Extended Forecast Discussion NWS Weather Prediction Center College Park MD 438 PM EDT Wed Oct 14 2020 Valid 12Z Sat Oct 17 2020 - 12Z Wed Oct 21 2020 ...Overview... A broad upper-level trough around a deep low spinning near Hudson Bay will remain the dominant feature across inland North America through early next week. It remains likely that moderate to heavy rainfall should occur over New England Saturday as a front and surface low move to the northeast (some high elevation snow is likely too). A round of snow is also expected in the Northern Rockies this weekend as colder air plunges southward and southeastward into the Northern High. Some snowfall may be significant and/or the first of the season. Hot temperatures in the Southwest will slowly trend cooler, but still near to above normal. ...Guidance Evaluation/Preferences... Through the 00Z/06Z guidance, the consensus showed broad troughing over about 2/3rd of the CONUS, perhaps slowly retrograding its axis westward by the middle of next week as embedded shortwaves nudge the pattern westward. The ECMWF ensembles have been more aggressive at this depiction than the GEFS members, but have trended in that direction with the updated forecast. The 00Z ECMWF/Canadian were close to that idea vs the generally flatter GFS runs. Given the trend toward more closed/cutoff features in the Pacific and Atlantic, preferred the ECMWF-led guidance but with some GEFS influence to moderate changes by the end of the period. Deterministic blend sufficed to start with the departing sfc low in New England but then transitioned to the ECMWF-Canadian cluster with the ensemble means thereafter. Notable differences in the northeastern Pacific led to low confidence there. ...Weather/Hazard Highlights... A low pressure system is expected to develop over the Northeast late in the week, and bring the potential for moderate to heavy rainfall along with thunderstorms to the region. This could help with drought conditions across much of the Northeast. The highest elevations of New England/Adirondacks could see some snow as well. A cool high pressure system coming in behind the cold front associated with that Northeast low will spread below normal temperatures by 5 to 15 degrees across the Plains to the eastern Seaboard through Sat. A potent cold front will cross the northern Plains to Lake Superior this weekend, reinforcing even colder temperatures over the central CONUS. Max temps in the 30s and 40s should spread east across the Northern Plains to the Upper Mississippi Valley Sat-Tue, which is 15 to 25 degrees below normal. Min temps in the teens and 20s are 10 to 20 degrees below normal. Precipitation is likely with this frontal system, and notable snow is forecast for the Northern Rockies and into the Northern High Plains. There is some potential for light snow into portions of the Upper Mississippi Valley as well. Then, light to modest rain totals are possible along the frontal boundary passing through the central U.S., but the timing of the front and thus the rain is questionable. Though the trend for the front has been slower, the threat for heavy rain remains quite uncertain. The Southwest from West Texas to California and the Central Great Basin will remain under an upper ridge through this weekend, causing dry conditions. Warmer than normal temperatures are forecast there, and upper 90s to low 100s are forecast for the lower deserts of Arizona and California. Some record highs are possible especially on Saturday. The upper ridge shifts farther west late this weekend, making for more moderate temperatures by early next week. Meanwhile, tropical showers are expected across southern Florida as temperatures remain mild and a few degrees above normal. Fracasso/Tate Hazards: - Heavy precipitation across portions of the Central Plains, the Northern Plains, and the Northern Rockies, Sat-Sun, Oct 17-Oct 18. - Heavy rain across portions of the Northeast, Sat, Oct 17. - Flooding occurring or imminent across portions of the Lower Mississippi Valley. - High winds across portions of the Great Lakes and the Upper Mississippi Valley, Sat-Sun, Oct 17-Oct 18. - Much below normal temperatures across portions of the Central Plains, the Upper/Middle Mississippi Valley, the Northern Plains, and the Northern Rockies, Sun-Tue, Oct 18-Oct 21. 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