Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 AM EDT Fri Oct 18 2019 Valid 12Z Mon Oct 21 2019 - 12Z Fri Oct 25 2019 ...Upper Midwest/Great Lakes Storm... ...Potential Tropical Cyclone Sixteen to threaten the Northeast... ...Heavy rain and mountain snow from the Cascades to the North-Central Rockies... ...Guidance/Uncertainty Assessment and Weather Highlights/Threats... An amplified and generally progressive flow pattern will support several significant weather systems over the lower 48 states next week. The WPC medium range product suite was primarily derived from a composite blend of reasonably well clustered guidance from the GFS/ECMWF/UKMET/Canadian Monday and Tuesday in a pattern with above normal forecast predictability, albeit with uncertainty with track/interaction of Potential Tropical Cyclone Sixteen as per NHC. Switched to quite compatable GEFS/ECMWF ensemble mean guidance later next week in a period of gradually increasing forecast spread, but with a pattern evolution offering at least average predictability given decent guidance continuity and system organizations. A closed upper low/trough will lift from the Plains through eastern North America early to mid next week. Deep surface cyclogenesis into the Upper Midwest/Great Lakes will act to ramp up winds and unsettled weather/wrap-back snow while also forcing a lead frontal system and Gulf of Mexico moisture return to combine with upper support to fuel a widespread swath of heavy rain/convection across the east-central states. Activity over the Northeast may be also significantly enhanced by interaction/merging with a Mid-Atlantic to New England extratropical coastal low and deepened moisture associated with current Potential Tropical Cyclone Sixteen. The pattern meanwhile reloads upstream as upper impulses/jet energies/height falls work progressively inland over the Northwestern U.S. early-mid next week that carve out another amplified central U.S. upper trough mid-later next week. A series of systems/frontal passages offer a risk of heavy rain and mountain snow from the Cascades to North-Central Rockies. Below normal temperatures will sweep down through the interior West/Rockies then Central U.S. Temperatures will become 10-15 degress below normal over the n-central states as the post-frontal high surges southward. Lead Gulf of Mexico moisture return into the central Gulf Coast and lower MS/TN Valleys may fuel enhanced rain/convection, with modest precipitation inland over the east-central states including some threat of wrapping snows for a cooling Upper Midwest. Schichtel 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