Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Mon Oct 01 2018 Valid 12Z Thu Oct 04 2018 - 12Z Mon Oct 08 2018 ...Prolonged wet pattern for the West/Rockies and a Central U.S. Heavy Rainfall Threat... ...Pattern Overview and Guidance/Predictability Assessment... The overall pattern through the extended periods is in fairly decent agreement with a digging longwave trough over the western states, sandwiched between a ridge over the Pacific and the East Coast/Atlantic Ocean. Deterministic and ensemble means depict a deepening low setting up over the Great Basin region by October 7th, with a few solutions suggesting it close off. This supports multiple waves of low pressure lifting from the Great Basin/Southern and Central Rockies into the Plains.The WPC medium range product suite was primarily derived from a blend of the GFS/ECMWF and GEFS/ECMWF ensemble means. ...Weather Highlights/Threats... Colder than seasonal normal temperatures and unsettled/wet weather is expected for the next several as a persistent and highly amplified trough aloft sets up over the West. Terrain and upslope enhanced snows will spread over the northern Rockies/Plains. With such a strong high in place over the East, waves along the frontal boundary (including remnants of Rosa) will have little eastward progression through next week. Multiple rounds of rain (and some northern fringe snow) to the same areas over several days giving way to wetter soils and rising rivers. Temperatures to the south of the front will be rather summer-like into the 80s and some 90s along the Gulf Coast. By the coming weekend, amplifying of the longwave trough into the west will nudge the trough axis eastward into the Great Basin. This will trigger cyclone development which will bringing more rain and high mountain snow into the north-central Rockies. As this system exits the Rockies and an emerges into the Southern/Central High Plains it will pose as a heavy rainfall and strong convection threat. This will promote a prolonged pattern that offers a risk of cell training within an increasingly deep moisture channel east of the western U.S. mean trough and around the amplified ridge holding in place over the East/Southeastern U.S. Campbell/Schichtel WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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