Extended Forecast Discussion NWS Weather Prediction Center College Park MD 1058 AM EST Mon Nov 12 2018 Valid 12Z Thu Nov 15 2018 - 12Z Mon Nov 19 2018 ...Overview and Guidance/Uncertainty Assessment... Models continue to agree on the overall pattern: the upper ridge strengthening over the West Coast with a downstream mean trough settling over the eastern U.S. The details in both of these features diverge with the different solutions. In the beginning of the medium range period, a closed upper low over the lower Mississippi Valley/Tennessee Valley will lift northward toward the Mid-Atlantic. In the east, the 06Z GFS is slightly faster with the progression of this closed low as compared with the 00Z ECMWF. Meanwhile, the 00Z CMC agrees with the slower solution. The 00Z UKMet was much faster and farther north with this low--thus, it was completely discounted. At the surface, the 06Z GFS was faster with the front as a result but both the GFS/ECMWF were still within a reasonable range of each other. In the northern tier states/Great Lakes, the 06Z GFS/00Z ECMWF are in agreement on the overall timing with the energy skirting across the Great Lakes. By the weekend, shortwave energy will slide down the upper ridge on the West Coast which will lead to a more rounded eastern mean trough. The details begin to become apparently different by the beginning of next week. Out west, the upper level ridge will begin to build across the West Coast. In the Pacific, a trough will begin to dig farther south and eventually split to become a closed low. This will lead to the ridge breaking down by the end of the weekend and into early next week. Once again, the 06Z GFS and the 06Z GEFS mean were more progressive with the low in the Pacific and faster with pushing the ridge inland while breaking down. The 06Z GEFS mean also continued to show more separation with the closed low than the 00Z ECENS mean. The operational models and their means all agree that the ridge weakens as it centers over the Central Great Basin while the closed low approaches the West Coast. WPC ended up using a blend of the 06Z GFS/00Z ECMWF throughout the medium range forecast due to their overall agreement with the pattern. Increased the usage of their respective means by the weekend and into Monday to help with the differences in detail. ...Weather Highlights/Threats... The system affecting the East will spread precipitation of various types northeastward during Thu-Fri. Best potential for at least some wintry weather will be over inland/higher elevation locations. Guidance spread for various aspects of this system keeps confidence lower than desired for timing as well as coverage/duration of the various precipitation types. Low pressure tracking over or near the upper Great Lakes late this week will bring an area of mostly light precipitation to the region. Behind this system expect cold cyclonic low level flow to generate an episode of lake effect snow. Meanwhile the combination of shortwave energy dropping out of Canada and low level upslope flow supported by high pressure building into the northern Plains may produce areas of snow over parts of the northern Rockies/High Plains around Fri-Sat. Trends continue to be toward less moisture reaching the Pacific Northwest with either light or no precipitation being most likely. Depending on the character of upper trough energy that may split offshore the West Coast, some light precipitation could reach California very late in the period but with below average confidence at this time. Locations from the West Coast to Intermountain West should see the most persistent warmth during the period with highs generally 5-15F above normal. The northern High Plains and vicinity should see a warm start to the period followed by a cooling trend into the weekend and then a warmer trend early next week. The South and East will tend to see below normal temperatures through the period. Best potential for minus 10-20F anomalies will extend from the southern Plains through much of the East on Thu and then with a reinforcing push of cold air progressing from the northern Plains into the East Sat-Mon. Reinhart WPC medium range 500 mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indexes are found 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