Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 350 AM EDT Tue Aug 28 2018 Valid 12Z Tue Aug 28 2018 - 12Z Thu Aug 30 2018 ...A slight risk of severe thunderstorms and excessive rainfall from the Middle Mississippi Valley to the Upper Great Lakes today... ...Excessive heat expected to continue across much of the southern and eastern U.S.... ...An Air Quality Alert due to wildfires remains in effect across southern Oregon... A cold front is currently stretching from Canada, across the Upper Great Lakes region, and southeastward into the Central Great Basin. Several areas of low pressure are embedded within the structure, enhancing the instability and lift in these locations. Strong southerly flow is pulling warm and moist air inland from the Gulf of Mexico towards the frontal boundary, while colder Canadian air continues to fill in behind. The clash of these two air masses is leading to showers and thunderstorms along and just ahead of the frontal boundary, enhanced by any embedded low pressure circulations. The Storm Prediction Center has issued a slight risk for severe thunderstorms stretching from the Middle Mississippi Valley northeast into the Upper Great Lakes today. The Weather Prediction Center has also issued a slight risk for excessive rainfall for the same region, as well as a moderate risk of excessive rainfall for southern Wisconsin and far northern Illinois, where a Flash Flood Watch as well as multiple advisories and warnings are ongoing. The risk of severe storms and excessive rainfall will slowly shift eastward with the movement of the cold front in the coming days. Meanwhile, for locations south and east of the cold front, the strong pull of warm and humid air is leading to suppressing heat. This heat is expected to persist through the coming days, with a strong upper level ridge in place, making it hard for the cold front to make much eastward progression. Many locations could see high temperatures in the mid and upper 90s today with heat indexes in the triple digits. Heat Advisories are in effect for portions of the Mid Mississippi Valley, including all of Central Illinois, lower Michigan, as well as across much of the Northeast and northern Mid-Atlantic. An Excessive Heat Warning is also in place today across the St. Louis metropolitan area. Elsewhere, a much colder Canadian airmass is shifting southward and across the Northwestern U.S.. The combination of cooler air and light winds is suppressing the ongoing fire concerns, and helping to alleviating the excessive smoke in the air. Only one Air Quality Alert remains in place for today across Southern Oregon, where an ongoing wildfire continues to burn. Meanwhile, heavy, wet snow was impacting the northern Rockies overnight, but should clear out throughout the morning. Wix Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php