Extended Forecast Discussion NWS Weather Prediction Center College Park MD 524 PM EDT Mon Oct 07 2019 Valid 12Z Thu Oct 10 2019 - 12Z Mon Oct 14 2019 ...Central Rockies to Northern Plains/Upper Midwest Snow Threat... ...Pattern Overview and Guidance/Uncertainty Assessment... The main weather driver in the medium range period (Thur-Mon) will be an amplified trough ejecting out of the Rockies on Thursday, closing off into a deep upper low over about northern Minnesota/U.P. Michigan by the weekend. This low should very slowly drift north/east into eastern Ontario by Monday morning, driving a cold front east across the Midwest to the East Coast. Meanwhile, a potential subtropical low should break off from the larger scale flow and linger off the New England coast through Saturday, before it gets sling-shot north towards the Canadian Maritimes. Across the board, models show above average agreement through day 7, which lends to better than normal forecast predictability during the medium range. The GFS continues to be a hair faster with the deep north-central U.S. low, which likely results in it being quicker to push the New England low northward. It is not fast enough to completely ignore, but the ECMWF/UKMET show slightly better continuity with the ensembles and thus were weighted more in the overall blend. The WPC medium range forecast suite was mainly derived from a composite blend of the ECMWF/UKMET/GFS days 3-5, with more ensemble mean weighting (ECENS/GEFS means) beyond to mitigate smaller scale detail differences. This maintains good WPC continuity in an active weather pattern. ...Weather Highlights/Threats... A strong cold front will dig through the western and central U.S. into Thu/Fri to bring well below average temperatures through the region. Some record values may be reached as daytime highs could be as much as 30-40 degrees below normal. Cooler air will tend to moderate and spread across the eastern states over the weekend as well. Along with colder temperatures, wrapback moisture and upslope flow supports a heavy snow threat from the Rockies to the Upper Midwest with upper closed low and surface frontal low track and development. A period of high winds is possible in this region as well as the surface low rapidly deepens and a strong pressure gradient develops on the backside of the storm. Ahead of the attendant cold front, rainfall will expand and offer a risk of locally heavy rainfall from the south-central Plains to the mid-MS Valley/Midwest in a region of enhanced moisture inflow return from the Gulf of Mexico. The rain threat in general will decrease farther east as the system lifts into Canada. Downstream, an organized coastal low off the Mid-Atlantic and New England will meanwhile offer a significant maritime threat and some coastal rainfall, dependent on how close the low tracks to the coast. NHC is also monitoring this system for potential subtropical development. Regardless, strong easterly onshore flow will be prevalent through southern New England into the coastal Mid-Atlantic around its circulation. Santorelli Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php - Heavy precipitation across portions of the Northern/Central Plains, the Great Lakes, the Upper Mississippi Valley, Thu-Sat, Oct 10-Oct 12. - Heavy rain across portions of the Central/Southern Plains, the Mississippi/Ohio Valley, the Great Lakes, and the Northeast, Thu-Fri, Oct 10-Oct 11. - Heavy snow across portions of the Central Rockies and the Central Plains, Fri, Oct 11. - Severe weather across portions of the Central/Southern Plains and the Middle/Lower Mississippi Valley, Thu, Oct 10. - Flooding occurring or imminent across portions of the Great Plains, the Mississippi Valley, and the Great Lakes. - Flooding likely across portions of the Northern Plains. - High winds across portions of the Central Rockies and the Central/Southern Plains, Thu, Oct 10. - Much below normal temperatures across portions of the Great Plains, the Rockies, the Northern/Central Great Basin, the Upper/Middle Mississippi Valley, California, the Pacific Northwest, and the Southwest, Thu-Fri, Oct 10-Oct 11. - Enhanced wildfire risk for part of southern California, Thu, Oct 10. - Heavy rain across portions of the Alaska Panhandle and mainland Alaska, Thu-Fri, Oct 10-Oct 11. 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