Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1150 AM EDT Wed Oct 17 2018 Valid 12Z Sat Oct 20 2018 - 12Z Wed Oct 24 2018 ...Pattern Overview... A relatively benign pattern shapes up the medium-range period through next Wednesday, with troughing persisting in the Northeast while a Rex block pattern develops and lingers in the West. The wettest part of the country should be along the Gulf Coast where moisture continues to circulate around a subtropical high centered over Cuba. The Pacific Northwest will see the next batch of precipitation arriving toward the middle of next week with little wintry weather expected in the higher elevations. ...Guidance/Predictability Assessment... Models and ensembles continue to offer good clustering through the next 5-6 days with expected timing/amplitude differences by next Tue/Wed. A deterministic blend of the GFS/ECMWF offered a good starting point close to continuity for Sat-Mon as a lead and secondary cold front push off the East coast and another Canadian front dips into the western Great Lakes. By next Tue/Wed an approaching Pacific system (or couple of systems) will eventually break the ridge over the West, but the ECMWF ensembles remain quickest to lower heights into the Pacific NW which is rather uncharacteristic in the longer term, but has been noted recently. Some spreads in the model solutions begin to show up on days 6 and 7 near the Canadian border regarding the cold high pressure system dipping into the Great Lakes and the NE U.S. The 00Z ECMWF now shows a pressure pattern in closer agreement with the GFS, which has been showing better consistency in that region. Therefore, the WPC morning grid file package is a consensus between the 00Z ECMWF/EC mean, 00Z and 06Z GFS, 00Z GEFS with more of the ensemble means incorporated for days 6 and 7. ...Weather Highlights/Threats... The Pacific Northwest will see several days of above average temperatures and dry conditions through the weekend. Rain chances will increase next week starting late Monday as the first cold front approaches the coast. Warm antecedent temperatures will preclude snow from all but the highest elevations, but that will change as cooler air works its way eastward. Rain will become widespread and moderate to locally heavy by midweek next week. The rest of the CONUS will see near to below average temperatures with the core of the coolest air from Texas northeastward to the Northeast/New England. Even Florida will slowly trend back toward more typical late October temperatures in the upper 70s (north) to mid 80s (south). Coastal Texas has the highest probability of the greatest amount of precipitation east of the Rockies due to an initial and then subsequent stationary boundary through the Gulf next to an inverted trough. Though most of this may stay offshore, areas near Brownsville may see several inches of rain over the period. Much less precipitation is expected elsewhere with each frontal passage except for perhaps Florida with strong easterly flow. Coastal WA/OR will see light-moderate rain develop and expand inland early next week as upper troughing approaches with several inches possible along the immediate coast by next Wednesday. Kong/Fracasso 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