Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1158 AM EDT Tue Oct 08 2019 Valid 12Z Fri Oct 11 2019 - 12Z Tue Oct 15 2019 ...Gradual moderation of record cold over parts of the West/Northern Plains... ...Blizzard conditions possible late this week over portions of the Northern Plains... ...Pattern Overview and Guidance/Uncertainty Assessment... The most dominant feature during the period will be a an anomalously deep upper low that should be strongest around early day 4 Sat as it tracks over northern Minnesota. The upper low will support a period of heavy snow and strong winds over some northern tier locations and make only gradual northeastward progress into southern Canada over the following days. Pacific flow will bring one shortwave to the Pacific Northwest by the start of the weekend and then the central U.S. early next week, followed by another shortwave that could approach the Northwest around day 7 Tue. Meanwhile a potential subtropical system could track just off the East Coast and could bring wind/wave effects to some areas along and offshore the New England and Mid-Atlantic coasts before lifting away during the latter half of the period. The National Hurricane Center is monitoring this area for development. Please reference their outlooks for more information. Broadly speaking an operational model blend represented consensus well early-mid period, followed by at least half ensemble mean input toward days 6-7 Mon-Tue. Versus the 00Z run, the 06Z GFS compared much better to other guidance for the system off the East Coast. On the other hand the 06Z GFS seemed a little fast with height falls ahead of the central U.S. trough extending from the deep northern tier storm. One other forecast consideration was that 00Z-06Z GFS runs were stronger than other guidance with upper troughing off California and northwestern Mexico by days 5-6 Sun-Mon. This ultimately led the GFS to bring a potential eastern Pacific tropical system and its associated moisture farther northeast than other solutions (including the GEFS mean). ...Weather Highlights/Threats... The deep northern tier storm should bring the best potential for the combination of strong winds and heavy snow to parts of the Dakotas and western Minnesota late this week. Rainfall of varying intensity will accompany the trailing front from the Great Lakes into the Lower Mississippi Valley/southern Plains. The rain will become lighter and more scattered as the front heads into the East. Northern tier/Great Lakes precipitation should persist for a while as moisture wraps around the slow moving system. Effects of the western Atlantic storm over New England and coastal Mid-Atlantic from Fri into the weekend will be sensitive to the storm's exact track and strength. Currently expect at least some rain to reach eastern New England with the potential for a fairly sharp gradient. A period of strong winds will also be possible along/offshore the coast. Toward next Tue there may be an increase of southern tier rainfall aided by focus along a returning Gulf Coast front and a cold front approaching from the Plains. How much if any eastern Pacific tropical moisture becomes involved is a major uncertainty at this time, with most guidance suggesting less than depicted by GFS runs. Expect the Pacific Northwest to see a period of mostly light precipitation this weekend with a wavy front crossing the region. Another area of moisture may approach/reach the area by next Tue. The amplified pattern bringing record cold to parts of the West and Plains should gradually moderate, with decreasing coverage of much below normal temperatures. However this moderation will be relative over the northern Plains where some highs may be more than 30F below normal this Fri and "only" 10-25F below normal by next Mon-Tue. Above normal temperatures will precede the cold front that crosses the eastern half of the lower 48 Fri into Sun, with modestly above normal readings persisting over Southeast through early next week. Rausch 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 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