Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Sun Oct 11 2020 Valid 12Z Wed Oct 14 2020 - 12Z Sun Oct 18 2020 ...Overview... A broad upper-level trough should become the dominant feature over the eastern two-thirds of the country with below normal temperatures settling into the area through next weekend. The northern tier states should see periods of rain from time to time due to relatively frequent passages of fronts and associated low pressure systems. By next weekend, shortwave energy should dip into the Pacific Northwest and northern Rockies, bringing another round of lower elevation rain and higher elevation snow. ...Guidance Evaluation/Preferences... Model guidance this morning generally shows decent agreement on the overall evolution of the synoptic pattern through the medium range. But uncertainty has increased for next weekend over the Northwest regarding the details of a shortwave trough dipping south from Canada into the region. The last few runs from the GFS have refrained from developing the shortwave in western Canada, leading to more upper-level ridging building back into the Pacific Northwest. On the other hand, the ECMWF solutions have continued to indicate development of this shortwave. Meanwhile, the ECMWF continues to indicate the possibility of cyclogenesis in the vicinity of New England on a rather sharp front. This scenario is supported by the CMC. The GFS remains progressive with the front and maintains a positively-tilted upper trough. In general, the recent GFS solutions have switched to a less amplified upper-level pattern than in the ECMWF. The WPC prognostic charts adopted an intermediate solution by blending the 00Z ECMWF/00Z EC mean with the 06Z GFS/06Z GEFS. More of the ensemble means were used to handle the uncertainty for Days 6 and 7. ...Weather/Hazard Highlights... A low pressure system moving across the Great Lakes Wed-Thu should bring some light to moderate rain across the region. More scattered showers and perhaps thunderstorms should accompany the trailing cold front down into the lower to mid-Mississippi Valley on Thursday. By later on Friday into next weekend, the ECMWF and CMC continue to support cyclogenesis along the front over New England with enhanced rainfall. The cold front will end the warm temperatures across the eastern U.S. as cooler air of 5 to 15 degrees below average spreads from west to east 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. Kong 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