Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 340 AM EDT Sat Aug 21 2021 Valid 12Z Sat Aug 21 2021 - 12Z Mon Aug 23 2021 ...Tropical Storm Henri to threaten portions of the Northeast and southern New England with dangerous storm surge, damaging winds, and heavy rain beginning as early as tonight... ...Scattered flash flooding possible across parts of the Tennessee Valley and Southeast today... ...Severe thunderstorms to potentially impact the northern/central Great Plains on Sunday... The main weather story this weekend is found across the Northeast and southern New England, as Tropical Storm Henri bears down on the region. Henri is currently churning over the western Atlantic Ocean and is forecast to accelerate northward today while also potentially strengthening into a hurricane. As it swings near the East Coast, rip currents and rough surf could lead to life-threatening conditions along beaches and coastal regions from the Southeast to Cape Cod. By tonight, outer rain bands and gusty winds will approach areas between coastal New Jersey and southeast Massachusetts. On Sunday morning, a nearby upper-level low spinning over the Mid-Atlantic States is forecast to interact with Henri and lead to a slight left turn toward Long Island. As a result, dangerous storm surge and damaging winds are anticipated between far northern New Jersey and southern New England on Sunday. The threat of downed trees and power lines may also extend farther inland through Monday across parts of the Hudson Valley, Connecticut, and central/western Massachusetts. Heavy rain is another dangerous hazard associated with Henri as it is expected to slow down after landfall and linger over the region on Monday. Upwards of 10 inches of rain could fall over portions of Long Island, southeast New York, northern New Jersey, and southern New England. This amount of rain may lead to considerable flash, urban, and small stream flooding. A Moderate Risk (level 3/4) of excessive rainfall has been issued for the aforementioned locations. Slow-moving thunderstorms are also expected to impact sections of the Tennessee Valley and Southeast today as rich atmospheric moisture remains prevalent throughout this part of the country. A few inches of rain could quickly fall in localized spots, resulting in scattered instances of flash flooding. A Slight Risk (level 2/4) of excessive rainfall has been issued from southern Illinois to central Alabama. A few intense downpours can't be ruled out across the Northern Rockies today as well, thanks to a potent upper-level trough swinging through the region. This piece of energy is forecast to eject into the Northern Plains by Sunday and spark scattered thunderstorms over the Northern and Central Plains. A few of these storms may turn severe, with damaging wind gusts, isolated tornadoes, and large hail possible. Elsewhere, Red Flag Warnings and a critical fire weather risk remains across parts of the central Great Basin to start the weekend. Air Quality Alerts are also in effect throughout central California and central/eastern Oregon due to thick wildfire smoke. Below average temperatures are forecast for much of the western and north-central U.S., while muggy heat and humidity remains over the Southern Plains and Lower Mississippi Valley. Scattered Heat Advisories and have been issued from eastern Oklahoma to southern Louisiana, where heat indices could approach 110F. Meanwhile, Excessive Heat Warnings in effect for parts of Louisiana and coastal Mississippi, including New Orleans, LA. Snell Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php