Extended Forecast Discussion NWS Weather Prediction Center College Park MD 303 PM EDT Wed Jul 29 2020 Valid 12Z Sat Aug 01 2020 - 12Z Wed Aug 05 2020 ...Heavy rainfall threat from the Ohio Valley to the Lower Great Lakes this weekend... ...Potential Tropical system threat for Florida/Southeast U.S. this weekend into early next week... ...Overview and Guidance/Predictability Assessment... The ridges over the West and Southeast/Bermuda will keep troughing established across the Pacific Northwest and the central/eastern part of the CONUS. This setup will be favorable for anomalous temperatures- warmer in the West, Southwest and Southeast while cooler across parts of the central/eastern U.S. Additionally, what is currently Potential Tropical Cyclone Nine may impact the Bahamas, Florida, and into the Southeast U.S. as a tropical storm by this weekend and into early next week. In general, deterministic and ensemble mean solutions remain fairly clustered through the course of the extended periods in regards to the big picture. Differences in QPF placement and timing where dependent on the evolution of the tropical cyclone and how progressive/slow the mid-upper level trough were, as this would shift the jet stream, areas of lift and instability as well. Chose to start with a general model blend of the 00Z ECWMF/CMC/UKMET/GFS initially, with increasing weights of the respective ensemble means in the later periods. Forecast confidence on this system is low at best, and so adjustments to the track are likely. ...Weather/Hazard Highlights... An area of low pressure will traverse along a wavy frontal boundary this weekend, from the Tennessee Valley to the Great Lakes; followed by another low in the Tennessee Valley early next week. Scattered to widespread showers and thunderstorms will fire up along this boundary from the central U.S. to the Mid-Atlantic and northward to the Lower Great Lakes/Northeast, keeping this section of the country saturated. With several inches of rain possible through the course of the extended period, the risk for excessive rainfall and subsequent flooding concerns will remain elevated for parts of the Mid-Mississippi/Tennessee/Ohio Valleys. At the same time, Potential Tropical Cyclone Nine (which will likely be a Tropical Storm prior to the medium range timeframe) is tracking West/Northwest south of Puerto Rico and is currently forecast to pass near Cuba and the Gulf side of Florida this weekend. With the tropical cyclone approaching Florida and areas to the north, heavy rainfall and gusty winds will likely proceed the cyclone, as well as, follow its path this weekend/early next week. It is expected to interact with the frontal boundary to the west which could ultimately spread heavy to possibly excessive rainfall northward into the Carolinas/Mid-Atlantic region early next week. As always, specific details in the track and timing are subject to change, therefore the latest information for this system should be monitored from the National Hurricane Center. Meanwhile, upper level high pressure anchored over the Southwest U.S. and building ridging northward should support moderately anomalous summer heat across the Intermountain West/Rockies/High Plains and the Southwest. Several locations could have weekend temperatures reaching the 90s to 100s, with the Southwest ranging from 110s to 120. The readings would average 5 to 10 degrees above the seasonal average. On the flip-side, portions of the Plains and Midwest will average 5 to 10 degrees cooler the inveterate trough in place. Campbell Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml