Extended Forecast Discussion NWS Weather Prediction Center College Park MD 119 AM EDT Sat Jun 13 2020 Valid 12Z Tue Jun 16 2020 - 12Z Sat Jun 20 2020 ...Heavy rain possible over parts of the Carolinas and southern Mid-Atlantic 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. along with ridging across the central U.S. (though flattening somewhat by later in the week) and across the North Atlantic Ocean. In-between the central U.S. and Atlantic ridges, guidance shows general consensus that shortwave energy will 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. This feature may linger over the region through much of the week and has the potential to bring one or more days of heavy rainfall to parts of the southern Mid-Atlantic/Carolinas and perhaps central and/or southern Appalachians. Farther west a series of 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 front should weaken across the Northern Plains on Tue. The second front will enter the Northwest early in the week and continue eastward thereafter. East of the Rockies the supporting dynamics with the latter front will likely be stronger, leading to greater southeastward progression into the Plains/Midwest/Great Lakes later in the week. With relatively strong upper ridging in place across the Plains at least through midweek, moisture advection northward into these fronts should be relatively modest, with some degree of capping inversion also likely to be present. Thus QPF amounts with each of these systems across the north central U.S. should remain light-moderate in most cases through midweek. Localized/isolated areas of heavy rainfall will be a possibility, however. Late in the week guidance suggests the second front could decelerate or stall over the Plains/Midwest, while solutions diverge over how much low level moisture may ultimately interact with the front. The central U.S. upper ridge will support very warm to hot conditions from the Central Plains into Upper Midwest through midweek, with some areas seeing highs and/or morning lows 10-15F above normal. During the latter half of the week expect above average temperatures to progress east across the Great Lakes/New England. Meanwhile cool conditions over the Northwest/northern Rockies early in the week (highs 5-15F below normal) will modify somewhat as the second northern tier front brings a cooling trend into the Plains during the latter half of the week. Clouds and rainfall near the eastern upper low may keep highs up to 10-15F below normal at some locations Tue-Wed, before temperatures begin to warm later in the week as the system weakens and moves away from the region. ...Guidance/Predictability Assessment... The 12Z ECMWF/UKMET solutions were preferred during the first half of the medium range. These solutions were closest to an ensemble-based consensus with the upper low across the eastern U.S. during days 3-5 (Tue-Thu). The GFS has continued to be on the northern/western side of the guidance spread with respect to the upper low, and this solution was not preferred. Use of ensemble means was increased gradually over time, with majority ensemble means in the forecast blend during days 6-7 (Fri-Sat), along with some continued use of the deterministic ECMWF. The GFS was also faster than consensus with the shortwave energy exiting the northern Rockies and crossing the Northern Plains/Upper Midwest by the middle of next week, which also factored into the decision to exclude the GFS from use during the medium range this forecast cycle. Ryan/Rausch 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