Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Wed Nov 02 2022 Valid 12Z Sat Nov 05 2022 - 12Z Wed Nov 09 2022 ...Some lingering heavy rain potential with the Saturday 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 models and means are still nudging a little faster for the initial Mississippi Valley system and associated fronts, but run-to-run changes seem to be getting a little less pronounced with time and clustering is gradually improving as well. An operational model composite handled this system well, accounting for lingering detail spread and uncertainty. The primary large scale issue behind this system is how amplified the West Coast trough becomes along with the specifics of energy rounding the trough and ejecting downstream during the first half of next week. Among the 12Z/18Z runs, these differences became noticeable by day 5 Monday with the GFS/GEFS starting to become more amplified than most other models to varying degrees. This leads to the embedded upper low off Vancouver Island or the Pacific Northwest coast tracking farther south by late in the period. In addition greater ridging downstream led to slower progression of ejecting shortwave energy and associated surface system early-mid week. These differences corresponded to the GFS/GEFS depicting a weaker/more open Alaska ridge compared to the majority. Such issues with Alaska ridging in the cold season tend to lower predictability downstream. Thus preferred tilting at least two-thirds toward the majority scenario which is closer to continuity, by way of more 12Z ECMWF/ECMWF mean weight relative to the 18Z GFS/GEFS mean. As seemingly confirmed by the new 00Z run, the 12Z CMC became suspiciously amplified with its east-central U.S. shortwave by next Wednesday and thus its input was minimized late. The new 00Z ECMWF, as well as the UKMET through the end of its run, now shift the balance of solutions more in the GFS direction--highlighting the ongoing uncertainty. Finally, details continue to fluctuate within a more broadly agreeable upper low expected to wobble from near the eastern Bahamas toward the southeastern U.S. coast (with accompanying surface low/trough). Specifics will depend in part on the uncertain details of flow to the west. A blend approach appears reasonable for depicting this feature. ...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. 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 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