Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1127 AM EDT Sun Oct 14 2018 Valid 12Z Wed Oct 17 2018 - 12Z Sun Oct 21 2018 ...Pattern Overview... Upper ridging over British Columbia and Florida will favor progressive troughing through the northern tier east of the Rockies with a closed low lingering across the Southwest. A couple Canadian fronts with limited moisture will swing through the Great Lakes/Northeast later this week into the weekend with a renewed push of cooler air. Florida will remain warm/hot with scattered showers/storms and the Pacific Northwest should see above average temperatures and dry conditions. ...Guidance/Predictability Assessment... A multi-model deterministic blend (GFS/ECMWF/UKMET) sufficed for the Day 3-5 (Wed-Fri) period as models showed generally good consensus with respect to the upper low lingering across the Southwest and with amplifying shortwave energy crossing the Great Lakes. By the weekend, a couple differences start to emerge. The first being how much erosion/flattening of the western North American ridge occurs as shortwave energy exits the northeastern Pacific. The ECMWF, and its ensembles, remain a bit more aggressive with flattening the ridge, while the GFS/GEFS are consistent with maintaining strong ridging, though the ECMWF may be starting to trend towards the stronger GFS ridging. In the East, the GFS/Canadian solutions remain much stronger/sharper with an upper trough swinging through, while the ECMWF and the ECENS/GEFS are weaker. For both systems in the Day 6-7 period, a majority ensemble mean blend (GEFS/ECENS) along with smaller contributions from the deterministic GFS/ECMWF seemed to provide a reasonable compromise and fits well with previous shift continuity. ...Weather Highlights/Threats... Below average temperatures will continue late this week into the weekend for the Southwest through the southern Plains (especially Texas) northeastward through the Ohio Valley into the Northeast. On the warm side of the stationary front, Florida will see warm/hot temperatures that may tie/break record highs at some locations and upper ridging across the Pacific Northwest will also lead to continued above normal temperatures for that region. Precipitation wise, the best chance for heavy rainfall remains along the southern/central Texas coast along an inverted trough and just to the northwest of a stationary boundary in the western Gulf. This signal has been steady for several model/ensemble cycles now. A lingering upper low in the Southwest will support rain/snow showers mostly focused in/along the higher terrain, and a stationary front across Florida will keep daily shower/storm chances in the forecast for much of the period. The rest of the lower 48 looks to be largely dry with some generally light rain/snow showers around the Lakes and into the Northeast along/ahead of the cold front next weekend. However, if a stronger/sharper upper trough in the East were to materialize (like the GFS is depicting), the chances for heavier precip along the front from generally the central Gulf Coast to the Mid-Atlantic would increase. Santorelli/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