Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 357 PM EDT Tue Aug 20 2019 Valid 00Z Wed Aug 21 2019 - 00Z Fri Aug 23 2019 ...Strong to severe thunderstorms possible Tuesday afternoon and evening across portions of central Plains, Ohio valley and Mid-Atlantic... ...Dangerous heat is expected for the Desert Southwest and across the midsection of the country as warmth persists across the bulk of the U.S.... A well-defined convective complex continues to advance from the mid Mississippi into the Ohio valley, producing showers and thunderstorms and areas of damaging winds and large hail. It is expected that severe weather will remain a threat as the system moves farther south and east across the Ohio valley Tuesday afternoon and evening. Farther east, expect showers and thunderstorms to continue to develop Tuesday afternoon ahead of a weaker system moving across the central Appalachians into the Mid-Atlantic region. Conditions are favorable for some of these storms to become strong to severe - producing damaging winds and large hail. Additional storms are forecast to develop Tuesday evening into the overnight hours over the central High Plains and along a strong frontal boundary sagging south into the central Plains. There is the potential for these storms to become strong to severe as well, with large hail and damaging winds the primary threat. As low pressure strengthens over eastern Canada, the leading edge of this front is expected to push east across the Great Lakes, with showers and thunderstorms developing along and ahead of the front. Severe storms will remain a concern, especially across portions of the northern Mid-Atlantic into the Northeast, where a weak upper level disturbance moving from the lower Great Lakes toward New England is expected to encourage storm development. Additional storms are also possible along and south of the front as it extends from the Northeast back through the Ohio valley into the central High Plains on Wednesday. Across portions of the central Plains into the lower Missouri and mid Mississippi valley, conditions will be favorable for heavy rainfall rates, which may result in flash flooding across portions of the region. Ahead of the front, seasonal to above-average temperatures will persist across much of the South and the East Coast through midweek. Dangerous heat and humidity has resulted in excessive heat warnings and heat advisories for Tuesday and Wednesday across a large portion of the south-central Plains to the lower Ohio and Tennessee valleys. With record-setting temperatures possible for portions of the Mid-Atlantic to southern New England, heat advisories are also in effect for the Philadelphia metro region. Meanwhile, below-average temperatures will extend south and east across the northern Plains and upper Midwest on Wednesday. Across the Southwest, well-above average to record-breaking temperatures are expected across the deserts of southern Nevada, California and Arizona, with excessive heat warnings in effect across the region into Wednesday. Pereira Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php