Extended Forecast Discussion NWS Weather Prediction Center College Park MD 101 AM EDT Wed Oct 03 2018 Valid 12Z Sat Oct 06 2018 - 12Z Wed Oct 10 2018 ...Stormy Pattern for the West/Rockies and a Central U.S. Excessive Rainfall Threat... ...Pattern Overview and Guidance/Predictability Assessment... Models and ensembles are reasonably well clustered with larger scale development of a highly amplified weather pattern for the nation this weekend into next week. This pattern offers height anomalies of 2+ standard deviations above/below normal with a digging western U.S. longwave trough sandwiched between ridges over the eastern Pacific and the East Coast/Atlantic Ocean. A deepening/closed low sets up over the Great Basin region and multiple waves lift from the Great Basin/Southern and Central Rockies into the Plains where a deep layered southerly funnel of Gulf of Mexico moisture pools to 2+ standard deviations from normal into/over a slow moving baroclinic zone. However, recent models are showing increased run to run variance with the timing and emphasis of smaller scale embedded systems embedded within the synoptic scale flow, especially the 00 UTC GFS. Accordingly, The WPC medium range product suite was primarily derived by blending the 18 UTC GEFS mean and 12 UTC ECMWF ensemble mean that agree to show a strong pattern signal. Applied stronger weighting to the ECMWF ensembles that maintain closer WPC continuity. ...Weather Highlights/Threats... Colder than normal temperatures and highly unsettled/wet weather will develop as a persistent and highly amplified trough aloft sets up and is reinforced over the West, centered from the Great Basin/Southwest to the Rockies. Terrain and upslope fed snows spread down to focus over the northern Rockies/High Plains, enhanced by a post-frontal cold high pressure surge into early next week. With such a strong warming/blocking ridge over the East, waves along/over central U.S. fronts will show little eastward progression. This will set the stage for a prolonger period favoring multiple rounds of heavy rain/convection with some far northern tier fringe snow. Training in a pronounced axis offers an extended threat of excessive rainfall. Warm sector temperatures south of the front will be summer-like, so a main frontal zone will remain quite defined. Elsewhere, a deep layered easterly fetch off the Atlantic fortifies and persists into next week into the Southeast, spreading showers across Florida and the Gulf Coast/northern Gulf of Mexico underneath a northward shifting eastern U.S. closed ridge aloft. This leave room for Atlantic energies and/or a Carribean based tropical disturbance to work into Florida and/or the Gulf of Mexico next week to enhance lift/moisture pooling. Models show a wide envelope of potential developments that is being monitored by WPC/NHC. 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