Extended Forecast Discussion NWS Weather Prediction Center College Park MD 300 AM EDT Mon Oct 24 2022 Valid 12Z Thu Oct 27 2022 - 12Z Mon Oct 31 2022 ...Guidance and Predictability Assessment... The WPC medium range product suite was mainly derived from a composite of reasonably well clustered guidance from the 18 UTC GFS and 12 UTC ECMWF/UKMET/Canadian models valid Thursday into Friday along with compatible input from the 01 UTC National Blend of Models (NBM) and WPC continuity. Latest 00 UTC model and ensemble guidance still seems in line with this forecast in a pattern with seemingly above normal predictability. Forecast spread grows steadily through the weekend into early next week, but generally within normal constraints and a solution closest to the ECMWF ensemble mean was preferred as of the ensemble systems seemed overall most iin line with a model composite and WPC continuity. ...Pattern Overview and Weather/Hazard Highlights... A northeastward lifting lead upper trough will clear the Northeast into eastern Canada early Thursday along with associated Atlantic moisture and showers, albeit with some Great Lake enhancement possible in the wake of passage. Southern stream flow amplification/separatiion from the Intermountain West to the Rockies into Thursday sets the stage for cold temperatures and some widespread precipitation to include a terrain enhanced heavy snow threat into the south-central Rockies. Additional upstream digging of Pacific system/upper energies into the West later week into early next week remains more uncertain in guidance, but the less defined ensemble means at least show 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 broad targeted change to NBM QPF was to trend amounts modestly toward WPC QPF continuity given run to run forecast variances in this flow. Meanwhile, the downstream ejection of a 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 instabiliy 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. Slow system translation and potential for cell training and repeat cells could lead to local runoff issues. ECMWF ensembles offer a relatively slower main system progression compared to the GEFS. The ECMWF ensemble mean track also seems best in line with a composite of recent GFS/ECMWF/Canadian/UKMET runs. The ECMWF ensemble mean coupled with some stronger/more separated southern stream system detail input from a model composite seems to offer a good forecast basis despite uncertainties. However due to forecast spread, suspect that both ECMWF ensembles and the 01 UTC NBM may be spreading the associated QPF field too quickly downstream from the south-central U.S. to the East later weekend into early next week given the closed nature of supporting low. This prompted an associated targeted change to the NBM. 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 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