Extended Forecast Discussion NWS Weather Prediction Center College Park MD 418 PM EDT Wed Jul 01 2020 Valid 12Z Sat Jul 04 2020 - 12Z Wed Jul 08 2020 ...Overview and Guidance Assessment... The large scale pattern over the CONUS during the medium range period (Sat July 4 - Wed July 8) is expected to feature a mean trough aloft over portions of western Canada and the far Pacific Northwest. Meanwhile, for the central/eastern U.S., upper level weakness/troughing over the Southeast early on is forecast to shear out or dissolve giving way to mostly zonal/weak flow by the middle of next week. Model agreement remains average throughout the period though embedded details are murky, especially with the evolution of individual shortwave troughs over the Northwest and potential low development along the Gulf Coast and Southeast. For the Northwest, there should be some broadening of the overall trough with some potential amplification by day 6/7 as depicted by the ECMWF and GFS. The upper ridge in place over the central U.S. is forecast to retreat toward the Southwest later in the period as more of a zonal flow sets up over the Great Lakes and Northeast. Finally, the models still suggest potential low pressure development along the Gulf Coast that then transitions off the Southeast coast before lifting northeast away from the east coast or shear out. For the WPC blend, the day 3/4 blend utilized the latest GFS and ECMWF followed by some inclusion of the UKMET and CMC given the relatively good agreement across the deterministic guidance. However, for the day 5-7 periods, higher components of the ECENS and GEFS was incorporated while maintaining some of the deterministic ECMWF. For the Southeast low, a blend of the deterministic ECMWF/GFS was utilized though the forecast confidence here is below average. ...Weather/Hazard Highlights... Low predictability and confidence in the evolution of the potential low development along the Gulf Coast and Southeast exists and while there is some signal for heavy rainfall given the higher PWs and stalling front in place, exact details and areas for potential excessive rainfall are not clear at this time. Future updates may be able to pinpoint details better. The Northern Plains will be the other primary area for heavy rainfall, thanks to a few waves of low pressure moving along frontal boundaries within an area of warm/moist air. Elsewhere across the CONUS, diurnally driven convection will be possible across the central Rockies as well as the Northeast and Mid-Atlantic but any large scale area for heavy rainfall is too uncertain at this point. Temperatures will largely be summer like for much of the CONUS with near to above normal temperatures expected virtually everywhere. The biggest anomalies reside across the Northern Plains to Great Lakes region where daily highs will top 10-15F above normal. Meanwhile, the combination of heat and humidity will produce excessive heat across portions of southern Florida and the Southwest with heat indices near 110F. Taylor 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 Hazards: - Heavy rain across portions of the Upper Mississippi Valley and the Northern Plains, Sat-Sun, Jul 4-Jul 5. - Heavy rain across portions of the Southeast, Sat-Mon, Jul 4-Jul 6. - Flooding possible across portions of the Middle Mississippi Valley and the Ohio Valley. - Flooding occurring or imminent across portions of the Middle Mississippi Valley and the Northern Plains. - Excessive heat across portions of California and the Southwest, Sat-Tue, Jul 4-Jul 7. - Excessive heat across portions of the Southeast, Sat-Wed, Jul 4-Jul 8. - Much above normal temperatures across portions of the Central Plains, the Middle Mississippi Valley, and the Southern Plains, Wed, Jul 8. - Much above normal temperatures across portions of the Great Lakes, the Mid-Atlantic, the Northeast, the Central Appalachians, and the Upper Mississippi Valley, Sat-Wed, Jul 4-Jul 8. - Much above normal temperatures across portions of the Upper Mississippi Valley, Sat-Sun, Jul 4-Jul 5. - Much above normal temperatures across portions of the Northeast, Tue-Wed, Jul 7-Jul 8. 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