. Ongoing heavy rainfall and strong to severe thunderstorms across the Lower Mississippi Valley;
Risk of flash flooding from the Gulf Coast to the Ohio Valley, shifting to the East Coast on Friday. Low pressure will move east from the Mississippi River Valley to the East Coast by Friday Night. This will deliver widespread rain to much of the eastern half of the U.S. with many locations likely to receive over an inch of rainfall. Ahead of the low, a warm, humid air mass will push well inland, supporting the development of thunderstorms as far north as the Great Lakes.
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Ridging over the West on Thursday will give way to a series of shortwave troughs, producing widespread precipitation including locally heavy high elevation snow accumulations from the Pacific Northwest and northern California to the northern Rockies. Rain rates at times will exceed 0.25 inches per hour. Areal average precipitation of 1 to 2 inches in expected with snow across the higher terrain. There is a very localized threat of flash flooding along the steeper slopes of the Sierra/Shasta Range and burn scars where soils are more sensitive.
A significant coastal storm will drive up the Southeast Coast into Offshore Waters of the East Coast through Wednesday. Expect locally heavy to excessive rain for the Coastal Carolinas and hurricane force winds for the Offshore East Coast Waters. A rapidly deepening surface low off the Mid-Atlantic coast will continue to bring rain to areas along the Northeast Coast into tomorrow, though the heaviest rainfall should remain offshore.
A strong cold front will move through the Mississippi and Ohio Valleys on Saturday and by the Eastern Seaboard on Sunday. Rain will spread to the Eastern Seaboard by Sunday morning. Within the low pressure system's cold sector, snow is expected through the Lower Great Lakes region and into southeastern Canada. A swath of 4 to 6 inches of snow is forecast for the Lower Great Lakes region into parts of northern New England through Sunday night, and a light glaze of ice is possible there as well. Ahead of the front, the East is expecting temperatures 10 to 20 degrees above average on Saturday, but by Sunday, the Ohio and Tennessee Valleys will see high temperatures 10 to 20 degrees below average, which is a large temperature swing between Saturday and Sunday. The East coast will cool down as well and last through the upcoming week.
A strong cold front will move through the Mississippi and Ohio Valleys on Saturday and by the Eastern Seaboard on Sunday. Widespread rain and thunderstorms are forecast near the front from the Lower Mississippi Valley northeastward through the Ohio Valley this afternoon and evening. Within the low pressure system's cold sector, snow is expected through the Lower Great Lakes region. A swath of 4 to 6 inches of snow is forecast for the Lower Great Lakes region through Sunday night.
A developing coastal storm approaches the Northeast/Mid-Atlantic region later today, with the possibility of a stall off the coast of Maine as well as a rapid plunge of cold air into the system bringing potential for a major snowstorm for the inland regions, particularly the Adirondacks and the Green Mountains, where there is potential of over 18" of heavy wet snow, as well as intense snow rates due to deformational dynamics. In the valleys, totals are expected to be much less, as high boundary layer temperatures will mean most precipitation will fall as rain until the colder airmass arrives. Models have also been suggesting a significant back-end upsloping event is possible, which would hamper cleanup efforts. High QPF numbers combined with an existing snowpack in these regions will lead to flooding concerns in the valleys. To the south, a significant coastal flooding event is forecast due a multitude of factors, including: astronomical high tides due a full moon, easterly winds piling up water along the coastlines, and the rapid intensification of the surface low. Across the entire region, at least 1" of QPF is expected, with the potential for 2" in select locations.