Extended Forecast Discussion NWS Weather Prediction Center College Park MD 431 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 moving into 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 a much earlier phasing of the southern stream low this weekend than the rest of the guidance. Meanwhile, confidence is increasing for a significant low pressure system to intensify and track northeastward across the central and northern Plains Sunday to Monday. 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 much of the West by Saturday with the arrival of the amplifying upper trough, hurling in the first major cool season-type precipitation event for the region. Precipitation in the form of higher elevation snow and lower elevation rain will be enhanced across favored windward terrain of the Cascades, Rockies, with the heaviest amounts likely along the Wasatch over the weekend. 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 to middle of next week in the Northwest as a couple additional Pacific systems are forecast to arrive. By early next week, an intensifying low pressure system forecast to track across the northern to central Plains Sunday to Monday will increase the threat of high winds across these areas, along with a threat of rain changing to a period of enhanced wintry precipitation on the back side of the low near the Canadian border. Farther south, rain chances should generally increase across the Plains and into the Mississippi Valley ahead of the upper trough and what appears to be a potent cold front. Areas of enhanced to possibly heavy rainfall are likely. Meanwhile, some enhanced rainfall is possible along or near the East Coast this weekend into Monday should a better-defined low pressure center forms along a coastal frontal boundary. Confidence remains low regarding where and how much rain could move onshore. Nevertheless, coastal/southeastern New England appears to have a greater chance of receiving the rain from this system due to its geographic protrusion into the Atlantic. Coastal Mid-Atlantic may also see some rain depending on how close the low tracks toward land. Elsewhere, some precipitation is also be possible across the higher elevation of Arizona into New Mexico during the weekend with the passage of the southern stream low. Temperatures are likely to be warmer than average across the mid-section of the country up into the Great Lakes for the weekend under a broad and deep southerly flow strengthening ahead of the developing western upper trough. Highs and lows of 10-20F above normal, with some spots higher, will be widespread. 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 Hazards: - High winds across portions of the Central and Northern Plains, Sun-Mon, Oct 23-Oct 24. - Heavy precipitation across portions of the Northern Plains, Sun-Mon, Oct 23-Oct 24. - Heavy rain across portions of the Mississippi Valley and Southern Plains, Mon, Oct 24. - Flooding occurring or imminent across portions of the Southeast. 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