Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1243 AM EDT Fri Jun 12 2020 Valid 12Z Mon Jun 15 2020 - 12Z Fri Jun 19 2020 ...Heavy rain possible over parts of the Mid-Atlantic/central Appalachians and eastern Carolinas next week... ...Overview and Weather/Hazard Highlights... Persistent upper-level ridging across Alaska and western Canada will favor broad cyclonic flow across the northwestern U.S., ridging across the central U.S., and across the North Atlantic Ocean. In between, guidance shows general consensus that shortwave energy should separate from the westerlies in the form of a cutoff mid/upper-level low across the central/southern Appalachians/Southeast/Mid-Atlantic early next week, with the potential for the system to linger/meander across the region through much of the week. This feature has the potential to bring a multi-day heavy rainfall event to portions of the Mid-Atlantic and central Appalachians, but the specifics of the eventual system will play a large role in the degree of heavy rain threat that develops, and models/ensembles portray a wide range of possibilities from a very heavy rain event to very little in the way of heavy rain. Farther west, several shortwaves will eject from the broad Pacific Northwest trough and traverse the northern periphery of the central U.S. ridge, each with an associated surface front. The first of these during the medium range should weak across the Northern Plains Mon-Tue, with another front crossing the northern Rockies during that time, and reaching the Northern Plains during the mid to latter part of next week. With relatively strong ridging in place across the Plains, moisture advection northward into these systems will be relatively modest, and some degree of capping inversion is also likely to be present. Thus, QPF amounts with each of these systems across the north central U.S. are relatively modest, although localized/isolated areas of heavy rainfall will be a possibility. The ridge will also promote well above average temperatures across much of the central U.S. next week. High temperatures are forecast to be 5 to 15 deg above average from the Central/Northern Plains to the Midwest/Great Lakes Mon-Wed, perhaps spreading east into portions of the Northeast by Thu-Fri. High temperatures across the Central/Southern Plains should reach well into the 90s, with perhaps some locations approaching 100. ...Guidance/Predictability Assessment... Models/ensembles showed a range of possibilities with respect to both timing and intensity of the eastern U.S. cutoff low next week. The GFS and GEFS were among the deepest solutions and the slowest to progress east, while the ECMWF and ECENS were the weakest with the system and quicker to move it east. These resulted in QPF differences as well, with the GFS/GEFS solution resulting in a more significant heavy rain event across the central Appalachians, and the ECMWF/ECENS solutions much lighter across the Appalachians, but with heavy rain across eastern North Carolina. In this scenario, believe that ensemble means provide quite a bit of utility and representing a consensus solution, and thus chose to use the ECENS/NAEFS ensemble means fairly heavily earlier in the forecast period than is typical. Among the deterministic guidance, the 12Z UKMET was the closest to a middle ground solution, largely in between the ensemble means for the upper low, and was also comparable to the ensemble consensus elsewhere across the CONUS. Thus, made some use of the UKMET during days 3-5 (Mon-Wed), before going entirely with a blend of the ECENS/NAEFS ensemble means days 6-7 (Thu-Fri). Ryan 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