Extended Forecast Discussion NWS Weather Prediction Center College Park MD 340 PM EDT Tue Oct 25 2022 Valid 12Z Fri Oct 28 2022 - 12Z Tue Nov 01 2022 ...Guidance and Predictability Assessment... The overall synoptic pattern during the medium range was captured reasonably well by the EC. The general trend has been a slowing one across the CONUS, with an increase in QPF in the Gulf Coast being the main implication. The past several runs of the EC and ECE have consistently signaled a slow moving upper low to weaken as it drifts across the Southeast/Gulf Coast. The GFS/CMC/UK suite have been less consistent in their placement of the upper low and the intensity of it. Therefore, a predominantly 00z EC/ECE blend was utilized throughout the medium range with no inclusion of the 00z CMC. There's a strong signal for heavy rainfall along the central Gulf coast this weekend in the 00z ECE exceedence probabilities, but not enough agreement from the 00z GEFS/CMCE to warrant the addition of a Slight Risk area. There's a reasonable signal for heavy snow in the downscaled ensemble runs through early next week. ...Pattern Overview and Weather/Hazard Highlights... The aspects of a series of Pacific systems into the West/Northwest heading into this weekend and through early next week remains uncertain and more run to run varied than normal in recent guidance, but a general model consensus/ECMWF ensemble mean suggests a system focus for periodic moderate precipitation from northern California and the Pacific Northwest inland across the northern Great Basin/Rockies to include terrain enhanced elevation snow. Latest guidance including the 00 UTC model suite shows a steady diet of systems, but with the strongest system passage/height fall focus seemingly on tap for Sunday into Monday. A targeted change was made to the day 5 winter weather outlook to depict increased downscaled ensemble signal for heavy snow in the northern Cascades. Meanwhile, a leading closed/separated southern stream system remains slated to slowly track across the south-central U.S. Friday and for the weekend before lifting/shearing northeastward toward the Appalachians by next Tuesday. This will act to focus some enhanced rain/convection given upper and surface system support to pool moisture/instability to fuel activity. There is a some guidance signal for locally moderate to heavy rainfall given the risk of repeat/training cells with overall slow system translation, albeit with details less certain given the nature of closed features. Guidance shows the greatest consensus on the potential for higher rain rates and more than a couple inches of rain on Friday, which despite overall dry antecedent conditions, could be enough to lead to at least a few local instances of flash flooding. This often happens with closed systems. Weekend to early next week rainfall from the South northeastward into the East were adjusted slower and accordingly increased relative to the NBM along the track of the system considering trends from deterministic guidance and the ECMWF ensemble mean. However, as expected compared to earlier in the period, the location of any enhanced rainfall is more uncertain and a broad areal average increase was included for now. Kebede/Schichtel 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 the Pacific Northwest and the Northern Great Basin, Sun-Mon, Oct 30-Oct 31. - Heavy rain across portions of the Lower Mississippi Valley and the Southern Plains, Fri, Oct 28. - Heavy rain across portions of the Southeast, the Lower Mississippi Valley, the Southern Appalachians, and the Tennessee Valley, Sat, Oct 29. - Flooding occurring or imminent across portions of the Southeast. - Much below normal temperatures across portions of the Central Plains, the Central Rockies, the Central Great Basin, the Northern Plains, the Northern Rockies, the Southern Rockies, the Northern Great Basin, the Southern Plains, and the Southwest, Fri, Oct 28. 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