Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1239 PM EDT Wed Jun 17 2020 Valid 12Z Sat Jun 20 2020 - 12Z Wed Jun 24 2020 ...Overview and Weather/Hazard Highlights... A slow moving upper-level low centered over the central Appalachians Sat is forecast to gradually weaken as it drifts northeastward through early next week, eventually shifting into the North Atlantic off Nova Scotia. Upstream, another slow moving upper low in the northern stream will drift east from northern Manitoba to northern Ontario through early next week with associated height falls and a cold front lingering over the Upper Midwest to central Great Plains. Ahead of this trough/cold front, high temperatures are forecast to remain 10 to 15 deg F above average from the Great Lakes to the northern New England into next week. The trailing end of this frontal boundary is expected to stall across the Central/Southern Plains and linger through early next week with some reinforcement, as the main low pressure system stalls over northeastern Ontario. The front will focus showers and thunderstorms Saturday night over the Upper Midwest with locally heavy rains possible. As the trough/upper low moves farther east, shower and thunderstorm activity should shift farther south and east, from the Southern Plains and Lower Mississippi Valley to the Ohio Valley then the Appalachians through Tuesday. The Southern Plains may see the greatest potential for locally heavy rain early next week under an upper-level trough and a low level flow pattern from the Gulf of Mexico. Out west, upper-level ridging should gradually strengthen and drift northeast over the Desert Southwest through early next week, but shortwave energy and a cold front from a Gulf of Alaska low will push across Washington state Saturday night into Sunday, and with the next one approaching late in the week. Given that the Sunday system will be heading into broad anticyclonic flow, and will be weakening as it moves ashore, precipitation across the Northwest should be relatively light, and primarily across the Olympics and northern Cascades. Additionally, as heights rise across the West next week, warming temperatures are also expected, with highs forecast to be 5 to 15 deg above average Sunday to Wednesday across much of the Great Basin. ...Guidance/Predictability Assessment... A general model blend of the 00Z ECMWF/06Z GFS with some 00Z CMC/UKMET along with means of the 06Z GEFS and 00Z ECENS were during days 3/4 (Saturday/Sunday). These solutions were reasonably compatible during that time frame with the main lows over the East Coast and the Canadian Shield. During days 5 to 7 (Monday to Wednesday), much more weight was placed on the 00Z ECENS/06Z GEFS ensemble means, along with some continued use of the 00Z ECMWF. The 06Z GFS continued a trend of some significant differences from the overall consensus later in the forecast period, becoming substantially more amplified and slower than it's ensemble mean with Canadian Shield low Monday/Tuesday. Ensemble means are in decent agreement with the Ontario low/trough and the western CONUS/Canadian Ridge and were heavily relied on by Day 6/Tuesday along with some 00Z ECMWF for detail as it is in line with the ECENS mean. Jackson 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