Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Sat Jul 01 2023 Valid 12Z Sat Jul 01 2023 - 12Z Mon Jul 03 2023 ...Severe thunderstorms and areas of heavy rain over the Midwest and Ohio Valley today are forecast to reach into the Northeast and Mid-Atlantic on Sunday... ...Excessive Heat Warnings and Advisories across much of California into the Desert Southwest as well as the Deep South... ...Air Quality alerts over parts of the Midwest, Great Lakes, and the Northeast, and Mid-Atlantic... The slow-moving weather pattern responsible for the severe thunderstorms and areas of heavy rain across the central portion of the country is showing signs of progressing eastward today as the western U.S. upper-level trough exits the Rockies into the northern Plains. Very active development of thunderstorm clusters are expected to shift farther east across the Midwest and the Ohio Valley today ahead of a warm front, where an enhanced risk of severe thunderstorms is anticipated by the Storm Prediction Center. These thunderstorms will likely contain heavy downpours, hail, damaging wind gusts, along with the possibility of flash flooding. A low pressure wave currently developing over the central Plains is forecast to move steadily northeastward into the Midwest by Sunday morning, and then enter the lower Great Lakes and the interior Northeast by Monday morning. Some strong thunderstorms are possible across the Mid-Atlantic later today or tonight ahead of the lifting warm front. Another round of scattered thunderstorms can be expected later on Sunday across the Mid-Atlantic and the central Appalachians ahead of a cold front while the Midwest and the Ohio Valley will begin to cool down and dry out behind the front. New England appears to be the wettest with this system through this weekend into Monday. Given the locally heavy rainfall that has occurred over the previous week, a Marginal Risk for Excessive Rainfall is in effect from the Ohio Valley into the Northeast on Sunday into early Monday. Meanwhile, the same upper trough ejecting into the central U.S. will begin to erode the upper ridge that has been responsible for the prolonged heat wave across the southern Plains and lower Mississippi Valley. As the upper ridge weakens, the highest temperatures and heat indices will slowly trend down, though sweltering heat is anticipated to continue across the Southeast, particularly along the Gulf Coast. Several cities across the lower Mississippi Valley and Southeast are expected to break their daily warmest nighttime low records through the weekend. Heat-related danger remains elevated due to the longevity of this heat wave. As the ridge moves across the south-central Plains, heat will build along the West Coast and reach portions of the Northern Plains by Sunday. Afternoon temperatures in the interior valleys of California may climb over 100F to near 110F at the hottest locations on Saturday. The Desert Southwest will see temperatures climb well into the 110s. The risk of heat-related illnesses will be high through the weekend. In addition to the heat and the severe storms, Canadian wildfire smoke is expected to continue impacting portions of Great Lakes and East Coast over the next few days. However, air quality is expected to slowly improve due to a combination of thunderstorm activity and dispersion of the smoke as we head into the weekend. Kong/Genz Graphics available at https://www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php