Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Thu Oct 25 2018 Valid 12Z Sun Oct 28 2018 - 12Z Thu Nov 01 2018 ...Guidance/Predictability Assessment and Preferences... The guidance forecasts troughing to redevelop mid-continent to the east of a positive mid-level height anomaly in the northeast Pacific/West Coast, downstream of a negative anomaly closer to the International Dateline. The guidance shows good agreement at 500 hPa, but this does not extend to their surface patterns. For Sunday, a blend of the 00z Canadian, 00z UKMET, 00z ECMWF, and 06z GFS is fine. The Canadian/ECMWF guidance depart from the ensemble mean solutions mid-continent, with the ECMWF too far north with a low in Canada and the Canadian too far south/too progressive with its lows in the Lower 58. For Monday and Tuesday, a compromise of the 06z GFS and 00z UKMET was preferred. Once the UKMET run ends, a compromise of the 06z GFS/00z ECMWF ensemble mean/00z NAEFS mean was used for Wednesday into next Thursday which were agreeable. This led to a speedier frontal progression than overnight continuity. ...Weather Highlights/Threats... Regarding precipitation, the most active area will be over the Pacific Northwest given the semi-permanent onshore/zonal flow regime through the period. This will be augmented during the passage of any notable shortwaves, especially the one arriving late this weekend. Several inches of rainfall are likely across the Olympics and Cascades given favorable upslope trajectories with snow expected over the higher elevations extending into the interior mountainous terrain. Across the Northeast, it will be intermittently wet over the region with snow possible over portions of the Appalachians. A heavy stripe of precipitation will be exiting northern Maine on Sunday morning as a wave exits the region while broad cyclonic flow and additional forcing keeps showers in the picture into early next week. Regarding that next trough crossing the central U.S. by mid-week, poleward moisture return should allow rainfall to break out along the slow-moving frontal zone across portions of the lower Mississippi Valley. Uncertainty remains high as the heavier amounts will be driven by where instability is more prevalent. Temperatures remain cool over large sections of the eastern U.S. given the lower heights traversing the region. Forecast anomalies should be around to 10 to 15 degrees below climatology, particularly over the Ohio Valley into the northeastern U.S. through early next week. Eventually numbers should return closer to average for late October given mid-southwesterly flow becoming established. Out to the western U.S., temperatures will be around 10 to 15 degrees above average, particularly over the Central Great Basin into the Rockies given the ridging aloft. As heights lower from Tuesday onward, a cool down is expected to shift eastward toward the central U.S. for much of next week. We wish Brenden well on his upcoming adventure in Sacramento after 12 years at HPC/WPC. We'll miss him. :) Roth/Rubin-Oster 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