Short Range Forecast Discussion NWS Weather Prediction Center College Park MD 514 PM EDT Wed Sep 23 2020 Valid 00Z Thu Sep 24 2020 - 00Z Sat Sep 26 2020 ...There is a moderate risk of excessive rainfall and a slight risk of severe thunderstorms over parts of the Lower Mississippi Valley... ...Air Quality advisories are across parts of California, Pacific Northwest, and parts of the Northern/Central Rockies... ...Temperatures will be 10 to 20 degrees above normal over parts of the Great Basin into the Central High Plains... ...Post-Tropical Cyclone BETA will slowly move northeastward and dissipate by Friday evening.... Post-Tropical Cyclone BETA will slowly move northeastward to the Tennessee Valley and dissipate by Friday evening. BETA will produce very heavy rain across parts of the Lower Mississippi Valley into the Tennessee Valley. The WPC has issued a moderate risk of excessive rainfall over parts of the Lower Mississippi Valley through Thursday morning. The heavy rain associated with BETA will produce numerous areas of flash flooding with some locally significant flash flood events possible. Many streams will also flood potentially affecting larger rivers. In addition, the SPC has issued a slight risk of severe thunderstorms over parts of the Lower Mississippi Valley. The main hazard will be frequent lighting, severe thunderstorm wind gust, and a few tornadoes through Thursday morning. Meanwhile, a front will move onshore over the Pacific Northwest moving inland to the Northern Plains by Friday. The system will produce rain over parts of the Pacific Northwest eastward into the Northern Rockies through Friday evening. A second front will come onshore late on Friday. Upper-level ridging will extend from the Southwest to the Northern Rockies that will move eastward to the Upper Great Lakes to the Southern High Plains by Friday. The ridging will allow temperatures to become 10 to 20 degrees above normal over parts of the Great Basin into the Central High Plains. Fire weather will be elevated to critical from parts of the Northern High Plains/Rockies to parts of the Great Basin as strong surface wind gusts and dry conditions sweep across ahead of a cold front. Smoke from wildfires will continue as air quality advisories are posted in response across parts of California, Pacific Northwest, and parts of the Northern/Central Rockies. Ziegenfelder Graphics available at www.wpc.ncep.noaa.gov/basicwx/basicwx_ndfd.php