WX Alert: Flash Flood Warning, Flash Flood Watch, Gale Warning, Hazardous Weather Outlook, Small Craft AdvisoryWXD Alert: Active Discussion, Observations
A low pressure system will move east from the Mississippi River Valley today, to the East Coast by Friday Night. This will deliver widespread rain to much of the eastern half of the U.S. over the next couple days with many locations likely to receive over an inch of rainfall. The primary surface low will shift from the Mid South, near Arkansas, today to the central Appalachians later on Friday. A trailing cold front will sweep across much of the Gulf Coast and Southeast. Ahead of the low and associated cold front, a warm, humid air mass will push well inland, supporting the development of thunderstorms as far north as the Great Lakes and Mid Atlantic. Some of the thunderstorms will be severe. The greatest risk of severe weather is in the Gulf Coast states today, and in the Southeast Atlantic Coast states from Virginia to Florida on Friday. The main threats with the severe storms will be damaging wind gusts and several tornadoes; some of the tornadoes in the South today and tonight could be strong. For more detailed information on the severe weather threat, refer to Storm Prediction Center forecasts. The thunderstorms and areas of heavy rain will also pose a risk for flash flooding over much of the eastern half of the U.S. in the next couple days, gradually shifting east with the low pressure system. Flash flooding will be most likely today in the Lower and Middle Mississippi River Valley; some locations could receive several inches of rain in a few hours. The risk of flash flooding on Friday should extend along most of the U.S. East Coast, from the northern border with Canada south to Georgia.
Risk of severe storms and 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.
Convective development begins in the evening hours of Friday as the first thunderstorms of the year for most of the region. At the moment, the areas most likely to see a thunderstorm are along the I-95 corridor through North Carolina, Virginia, Maryland, Delaware, and New Jersey. The northward extent of the convective development has been tricky to forecast, but the latest HRRR, the 12z NAM, and the 12z HRDPS have suggested that the NYC metro area, Long Island, and the Connecticut coastline will be enveloped by heavy rain