Extended Forecast Discussion NWS Weather Prediction Center College Park MD 257 AM EDT Sun Oct 11 2020 Valid 12Z Wed Oct 14 2020 - 12Z Sun Oct 18 2020 ...Overview... A broad upper-level trough is forecast to persist over much of the CONUS through the medium range period, while a lead frontal system spreads a cooler air mass from west to east across much of the country ahead of the trough axis, accompanied by light to moderate rain in the north-central to northeastern U.S. Then, another shortwave is currently forecast to dive into the Northwest by next weekend, causing another round of lower elevation rain and higher elevation snow and cooler temperatures. ...Guidance Evaluation/Preferences... The general upper-level pattern appears well predicted by the model guidance. This includes the shortwave energy dropping into the northwestern/north-central U.S. Wed which serves to deepen the trough through the end of the week and push a cold front across the central and eastern U.S. There are some differences in terms of the trough wavelength in the guidance with the 12Z CMC in particular, but not huge. Into the weekend as the first shortwave traverses the broad trough, the ECMWF runs remain persistent with developing a surface low around New England (and bringing heavier rains to the area) unlike the other deterministic guidance. There is some support for this solution from ensemble members, but remains uncertain at this time. Another area to watch with some model differences is the second shortwave moving into the West by the weekend. Model guidance for a few runs now has been persistent with this feature, until the 18Z GFS did not have a similar evolution of the shortwave. Thus utilized the 12Z GFS and GEFS rather than the 18Z, as the 12Z better matched recent trends. Overall, a multi-model deterministic blend was favored early in the period, with more usage of the 12Z GEFS and EC ensemble means by the weekend given some model variability in the smaller-scale features. ...Weather/Hazard Highlights... As a low pressure system moves across the Northern Plains and Great Lakes Wed-Thu, some light to modest rain is forecast along and ahead of its associated cold front for those areas into the Northeast. Some lake-enhanced rain totals are possible over the Great Lakes. Rain could persist across the Northeast through Saturday, but rain amounts will depend on the possible development and strength of a surface low pressure there. Ahead of the front, warm temperatures are forecast, but the front should spread temperatures that are 5 to 15 degrees below average across the Rockies to the Eastern Seaboard. The most notable temperature swings should be across the Central/Southern Plains, which will go from temperatures in the 80s and 90s Wed to highs in the 60s and 70s Thu-Fri. Through the end of the week, the Southwest into California and the Central Great Basin should be under the influence of an upper ridge south of the main trough. Warmer than average temperatures are forecast there, and upper 90s to low 100s are forecast for the lower deserts of AZ/CA/NV, which could be near high temperature records at some locations. In the Northwest, the shortwave likely influencing the region by the weekend will lead to another round of precipitation for the Cascades and the Northern Rockies, possibly spreading into the Northern High Plains. Colder than normal temperatures are predicted there by Sun. Meanwhile, showers are possible across southern Florida through the second half of the week. Tate 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