Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 424 PM EDT Tue Jul 18 2017 Valid 00Z Wed Jul 19 2017 - 00Z Fri Jul 21 2017 ...Heat is building eastward from the Plains towards the Midwest and into the Mid-Atlantic... ...Thunderstorms could become severe over the upper Midwest where heavy downpours could lead to flash flooding... ...Heavy late-day thunderstorms could lead to flash flooding in parts of the Desert Southwest... Under the influence of a high pressure cell aloft, the mid-section of the country will remain in the grip of a heat wave as we head into the middle of the workweek. Excessive heat warnings are already in effect as far east as the Midwest where high temperatures are forecast to exceed 100 degrees near St. Louis for the next few days. The heat is accompanied with dry conditions from the Midwest down into the central and southern Plains as the nearest significant precipitation is forecast to be across the upper Midwest ahead of a cold front. Thunderstorms that form over the upper Midwest could become severe today and tomorrow, where heavy downpours could lead to flash flooding. Farther east, an upper-level trough/cut-off circulation could help trigger scattered slow-moving thunderstorms over the Mid-Atlantic and into the Southeast late in the day today and Wednesday. The upper-level disturbance is forecast to drift just off the Carolina coast on Thursday which should keep much of the thunderstorms just offshore. Over the northern Plains, cool air behind the aforementioned cold front will continue to filter eastward into the Great Lakes on Wednesday and into New England Thursday morning. Meanwhile, a low pressure wave near the tail end of the front will begin to trigger showers and thunderstorms in the northern High Plains on Wednesday, spreading eastward across the upper Midwest Wednesday night, and into the lower Great Lakes by Thursday morning. Elsewhere, monsoonal moisture and daytime under a weak upper-level disturbance will help trigger showers and thunderstorms over parts of the Southwest/Great Basin and over the central and southern Rockies through Wednesday evening. Some of the storms could contain heavy downpours and could lead to localized flash flooding especially in the Desert Southwest. Kong Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php