Extended Forecast Discussion NWS Weather Prediction Center College Park MD 534 PM EDT Wed Oct 06 2021 Valid 12Z Sat Oct 09 2021 - 12Z Wed Oct 13 2021 ...First winter storm of the season possible for parts of the central and northern Rockies by early to middle of next week... ...Guidance Evaluation/preferences... For a medium range forecast, there's actually really good agreement through the entire period on the overall large scale setup which features a shortwave/closed low lifting through the southern Plains early next week, while troughing amplifies over the West and a well defined low pressure system emerges into the Central Plains by the middle of next week. There remains some relatively minor timing and detail differences, but these kinds of uncertainties may take until the short range to resolve. The WPC forecast used a general blend of the operational models (06z GFS, 00z ECMWF/CMC/UKMET) through day 5. For days 6 and 7, increased contributions from the ensemble menas to help mitigate those smaller scale uncertainties. This maintains good continuity with the previous WPC forecast helping to increase confidence some in the pattern and relevant weather hazards. ...Pattern Overview and Weather/Hazards highlights... While a lingering rainfall axis will continue into the weekend from the Mid-Atlantic/Central Appalachians to the Great Lakes, the focus this weekend should shift to the coast/offshore where a frontal boundary and area of low pressure, with limited tropical development probabilities, could bring some heavy downpours to portions of the North Carolina Outer Banks and southeast Virginia. Upstream, a front lifting through the north-central U.S. will bring moderate to locally heavy rainfall to parts of the northern Plains/Upper Midwest this weekend. Amplifying southern stream upper trough energy should act to focus moisture/instability to fuel an increasingly favorable convection and organized rainfall environment Sun/Mon for portions of the Plains, with the SPC noting a severe weather area across the southern Plains on Sunday in their day extended outlook. The system should then begin lifting and shearing over the Midwest/Great Lakes on Tuesday, with mainly light to moderate precipitation. Out West, moderate to heavy rainfall and mountain snow is possible across parts of the Pacific Northwest this weekend, with moisture shifting southward and inland with a wavy/lead front. Deep troughing and closed upper low development down over the Southwest/Great Basin into early-mid next week will bring much below normal temperatures behind the cold front with daytime highs as much as 25-30 degrees below normal across much of the interior West well into next week. This would support lowering snow levels in the mountains with potential for decent snow accumulations in the higher terrain of the northern Rockies beginning on Sunday. A low pressure system should eject out of the Rockies into the Plains, with increasing confidence in potentially heavy snowfall within an emerging deformation area on the back/west side of the low. This could bring the first winter storm of the season to portions of the central and northern Rockies. An axis of heavy rainfall is possible to the north of the low, with some mixing of snow not out of the question during the colder overnight hours. Gusty winds may also be possible across the central and northern Plains by Wednesday of next week as the surface low deepens through the central U.S.. Across the central and southern Plains, moderate to locally heavy rainfall is possible with another threat for severe weather on Tuesday into Wednesday as highlighted in the latest SPC extended outlook. Santorelli Hazards: - Heavy precipitation across portions of the Pacific Northwest and the Northern Great Basin, Sat-Mon, Oct 9-Oct 11. - Heavy precipitation across portions of the Central Rockies, the Central Plains, the Northern Plains, and the Northern Rockies, Wed, Oct 13. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sun, Oct 10. - Heavy rain across portions of the Central Appalachians, the Northern Plains, the Mid-Atlantic, the Southern Appalachians, the Upper Mississippi Valley, and the Southeast, Sat, Oct 9. - Heavy rain across portions of the Central Plains, the Middle Mississippi Valley, the Upper Mississippi Valley, and the Northern Plains, Wed, Oct 13. - Heavy snow across portions of the Central Plains, the Central Great Basin, the Northern Plains, the Northern Rockies, the Central Rockies, and the Northern Great Basin, Mon-Tue, Oct 11-Oct 12. - Severe weather across portions of the Central Plains, the Middle Mississippi Valley, the Lower Mississippi Valley, and the Southern Plains, Sun, Oct 10. - Severe weather across portions of the Central Plains and the Southern Plains, Tue, Oct 12. - Flooding possible across portions of the Great Lakes. Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php 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