Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 400 AM EDT Mon Aug 27 2018 Valid 12Z Mon Aug 27 2018 - 12Z Wed Aug 29 2018 ...Strong thunderstorms and heavy rainfall will impact the Upper Mississippi Valley and Upper Great Lakes Today... ...Excessive heat is expected across the Southern/Central Plains and the entire eastern third of the U.S. over the coming days... ...Ongoing fire weather concerns across the West... ...Accumulating Wet Snow forecast across the Northern Rockies today and tonight... An upper level trough is expected across the northwestern U.S. and the Dakotas through Tuesday, while an upper level ridge continues to build across the eastern third of the nation. Meanwhile at the surface, a active frontal zone is currently in place, draping from the Intermountain West northeast into the Northern Plains and Upper Mississippi Valley. A strong surge of warm, moist air is being pulled northward from the Gulf of Mexico towards the frontal boundary, resulting in showers and thunderstorms along and just ahead of the boundary. The best shower and thunderstorm activity will be found near the centers of low pressure embedded within the northern portion of the boundary. The Storm Prediction Center has outlined a large area encompassing much of the Upper Mississippi Valley and Upper Great Lakes region as being in a slight risk of severe storms through today. The Weather Prediction Center has also outlined much of the same region as being in a slight risk for excessive rainfall today as well. While a cooler airmass is in place behind the frontal boundary, the strong ridge in place across the eastern and southeastern U.S. will make it hard for the front to move east quickly. As a result, much of the southern and eastern U.S. will continue to see hot and humid southerly flow for much of the week. Above normal temperatures are expected in many locations. Heat Advisories have been posted across much of Illinois and along the Mid and Lower Mississippi River, as well as across portions of the Northeast and northern Mid-Atlantic. Special Weather Statements for heat are also in effect across portions of the Ohio Valley. Heat indices will exceed 100 degrees for many locations today and Tuesday. Across the Western U.S., fire weather concerns persist. A Red Flag Warning is in effect through this evening across the western Central Plains due to windy conditions and low humidity. Air quality also continues to be compromised by smoke from ongoing wild fires. Air Quality Alerts are ongoing across Central California, Southwest Oregon, northern Washington, Southern and Northern Idaho, and Northwest Montana. As mentioned above, much colder air is pushing in behind the frontal boundary. This cold air will make it into the Northern Rockies and Northern Plains today. In fact, there is enough cold air flowing across the Northern Rockies that accumulating wet snow is expected. Winter Weather Advisories are in effect with 4 to 8 inches forecast through Tuesday morning. Wix Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php