Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1156 AM EDT Sat Oct 05 2019 Valid 12Z Tue Oct 08 2019 - 12Z Sat Oct 12 2019 ...Another round of cold/snow for the Northern Rockies next Tue/Wed... ...Overview... A positive height anomaly near Labrador will favor troughing in the western to central states and increased precipitation for the Mississippi Valley. Western Atlantic ridging is forecast to compress into the subtropics, allowing a cutoff upper low to linger just offshore New England and Nova Scotia. ...Guidance/Uncertainty Assessment... For Tue-Thu, a blend of the latest runs of the GFS, ECMWF, and Canadian, with small contributions from the ECENS/GEFS means, offered a reasonable starting point as the western U.S. trough sinks through the Northern Rockies and emerges into the High Plains. By Fri-Sat, there remains some uncertainty regarding how quickly a possible cut-off closed low deepens over the Upper Mississippi Valley/Upper Great Lakes. The GFS continues to be slightly fast, while the Canadian and ECMWF are slower (Canadian a hair slower than the ECMWF). The ensemble means generally follow suit with their respective deterministic counterparts. The 00z ECMWF continues to represent a good middle ground solution. Though run-to-run continuity with this system is less than stellar, a trend may be emerging for a slower and more amplified/deeper upper low. This is in part because of a slower/farther westward cut-off low off the New England coast by mid to late next week. For both systems, a blend between the GFS/ECMWF and ensemble means, with more weighting on the ECMWF, provided a good blend for the end of the period. The result was a noticeably deeper system over the Upper Great Lakes and a surface low closer to the New England coast from previous WPC continuity. ...Weather Highlights/Threats... Central U.S. cold front will bring well below average temperatures to the West Wednesday onward--as much as 30-35 deg F anomalies (temperatures in the 30s). Montana will be the focus for the cold on Wednesday, followed by Wyoming to High Plains Thursday to the weekend. Cooler air will also spread southward to Texas and eastward to the mid-Mississippi Valley by Friday but with less intensity. This system also brings increasing potential for modest accumulating snowfall across parts of the Northern Rockies, with snow potential even spreading eastward even to many valley locations and eventually the Northern Plains. Ahead of the cold front, rainfall will expand and offers a risk to become locally heavy from the south-central Plains to the mid-MS Valley/Midwest later in the period with moisture inflow return from the Gulf. The low off the New England coast has trended a bit westward in model runs which now brings a threat for locally heavy rainfall to at least parts of coastal New England by Wednesday-Thursday next week. There remains plenty of model spread on how close the low tracks to the coast, so the details of how far west precipitation extends remains in question. 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 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