Extended Forecast Discussion NWS Weather Prediction Center College Park MD 334 PM EDT Mon Oct 24 2022 Valid 12Z Thu Oct 27 2022 - 12Z Mon Oct 31 2022 ...Guidance and Predictability Assessment... Model guidance was relatively consistent early in the period with a gradual increase in spread mainly related to the progression of a trough/closed low over the southern CONUS. A general model blend between the 06 UTC GFS and the 00 UTC CMC/ECMWF/UKMET was used early in the period with guidance depicting a deepening trough moving from the West out over the Plains Thursday into Friday, with a closed low developing over the Southern Plains. The 00 UTC ECMWF ensemble mean was steadily increased in the blend as it followed the 06 UTC GFS and 00 UTC CMC with a more progressive trough moving into the eastern CONUS. The 00 UTC ECMWF was an outlier in showing a slower progression and deeper closed low later into the period. Reliance toward the end of the period on the 06 UTC GFS, 00 UTC ECMWF ensemble mean, and 00 UTC GEFS mean helped to indicate the development of another less amplified trough along the West Coast while the 00 CMC was removed from the blend as it differed with subtle ridging indicated. The 00 UTC ECMWF was also an outlier as it developed a much deeper upstream Pacific system late in the period. ...Pattern Overview and Weather/Hazard Highlights... A northeastward lifting lead upper trough will clear the Northeast into eastern Canada early Thursday along with high pressure developing over the region. Temperatures look to be generally at or just above average for mid-Fall with the only precipitation chances increasing later in the period Monday into Tuesday. Southern stream flow amplification/separation from the Intermountain West to the Rockies into Thursday sets the stage for cold temperatures and the chance for some snow in the south-central Rockies. The additional upstream digging of another Pacific system/upper energies into the West later week into early next week remains a bit more uncertain in guidance, but a general model consensus shows potential energy available along with a periodic moderate QPF signature back across mainly the Northwest and inland into the north-central Great Basin and Rockies to also include some terrain enhanced elevation snows. A general model blend was used along with the NBM to keep continuity with the previous forecast and help spread amounts out across the region as the location of any locally heavier QPF was uncertain. Meanwhile, the downstream ejection of the likely closed/well separated southern stream system remains slated to track steadily over the south-central and southern U.S. late week through the weekend to focus enhanced rain/convection given upper support and pooling moisture and instability to fuel activity. The guidance signal for locally moderate to heavy rainfall continues to increase, albeit with details less certain given the nature of closed features and how progressive the system is. The QPF forecast trended higher and further east than the NBM/previous forecast by incorporating more of the deterministic guidance and the ECMWF mean which included more locally enhanced totals through the Southern Plains and Lower Mississippi Valley. Model guidance showed the greatest consensus on the potential for higher rain rates and more than a couple inches of rain on Friday, which, despite drought conditions, could be enough to lead to at least a few local instances of flash flooding. QPF amounts across the East were also increased relative to the NBM along the track of the system as it progresses through the Southeast Sunday and Monday as the deterministic guidance and ECMWF ensemble mean indicated the potential for locally heavier totals. 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. Putnam/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 rain across portions of the Southeast, the Southern Appalachians, the Lower Mississippi Valley, the Southern Plains, and the Tennessee Valley, Fri-Sat, Oct 28-Oct 29. - Flooding occurring or imminent across portions of the Southeast. - Much below normal temperatures across portions of the Central Rockies, the Central Great Basin, the Northern Rockies, the Southern Rockies, the Northern Great Basin, the Southern Plains, and the Southwest, Thu-Sat, Oct 27-Oct 29. 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