Extended Forecast Discussion NWS Weather Prediction Center College Park MD 500 PM EDT Wed Nov 02 2022 Valid 12Z Sat Nov 05 2022 - 12Z Wed Nov 09 2022 ...Lingering heavy rain potential Saturday afternoon/evening along Mississippi Valley system/front... ...Chilly pattern over the West with significant rain/mountain snow over some areas... ...Overview... Expect a leading Mississippi Valley system, as of early Saturday, to eject rapidly into Canada by Saturday night. As a strong upper ridge along and offshore the East Coast provides resistance, a portion of the front trailing from the surface low to stall and eventually lift northwest as a warm front before dissipating. Guidance suggests that the axis of an amplified mean trough will settle near the West Coast, but with some uncertainty over the amplitude of this trough/progression of ejecting energy due to differences in the depiction of a strong upper ridge that builds over Alaska and vicinity. At the very least this pattern should support several days of below normal temperatures across the West and multiple episodes of rain and mountain snow from the West Coast into the Rockies. A system emerging from the West could also produce meaningful precipitation across parts of the northern tier during the first half of next week. ...Guidance and Predictability Assessment... The deterministic and ensemble means have trended faster with the overall synoptic flow over the lower 48 during the medium range period. The 00z EC/UK/CMC and 06z GFS tended to handle the southern U.S. trough and eastern fairly well on day 3. The emergence of the amplifying eastern Pacific trough provides more of a challenge to the available guidance beyond day 3. The 00z ECE was introduced while the 00z UK was diminished on day 4 due to differences with respect to the approaching Pacific trough. There's a reasonable consensus on the orientation of the eastern CONUS ridge throughout the medium range, but uncertainty arises with the arrival of the upper low over the eastern Pacific. A blend consisting of the 00z EC/UK/CMC/GEFS/ECE and 06z GFS were used on day 5 to find some sort of middle ground solution with respect to the timing and intensity of this Pac NW system. The UKMET is dropped by day 6 and by day 7 we're left with the 00z ECE/CMCE/GEFS. ...Weather/Hazard Highlights... The leading system tracking northeastward from the Mississippi Valley on Saturday, along with its associated fronts, will produce some locally moderate to heavy rainfall but likely with lower totals than expected during Friday-Friday night. Areas of interest for enhanced rainfall will be over the Upper Midwest/Upper Great Lakes near the surface low track as well as over/near the Lower Mississippi Valley as the trailing front decelerates. Areas from the West Coast into the northern half of the Rockies should see multiple episodes of rain and higher elevation snow, with snow levels tending to decline with time as the mean trough aloft near the West Coast amplifies. Uncertainty over the precise amplitude of the trough lowers confidence in the precise focus of highest totals, but the best signal at the moment is generally over southern Oregon and northern California. Multiple systems may provide added focus. These include a front reaching the Northwest by Saturday and a system approaching the Northwest on Sunday. Any potential systems next week have lower confidence. This lower confidence extends to any low pressure that may extend into the Plains with an area of snow or rain depending on track/evolution. Moisture should eventually increase near the East Coast next week as the upper low initially over the eastern Bahamas retrogrades toward the southeastern U.S./Florida. After a brief rebound to only moderately below normal temperatures over the West during the weekend, the forecast of an amplifying upper trough next week should expand the coverage of highs 10-20F below normal across the West once again. Coldest air should extend from western Canada into Montana with some highs in that state 20-35F below normal Monday-Wednesday. In contrast to the somewhat winter-like temperatures over the West, the East will see temperatures more typical for earlier in the fall with a broad area of plus 10-25F anomalies, especially Saturday-Monday when daily records should be most numerous. Anomalies should be a little more extreme for morning lows versus daytime highs. Plus 10-20F readings should be more common by Tuesday-Wednesday. Kebede/Rausch 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 Hazards: - Heavy precipitation across portions of California, the Pacific Northwest, and the Northern Great Basin, Sat-Mon, Nov 5-Nov 7. - Heavy precipitation across portions of the Central Great Basin, California, and the Southwest, Sun-Tue, Nov 6-Nov 8. - Heavy precipitation across portions of the Northern Plains, the Northern Rockies, andthe Central Rockies, Sat-Sun, Nov 5-Nov 6. - Heavy rain across portions of California and the Pacific Northwest, Sat-Sun, Nov 5-Nov 6. - Heavy rain across portions of the Lower Mississippi Valley, and the Tennessee Valley, Sat, Nov 5. - Heavy snow across portions of the Northern Plains and the Northern Rockies, Mon, Nov 7. - High winds across portions of the Northern/Central Rockies and the Northern/Central Plains, Sat, Nov 5. 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