Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 PM EDT Wed Oct 19 2022 Valid 12Z Sat Oct 22 2022 - 12Z Wed Oct 26 2022 ...Overview... An energetic upper-level trough arriving and amplifying over the Pacific Northwest at the start of the medium-range period will likely become a major weather player as the trough progresses further downstream into the Plains during the weekend. Meanwhile, a southern stream upper low continues to introduce uncertainty into the forecast due to continued poor model agreement on the timing of interaction/phasing of the southern stream low with the northern stream trough. Another area of uncertainty is along the East Coast where model agreement remains poor regarding the degree of interaction between a smaller scale upper low and a lingering slow-moving front just offshore. ...Model and Predictability Assessment... While model guidance starts out with decent agreement on the amplifying troughing in the West this weekend, predictability and confidence quickly decrease early next week as models continue with the expected struggle of resolving its interaction with the southern stream upper low moving onshore across Baja California. In general, models have trended toward a faster downstream progression of the front across the Plains early next week and into the eastern U.S. by midweek. The 00Z Canadian model was an outlier with an much earlier phasing of the southern stream low this weekend than the rest of the guidance. As for the East Coast, there has been a gradual tendency for the rain to edge closer to land. The ECMWF has occasionally been the most aggressive in this regard. The 12Z GFS has indicated this tendency as well. It appears the threat of enhanced rainfall will be more likely across coastal New England. The WPC forecast was based on a blend of the 00Z ECMWF/EC mean with the 06Z GFS/GEFS, leaning toward the EC/EC mean blend by Days 6 and 7. This results in a faster eastward progression of the front from the Plains toward the eastern U.S. early to middle of next week than in previous WPC forecasts. ...Sensible Weather and Potential Hazards... Precipitation is likely across the much of the West by Saturday as the upper trough amplifies and the first surface cold front moves through, for one of the first major cool season-type precipitation events since much earlier this year. Precipitation will be enhanced across favored windward terrain of the Cascades, Rockies, and Wasatch over the weekend, with higher elevation snow and lower elevation rain. Confidence in a meaningful precipitation event remains fairly good, but exact amounts of rain/snow and timing will still need to be refined with time. Another couple of rounds of precipitation could continue/reform early next week in the Northwest but with even more uncertainty. Precipitation may also be possible across the Southwest for the weekend but will be dependent on the timing and track of the southern stream low and its eventual possible phasing. By early next week, precipitation chances should generally increase across the Plains and into the Mississippi Valley ahead of the upper trough and a developing low pressure system. Areas of enhanced to possibly heavy rainfall are likely, while there may be some snow on the backside of the surface low into the northern High Plains, but the specifics of both are not yet clear at this time. Meanwhile, some rain may be possible along or near the East Coast this weekend into Monday associated with a frontal boundary and possible low pressure system, but with low confidence on how much rain could fall onshore versus remaining offshore. Temperatures are likely to be warmer than average across the central U.S. for the weekend ahead of the developing western upper trough. Highs and lows of 10-20F above normal, with some spots higher, will be widespread across the Plains to Upper Midwest. Meanwhile, an area of below normal temperatures will expand from the West Coast states into the Great Basin and Rockies this weekend, with lows around 5-15F below average and highs 10-20F below average. Temperatures should cool to near normal and even below normal for the north-central U.S. next week as the upper trough and cold front(s) move through. This will push warmer than average temperatures into the northeastern U.S. by Monday-Wednesday. Kong/Tate 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, experimental excessive rainfall outlook, 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/#page=ero https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml