Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Thu Oct 15 2020 Valid 12Z Sun Oct 18 2020 - 12Z Thu Oct 22 2020 ...Overview... A couple of shortwave troughs rotating around the southern periphery of a large upper-level low centered over central Canada will move across the northern tier states during the medium range period. Wintry precipitation appears likely across the northern Rockies to the northern High Plains early next week. There is an increasing chance of enhanced rainfall over the upper Midwest by next Thursday with wintry precipitation possible for the northern portion of this area. ...Guidance Evaluation/Preferences... The model guidance this morning shows decent agreement with the general evolution of the synoptic pattern across North America. One notable difference between the ECMWF and the GFS is that the GFS has been bringing more cold air and surface high pressure down into the northern Rockies/Plains behind a low pressure system that is forecast to move away from the Great Lakes into eastern Canada on Sunday. By next Thursday or so, the pattern appears to favor cyclogenesis to occur over the central Plains. The 06Z GFS/GEFS solutions are slightly faster than the 00Z ECMWF/EC mean regarding this system. But given that it is a Day 7 forecast, this difference is well within what we typically see. The WPC prognostic charts were derived starting with a 60% of the 00Z ECMWF/EC mean with 40% of the 06Z GFS/GEFS, gradually trending toward a 25% blend of each of the four model components by Day 5 onward. ...Weather/Hazard Highlights... A surge of cold air from western Canada will be ushered down the Great Plains this weekend into early next week behind an intensifying low pressure system lifting away from the Great Lakes into eastern Canada. Max temperatures in the 30s and 40s are likely across the Northern Plains to the Upper Mississippi Valley through Tue, which is 15 to 30 degrees below normal. Min temperatures in the teens and 20s are 10 to 20 degrees below normal. Wintry precipitation is likely to accompany this cold surge across the northern Rockies into the northern High Plains Sunday into Monday. Snow is forecast for the higher elevations while rain may mix in for the lower elevations during the afternoon. This may be the first snowfall of the season for lower elevations of the north-central U.S. Some modest rainfall is expected to linger over the upper Midwest north of a stalled front. By next Thursday or so, there appears to be an increasing chance of enhanced rainfall over the upper Midwest with wintry precipitation possible for the northern portion of this area.. The Southwest from West Texas to California and the Central Great Basin will remain under an upper ridge through the early part of the week, leading to continued dry conditions. Warmer than normal temperatures are forecast there, and Sun in particular could see temperatures hitting 100 degrees for the lower deserts of Arizona and California. The upper ridge shifts farther west late this weekend, making for more moderate temperatures by early next week, though may stay slightly above average. Meanwhile, tropical showers are expected across southern Florida as temperatures remain mild and a few degrees above normal. Kong 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