Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 359 AM EDT Tue Aug 18 2020 Valid 12Z Tue Aug 18 2020 - 12Z Thu Aug 20 2020 ...Record heat expected to slowly become less intense across the western U.S... ...Relatively cool conditions expected from the Plains to the East Coast with areas of showers and storms from the Mississippi Valley to the East Coast... ...A stalled front will keep a good chance of showers and thunderstorms across Florida and into the Southeast... A strong mid/upper-level ridge of high pressure that is responsible for the heat wave across the western U.S. for the past few days is forecast to gradually weaken. This will allow the record heat to moderate progressively for the coming days. Nevertheless, high temperatures will soar well beyond the century mark, with many locations surpassing 110 degrees in the Desert Southwest, and perhaps isolated spots exceeding 120 degrees especially today. In addition, the hot and dry conditions will lead to elevated/critical fire danger, especially for the interior northwestern U.S. where lightning strikes associated with isolated afternoon/evening thunderstorms could ignite wildfires. Farther east, conditions will be quite different, with an upper-level trough forecast to dip across the Great Lakes and Northeast. This system will maintain near/below average temperatures for the majority of the eastern half of the nation. A cold front associated with the upper trough will bring a round of showers and thunderstorms to the Northeast early today before clearing out tonight. Meanwhile, a low pressure wave developing on a secondary cold front is expected to trigger a round of showers and storms for portions of the Ohio Valley into the central Appalachians today into this evening. The trailing portion of this frontal system is forecast to linger across the Mid-Atlantic to the Southeast/Gulf Coast into midweek, as a few weak waves of low pressure traverse the boundary. This pattern will keep scattered to numerous showers and thunderstorms in place from the Southeast to portions of the Mid-Atlantic for the days to come. Kong/Ryan Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php